Measuring bridge arrangement with automatically changing measuring ranges

Abstract

In the case of measuring bridge amplifiers for sensors, it often seems paradoxical that the required high amplification of the tap voltages from a measuring bridge is so easily achievable with electronics on the one hand, but on the other hand, a very high amplification severely restricts the range in which the measuring bridge can be used in a real application. In the current state of the art, only one operating state is provided for a measuring bridge adapted to the respective application, and any different measuring ranges are only available nested within each other. Using the same measuring bridge in at least two measuring ranges, which may also be adjacent, mutually exclusive, and automatically transition into one another, is not possible. To use measuring bridges in different, adjacent, or at a defined distance from each other measuring ranges, the measuring voltage at one of the tap nodes can be kept constant for a selected sub-measuring range, for example, by means of current taps, thus providing a first measuring range with very high resolution. By tapping the measuring voltages from the tap nodes at least once more using additional voltage taps, the same measuring bridge can be operated in a different operating mode outside the first measuring range. Multiple high-resolution measurement ranges can be achieved with the same measuring bridge.

Description

[0001] The invention relates to measuring bridge amplifiers for the use of the same measuring bridge in at least two measuring ranges, which may also be mutually exclusive and / or automatically and continuously transition into one another.

[0002] Measuring bridges are a readily understandable choice for very small changes in resistance values ​​(impedances) and are often already integrated into sensors (as components). Examples include piezoresistive pressure sensors, temperature sensors (at least one resistor in the measuring bridge is a temperature-dependent (NTC or PTC) resistor), force sensors (e.g., strain gauges attached for bending measurement in a measuring bridge), magnetic field sensors (AMR, GMR, TMR measuring bridges), light sensors, etc.

[0003] State-of-the-art 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 state of the art is well-established. The technical design and use of such measuring bridges is straightforward. The electronic evaluation and processing of the measured voltages is described in numerous publications. Datasheets for many operational amplifiers (op-amps), especially those with very high input impedances, such as instrumentation amplifiers, often include suggestions for using such amplifiers as measuring bridge amplifiers.

[0004] When working on sensory tasks, it often seems paradoxical that the required high amplification of the tap voltages from a measuring bridge is so easy to achieve on the one hand, but on the other hand, a very high amplification severely restricts the range in which the measuring bridge can then be used.

[0005] Sometimes it's advantageous to perform a measurement task in two separate measuring ranges. However, in the context of measuring bridges, different measuring ranges are not adjacent to each other, but rather nested within one another. Using the same measuring bridge in two measuring ranges that are adjacent, perhaps even at a certain distance from each other, is neither available nor intended; let alone the possibility that measuring ranges can be mutually exclusive and automatically transition into one another. State of the art (SdT): Definition of measuring bridges

[0006] A measuring bridge circuit is a representation of a measuring bridge arrangement by an electronic circuit (as a circuit diagram), but also refers to the tangible implementation (as hardware).

[0007] Measuring bridges consist of four resistors R1 to R4 connected to 4 nodes K1-K4 ( Fig. The resistors can be combined into a loop, or, from another perspective, into two voltage dividers (R1, R2 and R3, R4). These voltage dividers form the bridge arms of the measuring bridge. (In the literature, other elements may be designated as bridge arms; here, the definition as used applies.) At least one of these four resistors of the measuring bridge (as a sensor element) changes its value depending on a physical parameter (or other parameter) being measured. Each voltage divider, as a bridge arm (R1, R2 and R3, R4), represents a voltage with respect to the excitation voltage U. err represents an independently operating voltage divider.

[0008] Voltage dividers consist of at least two resistors (R1, R2) connected in series (in series) ( Fig. ), which divides a voltage (or voltage difference (u1-u3)) applied at supply points (1), (2) into partial voltages. In the case of a vertically represented voltage divider ( Fig. ) relative 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) (u3 because this voltage divider is located at the lower node K3 in a measuring bridge).

[0009] The voltage difference u1-u3 is the operating voltage (also: excitation voltage U). errThe difference between the voltage divider and the measuring bridge containing this voltage divider is independent of the selected reference point (ia will be GND). A similar principle applies if a constant current is applied and used as the operating mode.

[0010] The junction (3) of the two resistors in series is also referred to in this context as the tap node, because at this point there is a voltage U to be processed further. out The voltage that can be tapped is represented by a parameter to be measured. This voltage lies between u1 and u3, relative to the same reference point (ia GND), and is expressed either as the node voltage or as the output voltage U. out seen and described as such.

[0011] The tap nodes K2, K4 ( Fig. The two voltage dividers that make up a measuring bridge and form its branches are simultaneously tap nodes of the measuring bridge and are therefore not conceptually distinguished, except perhaps by specifying the primary origin of the tap node (as a voltage divider or measuring bridge tap node) or its function, e.g., by using indices. The difference in voltages at these two tap nodes is the "measuring voltage" of the measuring bridge, representing the magnitude of each parameter being measured, and is what a sensory measuring bridge provides.

[0012] A "measurement voltage" is the voltage provided for evaluation, in which a physical parameter to be measured is represented.

[0013] A voltage divider is considered unloaded if there is no other connection at the tap node through which any additional relevant current is drawn (or supplied) (e.g., during a measurement). mess =0).

[0014] A connection located at the tap node for measurements, which draws no current or such a small current that no relevant change in the node voltage is possible, is referred to here as a voltage tap.

[0015] In an unloaded voltage divider, this voltage divider divides the voltage across or at this voltage divider in proportion to the resistance values.

[0016] Such an unloaded voltage divider ( Fig. ) with defined excitation voltage U errThe voltages u1 and u3 at the supply points (1) (2) are here in the context and for differentiation (from later defined other types B and C) seen and referred to as voltage dividers of type A.

[0017] Each type of voltage divider has certain properties 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 gain 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.

[0018] The "primary function" is the function of a circuit for which it was designed and which it performs when it is in operation.

[0019] However, it only functions 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, for example, the output of an op-amp reaches the supply-related limit, the circuit leaves its operating range, then 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).

[0020] A type A voltage divider can be used with any resistance value for a very wide measuring range. This means that in all cases, i.e., with all conceivable resistance values ​​(with R1, R2 between 0 Ω and ∞ Ω), the output voltage U remains constant. out , with regard to a sensor-detectable parameter with a strictly monotonic characteristic curve (characteristic curve = functional representation of the output voltage U) out (above the physical target parameter to be measured) always between u1 and u3.

[0021] The representation of the resistance (plotted on the ordinate of a coordinate system) versus the value of the parameter to be measured (plotted on the abscissa) is the characteristic curve of a sensor element.

[0022] 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).

[0023] 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).

[0024] 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 which can change depending on the parameter to be measured.

[0025] The advantage of the voltage divider type A is therefore its inherently unlimited measuring range.

[0026] For measuring bridges that consist only of type A voltage dividers ( Fig. The same principle applies (any wide measuring range with a strictly monotonic characteristic curve). This type of measuring bridge is therefore probably the most frequently used and depicted in both teaching and prior art applications. Many measurements are performed using such measuring bridges in the prior art.

[0027] Extensions, additions, and modifications are possible on a measuring bridge, so that a distinction may need to be made between an original measuring bridge and "other" measuring bridges. Therefore, such a given measuring bridge should be considered and referred to as a "sensory measuring bridge," sensor measuring bridge, or "original measuring bridge." This measuring bridge contains at least one sensor element. That is, at least one of the resistors from R1 to R4 is a sensor element whose resistance changes depending on a parameter being measured.

