Method for determining an electrical conductivity value
The conductivity signal is determined by the signal quality indicator and dynamic factor of the conductivity sensor. Combined with the filtering function, the problem of interference during the measurement process of the conductivity sensor is solved, and fast response and reliable measurement results are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ENDRESS HAUSER CONDUCTA GMBH CO KG
- Filing Date
- 2022-08-30
- Publication Date
- 2026-05-19
AI Technical Summary
Existing conductivity sensors are susceptible to interference during measurement, leading to fluctuations in measured values and making it difficult to achieve fast response and reliable measurement results.
A method for determining the conductivity value of a measurement medium using a conductivity sensor includes providing a transmitting unit, a receiving unit, and a control unit; using signal quality indicators and dynamic factors to determine the conductivity signal; and combining filtering functions to optimize response time and anti-interference capability.
It achieves fast response time and reliable measurement results, reduces fluctuations in conductivity signals, and improves measurement accuracy and anti-interference capability.
Smart Images
Figure CN115791895B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for determining conductivity values and a conductivity sensor. Background Technology
[0002] In analytical measurement techniques, particularly in water management, environmental analysis, and industry (e.g., food technology, biotechnology, and pharmaceuticals), and for most diverse laboratory applications, analytes such as pH, conductivity, and even the concentration of analytes (e.g., ions or dissolved gases in gaseous or liquid measurement media) are crucial. These analytes can be acquired and / or monitored, for example, using electrochemical sensors (e.g., optical, potential, current, voltammetric, or coulometric sensors, and even conductivity sensors).
[0003] In the case of conductivity sensors, especially conductive conductivity sensors, the resistance of a liquid medium is determined by measuring at least one electrical variable (e.g., voltage and / or current). Typically, a sinusoidal AC voltage at the electrodes ensures current flow through the medium. Measurements can fluctuate due to component tolerances, parasitic interference fields around the sensor, and irregularities in the measured medium. To minimize these undesirable effects and obtain a digital output signal with the smallest possible change, the determined resistance or conductivity value is averaged. Depending on the filter depth, and therefore the magnitude of the value considered for filtering the average, the response at the filter output to changes in the measured value is more or less slow. A large filter depth results in a slow response time, but the advantage is less susceptibility to transient disturbances (e.g., EMC interference). A small filter depth results in a fast response time, but the disadvantage is greater susceptibility to transient disturbances. Summary of the Invention
[0004] Therefore, the object of this invention is to provide a method that can achieve fast response time and reliable measurement results.
[0005] According to the present invention, this objective is achieved by a method according to the present invention for determining the conductivity value of a measuring medium by means of a conductivity sensor.
[0006] The method according to the present invention includes the following steps:
[0007] - Provides a conductivity sensor having at least one transmitting unit, at least one receiving unit, and a control unit having a storage module.
[0008] - The stimulation signal is emitted into the measurement medium by the control unit at the transmitting unit.
[0009] - Receive the detection signal at the receiving unit.
[0010] - The control unit determines the signal quality indicator based on the detected signal.
[0011] - Determine the conductivity signal corresponding to the detected signal.
[0012] - Store conductivity signals,
[0013] - The dynamic factor is determined by the control unit based on the conductivity signal.
[0014] -Depending on the determined signal quality indicator and dynamic factor, the conductivity signal is filtered using a filtering function.
[0015] - Output the filtered measured value of the conductivity signal.
[0016] Using the method according to the invention, unforeseen interference effects, especially strong EMC effects, can be responded to quickly and qualitatively, so that the measured values of the conductivity signal can be displayed to the user in the best possible manner. Because the method according to the invention effectively reduces strong fluctuations in the measured values of the conductivity signal, improved measurements are thus possible for the user.
[0017] According to one embodiment of the present invention, the step of determining a signal quality indicator includes: evaluating the distortion of the detection signal relative to the stimulus signal using at least one evaluation method from the following group:
[0018] -Total Harmonic Distortion Assessment Methods
[0019] - Cross-correlation assessment method,
[0020] - Fast Fourier Transform evaluation method
[0021] - Signal amplitude evaluation method.
[0022] According to one embodiment of the present invention, the step of determining the dynamic factor includes: comparing the average value of the stored conductivity signal with the most recent conductivity value of the conductivity signal. The dynamic factor maps to the current rate of change of the conductivity signal.
