Sensor measuring bridge with extensions

Abstract

Amplifying the tap voltage from a measuring bridge is readily achievable electronically, but resolution and measuring range width are somewhat contradictory: the wider the measuring range required for a measurement project, the lower the achievable resolution. Conversely, the higher the desired resolution, the smaller the measuring range within which it can be achieved. Therefore, there is often a need to extend measuring ranges without sacrificing resolution. Voltage dividers can be used as extensions to measuring bridges, creating half-measuring bridges that—like the voltage dividers alone—represent functional halves of the sensor measuring bridge. This allows the task of the sensor measuring bridge to be divided into several subtasks. If partial measuring ranges are then located side-by-side on this basis, measuring range extensions can be achieved while maintaining high resolution. This results in a total measuring range, which is characterized by the measuring range widths of the partial measuring ranges and by the number of partial measuring ranges. In this way, it is possible to divide a larger measuring range into small, adjacent sub-measuring ranges or to combine large measuring ranges with high resolution.

Description

[0001] The invention relates to extensions of measuring bridges for high-resolution sensory use of a measuring bridge in a large measuring range and measuring bridge amplifiers adapted for this purpose.

[0002] State-of-the-art (SdT) measuring bridges, in which two interconnected voltage dividers interact, are a commonly used arrangement for acquiring not only physical parameters. The underlying theory of the SdT is well-established. The technical design and application of such measuring bridges appear straightforward. The electronic evaluation and further processing of the measured voltages are described in numerous publications. Datasheets for many operational amplifiers (op-amps), especially those with very high input impedances, such as instrumentation amplifiers (IVs), often include suggestions for using such amplifiers as measuring bridge amplifiers.

[0003] However, resolution and measurement range width are somewhat contradictory: the wider the measurement range required for a measurement project, the lower the achievable resolution and the greater the effort required. Conversely, the higher the desired resolution, the smaller the measurement range within which it can be achieved. Therefore, there is often a need to extend measurement ranges without sacrificing resolution.

[0004] Measuring bridges are a good choice when there are very small changes in the resistance or impedance of the sensor elements and are often already integrated components of sensors. Well-known examples include temperature sensors (at least one resistor in the measuring bridge is a temperature-dependent resistor, e.g., NTC (negative temperature coefficient thermistor) or PTC (positive temperature coefficient thermistor), piezoresistive pressure sensors, force sensors using adhesive-attached strain gauges for bending measurement with a measuring bridge), magnetic field sensors (AMR, GMR, TMR measuring bridges (magnetoresistive effects)), light sensors, etc. SdT: Definition of measuring bridges

[0005] Measuring bridges consist of four resistors R1 to R4 connected to 4 nodes K1-K4 ( Fig. ) to form a loop, or from another perspective to form two voltage dividers (R1, R2 or R4, R3).

[0006] Voltage dividers consist of two resistors (R1, R2) connected in series, which create a voltage (or voltages u1, u3) at supply points (1), (2) ( Fig. ) is supplied, dividing it into partial voltages. In a vertically represented voltage divider ( Fig. With respect to an arbitrary reference point (ia GND), a first voltage u1 is present at the upper supply point (1), and a second voltage u3 is present at the lower supply point (2). These can be alternating voltages or direct voltages.

[0007] Voltage dividers form the bridge arms of the measuring bridge. (In the literature, other elements may be referred to as bridge arms; here, the definition just given applies.) Each bridge arm represents a voltage with respect to the excitation voltage U. err represents an independently operating voltage divider.

[0008] At least one of these four resistors of the measuring bridge, acting as a sensor element, changes its resistance value depending on a physical parameter being measured, as well as other parameters (e.g., chemical parameters).

[0009] The dual meaning of the term "resistance" as a component or as a physical quantity can be assigned to the respective context and is known to those skilled in the art.

[0010] Fig. The SdT shows the basic structure of a measuring bridge consisting of voltage dividers, with some quantities defined for mathematical description: - The measuring bridge consists iW of four resistors R1, R2, R3, R4 ( Fig. (or R a , R b , R c , R d ( Fig. ), ◯ of which two resistors form a voltage divider, wherein ◯ the voltage dividers ia with the same voltage U err be operated and ◯ the voltage dividers operate independently of each other. ◯ The sequence of indices used to designate the resistors should resemble a circle forming a mesh. - The currents i1, i2, i3, i4 flowing through these resistors are designated and distinguished by the same index as the resistors. - The measuring bridge has four nodes, which are designated here as K1, K2, K3, K4 (starting from the top, counterclockwise). - The voltages u1, u2, u3, u4, which can be measured at these nodes, are designated with the same index as the nodes and thus distinguished. - The indices of different measuring bridges are distinguished by double indices or additional high bars, with a first index position differentiating the measuring bridge (i.e., R). 11 , R 12 , R 13 , R 14 for a first of possibly several measuring bridges; R 21 , R 22 , R 23 , R24 for a second of possibly several measuring bridges, etc.).

[0011] The two representations of Fig. For a measuring bridge, they represent essentially the same thing; however, the illustrations often need to distinguish whether a voltage divider is to be seen as part of a measuring bridge intended, specified, or already in use as a sensor (which is referred to as a sensor-based measuring bridge / sensor-based measuring bridge for differentiation purposes; Fig. ), or whether it should be viewed more generally and is, for example, only an addition or possibly also a measuring bridge equivalent (e.g. Fig. ) (su).

[0012] The different forms of representation are used in the respective context in various combinations of voltage dividers to distinguish whether a voltage divider is possibly part of a sensory measuring bridge (which has at least one sensor element and serves to detect a physical parameter) or whether "only" (one or two or possibly more) voltage dividers are present in the arrangement of a measuring bridge, as the right-hand illustration shows (e.g. Fig. ), or whether voltage dividers are merely additions.

[0013] An additional voltage divider added to a measuring bridge should be indexed with letters. This allows it to be distinguished from the voltage dividers of an originally specified sensor measuring bridge.

[0014] Overall, the following distinctions will be made: - "The one" originally specified (or the actual) sensor measuring bridge and its voltage divider. - Semi-measuring bridges consisting of a combination of voltage dividers of a sensor measuring bridge and at least one voltage divider addition (this will be defined in more detail). - Measuring bridge equivalents that consist only of voltage dividers added to a sensor measuring bridge and can each be seen as a measuring bridge configuration (this will be explained in more detail later).

[0015] To highlight, delimit, or illustrate the measurement bridge extensions for analysis and applications, this may be useful later (see...). Fig. ).

[0016] Each bridge branch represents a certain excitation voltage U. err This represents an independently operating voltage divider. Provided that (even with electronic conditioning) the measuring bridge voltage is unloaded, i.e., that i", = 0 on both sides (5), the following applies to the measuring voltage U: mess = U err (R4R2 - R3R1) / [(R3+R4)(R1+R2)].

[0017] When the same voltages are present at the tap nodes (5) of the voltage divider of the measuring bridge, the measuring bridge is considered "tuned" and designated as such. Tuning the bridge requires that R4R2=R3R1 (U mess (is then non-trivially zero). Rearranged into the form R1 / R2=R4 / R3, this means that the voltage dividers on both sides of the measuring bridge have the same ratio (and that there is an equal offset on both sides).

[0018] Measuring bridges are often integrated into sensors (as components). Typically, the resistors of the voltage dividers in such a measuring bridge are designed for the (specifically defined) operating point so that, in the tuned state, they have an approximately 1:1 ratio. This means the operating point offset is roughly centered, the measuring range extends approximately equally on both sides, and the sensitivity is also optimal at this point.

[0019] A measuring bridge operating at either a "very high" or "very low" frequency (e.g., with resistors on both sides in a ratio of 1:10, 1:100, or 100:1) would be calibrated, but the resistor configuration would be far from optimal. A measuring bridge whose voltage divider operates at a "very high" frequency on one side and a "very low" frequency on the other (e.g., with a voltage divider with resistors in a ratio of 1:100 on one side and 100:1 on the other) would be completely uncalibrated and practically unusable because small measurement voltages would be impossible to detect due to the large offset.

[0020] Such measuring bridges, which are not optimally designed and / or not coordinated, i.e., which operate significantly far from "reasonable" operating points, shall here be referred to as derailed measuring bridges.

[0021] The adjusted state allows an operating point for the measuring bridge to be defined. A specific operating point can be defined, for example, by (u1+u3) / 2; this can be seen as the average of the voltages applied to the voltage divider and is also, for example, the operating point in which the measuring bridge resistors have a ratio of 1 on both sides (i.e., R1 / R2=1), because then the resistances are equal.

[0022] Current and / or voltage measurements at the measuring bridge can be used to determine the state of the measuring bridge and from this the parameter to be measured can be deduced.

[0023] This can be achieved, among other things, with simple voltage taps (su) and subsequent processing of the measured voltage. It is essential that a voltage tap for measuring the node voltage is performed without current. Drawing current from the voltage divider tap node would distort the voltage at the tap node (in the sense that "the mathematical calculations no longer hold true"; a voltage would then be measured that is not solely determined by the voltage divider and "is not the intended voltage").