[0028] Measured values ​​change over time; otherwise, there would be no need to measure them constantly. This means that measurements are taken repeatedly at recurring intervals. The progression of measured values ​​over time—that is, the sequence and representation of successively acquired measurements—represents a "signal curve." This curve is considered and referred to as a "measurement signal." SdT: Definition of measuring bridge amplifier

[0029] However, the use of measuring bridges requires electronic processing of the often very small measurement voltages, which are provided as voltage differences at the tap nodes. This electronic processing, which can be quite complex and varied and often serves more than just amplification, is summarized here under the term "measuring bridge amplifier."

[0030] The measuring bridge together with the electronic processing (i.e. the measuring bridge amplifier) ​​form what is here called the measuring bridge arrangement.

[0031] 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 to provide a measuring voltage that is as proportional as possible to the physical parameter being measured. For this purpose, often very small voltages must be processed and amplified to a usable level, resulting in a technically easy-to-use unit (as a component, as a "sensor," etc.).

[0032] The most common measuring bridge configurations are probably those with voltage taps. This is shown below. Fig. A well-known basic circuit for a measuring bridge: 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 (e.g., temperature, pressure, field strength, light, etc.) but also on other parameters (e.g., humidity, gases, chemicals, etc.), which is to be measured using such a measuring bridge arrangement.

[0033] Each pair of these four resistors acts as a voltage divider, dividing the excitation voltage U applied to two opposite bridge nodes. err (4) In Fig. will U err supplied without potential (i.e., without GND reference); however, this is not important in this context.

[0034] For a technical application, the resolution achievable with such an arrangement is also crucial. Resolution refers to the smallest voltage difference that can be distinguished in a given application, within the processed voltage (in which the parameter to be measured is represented). The noise inherent in this voltage, and therefore unavoidable, represents the lower limit (highest possible resolution). After digitization, the ia is the voltage difference represented by one bit.

[0035] Provided that during a measurement (even with electronic processing) this measuring bridge voltage is not loaded, i.e., that there is no load on either side, i m If (5) = 0, the following applies to the measured voltage: U mess =U ref (R2R3-R4R1) / [(R1+R2)(R3+R4)].

[0036] So that in all cases i mess If =0 is ensured, then - as in Fig. As shown, the node voltages are tapped using op-amps (6) (7). The voltage tapped using such voltage taps (6) (7) can be further processed electronically; in Fig. For this purpose, for example, a standard subtraction circuit (8) is assumed to form a difference, which can also be used as a component (IC) as an instrumentation amplifier (cf. Fig. is available.

[0037] ( Fig. The left side shows the simple connection of such an instrumentation amplifier to a measuring bridge: The gain, which ultimately determines the slope of the characteristic curve on the right, is in this example determined by only a single resistor R. v defined, however, the op-amps required for voltage tapping have already been integrated into the IC (73) with the circuitry).

[0038] When the same voltages are present at the tap nodes (5) of the two voltage dividers of the measuring bridge, the measuring bridge is considered "tuned" and designated as such. Tuning the bridge requires that R2R3=R4R1 (U mess (is then non-trivial zero).

[0039] As explained above, it is essential that a voltage tap for measuring a 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 mathematics is no longer correct"; a voltage would then be measured that is not solely determined by the voltage divider and "is not the intended voltage").

[0040] By tapping this voltage and subsequently processing the measured voltage, the state of the measuring bridge can be determined and thus conclusions can be drawn about the parameter to be measured. SdT: Definition of operating modes and operating forms

[0041] In contrast to this voltage tap, the state of a measuring bridge can also be determined by selectively drawing a current from one of the measuring bridge nodes, e.g. by keeping the node voltage at a defined value.

[0042] This will be referred to here as a power tap.

[0043] 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 taps of the measuring bridge are kept at the same potential by the electronics, i.e., the measuring bridge is kept in a virtual short circuit.

[0044] A “virtual” short circuit means that, through operational amplifier (standard) circuits (an inverting amplifier circuit (11) and / or a current-to-voltage converter (12)), the two voltage divider taps are at the same potential, in Fig. e.g., to GND. The term virtual short circuit is used together with the term "current tap" (cf. Fig. (right) is used to describe the operating mode of the measuring bridge. Since, as is the case, for example, Fig. As shown on the left, measuring bridges can also be operated in mixed mode, but this may no longer be clearly distinguishable. Both voltage and current taps are used on this measuring bridge when operating in a virtual short circuit.

[0045] With the circuit of Fig. A different measuring bridge arrangement is shown: The voltage divider on the left side of the measuring bridge (R1, R2) remains unloaded (the op-amp input draws no current from the tap node here). On the right side, however, the voltage divider (R3, R4) is not only loaded in the sense of distorting a voltage, but is deliberately loaded so heavily that the voltage at the right tap node of the measuring bridge can be kept at a fixed voltage value. Fig. GND is assumed for this purpose, but any other voltage specification U is also possible. Bez be. (In the illustrations, only the name may be shown, not the text.) Bez so named because it doesn't always have to be a fixed tension, and moreover, it doesn't always have to be the same; in Fig. The two references “Bez” can be the same or different, for example.

[0046] Since the node voltages on both sides are at the same value (U) BezIf the measuring bridge is held at , GND), it will be operated in a “virtual short circuit” even though a current tap is only used on one side.

[0047] The term "virtual short circuit" is unambiguous for the measuring bridge arrangement and will be used here for this operating mode (both tap nodes are held at the same voltage). However, further distinctions often need to be made because this operation (cf. Fig. ) in the context of the invention, this can be an “intermediate operating state” (not only under the condition of a current tap), which is used specifically to set up different measuring ranges, but can be left and / or re-entered by the measuring bridge arrangement.

[0048] For measuring bridges that operate using voltage tapping, the same term describes both the operating mode and the method of signal acquisition at the measuring bridge. In the arrangement of the Fig. However, if, for example, the left measuring bridge tap is not loaded (voltage tap), the right measuring bridge tap deliberately loads the right voltage divider (R3, R4) (a "current tap"). Both tap types can therefore occur together, thus being used in a "mixed operation".

[0049] Despite the different operating models, in all cases ( Fig. and Fig. ) suitable measuring bridge circuits for many purposes, which are to be classified as equivalent with regard to the information they provide for sensory tasks based on a measuring bridge. SdT: Definition of measuring ranges

[0050] Electronic processing of the often very small voltage provided by a measuring bridge is an essential component of every measuring bridge arrangement.

[0051] Electronic circuits require energy and therefore must be powered electrically. However, the supply voltage range that can 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. An operational amplifier that can amplify a voltage between its inputs, for example, 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.

[0052] As long as the input voltage of an amplifier remains in a range of, for example, a few millivolts, this is fine; the amplifier (not just operational amplifiers) then provides an output voltage in the volt range, the shape of which corresponds to the shape of the input voltage (the measurement signal) in the millivolt range.

[0053] However, the operating range of the electronics is limited to this range. If a higher input voltage were applied to the operational amplifier, the op-amp would have to provide higher voltages and would therefore have to exceed its supply voltage range, which is impossible. The op-amp then remains stuck at a maximum value, either upwards or downwards; at least as long as the magnitude of the input voltage to be amplified is too high. The circuit is said to be in supply-limited operation or saturation; the circuit has then left its operating range.