[0023] According to one embodiment of the invention, the filtering function filters the conductivity signal over a first time span or a first number of measurements of the conductivity signal. The first time span or the first number varies depending on the signal quality indicator and the dynamic factor.
[0024] According to one embodiment of the invention, if the signal quality indicator is less than a threshold and if the dynamic factor is less than a first limit value, the first time span or the first number of measurements of the filtering function remains the same or remains unchanged. If the dynamic factor is between the first limit value and a second limit value, the first time span or the first number of measurements of the filtering function is reduced by a first reduction ratio RA1. If the dynamic factor is between the second limit value and a third limit value, the first time span or the first number of measurements of the filtering function is reduced by a second reduction ratio RA2.
[0025] According to one embodiment of the invention, if the signal quality indicator is greater than a threshold and if the dynamic factor is less than a fourth limit value, the first time span or the first number of measurements remains the same or unchanged. If the dynamic factor is between the fourth and fifth limit values, the first time span or the first number of measurements of the filtering function is reduced by a third reduction ratio RA3. If the dynamic factor is between the fifth and sixth limit values, the first time span or the first number of measurements of the filtering function is reduced by a fourth reduction ratio RA4.
[0026] According to one embodiment of the present invention, the filtering function includes moving average filtering.
[0027] According to one embodiment of the present invention, the stimulation signal is a periodic alternating current signal or an AC voltage signal.
[0028] The aforementioned objective is also achieved by the conductivity sensor according to the present invention.
[0029] The conductivity sensor according to the present invention comprises:
[0030] -At least one transmitting unit,
[0031] -At least one receiving unit,
[0032] - A control unit with a storage module.
[0033] The control unit is adapted to perform the method according to the invention. Attached Figure Description
[0034] The invention will be explained in more detail below based on the accompanying drawings. As shown below:
[0035] Figure 1 The details are schematic representations of the method according to the present invention.
[0036] Figure 2 yes Figure 1 Additional details,
[0037] Figure 3 It is a conductivity sensor. Detailed Implementation
[0038] Figure 1 and Figure 2 A method according to the present invention for determining the conductivity value of a measuring medium using a conductivity sensor 1 is shown. The conductivity sensor 1 is... Figure 3 For example, it is shown as a conductive conductivity sensor 1. However, this method can be similarly applied to, for example, an inductive conductivity sensor.
[0039] The conductivity sensor 1 includes at least one transmitting unit 2, at least one receiving unit 3, and a control unit 4 having a storage module 5. The control unit 4 is adapted to perform the method according to the invention. Figure 3 In the illustrated embodiment, transmitter unit 2 is the first electrode, and receiver unit 3 is the second electrode. Storage module 5 is adapted to store values, especially reference values, and to store signals, especially measurement signals.
[0040] The method according to the present invention is described below.
[0041] In the first step, the aforementioned conductivity sensor 1 is provided. The conductivity sensor 1 is exposed to the measuring medium, such as a liquid.
[0042] Next, a stimulation signal S1 is emitted into the measurement medium at transmitter unit 2. The stimulation signal S1 is preferably a periodic alternating current signal. The stimulation signal S1 can be, for example, sinusoidal, rectangular, or ramp-shaped. The emission of the stimulation signal S1 occurs via control unit 4. In control unit 4, different stimulation signals S1 are preferably stored for different measurement media with specific properties. For example, for measurements in ultrapure water, a frequency of stimulation signal S1 less than 100 Hz is selected. For measurements in brine, a frequency of stimulation signal S1 greater than 1000 Hz is selected. The frequency selected for the stimulation signal S1 depends on the ion mobility of the measurement medium, and therefore on the conductivity of the measurement medium. At high frequencies of the stimulation signal S1, ion accumulation at the electrodes is reduced due to rapid polarization changes.
[0043] In an optional step compatible with all the other steps mentioned, the stimulation signal S1 is stored by the storage module 5 of the control unit 4.
[0044] The reception of the detection signal D1 then occurs at the receiving unit 3. The detection signal D1 includes the stimulus signal S1, which is affected by the measurement medium, and in some cases, also includes interference signals from the environment of the conductivity sensor 1. Therefore, the detection signal D1 is, for example, distorted compared to the stimulus signal S1, or differs in amplitude, phase, or frequency. If a conductive conductivity sensor is involved, the detection signal D1 is a current and / or voltage signal. If an inductive conductivity sensor is involved, the detection signal D1 is a current signal and a voltage signal.