[0024] Unlike voltage taps (which refer to both the type of measurement signal tap and the operating mode of the measuring bridge), the state of a measuring bridge can also be determined by selectively drawing a current from one of the bridge nodes. This will be referred to here as current tapping and can involve maintaining the node voltage at a defined value.

[0025] A connection located at a tap node for measurements, which draws no current or such a small current that it does not cause any relevant change in the node voltage, is called a voltage tap. In principle, multiple voltage taps of this type can be provided at a single tap node (alone, multiple, and / or additionally), and theoretically even an unlimited number of them.

[0026] However, the state of the measuring bridge can also be determined and the parameter to be measured can be deduced using current taps that load the voltage divider tap nodes.

[0027] Here, only direct current voltages are used and considered, without the invention being exclusively applicable to them or being limited to them.

[0028] A combination of a single voltage divider from a sensor bridge and a single additional (possibly one of several) voltage divider(s) is still considered a measuring bridge (the voltage divider originating from the sensor bridge may still ensure sensor functionality) (cf. Fig. If the fact that such a combination exists is to be particularly emphasized, it is also seen as a half-measuring bridge and is referred to as such here for the sake of distinction (example: Fig. ).

[0029] A half-measuring bridge therefore consists of two voltage dividers, but only one of them comes from a sensor measuring bridge; the other is an additionally provided voltage divider.

[0030] If a measuring bridge arrangement consists only of voltage dividers without a sensor element, or only of voltage dividers that have been added solely for expansion purposes, then this shall be considered and referred to here as a measuring bridge equivalent. (szB) Fig. (the external resistors). Each pair of voltage dividers (of the potentially many) that are additionally provided to the sensor measuring bridge forms a measuring bridge equivalent. (In Fig. For example, the two outer voltage dividers together form a measuring bridge equivalent).

[0031] The voltage difference u1-u3 is the operating voltage (excitation voltage U). +err and U -err or U err ) both of the voltage divider and the measuring bridge containing these voltage dividers and is (as the difference u1-u3) independent of the respective chosen reference point (ia will be GND).

[0032] The connection point (3) of the two resistors in series of a voltage divider is also referred to as the tap node in the respective context, because at this point a voltage U, which may represent the parameter to be measured and is to be processed further, is present. out (or a current) can be tapped. U out With reference to the same reference point of voltages u1 and u3 (uU GND), it will lie between u1 and u3 and should be either the node voltage, the tap voltage or the output voltage U. out seen and thus designated (u3 because of the designation rules introduced above at the measuring bridge).

[0033] U out In the illustrations, "voltage" often does not denote a variable or a physical quantity, but is often only to be seen as a non-specific indication that a voltage U is present there that still needs to be processed further. outThe output can be tapped, but it may also represent a parameter to be measured. If a voltage at the output needs to be specified more precisely, then the ia in the subscript is additionally specified: U outCab For example, a voltage coming from a type C voltage divider (because of type C with current tap; su). However, from the same node of the same voltage divider on the same measuring bridge, a voltage U could also be measured. outAab come which may not actually be present there (because, for example, the actual voltage there is fixed or regulated at a defined value), but which can be calculated and this voltage U outAab It would have precisely this designation (su).

[0034] In this context, the terms uU and U1 must be distinguished. This distinction is only mentioned here because the two can be quite different. U2 = (R2u1+R1u3) / (R2+R1) describes, for example, the voltage at the tap node of an unloaded voltage divider. However, if the same expression (R2u1+R1u3) / (R2+R1) appears in the formulas for calculating a current tap at the same node, then it must be something comparable to a voltage with the same magnitude and unit, and therefore suitable for interpretation. This voltage, however, cannot be universally applicable, for example, due to the voltage specified there. Therefore, a distinction must be made between U2 and U1. outA12 = (R2u1 + R1u3) / (R2+R1) as a theoretical voltage present at K2 and u2 = (R2u1 + R1u3) / (R2+R1) as a measurably accessible voltage actually present at K2, which is referred to as u outA12and u2 may match, but do not necessarily have to match.

[0035] If the physically measurable voltages at the tap nodes K2 or K4 are meant, they are referred to here as u2 and u4, etc.

[0036] The tap nodes K2, K4 ( Fig. ; in Fig. the nodes K L , K R (for left - right)) of the two voltage dividers from which a measuring bridge is constructed and which form the bridge branches of the measuring bridge are also tap nodes of the measuring bridge.

[0037] The sensor measurement value, i.e., the voltage actually provided as the measuring voltage by a given sensor bridge, is the voltage difference between the tap nodes of the two voltage dividers of a measuring bridge. This can be measured directly with an instrument or, after electronic processing, is used for further use as the measuring voltage U. mess provided.

[0038] Such measured values ​​change over time (otherwise, there would be no need to measure them constantly). The progression that the measured values ​​represent over time, i.e., the sequence and presentation of successively acquired measured values, constitutes a signal waveform. This waveform is considered and referred to as a measurement signal.

[0039] A voltage divider is described as unloaded if there is no further connection at the tap node through which an additional relevant current draw (or supply) can occur. mess ).

[0040] In an unloaded voltage divider, this voltage divider divides the voltage across or at this voltage divider in proportion to the resistance values.

[0041] An unloaded voltage divider (i.e., without any additions, only with a voltage tap) in a measuring bridge ( Fig. or Fig. ) with defined excitation voltage U error with the voltages u1 and u3 at the supply points (1) (2). is seen here in the context and to distinguish it from two other types B and C (su) as a voltage divider of type A and is designated as such (su the description for the Fig. ).

[0042] A type A voltage divider can be implemented and used with any resistance value for a very wide measuring range. The output voltage U out In all cases, i.e., for all conceivable resistance values ​​(with R1, R2 between 0Ω and ∞Ω) with respect to a sensor-detectable parameter with a strictly monotonic characteristic curve, the value always remains between u1 and u3.

[0043] The representation of the resistance values ​​(plotted on the ordinate of a coordinate system) over the value of the parameter to be measured (plotted on the abscissa), which is present at this resistance value, is the characteristic curve of a sensor element.

[0044] Each voltage value at the voltage divider in which this sensor element is located can be uniquely assigned to this resistance value; this gives the characteristic curve for this voltage (plotted on the ordinate of a coordinate system) over the value of the parameter to be measured (plotted on the abscissa).

[0045] Each of these voltage values ​​can be assigned to a different voltage value (a different output voltage), e.g. after amplification; this results in a characteristic curve for this voltage (plotted on the ordinate of a coordinate system) over the value of the parameter to be measured (plotted on the abscissa).

[0046] The characteristic curve here is the functional representation of an output voltage, e.g. U. outfrom the measuring bridge or from the measuring bridge arrangement or an op-amp, understood across the respective physical target parameter to be measured (e.g. temperature, field strength, pressure, light intensity, etc.), which are available at the tap node of the voltage divider or the measuring bridge and change depending on the parameter to be measured.

[0047] The advantage of type A voltage dividers is their inherently unlimited measuring range. This is particularly relevant for measuring bridges constructed solely from type A voltage dividers ( Fig. The same applies in principle (any wide measuring range with a strictly monotonic characteristic curve). This type of measuring bridge is probably the most frequently used and presented in both teaching and applications of the SdT.

[0048] However, extensions, additions, and variations are possible on a measuring bridge, so a distinction must be made between an original measuring bridge and "other" measuring bridges. For this reason, such a given measuring bridge should be considered a "sensory measuring bridge" or an "original measuring bridge" and / or referred to as a sensor measuring bridge. This sensor measuring bridge contains at least one sensor element. That is, at least one of the resistors R1 to R4 is a sensor element. SdT: Definition of measuring bridge amplifier

[0049] Measuring bridge arrangements are designed to detect the often very small changes in parameter-dependent resistance values ​​(impedances) within the context of sensory tasks ("detection of a physical parameter") and, for this purpose, provide a measuring voltage that is as proportional as possible to the physical parameter. For this, very small voltages often need to be processed and amplified to a usable level, resulting in a technically easy-to-use unit (as a component, as a "sensor," etc.).

[0050] Therefore, the application of measuring bridges requires electronic processing of the often very small measuring voltages U. mess, which are provided by measuring bridges (as a voltage difference at the tap nodes). This electronic processing, which can be quite complex and varied and often serves more than just pure amplification, is summarized here under the term measuring bridge amplifier.

[0051] The measuring bridge together with the electronic processing (i.e. the measuring bridge amplifier) ​​form the measuring bridge arrangement, which exists as a circuit or can be represented as such.

[0052] A measuring bridge circuit is an electronic circuit (as a circuit diagram) of a measuring bridge arrangement, but also refers to the (tangible, implemented) realization as hardware.

[0053] The most common measuring bridge arrangements that work with voltage taps show Fig. A well-known basic circuit: The actual measuring bridge consists of the four resistors R1 to R4. At least one of these resistors has a value that depends on a defined physical parameter (temperature, pressure, field strength, light, etc.), but also on other parameters (humidity, gases, chemicals, etc.), and which is to be measured using such a measuring bridge arrangement.