[0054] The operating range of the electronics, in this sense, also defines what is called a measurement range. Valid values ​​for a measured parameter can only be obtained within a range in which a circuit can "operate." A real measurement range, therefore, can be smaller than the operating range of a given electronic circuit, but will almost certainly not be larger, and may be switchable. A measurement range specified for a circuit will at most be equal to, but almost certainly smaller than, this real measurement range.

[0055] The measurement range is therefore seen as a range defined for a measurement task, for which a quantity directly representing the physical parameter to be measured can be provided (parameter-proportional voltages or currents, but also analog or digital data, etc.), through which a measurement task can be solved with a defined resolution.

[0056] A necessary criterion for a measurement setup intended for such measurements to operate within the operating range of a physical parameter to be recorded is that all electronic components (with all their inputs and outputs) are located within a voltage range smaller than that determined by the power supply. In particular, all outputs of op-amps must be within a voltage range somewhat smaller than that defined by the respective circuit's power supply.

[0057] An operational amplifier in a measurement setup whose output is outside this operating range, close to the positive or close to the negative supply voltage, is in "saturation" or "supply-related limitation"; in this case, the measurement setup or part of the measurement setup has left the intended operating range and thus the measurement range specified for this measurement setup.

[0058] Leaving this working area in this sense is, in the case of prior art technical arrangements, an undesirable process which can be avoided by suitable measures and handling.

[0059] Due to this characteristic (of the electronics), state-of-the-art measuring bridge arrangements typically only operate in the immediate vicinity of the respective bridge's calibration point and / or offer limited sensitivity. However, within the immediate vicinity of the respective bridge's calibration point, a measuring bridge (with appropriate amplification and evaluation) can provide very high sensitivity. This applies both to measuring bridge arrangements that use voltage taps and to those where the bridge operates in a "virtual short circuit".

[0060] The properties of the measurement range definitions given by the choice of amplification factors in the state of the art are to be compared with Fig. The following will be displayed:

[0061] A measuring bridge arrangement for measuring a target parameter (in this example a temperature) can be implemented in the prior art by a series of amplifier stages (21) (22) (23) (24) or by parallel amplifiers (31) (32) (33) (34).

[0062] The small measuring bridge voltage (25), which changes depending on the target parameter, changes only slightly over the entire measuring range ia, but extends upwards and downwards to physical limits that are no longer of technical interest and is exactly zero at the tuning operating point.

[0063] The property of the measuring bridge to provide a zero voltage at the tuning point, which is not trivial, can conversely be used to define an operating point: The operating point is seen here as the (parameter) point in the characteristic curve where this characteristic curve crosses the zero line. (This does not always mean the same thing).

[0064] The measuring bridge real (in Fig. The measured voltage (indicated by (21) (31)) must be greatly amplified in order to detect the small voltage changes caused by the changing parameter. Diagram (25) in Fig. The graph shows the course of the very small voltage measured by the bridge over a wide measuring range of a parameter (temperature; plotted on the abscissa). The other diagrams are essentially only amplified versions of this characteristic curve (25).

[0065] Electronically implemented amplifier stages with very different gain factors v={α, β, γ} or {αβ and αβγ} can be used relatively easily in the state of the art to amplify the very small measuring voltage (25) and thus provide different measuring ranges in the arrangement.

[0066] The measured voltages (represented as characteristic curves over the parameter T) traverse the available voltage range (on the ordinate) at different speeds due to varying gains. Characteristic curves (26), (27), and (28) indicate the voltage profiles at the outputs of the different amplifier stages. Diagram (26) shows the voltage profile provided by the measuring bridge arrangement at the output of amplifier stage (24) or (33); the gain of the measuring bridge voltages (21) and (31) is greatest at v = αβγ. If the parameter being measured changes only slightly in this range, characteristic curve (26) traverses the supply-related voltage range from (38) to (39) very quickly.

[0067] Among the in Fig. The characteristic curves shown indicate the measurement ranges that arise in this way: The measurement range M1 (indicated by bar (36)) is defined, for example, by the range that the measurement signal at the output of the last amplifier stage γ (24) needs to traverse the available voltage range from (39) to (38), which happens very quickly due to the highest gain v=αβγ achieved there (characteristic curves (26)). Above and below the temperature range of M1 (36) (i.e., to the right and left of the measurement range M1, indicated below the characteristic curves by bars (35)), the output of the last amplifier stage (γ) lies within the limits imposed by the supply or other constraints. An amplifier stage (33) will exhibit the same characteristic curve if it would provide the same gain v=αβγ.

[0068] 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 v=αβ (characteristic curve (27)). Above and below the temperature range M2 (37), the measuring voltage (37) (or of amplifier (34)) at the output of amplifier β (23) is also limited by the supply-related constraints.

[0069] The measuring range M3 (characteristic curve (28)) is defined by the fact that at the output of the amplifier α (22) or (32), the measuring voltage traverses the available voltage range more slowly due to the lower gain v=α. The temperature range M3, as the operating range of the measuring bridge, extends beyond the range of interest here.

[0070] The measuring bridge continues to operate even in the "outer temperature ranges," i.e., in areas where all amplifiers are already operating within their supply-related limits (Diagram (25)). This means that the measuring bridge continues to deliver voltage values—far beyond the ranges defined by the gain—in which a physical parameter to be measured is still represented.

[0071] For each of the measurement ranges M1 to M3 defined in this way (bar (35)), an operating point AP1, AP2 and AP3 can be defined by the fact that the respective measurement curve at one of the outputs of the amplifier chain has a voltage of zero.

[0072] In this sense, an operating point (OP) is not a general characteristic curve point, but rather a point predetermined by the technical implementation within the realized arrangement. The design of an implementation can only approximate a potentially desired operating point as closely as possible.

[0073] To distinguish this from the state of the art, it should be noted that on each amplifier stage, the measurement range (ia) shown there is always completely within the preceding measurement range, and that the operating points ia are close to each other, but not necessarily exactly the same (offset). For example, in the Fig. The characteristic curves (26) and (28) (and also (25)) have the same operating points (29). The characteristic curve (28) has a different operating point (30).

[0074] This is easy to understand in a series of amplifiers (21), (22), (23), (24). The same result also occurs in a parallel arrangement if the gain factors are the same (31) with amplifiers (32) (33) (34).

[0075] In parallel-operating amplifiers, which could be implemented, for example, with instrumentation amplifiers using multiple taps, the diagrams shown (28), (27), (26) could be shifted with respect to the operating points by means of offset shifts. However, in the prior art, for various reasons, the direct adaptation of the measuring bridge to the respective task is generally intended.

[0076] The techniques known for this cannot perform the ia on one and the same measuring bridge for two measuring ranges simultaneously if these have to be located next to each other at a certain distance.

[0077] If, for example, one wants to access one measurement range alongside another for a sensor task, this cannot be achieved by simply choosing amplification factors (ia). Other designs are required.

[0078] In summary, the SdT can be classified as follows with regard to the measuring range: Because, due to the supply, the output of an amplifier cannot produce voltages greater than V + Since an electronic circuit can only operate within a defined range (somewhat smaller than the supply voltage) at a given gain factor, and the voltage supplied is smaller than the voltage provided by the power supply, the voltage from the measuring bridge cannot exceed these limits after amplification (at the output of an op-amp). At the same operating point, the gain defines the slope of the characteristic curve, which in turn limits the respective measuring range and defines the achievable resolution. The measuring range and the gain factor, and therefore the resolution, are mutually exclusive.

