Level measuring device

Abstract

The invention relates to a filling level measuring device for determining a filling level of a medium in a container, comprising: a signal generating device configured to generate an electrical signal comprising a step function or a pulse function; a measuring line which is connected, in particular electrically connected, to the signal generating device and extends from the process connection into the medium and into the medium, the measuring line being configured to conduct an electrical signal into the container and into the medium, the electrical signal being at least partially reflected at the surface of the medium and the reflected signal influencing the electrical signal; and an evaluation unit configured to determine the level of the medium based on the affected electrical signal.

Description

Technical Field

[0001] This invention relates to a level measuring device for determining the filling level of a medium inside a container. Background Technology

[0002] Accurately determining the level of storage tanks is a common requirement in various industrial applications. Different technologies are available to address this problem. For example, optical, radar-based, capacitive or conductive sensors, tuning forks, floats, or wired TOP (time-of-flight) methods can be used to determine the level.

[0003] In wired TOF, an electrical pulse is transmitted through a cable extending into the liquid in the tank. Because the cable has different effective impedances in the portions not extending into the liquid and in the liquid, the electrical pulse transmitted through the cable is reflected at the liquid surface (i.e., at the boundary between the two different impedances). Thus, the tank level can be inferred based on the flight time of the electrical pulse from the process connector to the liquid surface and the flight time of the reflected signal from the liquid surface back to the process connector.

[0004] However, pulse evaluation in wired Time-of-Flight (TOF) methods places high demands on the transmitting and receiving equipment, as they must provide high resolution (typically in the picosecond range), which increases complexity and cost. A further drawback is the need for numerous consecutive excitation signals to record the time of flight, negatively impacting energy consumption. Furthermore, existing methods result in significant high-frequency interference from the transmissions, as a portion of the high-frequency pulse signal is radiated through the measurement probe, which acts as an antenna. Therefore, such applications are generally limited to use within metal containers. Summary of the Invention

[0005] The purpose of this invention is to remedy the above-mentioned shortcomings and to provide an improved level measuring device and corresponding method for determining the level of a medium in a container.

[0006] The subject matter of the independent claims fulfills this purpose.

[0007] A first aspect of the present invention relates to a level measuring device for determining the level of a medium within a container, the level measuring device comprising:

[0008] A signal generating device configured to generate an electrical signal including a step function or a pulse function;

[0009] A measuring line, which is connected (especially electrically) to a signal generating device and extends from a process connection or may extend into a medium and into the medium, wherein the measuring line is used to conduct an electrical signal into the container and into the medium, wherein the electrical signal is preferably at least partially reflected at the surface of the medium and the reflected signal affects the electrical signal;

[0010] An evaluation unit is configured to determine the level of the medium based on the affected electrical signals.

[0011] This invention is based on the understanding that the reflection of an electrical signal at the surface of a medium affects or alters the original electrical signal, and this alteration is reflected in the form of the affected electrical signal. Therefore, the time of flight of the affected electrical signal can be determined (particularly indirectly), and thus the level of the medium can be determined. Specifically, the level of the medium can be determined without directly measuring or determining the time of flight of the electrical signal to and from the surface of the medium. The affected electrical signal is particularly the system's step or impulse response to an applied input signal.

[0012] When the time of flight of an electrical signal is mentioned herein, unless otherwise stated, it refers to the time of flight of the electrical signal from the process connector (or from the signal generating device) to the surface of the medium, and the time of flight of the reflected signal from the surface of the medium back to the process connector (and thus back to the evaluation unit).

[0013] For example, the signal generating device is a voltage source that generates a voltage, at least partially in the form of a step function or pulse function, and feeds it to the level measuring device. Specifically, the signal generating device is capable of rapidly turning on or feeding an electrical signal to the system, i.e., with a rise time shorter than 10 ns, 1 ns, or 100 ps. This, for example, ensures that the level measuring device can perform measurements with appropriate accuracy and resolution. For example, a rapid increase in the electrical signal can also be generated by "suddenly" feeding a constant electrical signal to the system via a switching switch. For example, the switch can be configured as part of the signal generating device and can turn the electrical signal on and off. In other words, the switch connects the signal generated by the signal generating device to the rest of the level measuring device and then disconnects it again, thereby generating the corresponding electrical signal.

[0014] Specifically, an electrical signal or voltage is applied to or transmitted via the measuring line. In this regard, the measuring line can be any suitable wire, particularly a cable capable of transmitting electrical signals, wherein the measuring line has a corresponding measuring line impedance, which depends particularly on the dielectric constant of the surrounding medium. For example, the measuring line may also include multiple connected metal components electrically connected to a metal probe extending into the medium. The metal components may, for example, be integrated into the wall of the container or arranged spaced apart from the wall.