[0054] So that in all cases i m If =0 is ensured, then - as in Fig. As shown, the node voltages are tapped using op-amps (6) and (7). The resulting voltage difference, thus obtained via a voltage tap, must be processed electronically. Fig. A differential standard circuit (8) is provided for this purpose after the voltage taps. (The one in Fig. The illustrated measuring bridge amplifier with op-amps represents a so-called instrumentation amplifier.

[0055] For a technical application, the resolution achievable with such an arrangement is crucial. Resolution here refers to the smallest voltage difference that can still be distinguished in a given application, within the processed voltage in which the parameter to be measured is represented.

[0056] The lower limit is the noise that is unavoidable at the voltage ia; this fundamentally limits the highest possible resolution. To the noise of the measuring bridge, the noise of the electronic components for the amplifier electronics is added until a usable quantity representing the physical parameter to be measured is obtained.

[0057] After digitization, the resolution ia is the difference in voltage that can be distinguished by 1 bit. The resolution of the parameter to be measured is defined by this barely distinguishable voltage, in the sense of an inverse function. Unless the noise itself is the focus of interest, a higher resolution than approximately half the average noise amplitude makes no sense.

[0058] Each bridge branch represents a certain excitation voltage U. err This represents an independently operating voltage divider. Provided that (even with electronic conditioning) the measuring bridge voltage is not loaded, i.e., that i m If (5) = 0 on both sides, the following applies to the measured voltage U mess = U err(R4R2 - R3R1) / [(R3+R4)(R1+R2)]. As defined above, this measuring bridge is considered "tuned" when the voltages at the tap nodes (5) of the measuring bridge's voltage dividers are equal. Therefore, tuning the bridge requires that R4R2 = R3R1. Rearranged, this means in the form R1 / R2 = R4 / R3 that the voltage dividers on both sides of the measuring bridge have the same ratio (and that there is an equal offset on both sides).

[0059] Due to the tuned state, an operating point for the measuring bridge can not only be defined but also measured with an amplifier if the parameter is measured at the zero crossing of a measuring bridge arrangement.

[0060] A special operating point can also be defined, for example, by (u1+u3) / 2; this is the operating point in which the measuring bridge resistances on both sides have the same ratio of 1 (i.e., R1 / R2=R4 / R3=1); the resistances of a voltage divider are then equal. SdT: Definition of operating mode

[0061] Current taps can be so extensive that the measuring bridge is essentially operated in a short circuit. The operating voltage U err The measuring bridge remains in place, but the voltages at the bridge's taps are kept at the same potential by the electronics. In this case, the measuring bridge is essentially kept in a (virtual) short circuit. Compared to the measuring bridge operating without a load (either unloaded or viewed as operating mode at the voltage tap), this is a different possible form of operation and is considered a different operating mode (operating mode: virtual short circuit).

[0062] Since this depends on the type of measurement signal taps and further processing, the type of voltage divider and its primary function are crucial here.

[0063] In addition to the voltage divider already described, which is referred to here as type A for the purpose of differentiation, at least two further types (referred to here as type B and type C for the purpose of differentiation) are relevant in the context of the invention, which are characterized by Fig. are introduced and presented.

[0064] An advantage of the previously described voltage divider of type A is the unrestricted measuring range for all resistance values ​​for R1 and R2 (or R4 and R3), although this requires a currentless voltage tap (see below). Fig. To ensure a current-free tap, an op-amp (13) is also required in this voltage divider.

[0065] In type B voltage dividers ( Fig. Not all resistance values ​​can be used. With these type B resistors, the output voltage U is... outof the operational amplifier (14) such that the voltage at the tap node (15) exactly matches the reference voltage U Bez (19) agrees. However, this circuit can be useful in the context of the invention with a measuring bridge.

[0066] In a type C voltage divider ( Fig. ) not all resistance values ​​can be used without restriction, since, due to the subsequent amplification, excessive amplification will drive the output voltage that the operational amplifier (16) can still provide into the (supply-related) limit.

[0067] Each type of voltage divider has certain characteristics that the voltage divider (with op-amp) is intended to provide in its specific combination and environment. The circuit was designed for a reason and a specific purpose. This originally intended function of a voltage divider (for type A, it's the direct voltage tap; for type B, the inverting amplifier function; and for type C, the I / O converter function) is referred to here as the "primary function." In other combinations, the primary function can be more complex.

[0068] The "primary function" is the function of a circuit for which it was designed and which it performs when it is in operation.

[0069] However, it only functions correctly when it is within its designated operating range; and this is only the case when the outputs of op-amps are within a slightly smaller voltage range than that defined by the circuit's power supply. If an op-amp output, for example, reaches its supply-related limit, then the circuit leaves its operating range, its primary functional range, and thus its primary measurement range (even if the voltage divider itself continues to operate and can still be used via additional voltage taps).

[0070] A necessary (but not sufficient) criterion for ensuring that electronics are within a designated operating range and can perform and ensure their primary function is that the op-amp output involved is within the voltage range defined by the respective supply of the circuit.

[0071] So that the output voltage U out remains safely within the range of the supply voltage (this is also the state in which the circuit can operate as intended and the voltage at the tap node (18) is at the reference voltage U Bez (where valid measurement data is possible) the gain must be limited for voltage dividers of type B and type C, i.e., for type C, R f They can only be designed to a limited extent; in type B, the measuring bridge resistances must not be too different (more precisely: R2 / R1 must not be too large).

[0072] By R f However, with type C, the gain can be easily and variably set over a very wide range. The advantage is that the gain can be determined by just this one resistor R. f It is good and can be adjusted to (almost) any size. This allows the operating range of the circuit, and therefore also a measurement range, to be defined.

[0073] From such voltage dividers of types A to C, measuring bridges with different properties can be constructed in various configurations and combinations, and are used, for example, in the designs of Fig. to find again: Fig. The diagram on the left shows a measuring bridge with voltage taps: The two measuring bridge voltage dividers are not loaded by the operational amplifier inputs.

[0074] The other two examples show measuring bridges that operate in a virtual short circuit because the measuring bridge taps are forcibly held at the same potential (GND) by the operational amplifiers: In the circuit in Fig. The two type C voltage dividers operate independently on both sides. Although the operating principle of this measuring bridge is very different compared to voltage taps, properties of the measuring bridge that are important for acquiring a parameter can be determined in a comparable manner.

[0075] In the rightmost (asymmetrical) circuit ( Fig. The voltage at the lower measuring bridge node is adjusted so that the left measuring bridge node is at ground (Type B). The left-hand voltage divider of the measuring bridge (R1, R2) remains unloaded (here, the input of the op-amp draws no current from the tap node); this constitutes a voltage tap. On the right side, the voltage divider there (R3, R4) is deliberately loaded so that the voltage at the right-hand tap node of the measuring bridge is at a fixed voltage value. Fig. GND is assumed for this; however, any voltage U can be specified. Bezbe.

[0076] Since (and if) the node voltages on both sides are kept at the same value (not always GND), this measuring bridge will also ( Fig. ) is operated in a "virtual short circuit" even though a current tap is only used on one side. However, the term "virtual short circuit" is unambiguous as the operating mode for this measuring bridge arrangement and should therefore be used for this operating mode regardless of the tap type.

[0077] In measuring bridges that operate using voltage taps, the same term describes both the operating mode and the method of signal acquisition at the measuring bridge using an op-amp. In the arrangement of the Fig. However, for example, the left measuring bridge tap is not loaded (voltage tap), while the right measuring bridge tap deliberately loads the right voltage divider (R3, R4) (a "current tap"). Both tap types are therefore used together, so to speak, in a "mixed operation"; however, this says nothing about the operating mode.

[0078] Will be in Fig. If the left op-amp is not used (then there is only a type A voltage divider on the left) and u2 is used as the reference potential for the right op-amp, then the operation for this measuring bridge remains the same (a voltage tap on the left, a current tap with the IU converter on the right, and the operating mode "virtual short circuit" also remains the same).

[0079] Despite the different operating modes, the same principles apply in all cases. Fig. We offer measuring bridge arrangements that are well-suited for many purposes (including analysis). With regard to the information they provide for sensory tasks based on a measuring bridge, they are considered equivalent.

[0080] The procedure required to tap a measurement voltage from a voltage divider or a measuring bridge can therefore differ. Simply tapping a voltage with an instrumentation amplifier is different from tapping a current with a voltage converter; the voltages obtained in this way (or otherwise) and thus actually available can also differ. However, the information obtained in each case is to be considered equivalent.

[0081] Regardless of the specific method used, the type of voltage acquisition, and the characteristics of the resulting measurement voltage, the process will be collectively described and referred to here as "tapping" or "acquiring" a measurement voltage or signal. This applies to direct voltage taps, current taps, and indirect voltage taps via current taps on the half-bridges; it also applies to different operating modes.

[0082] Indirect voltage taps via current taps on the half-bridges represent an important tap method for the measurement signals at the sensor bridge in the context of the invention. This is not part of the invention's invention, but is included here among the tap methods. The important aspect is the resulting indirect measurement signal tap from a sensor bridge via current taps from the provided additional voltage dividers, which also enables a circuit that can be considered the simplest possible measurement bridge amplifier arrangement.