[0079] A smaller measurement range due to higher gain always lies within the larger measurement range (with lower gain and resolution). These measurement ranges are therefore nested within each other as intervals.

[0080] This is known in the state of the art and is used accordingly. Different measurement ranges are essentially defined by the selected amplification factor.

[0081] In the context of this document, partial measurement ranges are to be understood as subsections from a potentially larger measurement range of a parameter, also in order to be able to distinguish adjacent measurement ranges from such nested measurement ranges of the state of the art.

[0082] This not only defines specific measuring ranges, but also allows for the definition of sub-measurement ranges within one or more other measuring ranges. For example, the temperature measuring range for monitoring a cooling system and the measuring range of a fever thermometer represent two distinct measuring ranges in this sense, or rather, sub-measurement ranges within the measuring range that a measuring bridge can offer, which is specified for a temperature measuring range of, for example, -30°C to 100°C. This inherently includes measuring range sections that can be adjacent or uninterrupted, that can be located close to each other or further apart, but which cannot be realized simultaneously in the SdT (Standard of Temperature). SdT: Definition of application-specific measuring ranges

[0083] However, it is not only the electronic characteristics of a measuring bridge arrangement that result in (i.e., with a measuring bridge, only one) differently extending measuring ranges that must be set up anew for each application. Naturally, the measuring tasks themselves require different measuring ranges in terms of both extension and location.

[0084] 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 (e.g., adjacent measuring ranges) can be met with current technology.

[0085] As peripheral topics, 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 incidence during an experiment within a narrow intensity range.

[0086] These include, for example, pressure measurements, where very different measuring ranges need to be covered, and e.g. - from the detection of sound or vibrations by microphones, - via the detection of small pressure differences (for example, for flow measurements or medical applications), - can reach gigantic pressures (e.g., for pressure measurements in the deep sea), etc. For the various applications, special pressure sensors are used in very different areas, 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 must be sought).

[0087] 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.

[0088] These include, for example, the temperature measurements already mentioned above. Using a sensor suitable for a potentially large overall measuring range ( Fig. With a measuring bridge suitable for the characteristic curve (51) and measuring range (52), applications in several partial measuring ranges could be realized. An arrangement that can provide, for example, the characteristic curve (51) would also be suitable for providing measurements in the narrow measuring range (65), e.g., of the zero point, e.g., with the characteristic curve (55), and / or as a fever thermometer in the narrow range (64) around 38°C, e.g., with the characteristic curve (54).

[0089] Due to the characteristics of the measuring ranges of bridge amplifiers shown above, different measuring ranges can be provided in the prior art, but these are only available in interval-nested form. Implementing different tasks in different, but separate, measuring ranges with different resolutions (using the same bridge) is not possible for both applications simultaneously in the prior art.

[0090] The characteristic curves (55) and (54) of the Fig. These are just examples of temperature measurement.

[0091] This creates a large number of tasks, which often occur simultaneously in experiments: - For a universal thermometer, a range of possibly -50 to +150° would be just right (e.g. characteristic curve (51) with measuring range (52)), - For environmental measurements, a range of possibly -30 to +50° is sufficient. - A fever thermometer should be designed for 33° to 43° (characteristic curve (54) with measuring range (64)). - In crystallization and freezing experiments with water, a range of -5° to +5° can be provided (characteristic curve (55) with measuring range (65)). - For evaporators (pressure-dependent) possibly from 80°C to 120°C. - In the freezer compartment, possibly -30°C to -10°C). - reach different distances in different other use cases each time.

[0092] The measurement task itself therefore results in very different measurement ranges, such as the Fig. represents, demanded.

[0093] Using temperature as an example, very different measurement ranges can be illustrated that can be measured with a measuring bridge by appropriately selecting the gain and offset (after adapting the measuring bridge to a intended operating point). In principle, everything could be achieved with a single measuring bridge arrangement. However, monitoring room temperature, the temperature of, for example, a cooking pot, or a freezer with an otherwise identical fever thermometer is rather uncommon. In fact, a separate design is preferred and manufactured for each application.

[0094] Reasons for this include the further processing steps of the measurement signals, which can introduce a number of problems; especially due to digitization.

[0095] In the prior art, resolution and measurement range are mutually limiting: The required resolution of a parameter to be measured requires a defined gain, which then defines or limits the measurable measurement range. And the supply-related limitation (57) (56) is always an obstacle.

[0096] To adequately process small measured values, electronic amplifiers are used in all arrangements. However, because the amplification technology is limited to a defined operating range by the power supply, the electronics almost always required when using a measuring bridge represent a limitation of the application of a measuring bridge arrangement.

[0097] For small measurement signals, a high gain (55) (54) is required. This causes the available voltage range to be traversed quickly, resulting in only a small measurement range (65) (64) being captured. The measurement voltage provided in an application (ia with an offset) often shifts the required, potentially small, measurement range by orders of magnitude on the scale of the respective parameter.

[0098] In the prior art, therefore, considerable effort often has to be expended on adapting the measuring bridge to a specific application. With the amplification methods available in the prior art, which are used to determine the characteristic curves of the Fig. This task cannot be realized, or can only be solved with great effort.

[0099] Summary of measuring ranges: Different measuring ranges are generally limited by the operating range of the electronics, but in the SdT ia (Standard of Testing), they are specified as requirements by the measurement task or the respective measurement objective. Measuring ranges, however, appear as technically given limits due to the operating range and the operating principle of the respective electronics (i.e., limiting the measuring range).

[0100] Measuring ranges are typically defined by an operating point and the selected gain, which determines the steepness of a characteristic curve.

[0101] Here, "measuring range" should 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).

[0102] 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) is the measuring range of a measuring bridge arrangement and is ia smaller than the operating range of the electronics. SdT: Definition of voltage dividers

[0103] To describe the invention, the voltage dividers that occur must be classified by definition: In addition to the voltage divider already shown, which is referred to as type A for the purpose of differentiation, at least two further types (which are referred to as type B and type C for the purpose of differentiation) are relevant in the context of the invention.

[0104] Fig. summarizes the relevant voltage divider types.

[0105] The measuring range provided by a type A voltage divider bridge is very large (unlimited); this requires a currentless voltage tap. Only by selecting a gain is this very large measuring range limited (as shown above). The measuring ranges defined in this way offer different resolutions. To ensure a currentless tap, an op-amp (17) is also required for this voltage divider, which is essential for voltage divider types B (op-amp (14)) and C (op-amp (16)). Fig. ; the op-amps marked as "additional" are additional voltage taps that do not restrict the primary function.

[0106] In the type B voltage divider ( Fig. (Without the op-amp marked as "additional"), not arbitrary resistor values ​​can be used. With these Type B components, 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. With high gain (e.g., with large R2 and small R1), the op-amp can enter saturation, where it can no longer operate. If values ​​for R1 and U are err If resistors R1 and R2 are fixed, then this either limits the value range for R2 (or the op-amp may reach its limit). If resistors R1 and R2 are fixed, then this limits the voltage. err one (or the op-amp may go into limiting). By adding a resistor between the output of the op-amp and the measuring bridge node K3 (in Fig. Is this the node where -U MBrIf the voltage divider is placed on a specific surface (not shown here), one of the new measuring ranges can be selectively reduced. As a limiting case, it should be noted that in this configuration, nonlinear components (e.g., diodes, NTCs) can also be used instead of a resistor.

