Method for selecting an optimal measuring range for a measuring device

Abstract

The invention relates to a method for selecting a measuring range for a measuring device, comprising: - providing a signal processing unit (20) having a signal input (21) and a signal output (22), - Providing a digital voltage signal (UD) at the signal input (21), - performing a first comparison between the digital voltage signal (UD) and a first signal component limit, - Setting a first binary state depending on the first comparison, - performing a second comparison between the digital voltage signal (UD) and a second signal component limit, - Setting a second binary state depending on the second comparison, - Filtering the digital voltage signal (UD), - Performing a third comparison between the filter voltage signal (UF) and a third voltage limit, - Setting a third binary state depending on the third comparison, - performing a fourth comparison between the filter voltage signal (UF) and a fourth voltage limit, - Setting a fourth binary state depending on the fourth comparison, - Evaluating the first binary state, the second binary state, the third binary state and the fourth binary state, - Outputting a result (R1, R2, R3, R4, R0) at the signal output (22), wherein the result (R1, R2, R3, R4, R0) depends on the evaluation of the binary states.

Description

[0001] The invention relates to a method for selecting an optimal measuring range for a measuring device and a measuring device for selecting an optimal measuring range.

[0002] In analytical measurement technology, particularly in water management, environmental analysis, industrial applications such as food technology, biotechnology, and pharmaceuticals, as well as for a wide variety of laboratory applications, measured variables such as pH, conductivity, or the concentration of analytes, such as ions or dissolved gases in a gaseous or liquid medium, are of great importance. These measured variables can be recorded and / or monitored using electrochemical sensors, such as optical, potentiometric, amperometric, voltammetric, or coulometric sensors, or conductivity sensors.

[0003] The analogue measured values ​​determined by these sensors are then converted into a digital measured value in order to be reliably transmitted, for example, to a control centre located far away from the sensor.

[0004] When converting an analog signal into a digital signal, it is particularly important that this is done with maximum accuracy. However, the analog-to-digital converter responsible for the conversion naturally has a limited resolution, e.g., 12 bits. Ideally, the signal to be converted should be converted by the digital converter in such a way that the converter's measuring range is fully utilized without exceeding the measuring range. For this reason, it is necessary to set the sensor's measuring range so that the analog signal is optimally tailored to the resolution of the analog-to-digital converter. This adjustment of the measuring range can, for example, be carried out once at the factory.

[0005] However, it becomes problematic when highly dynamic measured values ​​are to be expected, necessitating adjustments of the measuring range to the measured signal during a measurement with the sensor, or when different sensor types with different measuring behavior are to be operated with identical hardware, i.e. the same analog-to-digital converter. In addition, in the case of parasitic interference, the measured signal is overlaid by an interference signal, which unnecessarily increases the signal amplitude of the signal converted by the analog-to-digital converter. This interference-induced increase in the signal amplitude can indicate an erroneously necessary change of measuring range, which would not be necessary without the interference. This would result in a deterioration in the resolution of the measured signal.

[0006] It is therefore an object of the invention to propose a method which selects an optimal measuring range for the analog-to-digital converter during ongoing measuring operation despite the presence of interference signals.

[0007] This object is achieved according to the invention by a method for selecting an optimal measuring range for a measuring device according to claim 1.

[0008] The method according to the invention comprises: - Providing a signal processing unit with a signal input and a signal output, - Providing a digital voltage signal at the signal input, - performing a first comparison between the digital voltage signal and a first signal component limit, - Setting a first binary state depending on the first comparison, - performing a second comparison between the digital voltage signal and a second signal component limit, - Setting a second binary state depending on the second comparison, - Filtering the digital voltage signal, - Performing a third comparison between the filter voltage signal and a third voltage limit, - Setting a third binary state depending on the third comparison, - performing a fourth comparison between the filter voltage signal and a fourth voltage limit, - Setting a fourth binary state depending on the fourth comparison, - Evaluating the first binary state, the second binary state, the third binary state and the fourth binary state, - Output of a result at the signal output, whereby the result depends on the evaluation of the binary states.

[0009] The method according to the invention enables the simple and reliable selection of an optimal measuring range. It also allows for better detection of faults.

[0010] According to one embodiment of the invention, the first comparison checks whether more than 0.1% of the digital voltage signal is above a first upper voltage limit and below a first lower voltage limit.

[0011] According to one embodiment of the invention, the second comparison checks whether more than 40% of the digital voltage signal is above the first upper voltage limit and below the first lower voltage limit.