[0083] The reason is that voltage dividers operate independently of each other. Therefore, any combination of a voltage divider in the sensor bridge and an additionally added voltage divider can essentially be considered and used as a new measuring bridge. To distinguish them, these are called half-bridges and represent an important solution for eliminating the high offset voltages that mask the useful signals (i.e., what is actually of interest in the measurement signals). Based on Fig. This will be examined in more detail below; before that, the necessary half-measuring bridges will be defined. SdT: Definition of measuring ranges

[0084] Electronic conditioning of the small voltage provided by a measuring bridge is an essential component of every measuring bridge setup. Electronic circuits require energy and must be electrically powered; however, the supply voltage range that must be set up for this purpose is inherently limited. Electronic circuits can only operate within this limited supply range. This applies to all components of a circuit.

[0085] An operational amplifier that can amplify, for example, a voltage applied to its inputs by a factor of 1000 can only do so as long as the output does not have to provide voltages outside the supply voltage range. As long as the amplifier's input voltage remains within a range of, for example, a few millivolts, this works; the amplifier (not just operational amplifiers) provides output voltages in the volt range whose waveform corresponds to the waveform of the input voltage in the millivolt range (and the waveform of the physical parameter being measured).

[0086] However, the operating range of the electronics is limited to this range. If a larger input voltage were applied to the operational amplifier (e.g., 0.1V), the op-amp would have to exceed its supply range to achieve a gain of 1000, which is impossible. The op-amp then remains at a maximum value (e.g., +12V at the top or -12V at the bottom) as long as the magnitude of the input voltage to be amplified is too high.

[0087] Here, this is referred to as "supply-related limitation" or simply as limitation or saturation.

[0088] In this sense, the operating range of electronics also defines what is called a measurement range. Only within a range in which a system can "operate" can valid values ​​of a parameter to be measured be obtained.

[0089] A "measuring range" refers to the parameter being measured, but will always correlate with the operating range of the electronics. A real measuring range can be smaller than what the electronics' operating range can provide, but not larger. A measuring range specified for a system will at most be equal to, or even smaller than, this real measuring range of the electronics' functionality.

[0090] A necessary criterion for a measuring arrangement intended for such measurements to be located within this working range for a physical parameter to be recorded is that all components of the electronics (with all inputs and outputs occurring therein) are within the supply-related voltage range.

[0091] In particular, all outputs of op-amps are located within a voltage range that is somewhat smaller than that defined by the respective supply of the circuit (often already close to the positive or negative supply voltage).

[0092] The measuring range of a measuring bridge arrangement is therefore seen as a parameter range defined by the electronics, accessible for a measurement task, for which a quantity directly representing the parameter can be provided (parameter-proportional currents or voltages, but also analog or digital data, etc.).

[0093] The operational amplifiers of a measuring arrangement whose outputs may be located outside the operating range are in a "supply-related limitation" or in "saturation". In this case, the measuring arrangement or a part of the measuring arrangement has in any case left the intended operating range and thus also the measuring range that is specified for this measuring arrangement.

[0094] Due to this characteristic of the electronics, measuring bridge arrangements in the SdT ia only operate in the immediate vicinity of the respective calibration point of the measuring bridge and / or only allow for limited sensitivity. However, within the narrow range of the respective measuring bridge calibration point, a measuring bridge (suitably amplified and evaluated) can then offer very high sensitivity.

[0095] This applies both to measuring bridge arrangements that operate with voltage taps and to those in which the measuring bridge is operated in a "virtual short circuit" or otherwise.

[0096] Measurement ranges are therefore defined by the electronic processing that is always required, because the choice of the amplification factor determines how quickly the voltage range defined by the supply of the circuit is traversed.

[0097] This is supposed to be with Fig. As shown: Each measuring range has a defined parameter value, e.g., (29) (30), as the operating point, which lies within the measuring range (36) (37). However, the operating point is not necessarily a parameter value that one would ideally want, that was predetermined, or for which the measuring bridge arrangement was designed. The measuring bridge property that a zero voltage is provided at the tuning point (which is non-trivial) can, however, be used to specify an operating point that can also be determined metrologically.

[0098] The operating point here is the (parameter) point on the characteristic curve where the output voltage of an op-amp crosses the zero line (or, for example, in the case of a single-sided supply, an equivalent line). Fig. The characteristic curves (26) and (28), with their respective zero crossings, define a common operating point (29); the characteristic curve (27), with its zero crossing, defines another operating point (30). Around each such operating point lies a measuring range, which is shown in section (35) below the characteristic curves of the Fig. are indicated by beams.

[0099] Diagram (25), representing a characteristic curve, indicates the flat profile of the small measuring voltage of the measuring bridge over a wide measuring range for a parameter (in this example, a temperature; plotted on the abscissa). Electronically implemented amplifier stages with different gain factors ν = {α, β, γ} or {αβ and αβγ} can be easily implemented and used on the measuring bridge to amplify the small measuring voltage (25). Different measuring ranges are associated with the different gain factors: The characteristic curves (e.g., the output voltage of an op-amp plotted against the parameter T) traverse the available voltage range (40) at different speeds due to the different gains.

[0100] This defines the operating range, and this in turn defines the maximum possible measuring range. The operating point is defined by the zero crossing of the output voltages.

[0101] In Fig. The characteristic curves (26), (27) and (28) indicate the course of the voltages at the outputs of the different amplifier stages. For example, diagram (26) shows the course of the voltage provided by the measuring bridge arrangement at the output of amplifier stage (24) or (33); the gain of the measuring bridge voltages (21) (31) is greatest there with ν=αβγ; the characteristic curve (26) therefore also traverses the supply-related voltage range from (38) to (39) most quickly; the resulting measuring range (36) is small.

[0102] The measuring range M2 (37) is defined by the fact that the available voltage range is traversed less quickly at the output of the penultimate amplifier (23). The gain achieved there is ν=αβ (characteristic curve (27)). Above and below the temperature range M2 (37), the output of amplifier β (23) is within the supply-related limit and has therefore left the operating range of the electronics and thus also the measuring range.

[0103] The measuring range M3 (characteristic curve (28)) is defined by the fact that the measuring voltage (3) at the output of the amplifier α ((22) or (32)) traverses the available voltage range more slowly due to the lower gain ν=α.

[0104] It is important to note that the operating points AP1 (29) and AP3 (29) as well as AP2 (30) are relatively close to each other and that each measuring range lies within the preceding measuring range with a lower gain. The measuring range M1 (36) lies within the measuring range M2 (37), which in turn lies within the measuring range M3 (37). The measuring bridge itself (see characteristic curve (25)) operates with a very wide range to the right and left with respect to the parameter range.

[0105] With parallel-operating amplifiers, which can be achieved, for example, with instrumentation amplifiers using multiple taps, the diagrams shown (10), (11), (12) could be shifted with respect to the operating points by means of offset shifts. However, in the SdT (System of Technology), for various reasons, the direct adaptation of the measuring bridge to the respective task is generally intended. The techniques known for this cannot achieve this for three measuring ranges on one and the same measuring bridge simultaneously.

[0106] If measurement ranges are to be developed for a sensor task that are adjacent to each other and possibly even further apart, this cannot be achieved by simply selecting amplification factors ia. Other designs are required.

[0107] In the context of this document, partial measurement ranges are understood to be subsections from a potentially larger range of values ​​for a parameter. This is to be distinguished from the nested measurement ranges of the SdT (Standard of Technology). This can and should include the possibility that several sectionally defined partial measurement ranges can follow each other directly and that partial measurement ranges, when combined, define a larger measurement range.

[0108] However, it is not only specific measuring ranges that are redefined. Sub-measurement ranges within one or more other measuring ranges can also be defined. For example, the temperature measuring range for monitoring a cooling system and the measuring range of a fever thermometer, in this sense, simply represent two different measuring ranges or two sub-measurement ranges from the measuring range that a measuring bridge can offer, which is specified for the temperature measuring range of, for example, -30°C to 100°C. SdT: Definition of application-specific measuring ranges

[0109] The parameter space, as a range of values ​​in which a physical parameter to be measured can fundamentally be located, extends much further than would be accessible in the context of the technology under focus here.

[0110] Therefore, it is not only the inherent properties of measuring bridge arrangements that necessitate differently positioned and differently extending measuring ranges for the use of a measuring bridge. This is often required by the measurement task itself.

[0111] Take magnetic field measurements, for example: In technical settings, the field strength to be measured spans many orders of magnitude, from very weak (smaller than the Earth's magnetic field strength) to very high field strengths that don't occur naturally on Earth; and this also applies to different frequency ranges. While TMR and GMR measuring bridges can, for example, capture wide ranges of field strengths, in practice, comparable problems always need to be solved. However, not all requirements can be met using the SdT (Standard of Technology).

[0112] As a side topic, light sensors, e.g. measuring bridges made of photosensors, e.g. resistors, should be mentioned, which are intended to measure residual light (few photons), but also the more intense light incident during an experiment within a narrow intensity range.