[0107] An advantage of this amplifier circuit (inverting amplifier circuit) is that the output voltage U out The entire measuring range is linearly dependent on the resistance R1. If R1 is a fixed resistor, U can be used to determine the resistance. err The current is determined by R2. This circuit can be useful in the context of the invention with a measuring bridge to define one of the measuring ranges.

[0108] In the C-type voltage divider ( Fig. The primary function here is to keep the node voltage constant relative to the reference voltage U. BezDue to the subsequent amplification, arbitrary resistance values ​​cannot be used. A high amplification (determined by R) f ) can drive the output voltage of the operational amplifier (16) into a supply-related limit. If U out should remain within the range of the supply voltage (this is also the state in which the voltage at the tap node (18) is at the reference voltage U Bez (to be maintained) the gain must be limited. R f While the gain can only be set to a limited height for a defined measuring range, it can easily and variably adjust it over a very wide range. The advantage is that the gain can be determined by just this one resistor R. f It is easily adjustable (or simply switchable). The op-amp, marked as additional, does not interfere with the primary function.

[0109] Such single-stage amplifiers offer significant advantages in terms of their noise characteristics. It should also be noted, as a borderline case to this voltage divider, that in this configuration non-linear components (e.g., diodes, NTCs) can be used instead of a resistor.

[0110] For the reasons outlined, electronic evaluation often appears paradoxical in the current state of the art (due to the constantly necessary compromises): On the one hand, the high amplification for the tap voltages from the measuring bridge and the voltage dividers, which is so easily achieved with electronics, is needed for high-resolution sensors; on the other hand, precisely this (very high amplification within a supply-related limit) severely restricts the range in which the measuring bridge can be used in a real application.

[0111] Therefore, state-of-the-art measuring bridges are not always the best means of choice for solving sensory tasks, but they appear almost unbeatable when sensor elements are located in a measuring bridge or circuit and a limited measuring range needs to be resolved with high sensitivity.

[0112] In the current state of the art, only one operating mode and / or one operating state is provided for a measuring bridge adapted to the respective application, and (insofar as these measuring ranges differ in the current state of the art) they are only available as nested measuring ranges.

[0113] In this context, the object of the invention is to provide measuring bridge amplifier arrangements for measuring bridges which, compared to the prior art, can provide measuring ranges and form partial measuring ranges that can exist side by side with different measuring range widths and with different sensitivities in a wide parameter range, or which, alternatively, can also be inserted into existing measuring ranges, interrupting their operation.

[0114] This task, utilizing measuring bridges in different measuring ranges, adjacent to each other or at a defined distance from each other or in an intermediate range, is solved, - by keeping the voltage constant for a selected measuring range at at least one of the tap nodes of the voltage dividers from which the measuring bridge is constructed, thereby providing at least one first operating mode for at least one first measuring range, and - the voltage from this at least one tap node is tapped at least once more by additional voltage taps in order to be able to continue operating the same measuring bridge outside the first measuring range, possibly in a different operating mode.

[0115] The invention is based on the understanding that a measuring bridge can continue to operate normally outside the operating range defined by electronic processing. To solve this problem, the invention utilizes the fact that the tap node of a voltage divider in a measuring bridge can only be kept at a constant voltage once (e.g., by means of a current tap or otherwise), but voltage taps can be connected multiple times via op-amp inputs.

[0116] From another (but potentially very important) perspective, which directly relates to the task, the presented definitions of the different operating modes can be viewed as follows: A wide measuring range of the (normal) operation of a sensor bridge with voltage taps and lower gain is interrupted by the transition of the measuring bridge arrangement into measuring range (84) at the transitions (82) and (83) respectively, in order to achieve a higher resolution (characteristic curve (79)) in measuring range (84) with AP1 on the same measuring bridge. (cf. e.g., the one in Fig. The characteristic curve sections (80) and (81) shown, which operate in the measuring range (85) with the AP2). For this purpose, the voltage at a tap node of the voltage divider is kept constant in this measuring range and the measuring bridge is operated in a different operating mode.

[0117] In this case, one measuring range essentially overlaps the other measuring range, interrupting it in order to be able to work with a higher resolution in a smaller sub-measuring range.

[0118] Here too, the invention is based on the understanding that a measuring bridge continues to operate normally outside the working range defined by electronic processing, because the op-amp outputs of the electronic processing, which is intended for a defined measuring range, remain stable within the supply-related limit.

[0119] Although this is done in a modified mode (with a type A voltage divider and an additional parallel resistor, i.e., with a different measuring bridge design, because one of the measuring bridge resistors changes functionally), the sensor measuring bridge can still be used without restrictions with regard to the measuring range.

[0120] To keep the voltage at a tap node of the voltage dividers from which the measuring bridge is built constant, a current tap (voltage divider of type C) and / or a voltage divider of type B can be used, for example.

[0121] According to the invention, the measuring bridge arrangement is designed such that the electronic amplification leads the electronics into the supply-related or otherwise limited range when the parameter to be measured is outside the working range and thus outside the measuring range (or is brought into a stable state by other measures in which it remains stable). Description of the invention

[0122] The invention takes advantage of the fact that only one current tap can be provided at the tap node of a voltage divider (e.g. voltage divider of type C), but several op-amp inputs (voltage taps) can be connected.

[0123] The current tap in this type C voltage divider is used in such a way that the node voltage is kept stable at a fixed potential (at a fixed voltage value) by the op-amp drawing a current through the feedback resistor R. f It appropriately compensates for or adjusts.

[0124] However, by means of additional voltage taps, which are useless in the measuring range in which the current tap operates, the voltage divider of this measuring bridge arrangement can also be used outside this measuring range as a type A voltage divider.

[0125] Alternatively or in combination with the possibility just mentioned, the invention takes advantage of the fact that only one tap can be provided at the tap node of a voltage divider within the framework of a negative gain stage (ia a voltage divider of type B), but several additional voltage taps can also be connected here.

[0126] By means of additional voltage taps, which are in themselves useless in the measuring range in which the inverting amplifier operates, the voltage divider of this measuring bridge arrangement can again be used as a type A voltage divider outside this measuring range.

[0127] The additional voltage taps used in these designs are, for example, in Fig. indicated by the op-amps, which are explicitly marked as additional.

[0128] By using a measuring bridge configuration with at least one of these two tap types or with one of these operating modes, a high gain can be achieved at specific points (at the operating point) for defined small measuring ranges with high resolution.

[0129] In the areas outside these measuring ranges that are not perceptible to the electronics (because the electronics are limited by the supply), a measuring bridge still functions without restriction as a type A voltage divider, although possibly with a modified characteristic curve.

[0130] The use of a different measurement range is based on the understanding that a measuring bridge continues to operate normally outside the operating range defined by electronic processing, even if the op-amp outputs of the electronic processing (which is designed for a precisely defined measurement range) remain stable within the supply-related limit. While this occurs in a modified mode (as Type A and with an additional, parallel resistor, thus with a modified measuring bridge design because this single measuring bridge resistor has functionally changed), it can still be used without restrictions regarding the measurement range.

[0131] Fig. This is illustrated using the example of the circuit of the Fig. dar (identifier of the Fig. agree Fig. (to the EiEv-MeBrü):

[0132] If the primary function of the sensor bridge arrangement is Fig. When the device is functioning, meaning the parameter to be measured is in primary measurement range 2, and the output of the op-amp (75) is located on the characteristic curve to the right between the supply voltages, the two nodes K2 and K4 are held at the same voltage. Since the left voltage divider Fig. A type A voltage divider operates with a strictly monotonic characteristic curve over a wide range without restrictions.