[0015] The impedance of the measuring line can also depend on its geometry, which is preferably assumed to be constant herein. The impedance of the measuring line can be described as the characteristic impedance of the transmission path (e.g., a cable), which depends on the properties of the surrounding materials along that path. If the medium through which the signal propagates (and particularly its dielectric constant) changes, for example, from air to a liquid medium, the impedance of the measuring line will also change. The electrical signal originates from the process connector and is conducted to the medium via the measuring line. The measuring line is preferably electrically insulated from both the process connector and the medium. The process connector is, for example, a mechanical interface through which the level measuring device is securely mounted to a container and through which the measuring line is connected to the rest of the level measuring device. The electrical signal thus travels along the measuring line to the medium. Since the impedance of the measuring line within the medium is generally different from that outside the medium, an impedance jump occurs during signal transmission at the surface of the medium (i.e., the interface between the medium and air) or at the point where the measuring line penetrates the surface of the medium. This change in impedance causes the electrical signal to be reflected at the surface of the medium, where the reflected signal affects the original electrical signal. In the following text, the impedance of the portion of the measuring line extending into the medium is called the dielectric impedance, while the impedance of the portion of the measuring line not reaching the medium is called the reference impedance. The intensity of reflection depends particularly on the impedance difference between the reference impedance and the dielectric impedance. A larger impedance difference results in a correspondingly stronger reflection. In particular, the reflected signal is superimposed on the initially generated electrical signal, thereby attenuating or amplifying the original electrical signal. For example, amplification manifests as an increase in the amplitude of the electrical signal, while attenuation manifests as a decrease in the amplitude of the electrical signal. Attenuation of the electrical signal is particularly likely to occur if the reference impedance is greater than the dielectric impedance. Conversely, amplification of the electrical signal is particularly likely to occur if the reference impedance is less than the dielectric impedance. In particular, due to reflection, the reflection is superimposed on the excitation signal (i.e., the electrical signal), wherein the reflection has the same or opposite polarity as the excitation signal (depending on the nature of the impedance change), and is superimposed accordingly.

[0016] Therefore, the reflected signal alters the original electrical signal, particularly its amplitude. Thus, the time point of this change in the altered or affected electrical signal can be used to at least indirectly determine the time of flight of the signal, and consequently, the level of the medium. Since the intensity of the reflection, and therefore the effect of the reflected signal on the electrical signal, depends on the impedance difference between the reference impedance and the dielectric impedance, the reference impedance can be defined based on the dielectric impedance of the known medium. The reference impedance can be specifically defined such that the reflection of the electrical signal realized at the surface of the medium is as strong as possible to facilitate the detection of changes in the resulting electrical signal.

[0017] Therefore, the evaluation unit can determine the level of the medium based on the affected electrical signal. The evaluation unit is particularly used for processing and analyzing signals (such as affected voltage signals), especially in real-time processing and analysis. In this regard, the evaluation unit can handle both analog and digital signals. Furthermore, various calculations or comparisons can be performed using predetermined algorithms or stored rule sets to identify deviations, make decisions, or send further control commands to other system components. Therefore, the evaluation unit can also be configured as a control and evaluation unit. For example, the evaluation unit may include a microcontroller, digital signal processor (DSP), programmable logic controller (PLC), or computer. By integrating storage and processing functions, the evaluation unit can also store data and make the data available for analysis.

[0018] Advantageously, the variable time of flight in the electronics of the level measuring device does not affect the determination of the level or time of flight, because according to the invention, the level is determined based on the affected electrical signal, wherein the first edge of the electrical signal indicates the start time, and the reflected signal affects the electrical signal, such that the point in time of change can be assessed as the end of the time of flight measurement. A further advantage of the invention is that level determination can be achieved with considerably fewer transmission pulses compared to solutions according to the prior art. In the simplest case, the level determination according to the invention can be determined by means of a single transmission pulse. On the one hand, this leads to improved energy consumption of the level measuring device and reduced emissions caused by the sensor, thereby meeting regulatory requirements regarding EMC compatibility, allowing the level measuring device to be used without the use of metal containers. Furthermore, a fast response time is achieved by the level measuring device according to the invention. The level measuring device according to the invention is easier to implement and less expensive than conventional wired TOF methods. The level measuring device according to the invention is particularly suitable for measuring larger depths with an accuracy of 1 cm to 10 cm. For example, it can be used to measure water levels in locks or reservoirs. However, it can also be used in rainwater storage systems or in more compact applications to measure the cooling water level in the engine compartment.

[0019] Other embodiments of the present invention can be seen from the specification, dependent claims and drawings.

[0020] According to one embodiment, the evaluation unit is configured to determine a substitute variable based on an affected electrical signal, the substitute variable being proportional to the flight time of the electrical signal from the process connector to the medium surface and / or proportional to the distance between the medium surface and the process connector, and to determine the level of the medium based on the substitute variable, wherein the substitute variable preferably does not correspond to the flight time of the electrical signal. The substitute variable can be a variable different from the flight time of the electrical signal. Thus, the substitute variable can be used instead of the flight time of the electrical signal to determine the level of the medium. However, based on the substitute variable, the flight time of the electrical signal can be determined (particularly indirectly), thereby allowing the inference of the level of the medium. For example, the substitute variable can be a voltage value derived from the affected electrical signal, or a voltage value determined based on the affected electrical signal. The values ​​or magnitudes of all determined substitute variables (e.g., measured voltage values) can then be assigned to level values, which can then be defined as the determined level of the medium by means of an assignment table or other suitable method. In particular, the assignment table can be determined in advance empirically or calculated based on known system properties.

[0021] According to a first embodiment, the affected electrical signal has a pulse shape, wherein the evaluation unit is configured to generate a square wave signal based on the pulse width of the pulse (particularly the first pulse) of the affected electrical signal, the width of which substantially corresponds to the pulse width of the affected electrical signal, and to determine alternative variables based on the square wave signal. As described above, reflected signals affect electrical signals, particularly causing a decrease in the amplitude of the electrical signal. Therefore, the affected electrical signal has a pulse shape, characterized at least in that it has a rising edge when the electrical signal is generated and a falling edge when the reflected signal is received. The pulse width specifically corresponds to the flight time of the electrical signal from the process connector to the surface of the medium and back.