[0113] For example, there are pressure measurements, which need to cover different measuring ranges, ranging from the detection of sound or vibrations (e.g., by microphones) to the detection of relatively small pressure differences (for example, for flow measurements or medical applications), all the way to gigantic pressure ranges (e.g., pressure measurements in the deep sea), and so on. Special pressure sensors are used in very different areas for various applications, with the pressure sensor elements often already arranged in a measuring bridge configuration. And in all these applications, even if defined somewhat differently each time, comparable technical solutions can be seen (and sought).

[0114] Similar concepts can be found in the context of force sensors, strain gauges, etc. Depending on the task, measuring ranges and resolution requirements can vary considerably.

[0115] For example, there are the temperature measurements mentioned above, which are used in very different measuring ranges. In principle, everything could be achieved with a single measuring bridge, because only the operating point and the gain need to be appropriately selected. However, monitoring room temperature, the temperature in a cooking pot, or the temperature in a freezer with an identical fever thermometer is rather uncommon because, due to the properties of measuring ranges of measuring bridge amplifiers shown above, different measuring ranges (ia) can only be provided in interval-nested configurations. Resolution and measuring range are mutually limited in the SdT (Sensitivity of Temperature), with respect to a defined operating point (ia).

[0116] It is not possible to perform different tasks in different, but separate, measuring areas with different resolutions (for which the same measuring bridge is used) simultaneously in the SdT.

[0117] Summary of measuring ranges: Different measuring ranges in the SdT ia are defined by the measurement task or the respective measurement objective as a requirement. However, measuring ranges are only truly realized (limiting the measuring range) as technically given or occurring limits through the operating range and the operating mode of the respective electronics.

[0118] Here, "measuring range" should therefore not be understood as predefined target values ​​or requirements (of any kind), but rather as a range defined by the electronics (i.e., only after and through implementation). This range is accessible through measurement (recording a characteristic curve with a zero crossing).

[0119] Measuring ranges are defined by an operating point and the selected gain, which in turn defines and specifies the measuring range width.

[0120] The range of the physical parameter in which the physical parameter to be measured can be provided as and by a voltage or current or another quantity in which the parameter to be measured is represented at least proportionally (as linearly as possible, as strictly monotonically as possible, or at least monotonically) is therefore also the measuring range of a measuring bridge arrangement.

[0121] The required resolution of a parameter to be measured necessitates a defined gain, which in turn defines or limits the measurable range. If one wants to utilize a sensor bridge to cover one working range alongside another, primary working range, this cannot be achieved by simply selecting gain factors ia. For the reasons mentioned above, this is not feasible in the SdT (Sensor Design Technology).

[0122] In this context, it is an object of the invention to provide measuring bridge amplifier arrangements that can provide several measuring ranges with only a single sensor measuring bridge, which can be located directly next to each other or at some distance from each other, in order to combine small partial measuring ranges into a larger overall measuring range.

[0123] The basic premise of the invention is that if it is possible to create several partial measurement ranges, e.g. 4, 8, 16, 32, etc., directly next to each other and to include them in an evaluation concept, then this would represent a progressive extension of the measurement range while maintaining a very high resolution.

[0124] This would result in an overall measurement range, characterized partly by the measurement range widths of the individual sub-measurements and partly by the number of sub-measurements. The part of the creation of an overall measurement range that is determined by the number of sub-measurements represents a pre- or partial digitization of the overall range (counting them thus practically provides the upper bits of a digital representation of the overall measurement range).

[0125] Fig. This solution represents the approach and shows several characteristic curves above and below that follow each other directly, whereby each characteristic curve over the respective parameter (e.g. temperature, pressure, etc. plotted on the abscissa) could only be provided individually in the SdT with a measuring bridge.

[0126] The characteristic curve (50) of the Fig. , which can also be realized as a single characteristic curve in the large measuring range (57) in the SdT (cf. in Fig. e.g. characteristic curve (26)), here follows directly a preceding, iW similar characteristic curve (52) with the measuring range (54) and a further preceding characteristic curve (53) with the measuring range (55), which can be realized side by side according to the invention (but not in the previous SdT).

[0127] With a measuring bridge arrangement that can provide the two characteristic curves (52) (50) (or several) as partial measuring ranges (54) (51) with a single measuring bridge, a measuring range (56) twice as large could initially be covered. With more and more partial measuring ranges, a large overall measuring range (57) could be represented with consistently high resolution.

[0128] characteristic curves, e.g. (63) (64) ( Fig. below) have operating points (61) (62) and measuring ranges (58) (59) whose operating point position and measuring range width can be constructively defined, for example, by designing an additionally provided voltage divider and via the selected gain (by only one resistor).

[0129] A multiple indirect voltage tap at the sensor measuring bridge via a current tap at additionally provided voltage dividers, as a particularly preferred tap configuration according to the invention, enables both the simple design of operating points and measuring ranges, as well as a very simple technical solution with only one op-amp; this also introduces only very little additional noise.

[0130] A more extended measuring range can be achieved by a higher number of sub-ranges or, again, by lower gain with wider sub-ranges. With many such sub-ranges, a large overall measuring range can then be achieved (57). This is therefore also determined by the gain. (cf. e.g. in Fig. with (60); in the construction above, approximately 6 partial measuring ranges cover about one measuring range, which is covered below by only 4 partial measuring ranges).

[0131] The amplification required for maximum resolution through analog processing of the measurement voltages might only need to be designed once for small sub-measurement ranges (possibly even for just a single sub-measurement range, which, due to the consistently comparable setup, might be equally valid for all others within the overall measurement range). Because of the small sub-measurement ranges, the amplification can be very high, but it will also have limits. Since the maximum achievable resolution is limited by noise and digitization, this limit can be estimated: - The amplitude of the noise superimposed on a measurement signal defines an analog equivalent for one bit of the analog-to-digital conversion (U). Vers / 2 NThis defines a still meaningful amplification for the measurement signals of a measuring bridge. - With such maximum amplification, i.e., with maximum resolution, the number range 2 N The ADC's response is mapped once to the available supply voltage range, i.e., a single sweep of the supply range when the parameter to be measured changes, defined by u. Rausch *2 N (and via the inverse function) the smallest possible partial measurement range width. - Either u Rausch *2 N or U Vers / 2 N However, this represents fundamental limitations: ◯ Because: u Rausch *2 N would be the voltage that is amplified to U Vers to be mapped (or can be mapped); this defines a meaningful gain and / or prescribes the properties of the ADC; But: U Vers / 2 N(The voltage that then represents a bit) would be the voltage up to which the noise amplitude can still be meaningfully amplified (unless one wants to investigate the noise); this also defines the amplification that is just meaningful. Only the minimum of both is the analog amplification that makes technical sense. If the smallest partial measurement range is insufficient for a measurement project, then the desired measurement range can be increased. ◯ while maintaining the resolution (i.e. the gain) only by multiplying the partial measurement range width n-fold (the inventive idea) ◯ and / or by a smaller amplification of the measurement signals (foregoing higher resolution; cf. Fig. ) can be achieved.

[0132] Conversely, the same applies: if it is possible to divide an existing or desired larger measuring range into smaller, adjacent sub-measuring ranges, then a much higher resolution can be achieved in these sub-measuring ranges than is possible in the overall measuring range.

[0133] If many consecutive (countable) sub-measurement ranges form a large measurement range, the sequence of sub-measurement ranges would represent a pre-digitalization of the progressive measurement range extension. For example, if 64 = 2 6 If partial measurement ranges could be provided, the resolution (previously e.g. 10 bits of an ADC) would increase to 16 bits (the 6 bits of the pre-digitization simply placed in front of the 10 bits of the ADC digitization).

[0134] This fundamental solution, which is also an expanded problem, must therefore be solved by a technique that allows any number of small, high-resolution partial measurement areas to be positioned side by side and, if possible, directly sequentially. The invention utilizes the (to be defined shortly) measurement bridge extension, which will form half-measurement bridges and measurement bridge equivalents, and employs an indirect tap configuration for tapping the measurement voltages from these half-measurement bridges and measurement bridge equivalents.

[0135] This can be achieved, among other things, by using voltage taps on half-measuring bridges created by extending measuring bridges, but this would require instrumentation amplifiers, which are often relatively complex and can be expensive (and also generate more noise). The invention therefore preferentially utilizes measuring bridge amplifier designs in such half-measuring bridges, which can be considered the simplest of all.

[0136] The simplest solution is that every known bridge amplifier requires at least one op-amp and one resistor. The indirect tap method used here to obtain parameter-proportional measurement voltages from a sensor bridge via the half-bridges and bridge equivalents (to be defined shortly) requires only one op-amp and one resistor, thus representing the absolute minimum of technical effort and can therefore be considered the simplest solution. Measuring bridge extensions

[0137] To extend a measuring bridge, additional voltage dividers are added in parallel to the voltage dividers of a sensor measuring bridge. Each newly added voltage divider and one voltage divider of the measuring bridge together define a new half-measuring bridge, which is optimized for a small measuring range and can therefore process its measuring voltage even with high gain.