[0133] The right-hand voltage divider is a type C voltage divider. During the time that the output of the op-amp (47) is at the upper or lower limit, the parameters for the measuring bridge are changed: If the parameter to be measured is smaller than is defined by the measurement range 2 of this arrangement, then the output of the OpAmp (47) with U1 (75) lies in the lower limit.

[0134] The op-amp (47) simply can't do more than that. For the resistor R fNothing changes at the connection to node K4 (76); however, the connection at the output of the op-amp is now close to or directly at the supply of the measuring bridge, i.e., close to -V or the supply voltage, i.e., at node K3. Depending on the design, one can imagine (and show) that R f so that iW is parallel to R3.

[0135] The same thing happens above if the parameter P is larger than defined by measurement range 2; then the output of the opAmp (47) with U1 (75) lies within an upper limit.

[0136] For all values ​​of the parameter to be measured outside the small measuring range 2, R therefore lies f top or bottom, parallel to R4 or R3. Since the op-amp remains stable in this situation, only the parameters of the sensor bridge change (however, the smaller R is). f The stronger the better).

[0137] In a further development of the invention, measuring ranges can also be specifically delimited and defined by a smaller operating voltage range, for example, to more precisely define a specific measuring range. For this purpose, a window discriminator can, for example, use comparators to compare a voltage range (here, the output value of an op-amp) against voltage reference values, both above and below the specified range. If the voltage value of the op-amp output lies outside a range defined by reference values, the window discriminator generates a signal (high or low) that can be used to selectively control the op-amp, for example, into its limit or into a defined stable state. In this way, either the voltage value of the op-amp or the current fed back to the tap node can be kept at a defined, limited value.Since this (the use of window discriminators) can be used extensively, even without the supply-related limitations, this allows for greater freedom in the designs according to the invention.

[0138] To illustrate the invention, it suffices to represent the transitions between the different measuring ranges as supply-related limits. Outside a defined measuring range, or, as already described, automatically due to a supply-related limit, the circuit enters a saturation state, but remains stable in the outer regions and automatically returns from this saturation when the parameter to be measured returns to this measuring range.

[0139] It is essential that the voltage at the same node of a type B and type C voltage divider can be tapped again without this additional voltage tap disrupting the respective intended primary function. The primary function provided at the tap node, which, for example, keeps the node voltage stable at a reference value, e.g., zero, remains unaffected by such an additional voltage tap.

[0140] The additional voltage tap (at the sensor bridge) does not appear to be useful, since in the operating mode of the primary function only a stable node voltage can be found, and thus only this voltage is detected by the additional voltage tap. However, this changes when the op-amp reaches its supply-related limit (and remains stable there) and the operating mode of the sensor bridge changes.

[0141] However, this operating mode, in which the primary function is active and the additional voltage tap only sees a stable zero voltage, offers the possibility of determining the offset voltage of the primary function; this can be seen as a significant advantage. Furthermore, this can be an additional advantage because even during a current tap, such a voltage difference, which may not yet be zero but also not yet originating from type A voltage dividers, can provide additional information about the operating state or for monitoring the operating state.

[0142] The invention will be explained using examples: Fig. and b show the measuring bridge arrangement of the Fig. multiple operating modes and measuring ranges; Fig. shows the measuring ranges formed with a type C voltage divider and Fig. the measuring ranges to be formed with a voltage divider of type b.

[0143] The first example shows Fig. The circuit diagram of the measuring bridge arrangement is shown in the upper left. Fig. , which operates in a virtual short circuit and can establish two operating modes solely through the type C voltage divider. The diagrams on the right illustrate these two different operating states: The two nodes K2 and K4 are at the same potential, here GND. In the operating range designated for this right-hand voltage divider (the primary function), the op-amp (12) draws current through resistor R. f the voltage at node K4 affects the voltage U Bez (here GND).

[0144] In the intended operating state, the output of the op-amp (12) moves between U1 and U3; the voltage at node K4 is reliably set to U Bezor, in this case, GND is held. The measuring bridge arrangement operates in a working area 2 or in a measuring area M2; characteristic curve in Fig. 8% (46)).

[0145] If the output of the op-amp (12) is at the upper limit ( Fig. (top right), the opAmp (12) on this side can also be disregarded (13); it is then out of operation. Since the opAmp is out of operation and R f The maximum supply depends on the resulting [result]. Fig. already described situation Fig. top right. The resistor R f iW is only parallel to R4.

[0146] This parallel circuit transforms the right-hand voltage divider (originally R4 and R3) into a different one (but this changes with small R). f generally more, with large R f less). The originally given resistance R4 (which would only apply to a voltage divider of type A anyway) becomes R'4 = R4*R f / (R4+R f); but now actually of type A.

[0147] If the output of the op-amp (12) is at the bottom limit ( Fig. (bottom right) one can also imagine the opAmp (12) removed (14); it is then out of function and thus the resistor R f iW is only connected in parallel to R3. This parallel connection transforms the right voltage divider (R4 and R3) into a different one (but this changes with a large R). f less). The originally given resistance R3 (which would only apply to a voltage divider of type A anyway) becomes R'3 = R3*R f / (R3+R f ).

[0148] This defines a total of three working areas of the measuring bridge (without having considered the left side of the measuring bridge at all so far; cf. Fig. ): - A first measuring range, which is located to the left (43) of the working range (46) of the IU converter (12) and in which the measuring bridge operates with a voltage divider of type A on the right, which has the resistor R4 at the top and the resistor R'3 at the bottom. - A second measuring range corresponding to the operating range (46) of the IU converter (whose primary function is now active) and in which the voltage at node K4 of the voltage divider (R3, R4) is kept at a voltage value that corresponds to U Bez (possibly GND) is specified. - A third measuring range which is located to the right (44) of the operating range (46) of the IU converter (12) and in which the measuring bridge operates with a voltage divider of type A on the right, which has the resistor R'4 at the top and the resistor R3 at the bottom.

[0149] The measuring ranges that result from this arrangement upwards (44) and downwards (43) can (will) be different because of the parallel connection R4 / / R f and R3 / / R fThey can differ. If this is desired, for example, off-center measuring bridge tap nodes can be provided; for example, both upper resistances of the measuring bridge can be twice as large as the lower ones, or vice versa. This can be designed appropriately.

[0150] The fact that the slopes of the characteristic curves to the right and left of the primary function or the measuring range (46) can change and differ can therefore also be used effectively.

[0151] As just now Fig. shown for voltage divider type C, shows Fig. at the same measuring bridge arrangement (from Fig. The same applies to two further operating states that are provided solely by the type B voltage divider: The left op-amp (11) of the original circuit (type B voltage divider as the primary function) sets the voltage at node K2 to the voltage U via R2. Bezone (here GND) as long as the output of the op-amp (11) is between U +err and U +err moved out However, if the opAmp (11) is smaller than a minimum, then the resistor R2 with node K3 lies stably at -u.

[0152] As long as the output of the op-amp (11) remains stable at this lower saturation point, the op-amp (11) can be disregarded (10) and the lower measuring bridge node can be considered to be permanently connected to the lower supply voltage. This results in a measuring bridge in which R1 and R2 continue to operate like a normal measuring bridge with type A voltage dividers (and a stable excitation voltage).