[0022] Based on the affected electrical signal, a square wave signal (specifically an electrical square wave signal) can be generated, with its rising edge indicating the applied electrical signal and its falling edge indicating the detection of a reflected signal. In other words, the affected electrical signal is converted into a square wave signal, which represents only the width of the first pulse. Therefore, the width of the square wave signal corresponds precisely to the flight time of the electrical signal from the process connector to the surface of the medium and back. The square wave signal specifically contains the time-of-flight information required to determine the level of the medium. Instead of extracting this time-of-flight information in a time-consuming and costly manner using a corresponding ADC, the square wave signal can be used to determine a substitute variable, through which the level can be determined in a simpler way.

[0023] According to one embodiment, the evaluation unit is configured to use a threshold filter to generate a square wave signal based on the affected electrical signal, wherein if the affected electrical signal is less than a predetermined threshold, the square wave signal is substantially zero; if the affected electrical signal is greater than the predetermined threshold, the square wave signal takes a predetermined value that is not equal to zero. The evaluation unit is also configured to integrate the square wave signal using an integrator component to determine an integral value, and to determine the level of the medium based on the integral value. In this respect, the square wave signal has a predetermined value only if the affected electrical signal is greater than the predetermined threshold, thereby ensuring that only the time range before the drop caused by the reflected signal and after the initial increase of the electrical signal is recorded. In particular, the predetermined threshold is selected such that the predetermined threshold is greater than the signal amplitude after the drop in the affected electrical signal caused by the reflected signal.

[0024] To determine the level of the medium, a proxy variable proportional to the flight time of the electrical signal can be determined, and thus a proxy variable proportional to the distance to be determined, rather than determining the flight time of the electrical signal. For this purpose, the evaluation unit is configured to integrate the square wave signal using an integrator component to determine an integral value proportional to the flight time of the electrical signal. The level of the medium can then be determined based on the integral value. In this case, the integral value is used as a proxy variable.

[0025] Threshold filters may include, for example, comparators, diodes, or digital gates. Integrator components may also include capacitors and / or operational amplifiers. The operating modes of the level measuring device will be explained below by way of example only, using a comparator as a threshold filter and a capacitor as an integrator component; this statement also applies accordingly to diodes or operational amplifiers.

[0026] Once the comparator receives the affected electrical signal as a voltage signal, it compares the affected voltage signal, for example, with a predetermined reference voltage (corresponding to a predetermined threshold), and outputs the aforementioned square wave signal, which is particularly similar to the voltage signal. The current source can then be controlled to charge the capacitor based on the square wave signal. Therefore, the capacitor is charged only during the time period when the square wave signal value is not zero. In other words, the duration of capacitor charging corresponds to the flight time. Therefore, the voltage drop across the capacitor is particularly proportional to the flight time of the electrical signal. The voltage drop across the capacitor can then be sampled or measured, for example, by means of an analog-to-digital converter (ADC), and the level of the medium can be inferred based on the determined voltage value of the capacitor. Specifically, an assignment table can be used to assign an associated level value to the measured voltage value, which can be defined as a determined level value. Therefore, the determination of the level of the medium is particularly based on the measurement of the capacitor voltage. The pulse width can be determined indirectly or directly based on the voltage measurement result, and thus indirectly or directly based on the flight time of the electrical signal. The evaluation unit can be further configured to discharge the capacitor, particularly to fully discharge it, until the next measurement using a discharge circuit or a resistor connected in parallel with the capacitor.

[0027] According to one embodiment, the evaluation unit is configured to define a predetermined threshold based on the impedance difference between a reference impedance (representing the impedance of the portion of the measurement line not extending into the medium) and the dielectric impedance (representing the impedance of the portion of the measurement line extending into the medium). Specifically, this stems from the fact that the intensity of the reflected electrical signal, and therefore the effect of the reflected signal on the electrical signal, depends on the impedance difference between the dielectric impedance and the reference impedance. If the effect of the reflected signal on the signal amplitude of the electrical signal is known, i.e., the drop level of the electrical signal caused by the reflected signal (which is defined by the level of the impedance difference), the threshold can be set accordingly so that the square wave signal captures or simulates the corresponding rising and falling edges of the affected electrical signal as accurately as possible. In this regard, the predetermined threshold must be specifically defined such that the predetermined threshold is greater than the signal amplitude of the electrical signal after the drop affected by the reflected signal. In particular, this ensures that the signal value after the drop is not considered when determining the width of the square wave signal.

[0028] According to one embodiment, the evaluation unit is configured to continuously or at predetermined time intervals adjust (particularly decrease) a predetermined threshold of the threshold filter. Therefore, the predetermined threshold can be a variable threshold. By changing the threshold, the development of the affected electrical signal can be determined, and multiple reflection points can be identified based on the determined development. In this case, for example, multiple electrical signals can be sequentially generated via a signal generation device, wherein a different predetermined threshold is set for each generated electrical signal. In this case, a deterioration in the response time of the level measuring device can therefore be intentionally accepted in order to detect multiple reflection points.

[0029] According to one embodiment, the evaluation unit includes multiple threshold filters with different thresholds, specifically for detecting a range of different reflected signals. Electrical signals can be reflected at different points on the surface of a medium, generating multiple different reflected signals. However, multiple media can also be present within the container, causing electrical signals to be reflected at the surfaces of the respective media and generating corresponding reflected signals. For example, a first medium and a second medium can be present in the container, where the density of the first medium is lower than that of the second medium, thus the first medium "floats" on the second medium. The first and second media can have different impedances, resulting in different reflection intensities of the electrical signals from the two media, which in turn can be identified from the affected electrical signals.