[0012] According to one embodiment of the invention, the first upper voltage limit is between 0.5V and 5.0V, preferably between 1.0V and 3.0V, particularly preferably between 1.8V and 1.9V, and the first lower voltage limit is between 0.1V and 0.2V.

[0013] According to one embodiment of the invention, a fast Fourier transform and frequency filtering or a lock-in amplifier is used for filtering.

[0014] The above-mentioned object is also achieved by a measuring device according to claim 6.

[0015] The measuring device according to the invention comprises: - a sensor which is suitable for generating an analogue voltage signal, - a measuring unit connected to the sensor and capable of converting the analogue voltage signal into a digital voltage signal, - a signal processing unit connected to the measuring unit, wherein the signal processing unit is suitable for carrying out the method according to the invention.

[0016] The invention is explained in more detail with reference to the following description of the figures. They show: - Fig. 1: an exemplary representation of a measuring device according to the invention; - Fig. 2: a representation of an exemplary voltage signal; - Fig. 3: a representation of the voltage signal from Fig. 2 in the frequency range; - Fig. 4: an example representation of an evaluation table.

[0017] The measuring device 100 according to the invention comprises a sensor 1, a measuring unit 10 and a signal processing unit 20. According to one embodiment of the invention, the measuring device 100 further comprises a user interface 30.

[0018] Sensor 1 is, for example, a conductivity sensor or another sensor that measures and evaluates an analyte-dependent, here so-called raw voltage signal U. In the case of a conductivity sensor, the raw voltage signal U corresponds to the voltage induced at the receiver coil.

[0019] The measuring unit 10 has an amplifier unit 11 and an analog-to-digital converter 12 and is connected to the sensor 1. The amplifier unit 11 is suitable for amplifying or attenuating the raw voltage signal U so that an optimal measuring range is selected. The amplifier unit 11 is suitable for being controlled via a result R1, R2, R3, R4, R0 in order to select a specific measuring range. This means that the amplification of the analog voltage signal UA is either attenuated or amplified. For example, a first measuring range extends to voltages between 0V and 2V. A second measuring range is, for example, between 0.5V and 1.5V. The raw voltage signal U is an analog signal generated by the sensor 1. The analog-to-digital converter 12 is connected downstream of the amplifier unit 11 and converts the analog raw voltage signal U into a digital voltage signal UD. The analog-to-digital converter 12, for example, has a resolution of 12 bits.

[0020] The signal processing unit 20 has a signal input 21, a signal output 22, and a warning output 23. The signal input 21 is connected to the measuring unit 10. The digital voltage signal UD is read by the signal processing unit 20 via the signal input 21. The maximum voltage UM of the analog-to-digital converter 12 is stored in the signal processing unit 20.

[0021] Likewise, a first upper voltage limit UL, a first lower voltage limit UL', a first signal component limit L1, a second signal component limit L2, a third voltage limit L3 and a fourth voltage limit L4 are stored in the signal processing unit 20.

[0022] The first upper voltage limit UL is, for example, between 0.5V and 5.0V, preferably between 1.0V and 3.0V, particularly preferably between 1.8V and 1.9V.

[0023] The first lower voltage limit UL' is, for example, between 0.1V and 0.2V. Preferably, the first upper voltage limit UL is selected depending on the maximum control range of the analog-to-digital converter 12. In the present example, the maximum voltage UM of the analog-to-digital converter 12 is 2V.

[0024] The first signal component limit L1 is, for example, between 0.1% and 0.5% of the digital voltage signal UD, which is above the first upper voltage limit UL and below the first lower voltage limit UL'.

[0025] The second signal component limit L2 is, for example, between 40% and 60% of the digital voltage signal UD, which is above the first upper voltage limit UL and below the first lower voltage limit UL'.

[0026] The third voltage limit L3 is, for example, between 0.5V and 5.0V, preferably between 1.0V and 3.0V, particularly preferably between 1.8V and 1.9V.

[0027] The fourth voltage limit L4, for example, is between 0.1V and 0.2V.

[0028] The signal processing unit 20 is designed to compare the digital voltage signal UD with the limits UL, UL', L1, L2, L3, L4 stored in the signal processing unit 20. The warning output 23 is connected to the user interface 30.

[0029] The user interface 30 is suitable for outputting a warning message to a user. The user interface 30 is, for example, a display, a loudspeaker, or another means of communication for communicating with a user. For example, the warning message is an indication that a fault is currently present.

[0030] The following describes a method for selecting an optimal measuring range for the measuring device 100 described above.