[0153] On this left side, the voltage divider itself does not change, but the lower node K3 is on a varying lower voltage during the primary function, but from now on on a fixed lower voltage.

[0154] Thus, (now disregarding the right side of the measuring bridge) the following also apply to this side of the measuring bridge arrangement: Fig. at least two measuring ranges: The operating range intended for the type B voltage divider, in which the node voltage at K2 is kept constant (and in which U out (from the opAmp (11) an output voltage can be), can e.g. in Fig. below the limit (45). In this operating range and operating mode, for example, the output voltage of OpAmp (11) can continue to decrease downwards towards -u until a limit (45) is reached and a stable state is established for the other operating modes.

[0155] In some cases, the right and left sides can operate against each other or together in one of the operating areas defined by the boundary (45).

[0156] The entire measuring range of the circuit (41) extends very far both upwards and downwards; each range has its own characteristics. Depending on the design, several measuring ranges of varying widths and resolutions can be implemented with each of the two configurations on the right and left, which can be used individually or in combination. Further ranges for additional voltage taps can be derived from this.

[0157] Outside these measuring ranges, the electronics operate within the limitations imposed by the power supply. Such "outside ranges" are not perceptible to the electronics, but the measuring bridge continues to function fully as a type A voltage divider (albeit possibly with a modified characteristic curve).

[0158] The measurement ranges in which the primary functions operate are determined by the gain (fast or slow sweep through the available voltage range) and by the available voltage range.

[0159] However, using window discriminators or comparators, measuring ranges can be specifically delimited, modified and defined by a smaller operating voltage range, e.g. to be able to more precisely limit a specific measuring range.

[0160] Outside the defined measuring range, or automatically due to a supply-related limitation as already described, the circuit enters a saturation state, but remains stable in the outer areas and automatically returns from this saturation when the parameter to be measured returns to this measuring range.

[0161] It is essential that the voltage can be tapped again at the same node of a type B and type C voltage divider without this additional voltage tap disrupting the intended function.

[0162] The additional voltage tap initially appears pointless, since in the intended operating mode only a stable node voltage is present, and only this voltage is detected by the additional voltage tap. However, this changes when the operational amplifier reaches its supply-related limit (and remains stable there) and the operating mode of the measuring bridge changes.

[0163] Furthermore, it is possible to measure offset voltages with it.

[0164] The measuring bridge arrangement of the Fig. In the described form, the measuring range currently represents one of which extends, for example, from far below to a limit (45). From there upwards, the measuring bridge arrangement is in a different state.

[0165] The left side of the measuring bridge remains stable in this other state, however, at the top.

[0166] When the parameter to be measured enters or is located within the measuring range (46), the type C voltage divider on the right is activated. Its primary function is to keep node K4 at a constant potential, here GND.

[0167] Additional voltage taps would not impair the primary functions currently under consideration. Therefore, measurement voltages could still be tapped directly from the measuring bridge using an instrumentation amplifier. This is discussed here in Fig. represented by the characteristic curve extensions above (44) of the measuring range (46) and below (43).

[0168] As a second example, Fig. the measuring bridge arrangement of the Fig. This requires only an op-amp (47) and a resistor (71) in addition to the sensor bridge (72) itself. This is therefore the simplest possible measuring bridge arrangement (EiEv-MeBrü). The measuring bridge operates in a virtual short circuit in the primary measuring range; on the left, the voltage at node K2 (77) is tapped using a voltage tap (at the voltage divider R1-R2 of type A). On the right, at node K4 (76), a current tap (voltage divider R3-R4 of type C) keeps node K4 at the same potential.

[0169] The operation of the instrument amplifier (73) additionally connected to the measuring bridge corresponds, in essence, only to the measuring bridge arrangement of the Fig. (combined in one IC). The op-amp (48) of the IC simulates the voltage difference between the voltages at inputs (76) and (77).

[0170] Fig. The corresponding characteristic curve diagram and the measuring ranges are shown. The characteristic curve (78) for a pressure sensor measuring bridge is depicted; that is, the differential voltage to be measured at tap nodes K2 and K4 is shown as a function of the pressure P as the parameter to be measured. The curve (78) is very flat, but would extend very far to the right, towards high pressures, and to the left, towards a vacuum.

[0171] Due to the simplicity of the circuit, for example a battery (U) is sufficient. err ) for supplying power to the measuring bridge and also to supply power to the electronics. A ground reference can be established as shown in Fig. shown (49), or, if the instrumentation amplifier is not connected, e.g. by connection at node K3 (77) or otherwise. Outputs U1 (75) and U2 (74) provide outputs for two measuring ranges that can be measured simultaneously with the measuring bridge. The characteristic curve (79) is displayed at output U1 (75). Fig. ) modeled; at output U2 (74) the characteristic curve (80) or (81) ( Fig. ).

[0172] This “simplest measuring bridge ever” forms the characteristic curve (79) at output U1 (75) in Fig. after: If the pressure P to be measured is below the limit (82), then U1 ( Fig. ) below in the boundary, R f It then lies in parallel with R3. This operating state is maintained even at lower pressures. A slightly modified measuring bridge with a different resistor R'3 and a different operating mode (both voltage dividers are now type A) continues to operate. The measuring bridge voltage can be tapped from the instrumentation amplifier (73) and processed normally; this defines the characteristic curve (81) with a slope defined by this measuring bridge configuration.

[0173] If the pressure P to be measured is above the limit (83), then U1 ( Fig. ) at the top of the boundary, R fIt then lies in parallel with R4. This operating state is maintained even at higher pressures. A slightly different measuring bridge than before, with a slightly different resistor R'4 and again with a different operating mode (both voltage dividers are of type A), continues to operate. This can again be determined by the instrumentation amplifier (73) in Fig. The data is tapped and processed normally. This defines the characteristic curve (80) with a slope defined by this measuring bridge configuration (possibly a different one).

[0174] In situations where the pressure P to be measured is located between the limits (82) and (83) (in measuring range 1 (84) with operating point AP1), the OpAmp (47) keeps the two voltages at nodes K2 and K4 at the same potential, the instrumentation amplifier “sees” only the offset voltage of the OpAmp (47) in this range (84) (which is thus advantageously accessible to a measurement).

[0175] The total measuring range (85) of the arrangement is therefore very long, but has several partial measuring ranges with different resolutions or is interrupted by a partial measuring range (84) that inserts in between.

[0176] Fig. Figure 9 shows an oscilloscope recording of transitions between the measurement and operating ranges. The parameter to be measured (pressure measurement) is to be recorded in a measurement range where high resolution is required. For testing purposes, the pressure (as the parameter to be measured) initially drops, reaches a minimum, and then rises again. The x-axis (98) is therefore a time axis. - At (90) the measuring bridge arrangement enters the high-resolution measuring range in which the OpAmp (47) ( Fig. ) comes out of the limit (93) and is now operating. In this measuring range, the voltage measurement with the IV (73) only detects an offset value (91) of the op-amp (47). - At (92) the measuring bridge arrangement leaves this high-resolution measuring range again because the OpAmp (47) enters the limit (94) here and remains stable there. - At (95) the measuring bridge arrangement returns from the limit (94) into the high-resolution measuring range in which the OpAmp (47) operates again.

[0177] As can be seen, the transition between the work areas occurs quickly due to the comparator effect.