[0138] Multiple voltage taps, which can also be used in conjunction with current taps, are an essential feature of the invention. Sensor measuring bridges can thus be extended so that a large number of new half-measuring bridges can be created based on an original sensor measuring bridge. Fig. shows such extensions of a sensor measuring bridge:

[0139] For example, one can imagine that from a given sensory measuring bridge ((66) in Fig. On the left side, one of the two voltage dividers is ignored, and a precisely known additional voltage divider is placed in parallel to the isolated voltage divider. For example, if the right voltage divider of the sensor measuring bridge (68a) is ignored and the additional voltage divider (67b) is added to the left voltage divider (67a) of the sensor measuring bridge, then such a half-measuring bridge (67) is created on the left side. On the right side of the sensor measuring bridge, a second half-measuring bridge (68) is created in the same way from the existing voltage divider (68a) and the additionally added voltage divider (68b). Since all voltage dividers operate independently of each other, neither the original sensor measuring bridge nor any of the newly created half-measuring bridges are affected in their function by these additional voltage dividers.

[0140] The two voltage dividers that make up a given sensor bridge are first conceptually separated. Then, an additional voltage divider is added to each of these two voltage dividers, and the combination of the additional voltage divider with the voltage divider of the sensor bridge is considered a new measuring bridge. The voltage divider that was "ignored" in each case remains; therefore, the sensor bridge remains unchanged and its functionality is unaffected in the arrangement (middle circuit of the Fig. with (67) (68)).

[0141] In this way, new measuring bridges can be created using the two additional voltage dividers ( Fig. ). If the voltage dividers of the sensor measuring bridge remain unloaded, all voltage dividers can be used independently of each other, including all newly created voltage divider combinations, and the sensor measuring bridge can continue to be used.

[0142] To ensure that the voltage dividers of the sensor measuring bridge remain unloaded, voltages at the sensor measuring bridge can only be tapped using voltage taps (i.e., with instrumentation amplifiers or with op-amp inputs).

[0143] In Fig. With two additional voltage dividers, a total of four (three new) measuring bridges are available (circuit in the middle): - The original sensor measuring bridge (66) is recognizably retained (for this one must think of (67) and (68) or (67a) and (68a) as being joined together again), - two new half-measuring bridges (67) (68) are being built and - the two newly added voltage dividers alone clearly also represent a measuring bridge configuration; these additionally form a measuring bridge equivalent, which shall be referred to as such here.

[0144] Furthermore, sensor bridges can be extended not only by adding one or two additional voltage dividers on one or both sides of the sensor bridge or one of the voltage dividers contained therein, but by adding several (and furthermore: very many) new voltage dividers (69) (70) (in Fig. The right-hand circuit with (69) and (70). Thus, from the single sensor bridge voltage divider and the many additionally added new voltage dividers (which have only been conceptually assigned to one side), many new half-bridges are created, which can operate independently of each other and in parallel to the original sensor bridge, as long as further voltage taps are used there.

[0145] Furthermore, the additionally added new voltage dividers (considered in pairs) result in many new measuring bridge equivalents.

[0146] In the example of the arrangement Fig. On the right, with n=8 additional voltage dividers provided to the sensor measuring bridge (n is the sum of the voltage dividers (69b) plus (70b)), there is a sensor measuring bridge, 8 half measuring bridges and n(n+1) / 2=36 measuring bridge equivalents).

[0147] The chosen assignment of the additional voltage dividers to the right (70) or left (69) side of the original sensor measuring bridge is arbitrary in itself, since all voltage dividers are supplied with the same voltage U err They are supplied with power and operate independently of each other. Only the common tap of a voltage from the half-measuring bridge as the measuring voltage truly defines such a half-measuring bridge. But not every measuring bridge equivalent is used.

[0148] Such extensions of a sensor measuring bridge by means of additional voltage dividers are also possible if the sensor measuring bridge operates in a different operating mode, e.g. in a virtual short circuit.

[0149] This will be done with Fig. As shown: The basic circuits with voltage divider (72a) and op-amp (73) on the left and voltage divider (74a) and op-amp (77) with resistor Rf (77a) on the right together form a measuring bridge arrangement that operates in a virtual short circuit. On the left are the extensions (71) to a type B voltage divider (type B op-amp is (73)); on the right are the extensions (75) to a type C voltage divider (op-amp is (77)). The half-measuring bridges (72) and (74), reassembled here, again form the sensor measuring bridge, which operates with its original primary function in the virtual short circuit. This will therefore continue to operate as originally intended, unaffected by the additionally added voltage dividers, as long as only additional voltage taps are used on the sensor measuring bridge itself.Only by tapping a voltage from one of the half-measuring bridges as a measuring voltage does the voltage dividers functionally come together, and only then does a functioning half-measuring bridge truly define one.

[0150] The additional voltage dividers (71) (75) can be used for both voltage and current taps (e.g., (76)). A current tap using an IU converter (76), for example, at an additional voltage divider in the half-bridge (75), would not affect the sensor bridge itself. Regardless of the reference voltage used by the IU converter (76) (here, GND), only the tapping of a measurement voltage from one of the half-bridges combines the voltage dividers and defines a half-bridge.

[0151] Therefore, when evaluating half-bridges, the taps on the sensor bridge must always be voltage taps. The taps on any additionally added voltage dividers can be either voltage or current taps. This means that only the combinations of current tap-voltage tap and voltage tap-voltage tap are available on the half-bridges.

[0152] For example, if a voltage divider of type B (72) (73) is used (in Fig. On the left), additional voltage dividers (71) can be inserted. Current taps at these additional voltage dividers of the sensor bridge on the left are also useful, for example, if the op-amp (73) can / should enter saturation and thus a different operating mode can be assumed, in which the left sensor bridge voltage divider (72) continues to operate as a type A voltage divider even when supply-related limitations of the op-amp (73) have already been reached. Taps at these additionally added voltage dividers can therefore be voltage or current taps.

[0153] If only voltage taps are used (i.e., half-bridges are operated at the voltage tap), then instrumentation amplifiers are required. The effort involved is somewhat greater than for a current tap. Current taps are also easier to handle and design: therefore, current taps are preferred here and are shown in detail, although this does not expressly exclude other tap configurations or limit the invention to them.

[0154] If a type C voltage divider (74) is used in the sensor bridge (op-amp (77) forms an IU converter), additional voltage dividers (75) can also be inserted. Current taps (76) on the additional voltage dividers can also be used here (e.g., (76)), whereby the reference voltage (here GND, but this can be different) allows for variations.

[0155] It is important to see that the evaluation of a sensor measuring bridge can be broken down into the evaluation of half-measuring bridges, which can now include several partial measuring ranges: Fig. This section outlines the strategic advantages achievable through extensions to a sensor measuring bridge in connection with the half-measuring bridges: A sensor measuring bridge ( Fig. (above) consists of two voltage dividers which, with respect to a parameter to be measured, define the two functions f 12 (72) and f 43 (71) provide the voltages at the tap nodes. The sensor bridge thus provides two partial functions f via the voltage dividers. 12 and f 43 Ready. The first two together then give the overall function of the sensor measuring bridge above with Z(t).

[0156] As mentioned above, these voltage dividers operate independently of each other; therefore, f 12 and f 43also functions that can be viewed independently, each providing a part of an overall function in which the parameter to be measured is represented (even with potentially very small changes over time).

[0157] First both functions f 12 (72) and f 43 (71) together with f 12 -f 43 the objective function Z(t) of a sensor measuring bridge, in which the smallest changes of the physical parameter to be measured are reflected.

[0158] The two measuring bridge branches (voltage divider of the sensor measuring bridge) have, in a sense, divided the task between them.

[0159] Even the smallest changes in a physical parameter measured by the sensor bridge represent a function in time as a measurement signal. The measurement signal from the sensor bridge, as the output or useful function, is therefore Z(t) = f 12 -f 43 .

[0160] The sensor measuring bridge is now conceptually divided again into the two voltage dividers on the right and left. Then each side is extended with a newly added voltage divider, on the left with R. a and R b right with R c and R d The new half-measuring bridges are being built (see in Fig. the middle row), of which the two new functions L(t)=f 12 -C L (left) and R(t)=f 43 -C R (right) are provided as measurement signals. The transition (74) from the left voltage divider of the sensor measuring bridge to a half-measuring bridge and the transition (73) from the right voltage divider of the sensor measuring bridge to a second half-measuring bridge is, according to the explanations regarding Fig. This can now be understood.

[0161] Now, however, two half-bridges (to the right and left of the sensor bridge) share the overall task of the sensor bridge. These partial functions of the two half-bridges still fully encompass all the functions of the sensor bridge. The tasks previously seen solely in the two voltage dividers located to the right and left of the sensor bridge are transferred via (74) (73) to the functions of the two newly formed half-bridges (which are also seen as parts of a complete function and are located to the right and left).

