Inductive conductivity sensor circuit, sensor and method of operating the circuit

Abstract

The invention relates to an inductive conductivity sensor circuit, a sensor and a method of operating the circuit. A circuit (1) for an inductive conductivity sensor comprises a secondary coil (10) having a first coil terminal (11) and a second coil terminal (12), a switch (20) having a first switch terminal (21), a second switch terminal (22) and a third switch terminal (23), a first potential terminal (30), a control unit (40) having a first control terminal (41) and a second control terminal (42), wherein the first coil terminal (11) is connected to the first control terminal (41) and the second coil terminal (12) is connected to the first switch terminal (21), wherein the second switch terminal (22) is connected to the first potential terminal (30) and the third switch terminal (23) is connected to the second control terminal (42).

Description

Technical Field

[0001] This invention relates to a circuit for an inductive conductivity sensor, an inductive conductivity sensor, and a method for operating the circuit. Background Technology

[0002] In analytical measurement techniques for environmental analysis, particularly in water management; in industry, such as food technology, biotechnology, and pharmaceuticals; and for the most diverse laboratory applications, the concentration of the analyte, such as pH, conductivity, and even analytes (e.g., ions or dissolved gases in a gaseous or liquid measurement medium), is crucial. These analytes can be acquired and / or monitored, for example, using electrochemical sensors (such as optical sensors, potentiometric sensors, current sensors, voltammetric sensors, or coulometric sensors) and even conductivity sensors.

[0003] Ideally, sensors should operate reliably for as long as possible and detect faults as quickly as possible in the event of a failure.

[0004] Given that inductive conductivity sensors have transmitting and receiving coils, it is necessary to regularly check for inter-turn faults in any of the coils.

[0005] Previously, in the prior art, a conductor loop with a predetermined reference resistance was added between the transmitting and receiving coils to test the function of the receiving coil. However, the presence of the conductor loop can cause signal distortion of up to 5%, especially when inductive conductivity sensors are used to measure highly conductive media. Therefore, to date, even in highly conductive media where the inductive conductivity sensor does not need to be disassembled, there is no known solution in the prior art that can reliably test the function of the receiving coil, in particular. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a circuit for an inductive conductivity sensor that allows overcoming the disadvantages of the described prior art.

[0007] This objective according to the invention is achieved by a circuit for an inductive conductivity sensor.

[0008] The circuit according to the present invention includes:

[0009] - A secondary coil, which has a first coil terminal and a second coil terminal.

[0010] - A switch having a first switch terminal, a second switch terminal, and a third switch terminal.

[0011] -First potential terminal,

[0012] - A control unit having a first control terminal and a second control terminal.

[0013] The first coil terminal is connected to the first control terminal, the second coil terminal is connected to the first switch terminal, the second switch terminal is connected to the first potential terminal, and the third switch terminal is connected to the second control terminal.

[0014] The control unit is adapted to switch the switch between a first position and a second position, wherein in the first position, the first switch terminal is connected to the second switch terminal, and in the second position, the first switch terminal is connected to the third switch terminal.

[0015] The control unit is adapted to issue a test signal at the second control terminal, and the control unit is adapted to receive and evaluate the test signal for a test response at the first control terminal, and to process the test signal...

[0016] The secondary coil is adapted to detect a measurement signal, and the control unit is adapted to receive and evaluate the measurement signal at a first control terminal.

[0017] Using the circuit according to the invention, it is possible to test whether the secondary coil of an inductive conductivity sensor is operating normally, regardless of the primary coil of the same inductive conductivity sensor. Similarly, it enables the testing of whether components in the circuit of the secondary coil are operating normally in test mode. Furthermore, due to this circuit, signal distortion in measurement mode is minimized or prevented to the greatest extent possible. Therefore, the ultimate goal is to overcome the shortcomings of existing inductive conductivity sensors.

[0018] According to one embodiment of the present invention, a first amplifier and a voltage divider are arranged between a second control terminal and a third switch terminal. The voltage divider has a first resistor and a second resistor. The voltage divider has a first voltage divider terminal connected to the first resistor and the second control terminal, a second voltage divider terminal connected to the second resistor and a second potential terminal, and a third voltage divider terminal arranged between the first resistor and the second resistor. The first amplifier has an amplifier input connected to the third voltage divider terminal and an amplifier output connected to the third switch terminal.

[0019] According to a further embodiment of the invention, a second amplifier is disposed between a first coil terminal and a first control terminal. The second amplifier has a first amplifier input, a second amplifier input, and an amplifier output. The first amplifier input is connected to the first coil terminal. The second amplifier input is connected to the amplifier output via a fourth resistor, and the amplifier output is connected to the first control terminal.

[0020] According to one embodiment of the present invention, a third resistor is arranged between the first coil terminal and the first control terminal.

[0021] According to one embodiment of the present invention, the control unit has a filter for analog signal processing.

[0022] The aforementioned objective is also achieved through an inductive conductivity sensor.

[0023] The inductive conductivity sensor according to the present invention comprises:

[0024] - Primary coil,

[0025] - The circuit according to the present invention.

[0026] The primary coil is connected to a control unit, which is adapted to send a stimulation signal to the primary coil in order to detect a measurement signal in the secondary coil.