[0030] Therefore, this level measuring device is particularly equipped with multi-echo capability, meaning it can identify and process multiple reflections or echoes from a single electrical signal or pulse. As already described, one advantage of a multi-echo system is its ability to detect multiple reflections from different surfaces or materials within the container. This allows information about different levels or layer boundaries to be recorded during a single measurement or during multiple consecutive measurements. Furthermore, detecting multiple reflection signals improves the reliability of level measurements because additional information can be used to obtain more accurate measurement results. Additionally or alternatively, the quantity of medium can be determined in the first step, and then a comparator can be set in the second step to measure only the distance to the selected medium.

[0031] According to one embodiment, the evaluation unit is configured to sample the integrated signal generated by integrating the square wave signal using an analog-to-digital converter (ADC) with a sampling frequency of less than 10 MHz, less than 1 MHz, less than 100 kHz, less than 10 kHz, or less than 1 kHz to determine the integral value. For example, if the integration of the square wave signal occurs by charging a capacitor for a predetermined time period (corresponding to the width of the square wave signal), the voltage drop across the capacitor can be sampled, for example, using the ADC, to determine a corresponding voltage value proportional to the time of flight of the electrical signal. In particular, the ADC can be integrated into a microcontroller or system-on-a-chip (SoC).

[0032] Advantageously, level determination can be achieved without using expensive and energy-intensive evaluation components, but rather with the aid of a simple ADC implementation, which reduces the requirements for the ADC due to the simplicity of the signal. In particular, this is because a direct time-resolved method is not used to determine the level.

[0033] According to one embodiment, the measuring line comprises a coaxial cable. The advantage of coaxial cables is that they have a defined characteristic fundamental impedance, typically between 50 ohms and 75 ohms, and remain constant along their entire length. This is important for level determination because the reflected signal is unaffected by the characteristics of the measuring line and therefore depends primarily on the impedance difference between the reference impedance and the dielectric impedance. In other words, the constant fundamental impedance of the coaxial cable ensures that no additional reflections occur due to fluctuations in the fundamental impedance. The fundamental impedance is, for example, the impedance of an electronic component that is unaffected by the surrounding medium (e.g., in an ideal vacuum or open space). A further advantage of coaxial cables is that the signal is immune to electromagnetic interference (EMC). Due to the constant characteristics of coaxial cables, accurate and reliable transmission of both electrical and reflected signals can be ensured.

[0034] According to one embodiment, the measuring line does not include a coaxial cable. In this case, the level measuring device can, for example, tolerate tolerance jumps in the process connection, i.e., signal deviations that may be caused by unstable transmission of electrical or reflected signals. Advantageously, costs can be reduced by using a measuring line that does not include a coaxial cable. However, it should be noted that the affected electrical signal and therefore its processing become more complex. After the electrical signal is applied, i.e., after the initial rising edge of the electrical signal, a reflection of the same polarity as the electrical signal (caused by the measuring line) occurs, thereby increasing the amplitude of the affected electrical signal. After receiving the signal reflected at the surface of the medium, the drop in the affected electrical signal is subsequently recorded, as described above. In order to better evaluate the resulting affected electrical signal by means of a comparator circuit, it can be differentiated beforehand. If the system does not have multi-echo capability, the impedance in the system must be specially designed so that no reflected signal is reflected back to the process connection, because these multi-echoes would hinder the simple evaluation of the affected electrical signal by means of a comparator circuit.

[0035] According to one embodiment, the electrical signal comprises multiple square wave pulses, and the affected electrical signal comprises multiple pulses, particularly pulses of the same type, wherein the evaluation unit is configured to determine the DC component of the affected electrical signal and determine the level of the medium based on the DC component of the affected electrical signal. Specifically, the individual square wave pulses can be assigned to different measurements. For example, the width of the square wave pulses can be designed such that the pulse width of the associated pulses of the affected electrical signal can be clearly determined. In other words, each square wave pulse is used as a separate step function and applied to the system over a predetermined time period, wherein the predetermined time period is defined by the width of the corresponding square wave pulse. As described above, the affected electrical signal can be further processed by means of a comparator circuit. In the present case, the output signal of the comparator circuit will comprise a series of square wave pulses, wherein each square wave pulse of the output signal is assigned to a corresponding pulse of the affected electrical signal and represents the corresponding measurement result. To determine the mean of the measurement results, for example, the DC component of the comparator's output signal can be determined by means of a low-pass filter. In this regard, a particularly advantageous embodiment is the use of a simple low-pass filter whose output signal is digitized by means of an ADC, allowing the DC component to be determined digitally. For example, the DC component can be determined by calculating the Fourier transform of the digitized signal at 0 Hz, which specifically corresponds to the moving average of a time signal. Therefore, the mean can be determined using simple and inexpensive hardware.

[0036] Alternatively, multiple individual level measurements can be determined based on one of the above embodiments, and the mean of the determined levels can be calculated to determine the final level value.

[0037] According to one embodiment, the signal generation device is configured to generate square wave pulses of the electrical signal at variable time intervals. This ensures compensation for coherent EMC interference that cannot be suppressed through multiple measurements and subsequent averaging. In other words, the square wave pulses are not generated according to a fixed transmission period, but can be generated randomly or according to another aperiodic pattern. For example, the time interval between two consecutive square wave pulses can be randomly selected from time intervals (including the time interval between the minimum and maximum time interval values). Aperiodic signals can be processed in a particularly simple manner by means of a comparator for the proposed evaluation or processing, because the associated evaluation can be performed asynchronously and there is no fixed clock reference for the electrical signal. Therefore, the emission of the system can be further reduced.