[0162] It can be said that the partial function (72) (71), which each of the two voltage dividers of a sensor measuring bridge (99) contributes to the overall function of a respective sensor measuring bridge (99), transforms (74) (73) into a partial function of each half-measuring bridge (74a) (73a), whose measuring voltages can be evaluated independently of the specified sensor measuring bridge (99). The portion of sensor information that the respective voltage divider in the sensor measuring bridge detects or contributes is incorporated into the overall function of the half-measuring bridge unaltered and unchanged.

[0163] The difference between these two new sub-functions L(t) = f 12 -C L and R(t) = f 43 -C R so in Diff = L(t) - R(t) = (f 12 -C L ) - (f 43 -C R ) = (f 12 - f 43 ) - (C L - C R ) is that, - what the measuring bridge alone provides with Z(t) (all the information about the parameter to be measured is in f 12 -f 43 (= Z(t)), so the diff remains preserved). - The new component, which only comes from the measuring bridge equivalent (from the additionally added voltage dividers), represents "merely" a constant here. - The voltage of the measuring bridge equivalent roughly describes the position of the sensor measuring bridge as a constant.

[0164] This defines the task of the sensor measuring bridge. Fig. The task has been transferred to two half-measuring bridges and to the measuring bridge equivalent; or rather, the overall task of the sensor measuring bridge as such has been divided between these half-measuring bridges.

[0165] For these two half-bridges, it must be shown how the measured voltages are to be evaluated. For this purpose, the abstract form of the representation of the middle row of the Fig. into the actual constructions of half-measuring bridge circuits of the lower row of the Fig. over. (As already mentioned, instrument amplifiers can also be used here).

[0166] Since these steps can be performed multiple times for extensions on both sides of the sensor measuring bridges, this can be done with Fig. The diagram shown can be executed multiple times, for example with several additional voltage dividers with different resistances. a 'and R b ', with different gain, with several half-measuring bridges and many measuring bridge equivalents, e.g., eight times. This allows for the creation of many individual characteristic curves (e.g., of the Fig. ) can now be achieved relatively easily and with simple technology. Fig. The figure (bottom line) shows that for the two half-measuring bridges only one op-amp and one additional resistor are needed per half-measuring bridge, i.e., the least possible effort is required.

[0167] Due to the ability to adjust the gain separately for each half-bridge, a very high gain can be selected on both sides for each half-bridge (see the circuits below with the IU converters (77) (78)). The output voltages (80) (79) thus contain the (already highly amplified) voltages from the sensor bridge, while the high offset is "hidden" in the bridge equivalents. A high offset of the original sensor bridge plays a role in the voltages (79) (80) of the Fig. only a minor role.

[0168] With several additional voltage dividers, many half-bridges can be formed on both sides of a sensor measuring bridge; this creates new half-bridges for many operating points, which, for example, at equidistant intervals and with a constant measuring range width, define the characteristic curves of the Fig. or (63) (64) be able to train.

[0169] A key aspect of the arrangement of the Fig. This is therefore the evaluation of the half-measuring bridge.

[0170] The half-bridge amplifiers can be designed relatively simply, so that each of these half-bridges can be adapted to this task with regard to the measuring range width and its operating point (and thus also the distances between the operating points). Voltage taps can be used for this purpose, and current taps can also be used on the side of the supplied voltage divider.

[0171] The measurement signals from the half-bridge amplifiers can therefore be obtained using the relatively simple technique (in itself with the simplest measurement bridge arrangement possible), which also provides the indirect voltage taps (and introduces only the slightest additional noise with the electronics): Fig. The figure on the left shows the left part of a sensory measuring bridge (100a), which is equipped with R a and R bwas extended as an additional voltage divider (100b) and on the right the right part of a sensory measuring bridge (101a), which is connected to R c and R d (101b) has been extended. This only corresponds to a more accurate representation of the bottom line of the Fig. with two half-measuring bridges (100) (101)

[0172] It should be noted, however, that these are constructions that can be present multiple times to the right and left of the sensor measuring bridge (except for the bridge itself), which are then combined again (one half-measuring bridge from the right, one half-measuring bridge from the left) to create one of the characteristic curves of the Fig. e.g. (50) (52) to train.

[0173] Since all voltage dividers (100a) (100b) (101a) (101b) operate independently of each other, any combination of one of the additionally added voltage dividers and one of the voltage dividers of the sensory measuring bridge (which are located on the far right and left here) can be considered and used as new measuring bridges. To distinguish them, these are therefore referred to as half-measuring bridges.

[0174] A mathematical analysis of the circuits, - left with the approach i a +i f =i b , also (u1-u KL) / R a +(U outCab -u KL ) / R f = (u KL -u3) / R b leads via R f U outAab + U outCab = u outA12 (R f / R a / / b +1) with c1=R f u outAab and c2= (R f / R a / / b +1) to a formula of the structure c1+U outCab =c2 U outA12 , and - on the right with the approach i c +i f = id , also (u1-u KR ) / R c +(U outCcd -U KR ) / R f = (u KR -u3) / R d via RF and outAcd + U outCcd = (R f / R c / / d +1) u outA43 with c1=R f u outAcd and c2= (R f / R c / / d +1) to a formula of the structure C1+U outCcd =c2 u outA43 .

[0175] In this case, c1 and c2 do not have to be the same on the right and left.

[0176] U outCcd and U outCab are the output voltages of the op-amps with which the current taps (IU converters) are connected to the C-type voltage dividers with R a and R b or R c and R d are realized; U outAab and U outAcd are fictitious stresses that occur at node K L (104) (with u outAab ) or at node K R (105) (with u outAcd), i.e., at the additional voltage dividers provided for the extension, which would only be present if the respective voltage divider were unloaded; u outA43 and u outA12 represent the two voltages u2 and u4 at the unloaded tap nodes of the sensor measuring bridge.

[0177] As an analysis shows, the resistances of the two additional voltage dividers do play a role in the constants c1 and c2. However, they are irrelevant for the sensory function, which is expressed in U. outCab and U outCcd The circuit represents the resistances of the voltage dividers of the sensor bridge, but these are irrelevant; only the resistances of the voltage dividers are and remain relevant for the sensor function. The circuit thus represents a tap configuration from the voltage dividers of the sensor bridge, which operates via the illustrated detour of a current tap at the additional voltage divider provided for the extension.

[0178] Such current taps on voltage dividers added for extension, which are parallel to the voltage divider of the sensory measuring bridge, then represent, if for U Bez (102) (103) the tap voltage from the voltage dividers (100a) (101a) of the sensor measuring bridge is used, represents an indirect voltage tap from the respective voltage divider of the sensor measuring bridge.

[0179] Such an indirect voltage tap from the sensor bridge differs from a direct voltage tap or a current tap in the state of the art. Importantly, however, such indirect access methods can be implemented and applied multiple times to the same sensor bridge.

[0180] The constants c1 and c2 (which can be calculated in advance for each half-measuring bridge) can be replaced by a virtually free choice of resistors, e.g., R f , R c and R d, defined or designed, which can greatly simplify the design of the measuring bridge arrangement.

[0181] Additional advantages include: - The detour of current taps at (possibly several) additional voltage dividers located in parallel to a sensor measuring bridge represents a tap method that, due to the small number of components, has very few additional noise sources. - The high value over only one resistance R f defined and definable gain and that via only two resistors (e.g. R a , R b The defined operating point definition allows for easy determination of the operating point and measurement range widths. Since the additional voltage dividers are designed and "adapted" for the respective defined measurement range, the gain within that range can be made arbitrarily large and implemented with a uniform amplifier type ("the simplest ever"). This represents a simplification and can also be seen and used as a "Yor digitization".

[0182] Whether and in which combination of the used taps such an indirect tap is also useful must be examined and defined in each individual case. Limitations, extensions and possibilities must be considered on a case-by-case basis.

[0183] This means Fig. This represents a measuring bridge arrangement in which the bridge's behavior can be determined on a very small scale using electronics that only need to be designed once and are already known. In the combined output voltages of the two sides, all changes to a parameter being measured are still present, even on a very small scale, and unchanged, even if the sensor bridge itself is operating far from its calibrated state.

[0184] By using a single sensor measuring bridge, new evaluation methods for sensory tasks are enabled by extending its capabilities.

[0185] Thus, even with a measuring bridge located far from the tuning point, a parameter to be measured can be acquired with high resolution from the measuring voltages of the newly created half-measuring bridges resulting from the extension. This would not be possible on the SdT because the high offset of the sensor measuring bridge voltage prevents the ia.

[0186] Thus, with and to just one sensor bridge in the measuring bridge arrangement, wide or extended measuring ranges are created, i.e., only because additional voltage dividers are added in parallel to the two voltage dividers of the given sensor bridge, whereby - New half-measuring bridges are created (each consisting of a voltage divider of the sensor measuring bridge and an additionally provided voltage divider) and - the additionally provided voltage dividers (in pairs) can form half-measuring bridges or measuring bridge equivalents.

[0187] If initial measurement voltages are provided on both sides of the potentially numerous new half-bridges, which are created together with a voltage divider of the original sensor bridge, then these initial measurement voltages collectively represent all (even the smallest) changes in the parameter being measured. The measurement signal from the sensor bridge remains completely intact, and due to the tuning of the half-bridges, this can be achieved (even with very high gain) using essentially the same technique, without having to consider any supply-related limitations.