[0031] First, of course, the signal processing unit 20 described above is provided. Furthermore, the digital voltage signal UD is provided at the signal input 21 of the signal processing unit 20.

[0032] Fig. Figure 2 shows an example digital voltage signal UD. It is clearly visible that a low-frequency sinusoidal signal is superimposed by a high-frequency interference signal. It is also clearly visible that the digital voltage signal UD partially exceeds the first upper voltage limit UL and falls below the first lower voltage limit UL'.

[0033] A first comparison is then performed between the digital voltage signal UD and the first signal component limit L1. This check determines whether more than, for example, 0.1% of the digital voltage signal UD is above the first upper voltage limit UL and below the first lower voltage limit UL'.

[0034] Next, a first binary state is set based on the first comparison. If the digital voltage signal UD does not exceed the first signal component limit L1, the first binary state is set to 0.

[0035] If the digital voltage signal UD exceeds the first signal component limit L1, the first binary state is set to 1.

[0036] Subsequently, a second comparison is performed between the digital voltage signal UD and the second signal component limit L2. This check determines whether, for example, more than 40% of the digital voltage signal UD is above the first upper voltage limit UL and below the first lower voltage limit UL'.

[0037] A second binary state is then set depending on the second comparison. If the digital voltage signal UD is below the second signal component limit L2, the second binary state is set to 0. Otherwise, the second binary state is set to 1.

[0038] Next, the digital voltage signal UD is filtered to produce a filter voltage signal UF. During the filtering step, the digital voltage signal UD is first mapped from the time domain to the frequency domain. During the filtering step, for example, a fast Fourier transformation, preferably a discrete Fourier transformation, is applied. Here, the digital voltage signal UD is transformed from the time domain to the frequency domain, with frequencies that lie in ranges in which no measurement signals are expected being filtered out. The filtering is carried out, for example, using a bandpass filter, low-pass filter, or a lock-in amplifier. For example, if a conductivity sensor is used and the coil is supplied with a transmission signal with a transmission frequency of 50 Hz, a reception signal with a reception frequency of 50 Hz can be expected at the reception coil.

[0039] However, it is also possible to use a different, advantageously frequency-selective filtering method, so that a complex voltage is obtained after filtering. Advantageously, the complex voltage is specified in magnitude and phase, and the magnitude is used as the filter voltage signal UF. The filter voltage signal UF thus has exclusively positive voltage values.

[0040] A third comparison is then carried out between the filter voltage signal UF and a third voltage limit L3 (see Fig. 3).

[0041] A third binary state is then set depending on the third comparison. If the filter voltage signal UF is below the third voltage limit L3, the third binary state is set to 0. If the filter voltage signal UF is above the third voltage limit L3, the third binary state is set to 1.

[0042] Furthermore, a fourth comparison is carried out between the filter voltage signal UF and the fourth voltage limit L4.

[0043] A fourth binary state is then set depending on the fourth comparison. If the filter voltage signal UF is above the fourth voltage limit L4, the fourth binary state is set to 0. If the filter voltage signal UF is below the fourth voltage limit L4, the fourth binary state is set to 1.

[0044] As in Fig. As can be seen in Figure 3, the useful signal is easily separated from the noise signal thanks to the signal's frequency domain analysis. It is important that the useful signal does not come too close to the limits of the analog-to-digital converter 12, e.g., 0V and 2V, to prevent information loss due to overloading of the analog-to-digital converter 12.

[0045] The binary states are stored in a memory of the signal processing unit 20 for later comparison with an evaluation table.

[0046] Fig. Figure 4 shows the evaluation table with all possible combinations of the above-mentioned binary states. The first column represents the result of the first comparison. The fourth column represents the result of the second comparison. The third column represents the result of the third comparison. The second column represents the result of the fourth comparison.

[0047] The four binary states are then evaluated. This means that the stored binary states determined above are used and compared with the evaluation table. In other words, the evaluation table is searched for the row containing the combination of binary states that matches the four binary states determined through the four comparisons mentioned above.

[0048] The fifth column of the evaluation table contains results R0, R1, R2, R3, R4 or status evaluations and / or commands. Depending on the existing combination of binary states, a measuring range change must be initiated. For example, if the binary combination "0100" (from line 5 of the evaluation table in Fig. 4), the measuring range must be reduced because the wanted signal is too weak (first result R1). If the binary combination "1010" is present, the measuring range must be increased because the wanted signal is slightly too strong (second result R2). If the binary combination "1011" is present, the measuring range must be significantly increased because the wanted signal is much too strong (third result R3).