[0038] According to a further embodiment, the reference impedance is larger than the dielectric impedance, particularly by 5, 10, 12, or 15 times. Specifically, the reference impedance can be adapted to the dielectric impedance such that the electrical signal is reflected as strongly as possible at the dielectric surface, so that the corresponding reflection can be detected from the affected electrical signal in a simple manner. If the dielectric is water, the reference impedance can be, for example, 50 ohms, 60 ohms, or 75 ohms.

[0039] In one embodiment, the measuring line is short-circuited at the end facing the medium. The short circuit is specifically located within the medium, such that when reflection at the medium boundary is incomplete, a residual portion or residual wave of the electrical signal will be reflected at the short circuit. If the effect of the electrical signal can only be identified by the reflection caused by the short circuit, especially if the effect of the short-circuit-induced reflection on the electrical signal is known, then it can be determined that the level is below the detection range. Furthermore, based on the affected electrical signal, sensor defects can be ruled out.

[0040] According to one embodiment, the measuring line (particularly a coplanar line or microstrip line) is arranged together with the evaluation unit and signal generation device on the same circuit board. Therefore, the level measuring device can be formed very compactly and its manufacturing cost can be very low. This is particularly advantageous for the use of small storage tanks. In particular, the level measuring device can be configured to protect the electronic components, other than the measuring line, from water corrosion, for example by means of grouting, and housed in a corresponding housing, allowing the level measuring device to be directly installed inside the container.

[0041] Another aspect of the present invention relates to a method for determining the level of a medium in a container, the method comprising the following steps:

[0042] An electrical signal with a step function or pulse function is generated by means of a signal generation device;

[0043] Electrical signals are transmitted to the container and into the medium via measuring lines, wherein the measuring lines extend from the process connection to the medium and into the medium.

[0044] At least a portion of the electrical signal is reflected from the surface of the medium, wherein the reflected signal affects the electrical signal, and

[0045] The level of the medium is determined by an evaluation unit based on the affected electrical signal.

[0046] According to one embodiment, the electrical signal is conducted with a substantially constant fundamental impedance. The level measuring device can, for example, be configured such that the fundamental impedances of the electrical components are close to each other. In particular, the electrical signal or reflected signal is conducted along the measuring line with a substantially constant fundamental impedance. As already described, this can be achieved by means of a coaxial cable.

[0047] According to the present invention, the description of the level measuring device applies accordingly to the method. This is particularly relevant to the advantages and embodiments.

[0048] It should be noted that any combination of the above embodiments is possible unless explicitly excluded. Attached Figure Description

[0049] The invention will now be presented by way of example only with reference to the accompanying drawings. The drawings show:

[0050] Figure 1 This is a schematic representation of a level measuring device.

[0051] Figure 2 A detailed schematic representation of the level measuring device;

[0052] Figure 3 The circuit diagram of the level measuring device (a), the electrical signals affected by different levels (b), and the associated output voltage (c) are shown.

[0053] Figure 4 The circuit diagram of the level measuring device is shown in (a), the electrical signals affected by different levels are shown in (b), the output signal of the first comparator is shown in (c), the output signal of the second comparator is shown in (d) and the associated output voltage is shown in (e).

[0054] Figure 5 The step response of a level measuring device with a coaxial cable is represented (a), the step response of a level measuring device without a coaxial cable is represented (b), and the impulse response is represented (c).

[0055] Figure 6 A schematic diagram of an evaluation unit used to process multiple level measurement results;

[0056] Figure 7 This is an example of a level measuring device. Detailed Implementation

[0057] Figure 1A schematic representation of a level measuring device 12 for determining the level of medium 14 in container 16 is shown. The level measuring device 12 includes a signal generating device in the form of a voltage source 18 configured to generate an electrical signal, i.e., a voltage signal, comprising a step function or a pulse function. The level measuring device 12 also includes a measuring line 20 specifically connected to the voltage source 18 and extending from process connection 22 into and into the medium 14, wherein the measuring line 20 is used to conduct the voltage signal into container 16 and into the medium 14, the voltage signal being at least partially reflected at the surface of the medium 14, and the reflected signal affecting the voltage signal. Furthermore, the level measuring device 12 includes an evaluation unit 24 configured to determine the level of medium 14 based on the affected voltage signal.

[0058] Figure 2 A detailed schematic representation of the various components of the level measuring device 12 is shown. In this respect, the voltage source 18 of the level measuring device 12 generates a voltage signal in the form of a step function. The voltage signal is applied to the measuring line 20 via a first resistor 26 and a process connector 22. Specifically, the voltage wave of the voltage signal generated by the voltage source 18 reaches the process connector via the first resistor 26 and reaches the comparator 30 via a second resistor 28. If the circuit impedance at the measuring line interface is different from the impedance of the measuring line 20, especially from the reference impedance 46, a discontinuity may occur in the impedance development at the process connector 22. Preferably, the circuit impedance and the reference impedance 46 are approximately similar to each other, so that there is no discontinuity or impedance jump at the process connector 22. Therefore, the voltage wave travels from the process connector point 22 through the measuring line 20 to the medium 14, and after reaching the surface of the medium, is reflected by the surface of the medium, resulting in a reflected signal traveling from the surface of the medium to the process connector 22.

[0059] The reflection of the voltage wave is caused by the impedance difference between the impedance of the measuring line outside the medium 14 (i.e., reference impedance 46) and the impedance of the measuring line 14 inside the medium (i.e., medium impedance 48). The greater the impedance difference, the more pronounced the voltage wave reflection. The voltage wave reflection (i.e., the reflected signal) affects the voltage signal because the reflected signal causes the voltage signal to drop. The affected voltage signal (especially present at the input of comparator 30) is further processed by comparator 30 to extract information from the affected voltage signal, which can be used to determine the level of the medium 14 in container 16. For this purpose, comparator 30 compares the affected voltage signal with a predetermined comparison voltage, which in this example is generated by a digital-to-analog converter (DAC) 32, which can be configured as part of a microcontroller 34. The comparison voltage of comparator 30 can be variable and can be continuously or at predetermined intervals by means of DAC 32.