[0045] In the next step, control unit 4 determines a signal quality indicator SI based on the detection signal D1 and / or the stimulus signal S1. This includes, for example, evaluating the distortion of the detection signal D1 relative to the stimulus signal S1. In other words, this is therefore a classification of the quality of the detection signal D1. For example, the stimulus signal S1 has a quality = 1 (see...). Figure 1 For example, if the detection signal D1 has almost no noise, then the detection signal D1 has high quality, that is, close to 1, for example, 0.9 (see...). Figure 1 (Upper sinusoidal signal). Therefore, the stimulus signal S1 is almost unaffected by the measurement medium, resulting in a low signal quality indicator SI. If the detection signal D1 has strong distortion, then the detection signal D1 has poor quality, for example, 0.5 (see upper sinusoidal signal). Figure 1 (Lower sinusoidal signal). For example, with a signal quality indicator SI of 0.5, there are particularly many interfering frequencies or bubbles in the measurement medium.
[0046] The evaluation of the detection signal D1 occurs through at least one evaluation method from the following group:
[0047] -Total Harmonic Distortion Assessment Methods
[0048] - Cross-correlation assessment method,
[0049] - Fast Fourier Transform evaluation method
[0050] - Signal amplitude evaluation method.
[0051] Total Harmonic Distortion (THD) assessment methods involve determining the so-called distortion factor. The distortion factor provides information about the "cleanliness" of the signal. In other words, the distortion factor is a measure of the distortion of the original sinusoidal AC signal caused by the nonlinear behavior of a component or device. When using a THD assessment method, a sinusoidal signal is preferably used as the stimulus signal S1. Therefore, if the distortion factor is small, the signal quality indicator SI is close to a value of 1. Thus, in this assessment method, only the detection signal D1 is used.
[0052] The cross-correlation assessment method involves evaluating the similarity between the received detection signal D1 and the emitted stimulus signal S1. Therefore, if the detection signal D1 is determined to be highly similar to the stimulus signal, the signal quality indicator SI is close to a value of 1. In this assessment method, both the detection signal D1 and the stimulus signal S1 are therefore used.
[0053] The Fast Fourier Transform (FFT) evaluation method involves analyzing the frequencies present in the detection signal D1. The spectrum is determined, and the presence and level of secondary frequencies are evaluated in addition to the initial frequency of the stimulus signal S1. These secondary frequencies are then filtered out using a suitable digital filtering method, and the remaining measured signal is evaluated. If a small number of secondary frequencies and / or low-amplitude secondary frequencies are thus identified, the signal quality indicator SI approaches a value of 1. Therefore, in this evaluation method, the detection signal D1 and the stimulus signal S1 are used.
[0054] The signal amplitude evaluation method involves assessing the signal amplitude of the detection signal D1. This method is computationally inexpensive. Ideally, the detection signal D1 will have the same signal amplitude for each recording cycle. However, when the stimulus signal S1 is attenuated by an interference source, the measured value of the signal amplitude of the detection signal D1 changes. If the difference between the maximum and minimum recorded signal amplitude is calculated, this value can be interpreted as a measure of the effect of the interference. In the case of a small signal amplitude difference, a signal quality indicator SI close to a value of 1 is thus determined. In this evaluation method, therefore, the detection signal D1 and the stimulus signal S1 are used.
[0055] In another step, a conductivity signal L1 corresponding to the detection signal D1 is determined based on the detection signal D1. The typical characteristic values of the detection signal D1 are thus converted into corresponding values for the conductivity signal L1 using formulas known to those skilled in the art and specific unit constants of the sensor element. These typical characteristic values can be, for example, the amplitude, RMS value, or rectified value of the detection signal.
[0056] The conductivity signal L1 is then stored in the storage module 5 of the control unit 4. Therefore, later processing or evaluation of the conductivity signal L1 is possible.
[0057] In another step, the dynamic factor DF based on the conductivity signal L1 is determined by the control unit 4. The step of determining the dynamic factor DF involves comparing the average value of the conductivity signal L1 stored in the storage module 5 with the most recent conductivity value of the conductivity signal L1, where the dynamic factor DF maps to the current rate of change of the conductivity signal L1. Here, "most recent" means the last value determined in chronological order.
[0058] In the next step, depending on the determined signal quality indicator SI and the determined dynamic factor DF, the conductivity signal L1 is filtered by the filtering function FF.
[0059] The filtering function FF preferably includes moving average filtering. As an alternative to or supplement to moving average filtering, the filtering function FF includes exponential filtering, FIR filtering, or IIR filtering.