[0178] The two measuring ranges of the measuring bridge arrangement of the Fig. are clearly recognizable: The op-amp (47) is in a limit state (93) or (94) before (90) and between (92) and (95). In this state, the instrumentation amplifier (73) operates in one of the characteristic curve regions (80) (81); the pressure curve can be detected by the instrumentation amplifier (73), but not by the op-amp (47). Voltages are available at output (74) that only slightly amplify the pressure curve, but over a wide measuring range (see...). Fig. The measuring bridge arrangement also works here.

[0179] Between (90) and (92) and after (95) the OpAmp (47) operates as the “simplest measuring bridge ever”, now with respect to the pressure range in a small measuring range, but also with high resolution, while the instrumentation amplifier at output (74) can only detect the offset voltage (91) of the OpAmp (47).

[0180] Finally, it should be explained how the characteristic curves of the Fig. , which have so far only been described as requirements, can be realized: To do this, imagine two identical circuits of the Fig. before: A first circuit implements the characteristic curve (55) ( Fig. ) with the measuring range (65). A second circuit implements the characteristic curve (54) with the measuring range (64). The circuits of the two op-amps, each with only one resistor, are implemented on opposite sides, one on the right and one on the left.

[0181] An additional instrument amplifier can be designed for the sensor measuring bridge, which allows the characteristic curve (51) to be defined.

[0182] Below the measuring range (65) ( Fig. ) and above the measurement range (64), both op-amps are within their limits. In the parameter range below (65), there is a resistor R in each case. f parallel to R2 the other R fparallel to R3, in the parameter range above (64) there is each an R f parallel to R1 the other R f lies parallel to R4.

[0183] Between the measuring ranges (65) and (64), one of the op-amps is located at the top, the other at the bottom of the boundary. Depending on which side (right or left of the sensor measuring bridge) the boundary is located, the R f parallel to one of the sensor bridge resistors above or below, i.e., "crosswise", but also in a stable state. The state between the measuring ranges (64) (65) is therefore also stable.

[0184] In all three measurement ranges, the two circuits seen separately so far operate stably with only different type A voltage dividers.

[0185] If one simply superimposes the two circuits, i.e., uses only one sensor bridge with the defined modifications for both sides, thus retaining the respective circuits on both sides, then one obtains the arrangement of the Fig. .

[0186] When correctly configured, the EiEv-MeBrü on the right operates with OpAmp (47) as described above, using a modified sensor bridge in one of the two measuring ranges (54) or (55). The same applies to the OpAmp on the other side.

[0187] Although one of the two sides is within the limit while the other side is operating, in all cases a stable sensor measuring bridge exists which has stable and unambiguous parameters in the respective measuring range (54) or (55) and even in the respective environment.

[0188] The two op-amp outputs each form one of the two measurement ranges (54) or (55); the additional instrumentation amplifier provides the characteristic curve (51) outside these two measurement ranges.

[0189] If the parameter to be measured is located in one of the two measuring ranges (64) (65), the two nodes of the measuring bridge are each virtually short-circuited.

[0190] Only once does the voltage at node K2, taken from the voltage tap of the OpAmp (47), determine what voltage should be at node K4.

[0191] The other time, the voltage at node K4, tapped by the voltage tap of the other op-amp (70), determines what voltage should be at node K2.

[0192] Designing such a circuit is not entirely straightforward, but it can be managed well with standard simulation programs and the design can be simple. Suitable tools allow for easy verification.

[0193] The circuit of the Fig. The invention demonstrates details in several respects: - At each tap node of a voltage divider of the sensor measuring bridge, there is a current tap, in addition to several voltage taps. - In Fig. Instrumentation amplifiers (not shown) can be connected to sensor bridges multiple times because they only introduce voltage taps into the arrangement without interfering with the primary functions (of the IU converter). - A type C voltage divider operates further than a type A voltage divider with modified parameters in areas where the electronics are limited by the supply. - Since a voltage tap does not interfere with the primary functions of the IU converters, the cross-reference of the reference voltages also does not interfere with any of the primary functions located on the right or left. - Since (and if) the measurement ranges provided by the primary functions (54) (55) ( Fig. Since the two op-amps (70) (71) do not overlap, they do not interfere with each other outside their respective measurement ranges.

[0194] The circuit of the Fig. In addition to a wide measuring range (51) ( Fig. ) with low resolution two measurement areas located at a considerable distance from each other with high resolution (54) (55).

Claims

[1] Measuring bridge arrangement with a sensor measuring bridge (72) and at least one measuring bridge amplifier (47) (73), characterized by , that at at least one measuring bridge tap node (K4 (76) or K2 (77)) the voltage is set to a predetermined value u Bez is held and / or regulated and Additional voltage taps can be used from the same tap nodes (76) (77) to enable processing of the voltage provided by the sensor measuring bridge in areas (80) (81) also outside the first measuring range (84) (46). [2] Measuring bridge arrangement according to claim 1, characterized by , that a current-to-voltage converter (IU converter) (47) (12) in a first measuring range (84) (46) the voltage at one of the measuring bridge tap nodes by means of a current tap to a first defined value u Bez ( Fig. pulls and holds and / or an inverting amplifier circuit (11) using a voltage tap to reduce the voltage at a measuring bridge tap node to a defined value U Bez ( Fig. pulls and holds, thus defining further measuring ranges. [3] Measuring bridge arrangement according to claim 1, characterized by , that at least one measuring range is defined by the operating range of the electronics in such a way that outside this operating range the output of the OpAmpr falls within the supply-related limitation. [4] Measuring bridge arrangement Claim 1, characterized by , that by means of an inverting amplifier stage (11) the voltage at a tap node (K2) of the sensor measuring bridge is kept stable in order to form operating states of the measuring bridge and the measuring bridge amplifier which are above and below a limit (45). [5] Measuring bridge arrangement with a sensor measuring bridge (72) in which measuring voltages (78) are tapped from the tap nodes (K2, K4) by means of voltage taps (76) (77), amplified (73) (47) and provided (80) (81), characterized by , that in a partial measurement range (84) (46) at at least one of the tap nodes (K4) of the sensor measuring bridge (72) the voltage is held at a defined level in order to provide a higher gain (79) for the limited partial measurement range (84) (46) than outside (80) (81) of this limited measurement range or partial measurement range (84). [6] Measuring bridge arrangement according to one of claims 1 to 5, characterized by , that the sensor measuring bridge is operated in a virtual short circuit by one of the two tap nodes of the sensor measuring bridge supplying the reference voltage for an IU converter circuit that performs a current tap at the other tap node. [7] Measuring bridge arrangement according to one of claims 1 to 6, characterized by , that a measuring bridge arrangement whose sensor measuring bridge is operated in virtual short circuit has additional instrument amplifiers or amplifiers at the measuring bridge terminals to detect the voltage difference between tap nodes. [8] Measuring bridge arrangement according to claim 7, characterized by , that an amplifier or instrumentation amplifier is additionally provided at the measuring bridge connections (76) (77) in order to measure the voltage difference between the tap nodes as an offset voltage even during active current taps in the measuring ranges (84) (46) ( Fig. ). [9] Measuring bridge arrangement according to claim or 5, characterized by , that with current taps on both sides of a sensor measuring bridge, the voltage at the tap node is kept at the level specified by the tap node of the other side ( Fig.), thereby providing two high-resolution measurement ranges (54) (55) located at a distance from each other, in addition to at least one long-range measurement range (e.g. (51) ( Fig. )) will be provided at a lower resolution.

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