[0060] As already described, the reflected signal affects the voltage signal by causing a voltage drop. In this respect, the level of the voltage drop depends on the level of the impedance difference between the reference impedance 46 and the dielectric impedance 48. For example, if the reference impedance 46 is 10 times larger than the intermediate impedance 48, it will result in a voltage drop of up to 90% on the original voltage. Based on this knowledge, the comparison voltage of comparator 30 can be defined such that the output signal (square wave signal) of comparator 30 depicts the rising edge and falling edge of the affected voltage signal, the falling edge being caused by the reflected signal. For example, if the reflected signal causes a voltage drop of 90%, the comparison voltage can be set to 20% of the initial voltage signal value. The width of the square wave signal output by comparator 30 then corresponds to the flight time of the voltage wave from the process connector to the dielectric surface and back. For all affected voltage signal values ​​greater than the predetermined comparison voltage, the output signal of comparator 30 has a voltage value V. high ; and for all affected voltage signal values ​​less than a predetermined comparison voltage, the output signal of comparator 30 has a voltage value V. low Or the voltage value is 0 V. Based on the output signal of comparator 30, current source 38 is then controlled by switch 36 to charge output capacitor 40 within a time period defined by the square wave signal. The voltage drop across output capacitor 40 is proportional in this respect to the flight time of the voltage wave from process connection 22 to the surface of the medium and back, or inversely proportional to the level of medium 14 in container 16. Therefore, the level of medium 14 in container 16 can be inferred from the voltage measurement of output capacitor 40. Accordingly, time measurement (i.e., measurement of the flight time of the voltage wave) is thus converted into voltage measurement. For example, the measurement and detection of the voltage of output capacitor 40 can be made possible by a corresponding ADC 62 (not shown) of microcontroller 34.

[0061] Figure 3(a) shows a circuit diagram of the level measuring device 12. In this respect, a voltage signal from the voltage source 18 is suddenly applied to the measuring line 20 via a first resistor 26 via a fast switch 42. The switch 42 is moved to a closed or open position via a pulse generator 44. A series of square wave pulses can be generated by alternately opening and closing the switch 42. As already described, the voltage wave of the voltage signal can be conducted to the medium 14 via the measuring line 20, wherein the measuring line 20 outside the medium 14 has an associated reference impedance 46, while the measuring line 20 inside the medium 14 has an associated dielectric impedance 48. Due to the impedance difference between the reference impedance 46 and the dielectric impedance 48, a voltage wave is reflected back to the process connector, causing a voltage drop in the voltage signal. The affected voltage signal can be used to charge the output capacitor 40, and thus infer the level of the medium 14 in the container 16. In this embodiment, a diode 50 is used instead of the comparator 30 described above to define the voltage threshold and generate a square wave signal with a width corresponding to the flight time of the voltage wave.

[0062] Figure 3 (b) shows the affected voltage signal extracted at the input of diode 18. As can be seen from the figure, after an initial sharp rise, the voltage signal drops to a value corresponding to approximately 20% of the initial voltage value, where the voltage drop is caused by the reflected signal. Figure 3 As can be seen in Figure (b), the further drop or rise of the affected voltage signal is due to further reflection of the voltage wave. However, the time of the first falling edge is particularly relevant in order to determine the flight time of the voltage wave and thus the level of the medium. Accordingly, the diode 50 is configured such that the comparison voltage is greater than 20% of the output voltage value of the voltage source 18, such that the width of the resulting square wave signal is equal to the width of the affected voltage signal from the first rising edge to the first falling edge. In this example, the comparison voltage of the diode is 30% of the turn-on voltage of the voltage source 18. Figure 3 (b) shows the voltage signals affected at different levels. The levels include a first level, a second level, and a third level, where the first level is higher than the second level, and the second level is higher than the third level. Figure 3 As shown in (b), due to the shorter flight time of the voltage wave, the voltage signal at the first level decreases earliest. Correspondingly, the voltage signal at the second level decreases earlier than the voltage signal at the third level.

[0063] Figure 3 (c) shows the development of the output capacitor voltage under different material levels. It can be seen from the figure that when the voltage value of the square wave signal is V... high During the duration of the signal, the voltage of output capacitor 40 increases linearly. Once the square wave signal drops back to 0V, output capacitor 40 will stop charging and will remain at the reached voltage level. Figure 3 (c) It can be seen that the voltage drop across the output capacitor 40 is higher for lower levels than for higher levels. This is because the charging time of the output capacitor ideally corresponds to the flight time of the voltage wave, and therefore the charging time is longer at lower levels than at higher levels.