[0049] This evaluation also allows for immediate detection of interference. For example, if the binary combination "1000" or "1001" is present, an interference must be present. In particular, the interference must be such that it does not impair the detection of a sufficient useful signal. The interference can therefore be detected, but the measurement does not need to be restricted within the selected measuring range. Therefore, the measuring range does not need to be adjusted (fourth result R4).

[0050] If the useful signal is within the desired limits, nothing needs to be done (fifth result R0).

[0051] Furthermore, the results R1, R2, R3, R4, R0 are output depending on the evaluation of the binary states at signal output 22. For example, if in the comparisons described above an exceedance of the third voltage limit L3 was identified only in the third comparison, only the third binary state was set to 1 and the other binary states were set to 0. Consequently, when evaluating the binary states in the evaluation table, row five is recognized as appropriate. The corresponding result in the fifth column (first result R1), or instruction in this case, is to reduce the measuring range. Thus, the first result R1 is output by the signal processing unit 20. The measuring unit 10 receives this instruction and adjusts the gain, i.e. the measuring range, in the amplifier unit 11 accordingly.

[0052] If the combination in line 11 is recognized during the evaluation of the binary states, the second result R2 is output to cause an increase in the measuring range.

[0053] If the combination in line 12 is recognized during the evaluation of the binary states, the third result R3 is output to double the measuring range.

[0054] If the combination in line 9 or 10 is detected during the evaluation of the binary states, a fourth result R4, i.e., a fault warning signal, is output to indicate the presence of a fault. The fourth result R4, i.e., the fault warning signal, is output directly to user interface 30, for example, via warning output 23. User interface 30 then outputs a warning message to the user. For example, the display indicates that a signal fault is present.

[0055] For the other binary combinations, the fifth result R0 is output as mentioned above, which signals that no change of measuring range is necessary. List of reference symbols 1 sensor 10 measuring units 11 Amplifier unit 12 analog-to-digital converters 20 Signal processing unit 21 Signal input 22 Signal output 23 Warning output 30 User interface 100 measuring device UA analog voltage signal UD digital voltage signal UF filter voltage signal UM maximum voltage UL first voltage limit UL' first voltage lower limit L1 first signal component limit L2 second signal component limit L3 third voltage limit L4 fourth voltage limit R1 first result R2 second result R3 third result R4 fourth result R0 fifth result

Claims

[1] A method for selecting a measuring range for a measuring device, comprising: - providing a signal processing unit (20) having a signal input (21) and a signal output (22), - Providing a digital voltage signal (UD) at the signal input (21), - performing a first comparison between the digital voltage signal (UD) and a first signal component limit (L1), - Setting a first binary state depending on the first comparison, - performing a second comparison between the digital voltage signal (UD) and a second signal component limit (L2), - Setting a second binary state depending on the second comparison, - Filtering the digital voltage signal (UD), - performing a third comparison between the filter voltage signal (UF) and a third voltage limit (L3), - Setting a third binary state depending on the third comparison, - performing a fourth comparison between the filter voltage signal (UF) and a fourth voltage limit (L4), - Setting a fourth binary state depending on the fourth comparison, - Evaluating the first binary state, the second binary state, the third binary state and the fourth binary state, - Outputting a result (R1, R2, R3, R4, R0) at the signal output (22), wherein the result (R1, R2, R3, R4, R0) depends on the evaluation of the binary states. [2] Method according to claim 1, wherein the first comparison checks whether more than 0.1% of the digital voltage signal (UD) is above a first upper voltage limit (UL) and below a first lower voltage limit (UL'). [3] Method according to claim 2, wherein the second comparison checks whether more than 40% of the digital voltage signal (UD) is above the first upper voltage limit (UL) and below the first lower voltage limit (UL'). [4] Method according to claim 2 or 3, wherein the first upper voltage limit (UL) is between 0.5V and 5.0V, preferably between 1.0V and 3.0V, particularly preferably between 1.8V and 1.9V and the first lower voltage limit (UL') is between 0.1V and 0.2V. [5] Method according to one of the preceding claims, wherein the filtering uses a fast Fourier transform and a frequency filtering, or a lock-in amplifier. [6] Measuring device (100) comprising, - a sensor (1) which is suitable for generating an analog voltage signal (UA), - a measuring unit (10) which is connected to the sensor (1) and is suitable for converting the analogue voltage signal (UA) into a digital voltage signal (UD), - a signal processing unit (20) connected to the measuring unit (10), wherein the signal processing unit (20) is suitable for carrying out the method of the preceding claims.

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