[0060] The filtering function FF filters the conductivity signal L1 over a first time span Z1 or a first quantity A1 of measured values MW. The first time span Z1 is, for example, 10 seconds. The first quantity A1 includes, for example, 30 measured values.
[0061] The first time span Z1 or the first quantity A1 varies depending on the signal quality indicator SI and the dynamic factor DF. Therefore, in the case of poor signal quality, strong filtering occurs if the signal quality indicator SI is less than or equal to the threshold SW. Conversely, in the case of good signal quality, normal filtering occurs if the signal quality indicator SI is greater than the threshold SW (see...). Figure 1 ).
[0062] If the signal quality indicator SI is less than or equal to the threshold SW, for example, less than or equal to 0.5, and if the dynamic factor DF is less than the first limit value G1, then the measured values of the first time span Z1 or the first quantity A1 of the filter function FF remain the same. The first limit value G1 is, for example, 16%. This means that the most recently measured conductivity value of the conductivity signal L1 differs by 16% from the average of the previously considered measured conductivity values of the conductivity signal L1.
[0063] However, if the dynamic factor DF lies between the first limit value G1 and the second limit value G2, the measured value MW of the first time span Z1 or the first quantity A1 of the filtering function FF is reduced by a first reduction ratio RA1, for example, 20%, thus reducing for example 2 seconds or 6 measurements (at a sampling frequency of 3 Hz). The second limit value G2 is, for example, 24%. The reduction in the first time span Z1 or the reduction in the measured value considered for the filtering function FF occurs when the oldest measured value is discarded; therefore, the first time span Z1 is, for example, only 8 seconds long and includes, for example, only 24 measurements (at a sampling frequency of 3 Hz).
[0064] If the dynamic factor DF is between the second limit value G2 and the third limit value G3, then the measured value MW of the first time span Z1 or the first quantity A1 of the filtering function FF is reduced by a second reduction ratio RA2, for example, 30%, thus reducing for example 3 seconds or 9 measurements (at a sampling frequency of 3Hz). The third limit value G3 is, for example, 28%.
[0065] If the signal quality indicator SI is greater than the threshold SW, for example, greater than 0.5, and if the dynamic factor DF is less than the fourth limit value, then the measured value MW for the first time span Z1 or the first quantity A1 remains the same. The fourth limit value G4 is, for example, 2%. This means that the most recently measured conductivity value differs from the average of the considered past conductivity values by only 2%.
[0066] If the dynamic factor DF is between the fourth limit value G4 and the fifth limit value G5, the measured value MW of the first time span Z1 or the first quantity A1 of the filtering function FF is reduced by a third reduction ratio RA3, for example, 20%, thus reducing for example 2 seconds or 6 measurements (at a sampling frequency of 3Hz). The fifth limit value G5 is, for example, 3%.
[0067] If the dynamic factor DF is between the fifth limit value G5 and the sixth limit value G6, the measured value MW of the first time span Z1 or the first quantity A1 of the filtering function FF is reduced by the fourth reduction ratio RA4, for example, 30%, thus reducing by, for example, 3 seconds or 9 measurements (at a sampling frequency of 3Hz). The sixth limit value G6 is, for example, 4%.
[0068] You can select any number of limit values and the associated reduction or reduction percentage for the time span or number of measurements. If the dynamic factor is particularly high, you can also reduce the first number of measurements MW of the filtering function A1 by 100%.
[0069] Of course, a different threshold SW or limit value can be selected than the specified value, provided that the limit value increases if the signal quality indicator SI indicates signal interference. Therefore, the following scenario is achieved: under strong interference, the averaging filter is adjusted to be more tolerant, thus ensuring a low-noise output signal even under interfered measurements.
[0070] In another step, the filtered conductivity signal is output as a filtered measurement value MW. The filtered measurement value MW is, for example, the average value of the conductivity signal L1, which is determined by the filtering function FF.
[0071] For example, the output occurs via an indication on a display (not shown) or by transmitting the measured value MW to the user interface via a communication unit (not shown).