[0064] Figure 4 (a) A circuit diagram of the level measuring device 12 is shown. Figure 3 Compared to the circuit diagram in (a), the level measuring device 12 includes a first comparator 52 and a second comparator 54. Another difference is that instead of using an output capacitor 40, an operational amplifier 56 is used to integrate the square wave signal generated by the first comparator 52. However, in this embodiment, since the signal value is not stored as with the output capacitor 40, the integrated value must be extracted directly. As explained above, the first comparator 52 will... Figure 4 The affected voltage signal shown in (b) is compared with a comparison voltage that is greater than the voltage value of the affected voltage signal after the first voltage drop caused by the reflected signal. Therefore, the comparator's output signal simulates the first rising and first falling edges of the affected voltage signal, as shown in (b). Figure 4 As shown in (c). On the other hand, the second comparator 54 is configured such that its comparison voltage is lower than the voltage level of the affected voltage signal after the first drop, but higher than the voltage level of the affected voltage signal after the second drop, for example, the second drop is caused by further reflection. The resulting signal, i.e., the output signal of the second comparator 54, is as follows: Figure 4 As shown in (d). Therefore, an additional comparator can be used to capture multiple reflections, thus creating a system capable of multiple echoes. Figure 4 (a) does not provide further processing of the output signal of the second comparator 54. However, in principle, the output signal of the second comparator 54 can be processed in the same way as the output signal of the first comparator 52, for example, in this case, by means of a corresponding operational amplifier. The output signal of the operational amplifier 56 is as follows: Figure 4 As shown in (e), where, as Figure 3 (c) As shown, a higher amplitude voltage signal indicates a lower level, and therefore the voltage wave has a longer flight time.

[0065] exist Figure 5 In (a), when the level measuring device 12 is equipped with a coaxial cable as the measuring line 20, the affected voltage signal (i.e., the step response) of the step function is plotted as the input voltage signal. The affected voltage signal has a pulse shape, characterized by a rising edge when the electrical signal is generated and a falling edge when the reflected signal is received. The pulse width in this respect corresponds to the flight time of the voltage wave.

[0066] exist Figure 5 In (b), when the level measuring device 12 is not equipped with a coaxial cable as the measuring line 20, the affected voltage signal (i.e., the step response) of the step function is plotted as the input voltage signal. After the voltage signal is applied (i.e., the rising edge of the voltage signal), a reflection with the same polarity as the voltage signal is generated by the measuring line 20, thereby increasing the amplitude of the affected voltage signal. After receiving the signal reflected from the medium surface, the decrease in the affected voltage signal can be recorded.

[0067] exist Figure 5 In (c), the affected voltage signal (i.e., the impulse response) of the impulse function is plotted as the input voltage signal. As can be seen from the figure, the applied input pulse, after the corresponding flight time, can be identified as a reflected pulse in the affected voltage signal. The advantage of using the impulse function as the input voltage signal is that, as expected, even with a reduced amplitude of the reflected pulse, a medium with a low dielectric constant can be detected. Furthermore, a small impedance difference between the dielectric impedance 48 and the reference impedance 46 can be detected.

[0068] Figure 6 A schematic representation of an evaluation unit 24 for processing multiple level measurements is shown. Evaluation unit 24 includes a comparator 30 and an averaging unit 58, which includes a low-pass filter 60 and an analog-to-digital converter (ADC) 62, and receives the affected voltage signal via a preprocessing circuit 64, which includes an additional voltage source 18 and a measurement line 20. In this example, the voltage signal generated by the voltage source 18 is periodically turned on and off via a fast switch 42, or periodically connected to and disconnected from the voltage source 18, such that the output signal (i.e., the unaffected voltage signal) comprises multiple square wave pulses. Each square wave pulse can be assigned to a corresponding measurement result. Accordingly, the voltage signal affected by the reflected signal similarly has... Figure 6 The pulse shape is depicted. The corresponding pulse of the affected voltage signal has the following characteristics: a first rising edge, which is caused by the corresponding turn-on voltage of the fast switch 42 and causes the voltage to increase to a first voltage level; a first falling edge, which is caused by the reflected signal and causes the voltage to drop to a second voltage level; and a second falling edge, which is caused by further reflection of the voltage signal or voltage wave and / or the turn-off voltage of the fast switch 42 and causes the voltage to drop to the output level or zero level.

[0069] The affected voltage signal is further processed by comparator 30, wherein the comparison voltage of comparator 30 is set to be greater than a second voltage level. Therefore, the signal component of the affected voltage signal after the first drop is filtered out, so that the signal output by comparator 30 is retained, and the signal includes a series of square wave pulses.

[0070] The individual pulses of the output signal of comparator 30 can be assigned to the corresponding measurements. The individual pulses of the output signal of comparator 30 may differ from each other, at least slightly, in both width and amplitude. Therefore, it is advantageous to calculate the mean of the individual measurement results to improve the overall measurement accuracy. For this purpose, the mean of the individual measurement results can be determined by means of the mean calculation unit 58. This can be done particularly simply by determining the DC component G of the pulse-shaped output signal of comparator 30. In this regard, high-frequency signal components are removed by means of a low-pass filter 60, such that the output of the low-pass filter 60 mainly comprises the DC component G of the input signal. The signal can then be digitized by means of an ADC 62, and the DC component G can be determined digitally, for example, by determining the Fourier transform of the digitized signal at 0 Hz, which corresponds to the moving average of the time signal. Therefore, the mean can be determined by means of simple and inexpensive hardware.

[0071] Figure 7 An embodiment of the level measuring device 12 is illustrated, wherein the measuring line 20, evaluation unit 24, and voltage source 18 are arranged on the same circuit board 66. Therefore, the level measuring device 12 can be formed very compactly and can be manufactured inexpensively. In addition to the measuring line 20, the electronic components are moisture-proofed within the upper part 68 of the level measuring device 12 by grouting, so that the level measuring device 12 can be directly mounted in the container 16 of the medium 14. For example, the measuring line 20 can be configured as a coplanar line or a microstrip line.