[0188] If further (other) second measuring voltages are provided by the half-measuring bridges or measuring bridge equivalents, which can each be seen in pairs in the additionally provided voltage dividers, then the position of the measuring bridge on a larger scale is represented in the second measuring voltages.

[0189] The measurement signal position on a large scale can be determined from the voltage difference at node K. L and K R It could be determined, but could also be disregarded as "compensated".

[0190] In this context, if one imagines, for example, a (initially only fictitious) tension staircase ( Fig. If the function is presented as a function that describes the position of the characteristic curves on a large scale, then it can be used to describe compensation or to describe the upper bits and the associated voltage of a fictitious ADC. Similarly, the step height (e.g., the jump in the step voltage from (54) to the step voltage of (51)) must be seen as an additive component that allows the subsequent characteristic curve to be computationally raised by one step. The step height should be considered to be as high as the voltage range available for recording a single characteristic curve.

[0191] This is theoretically easy to implement because the steps (65) are already present as the voltages of the measuring bridge equivalents of the various half-measuring bridges involved and can actually only be used separately for a large-scale assignment.

[0192] The first and a second measuring voltage together then yield the measuring voltage provided by the entire measuring bridge arrangement; and this is repeated multiple times with each additional voltage divider. Generally, at least one of the first measuring voltages provided by one of the newly formed half-measuring bridges is combined with at least one of the second measuring voltages, which can be generated in pairs from the additional voltage dividers of the measuring bridge equivalents, to form at least one common measuring voltage. However, the offset-loaded voltage no longer needs to be directly evaluated by the sensor measuring bridge.

[0193] The amplification of the half-measuring bridges formed from a voltage divider of the sensor measuring bridge and an additionally provided voltage divider is carried out in such a way that the original sensor measuring bridge - can be operated without further coordination or adjustment (which can apply to any measuring range) and - the newly defined half-measuring bridges (through the newly added voltage dividers) are operated in a coordinated manner.

[0194] For this purpose, measuring voltages are used. - both from the newly defined and coordinated half-measuring bridges (which can be done with very high amplification and an iW identical technique) - as well as from the measuring bridge equivalents (but only slightly amplified).

[0195] The measuring voltage, which can be tapped from the sensor measuring bridge, is no longer used directly.

[0196] These two types of measuring voltages are processed into a common measuring voltage, which is then provided as a measuring voltage by the measuring bridge arrangement.

[0197] One difference to the SdT is therefore already in that the sensor measuring bridge - the voltage difference is no longer taken directly from the tap nodes as a measuring voltage, amplified, and made available for further evaluation, but now only - first measuring voltages from the newly formed half-measuring bridges and - a second measuring voltage is used and processed by the newly formed measuring bridge equivalents.

[0198] The voltage of the sensor bridge no longer needs to be directly evaluated (but can still be used via additional voltage taps or an instrumentation amplifier). No measures are required at the sensor bridge itself to achieve direct calibration.

[0199] The (analog) evaluation can be designed in such a way that the electronics do not have to leave the available voltage range (operating range) (even if they are possibly derailed, i.e., already operating far from the tuning point); that is, at any given time there is at least a part of the electronics with an output that is not limited (due to the supply) and that can provide valid measurement voltage values ​​for a defined partial measurement range without, for example, the need for measurement range switching.

[0200] Expanding on these basic ideas, instead of potentially many additional voltage dividers (analog or digital), potentiometers (pots) can also be used (a potentiometer is essentially a variable voltage divider); a circuit with potentiometers places only slightly different demands on the evaluation. A standard voltage divider can also be modified with a potentiometer.

[0201] By using a finely graduated (e.g. with three gain levels) partial measurement range utilization, high-resolution measured values ​​can be obtained with a single sensor bridge, which can be assigned to many small measurement ranges and which together can cover a large measurement range.

[0202] The combination of both allows the behavior of a sensor bridge or the behavior of the parameter to be measured to be determined with high resolution on a very small scale using electronics that only need to be designed once (even in operating points of the voltage dividers that are far removed from the tuned state of a deranged sensor bridge), and at the same time also allows the state of the measuring bridge to be determined on a very large scale, i.e., the widely separated operating point distance via the measuring bridge equivalents.

[0203] The analog gain can be increased by a factor that allows the total measurement range to be divided into sub-ranges. A single measuring bridge provides more sub-ranges, which can be individually adapted to the specific measurement objective or (designed only once) used multiple times with different operating points. In this way, the range of values ​​for the parameter to be measured, originally achievable with a measuring bridge arrangement, can be expanded to include further values ​​for various applications.

[0204] To determine, for example, which op-amp output or sub-range is currently relevant—that is, to ascertain the values ​​of the upper bits of the overall digitization—it may suffice to detect the currently active channel via the amplifier output. Analog XOR circuits (similar to bridge rectifiers) or XOR gates with sufficient voltage rating (e.g., 18V CMOS gates) can be used for this purpose. Using standard methods, a partial digitization with a significant resolution gain can then be achieved with an ADC (which only needs to be designed and implemented once for the partial digitization). Prepending the counter value of the sub-range as the uppermost bits results in a full digitization.

Claims

[1] Measuring bridge arrangement with sensor measuring bridge (66) (99) and measuring bridge reinforcement (77) (78) characterized by , that additional voltage dividers (69b) (70b) (71) (75) are connected in parallel to the voltage dividers (69a) (70a) (72a) (74a) of a sensor measuring bridge (66), so that these additional voltage dividers - together with a voltage divider (69a) (70a) of the sensor measuring bridge form half-measuring bridges (69) (70) and - even be able to form paired measuring bridge equivalents ( Fig. ), and - the first measuring voltages (79) (80) (53) (63) are provided by the new half-measuring bridges (69) (70) (100) (101), - second measuring voltages (65) are provided by the measuring bridge equivalents, which are simultaneously provided by the measuring bridge arrangement. [2] Measuring bridge arrangement according to claim 1 characterized by, that the partial function (72) (71), which each of the two voltage dividers of a sensor measuring bridge contributes to the overall function of the sensor measuring bridge, passes unchanged (74) (73) into the partial function of each half measuring bridge (74a) (73a), whose measuring voltage can be evaluated independently of the sensor measuring bridge and is provided as a first measuring voltage. [3] Measuring bridge arrangement according to claim 1 or 2 characterized by , that without directly including the voltage difference from the sensor measuring bridge as a measuring voltage in the evaluation, first measuring voltages from at least one of the formed half measuring bridges are provided and these are linked with at least one of the second measuring voltages of measuring bridge equivalents to at least one measuring voltage of the sensor measuring bridge arrangement. [4] Measuring bridge arrangement according to one of claims 1-3 characterized by, that at least one additional voltage divider (69b) (70b) is provided in parallel to the voltage dividers (69a) (70a) of the sensor measuring bridge (66), which defines the tuning state of a new half measuring bridge (69) (70) (100) (101) thus created and therefore an operating point (61) (62) of a characteristic curve (63) (64). [5] Measuring bridge arrangement according to one of claims 1-4 characterized by , that the voltage dividers (69a) (70a) of a sensor measuring bridge (66) are connected in parallel with additional voltage dividers (69b) (70b), which define operating points (61) (62) and measuring range widths (58) (59) via the amplification of the newly created half-measuring bridges, so that the characteristic curves (63) (64) lie directly next to each other and can follow each other directly. [6] Measuring bridge arrangement according to one of claims 1 to 5 characterized by, that measuring ranges (54) (51) (55) or partial measuring ranges of the half-measuring bridges follow each other closely, so that the quantization of a larger measuring range (57) is achieved. [7] Measuring bridge arrangement according to one of claims 1 to 6 characterized by , that the sensor measuring bridge (66) (99) is operated with voltage taps only in a deranged mode far from the tuning point of the sensor measuring bridge without measures for adjustment or tuning. [8] Measuring bridge arrangement according to one of claims 1 to 7 characterized by , that without using the measuring voltage of the sensor measuring bridge (66) (99) as a voltage difference, at least one evaluation from one of the half measuring bridges with a very high analog gain does not have to leave the available voltage range. [9] Measuring bridge arrangement according to one of claims 1 to 8 characterized by, that an additional voltage divider, which is added to one of the voltage dividers of the sensor measuring bridge on at least one of the two sides and thus forms a half measuring bridge, is a digital or analog potentiometer or that a digital or analog potentiometer is part of such an additional voltage divider. [10] Measuring bridge arrangement according to one of claims 1 to 9 characterized by , that half-measuring bridges (74a) (73a) (100) (101) from the voltage dividers (100a) (101a) of a sensor measuring bridge (99) with each an additionally provided voltage divider (100b) (101b) are operated in virtual short circuit by one of the two tap nodes of the sensor measuring bridge supplying the reference voltage (102) (103) for an IU converter circuit (77) (78) which performs a current tap at the tap node (104) (105) of an additionally provided voltage divider (100b) (101b).

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