[0072] List of reference numerals
[0073] 1. Conductivity sensor
[0074] 2. Launching Unit
[0075] 3 Receiving Unit
[0076] 4 Control Unit
[0077] 5 Storage Modules
[0078] A1 First Quantity
[0079] D1 Detection Signal
[0080] DF dynamic factor
[0081] FF filtering function
[0082] G1 First Limit Value
[0083] G2 Second Limit Value
[0084] G3 Third Limit Value
[0085] G4 Fourth Limit
[0086] G5 Fifth Limit Value
[0087] G6 Sixth Limit Value
[0088] L1 conductivity signal
[0089] MW measurement value
[0090] RA1 First Reduction Ratio
[0091] RA2 Second Reduction Ratio
[0092] RA3 Third Reduction Ratio
[0093] RA4 Fourth Reduction Ratio
[0094] S1 stimulus signal
[0095] SI signal quality indicator
[0096] SW threshold
[0097] Z1 First Time Span
Claims
1. A method for determining the conductivity value of a measuring medium using a conductivity sensor (1), wherein the method comprises the following steps: - A conductivity sensor (1) is provided, comprising at least one transmitting unit (2), at least one receiving unit (3), and a control unit (4) having a storage module (5). -The control unit (4) transmits the stimulation signal (S1) into the measurement medium at the transmitting unit (2). - Receive the detection signal (D1) at the receiving unit (3), -The control unit (4) determines the signal quality indicator (SI) based on the detection signal (D1). - Determine the conductivity signal (L1) corresponding to the detection signal (D1). - Store the conductivity signal (L1), -The dynamic factor (DF) is determined by the control unit (4) based on the conductivity signal (L1). - Depending on the determined signal quality indicator (SI) and the dynamic factor (DF), the conductivity signal (L1) is filtered by the filtering function (FF). - The filtered measurement (MW) of the output conductivity signal.
2. The method according to claim 1, wherein, The step of determining the signal quality indicator (SI) includes: evaluating the distortion of the detection signal (D1) relative to the stimulus signal (S1) using at least one evaluation method from the following group: ○Total Harmonic Distortion Assessment Methods ○ Cross-correlation assessment method, ○ Fast Fourier Transform evaluation method, ○ Signal amplitude evaluation method.
3. The method according to claim 1 or 2, wherein, The step of determining the dynamic factor (DF) includes: comparing the average value of the stored conductivity signal (L1) with the most recent conductivity value of the conductivity signal (L1), wherein the dynamic factor (DF) maps the current rate of change of the conductivity signal (L1).
4. The method according to claim 1 or 2, wherein, The filtering function (FF) filters the conductivity signal (L1) at a measurement (MW) of a first time span (Z1) or a first quantity (A1) of the conductivity signal (L1), wherein the first time span (Z1) or the first quantity (A1) varies depending on the signal quality indicator (SI) and the dynamic factor (DF).
5. The method according to claim 4, wherein, If the signal quality indicator (SI) is less than the threshold (SW), and if the dynamic factor (DF) is less than the first limit value (G1), then the measured values of the first time span (Z1) or the first quantity (A1) of the filtering function (FF) remain the same. Furthermore, if the dynamic factor (DF) is between the first limit value (G1) and the second limit value (G2), the measured value (MW) of the first time span (Z1) or the first quantity (A1) of the filtering function (FF) is reduced by a first reduction ratio (RA1). Furthermore, if the dynamic factor (DF) is between the second limit value (G2) and the third limit value (G3), the measured value (MW) of the first time span (Z1) or the first quantity (A1) of the filtering function (FF) is reduced by a second reduction ratio (RA2).
6. The method according to claim 5, wherein, If the signal quality indicator (SI) is greater than the threshold (SW) and if the dynamic factor (DF) is less than the fourth limit value, then the measured value (MW) of the first time span (Z1) or the first quantity (A1) remains the same. Furthermore, if the dynamic factor (DF) is between the fourth limit value (G4) and the fifth limit value (G5), the measured value (MW) of the first time span (Z1) or the first quantity (A1) of the filtering function (FF) is reduced by a third reduction ratio (RA3). Furthermore, if the dynamic factor (DF) is between the fifth limit value (G5) and the sixth limit value (G6), the measured value (MW) of the first time span (Z1) or the first quantity (A1) of the filtering function (FF) is reduced by a fourth reduction ratio (RA4).
7. The method according to claim 1 or 2, wherein the filtering function (FF) includes moving average filtering.
8. The method according to claim 1 or 2, wherein the stimulation signal (S1) is a periodic alternating current signal or an AC voltage signal.
9. A conductivity sensor (1), comprising: -At least one transmitting unit (2), -At least one receiving unit (3), - A control unit (4) having a storage module (5), The control unit (4) is adapted to perform the method according to any one of claims 1 to 8.