[0072] List of reference numerals

[0073] 12. Level measuring device

[0074] 14. Medium

[0075] 16 Containers

[0076] 18 Voltage Source

[0077] 20 measuring lines

[0078] 22 Process connectors

[0079] 24 Evaluation Units

[0080] 26 First Resistor

[0081] 28 Second Resistor

[0082] 30 comparators

[0083] 32 Digital-to-Analog Converter

[0084] 34 microcontrollers

[0085] 36 switches

[0086] 38 Power Supply

[0087] 40 Output capacitor

[0088] 42 Quick Switch

[0089] 44 Pulse Generator

[0090] 46 Reference Impedance

[0091] 48. Dielectric Impedance

[0092] 50 diode

[0093] 52 First Comparator

[0094] 54 Second comparator

[0095] 56 Operational Amplifier

[0096] 58 Mean Calculation Units

[0097] 60 Low-pass filter

[0098] 62 Analog-to-Digital Converter

[0099] 64 Preprocessing Circuit

[0100] 66 Circuit Boards

[0101] 68. Upper part of the level measuring device

Claims

1. A level measuring device for determining the level of a medium inside a container, the level measuring device comprising: A signal generating device configured to generate an electrical signal including a step function or a pulse function; A measuring line, connected to the signal generating device and extending from the process connector into and into the medium, wherein the measuring line is used to conduct the electrical signal into the container and into the medium, wherein the electrical signal is at least partially reflected at the surface of the medium, and the reflected signal affects the electrical signal; and An evaluation unit is configured to determine the level of the medium based on the affected electrical signal.

2. The level measuring device according to claim 1, characterized in that, The measuring line is electrically connected to the signal generating device.

3. The level measuring device according to claim 1, characterized in that, The evaluation unit is configured to determine a substitution variable based on the affected electrical signal and to determine the level of the medium based on the substitution variable, the substitution variable being proportional to the time of flight of the electrical signal from the process connector to the surface of the medium and / or proportional to the distance between the surface of the medium and the process connector; The substitution variable does not correspond to the flight time of the electrical signal.

4. The level measuring device according to claim 3, characterized in that, The affected electrical signal has a pulse shape; The evaluation unit is configured to generate a square wave signal based on the pulse width of the pulse of the affected electrical signal and to determine the substitution variable based on the square wave signal, the width of the square wave signal being substantially corresponding to the pulse width of the affected electrical signal.

5. The level measuring device according to claim 4, characterized in that, The evaluation unit is configured to generate a square wave signal based on the pulse width of the first pulse of the affected electrical signal.

6. The level measuring device according to claim 4, characterized in that, The evaluation unit is configured to generate the square wave signal based on the affected electrical signal using a threshold filter, wherein if the affected electrical signal is less than a predetermined threshold, the square wave signal is substantially 0; if the affected electrical signal is greater than the predetermined threshold, the square wave signal is a predetermined value not equal to 0. The evaluation unit is configured to integrate the square wave signal using an integrator component to determine an integral value, and to determine the level of the medium based on the integral value.

7. The level measuring device according to claim 6, characterized in that, The evaluation unit is configured to define the predetermined threshold based on the impedance difference between a reference impedance and a dielectric impedance, wherein the reference impedance represents the impedance of the portion of the measurement line that does not extend into the dielectric, and the dielectric impedance represents the impedance of the portion of the measurement line that extends into the dielectric.

8. The level measuring device according to claim 6, characterized in that, The evaluation unit is configured to continuously or at predetermined time intervals adjust a predetermined threshold of the threshold filter.

9. The level measuring device according to claim 8, characterized in that, The evaluation unit is configured to continuously or at predetermined time intervals decrease a predetermined threshold of the threshold filter.

10. The level measuring device according to claim 6, characterized in that, The evaluation unit includes multiple threshold filters with different thresholds.

11. The level measuring device according to claim 6, characterized in that, The evaluation unit is configured to sample the integral signal generated by integrating the square wave signal using an ADC with a sampling frequency of less than 10 MHz, less than 1 MHz, less than 100 kHz, less than 10 kHz, or less than 1 kHz, in order to determine the integral value.

12. The level measuring device according to claim 1, characterized in that, The measuring line includes a coaxial cable.

13. The level measuring device according to claim 1, characterized in that, The electrical signal includes multiple square wave pulses, and the affected electrical signal includes multiple pulses; The evaluation unit is configured to determine the DC component of the affected electrical signal and to determine the level of the medium based on the DC component of the affected electrical signal.

14. The level measuring device according to claim 13, characterized in that, The affected electrical signals include multiple pulses of the same type.

15. The level measuring device according to claim 13, characterized in that, The signal generating device is configured to generate square wave pulses of the electrical signal at variable time intervals.

16. The level measuring device according to claim 1, characterized in that, The reference impedance is greater than the dielectric impedance.

17. The level measuring device according to claim 16, characterized in that, The reference impedance is 5, 10, 12, or 15 times greater than the dielectric impedance.

18. The level measuring device according to claim 1, characterized in that, The measurement lines, the evaluation unit, and the signal generation device are arranged together on the same circuit board.

19. The level measuring device according to claim 18, characterized in that, The measurement line is either a coplanar line or a microstrip line.

20. A method for determining the level of a medium in a container, comprising the following steps: An electrical signal with a step function form is generated using a signal generation device. The electrical signal is conducted to the container and into the medium via a measuring line, wherein the measuring line extends into and into the medium. A portion of the electrical signal is reflected from the surface of the medium, wherein the reflected signal affects the electrical signal, and The level of the medium is determined by means of an evaluation unit based on the affected electrical signal.

21. The method according to claim 20, characterized in that, The electrical signal is transmitted with a substantially constant basic impedance.

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