[0027] The aforementioned objective is also achieved by a method for operating a circuit for an inductive conductivity sensor.

[0028] The method according to the present invention includes the following steps:

[0029] -Provide a circuit according to the invention,

[0030] - Measuring a measurement signal, wherein the measurement includes controlling a switch via a control unit to place the switch in its first position, and the measurement also includes evaluating a measurement signal detected in the secondary coil via the control unit.

[0031] - Testing the circuit, wherein the test includes controlling a switch via a control unit to place the switch in its second position, and the test also includes transmitting a test signal via the control unit at a second control terminal, and the test further includes evaluating a test response generated by the test signal at a first control terminal.

[0032] According to one embodiment of the present invention, the test signal is an AC voltage signal.

[0033] According to one embodiment of the present invention, the testing step includes comparing a test signal with a test response via a control unit.

[0034] According to one embodiment of the present invention, the method further includes outputting a status log of the circuit.

[0035] The above objective is also achieved by a method for testing circuits used in inductive conductivity sensors.

[0036] The method according to the present invention includes the following steps:

[0037] -Provide a circuit according to the invention,

[0038] - Testing the circuit, wherein the test includes controlling the switch to its second position via a control unit, and the test also includes transmitting a test signal via the control unit at a second control terminal, and the test further includes evaluating the test response generated by the test signal at a first control terminal. Attached Figure Description

[0039] The invention will be explained in more detail below with reference to the accompanying drawings. As shown below:

[0040] - Figure 1 Exemplary characterization of the inductive conductivity sensor according to the present invention,

[0041] - Figure 2 Exemplary characterization of a circuit according to the invention for an inductive conductivity sensor. Detailed Implementation

[0042] Figure 1 An inductive conductivity sensor 100 according to the present invention is shown, which has a primary coil 110 and a secondary coil 10. The primary coil 110 is, for example, a coil that emits a stimulation signal ST. The secondary coil 10 is, for example, a coil that detects the stimulation signal ST, which is emitted by the primary coil 110 and converted into a measurement signal MS by the measurement medium. A control unit 40 is connected to the primary coil 110 and the secondary coil 10 (see...). Figure 1 ).

[0043] The inductive conductivity sensor 100 is suitable for exposure to a measurement medium in order to determine the conductivity of the measurement medium.

[0044] Figure 2 A circuit 1 according to the present invention is shown, which is used to control at least the secondary coil of an inductive conductivity sensor 100. The circuit 1 includes a secondary coil 10, a switch 20, a first potential terminal 30, and a control unit 40.

[0045] Switch 20 is preferably a multiplexer. The first potential terminal 30 is, for example, a ground potential or a different predetermined potential. Control unit 40 is, for example, a microcontroller. Switch 20 is suitable for placement in explosive areas.

[0046] The secondary coil 10 has a first coil terminal 11 and a second coil terminal 12. The switch 20 has a first switch terminal 21, a second switch terminal 22, and a third switch terminal 23. The control unit 40 has a first control terminal 41 and a second control terminal 42.

[0047] The first coil terminal 11 is connected to the first control terminal 41. The second coil terminal 12 is connected to the first switch terminal 21, wherein the second switch terminal 22 is connected to the first potential terminal 30, and the third switch terminal is connected to the second control terminal 42.

[0048] Control unit 40 is connected to switch 20 to control its switching position (see Figure 2 (The dashed line in the diagram). Control unit 40 is adapted to switch switch 20 between a first position P1 and a second position P2, in which the first switch terminal 21 is connected to the second switch terminal 22 (see [reference]). Figure 2 In this second position P2, the first switch terminal 21 is connected to the third switch terminal 23 (see...). Figure 2 (The dashed arrows and dashed switch positions are shown in the diagram). Control unit 40 is adapted to transmit a test signal PS at the second control terminal 42, and control unit 40 is adapted to receive and evaluate the test signal PS as a test response PA at the first control terminal 41. The transmission of the test signal PS and the reception of the test response PA will be discussed in detail later.

[0049] The control unit 40 is connected to the primary coil 110 and is adapted to send a stimulation signal ST to the primary coil 110 to generate and ultimately detect a measurement signal MS in the secondary coil 10. Alternatively, the stimulation signal ST may also be generated by a separate further control unit (not shown) of the inductive conductivity sensor 100.

[0050] Secondary coil 10 is adapted to detect the measurement signal MS, while control unit 40 is adapted to receive and evaluate the measurement signal MS. The evaluation of the measurement signal MS will be discussed in detail later.

[0051] According to one embodiment, which is compatible with the further embodiments described herein, a first amplifier 50 and a voltage divider 60 are arranged between a second control terminal 42 and a third switch terminal 23.

[0052] Voltage divider 60 has a first resistor R1 and a second resistor R2, and first voltage divider terminals 61, 62, and 63. First voltage divider terminal 61 is connected to the first resistor R1 and to a second control terminal 42. Second voltage divider terminal 62 is connected to the second resistor R2 and a second potential terminal 31. Third voltage divider terminal 63 is disposed between the first resistor R1 and the second resistor R2. First amplifier 50 has an amplifier input 51 and an amplifier output 52. First amplifier 50 is, for example, an operational amplifier. Second potential terminal 31 is, for example, ground potential or a different predetermined potential. Amplifier input 51 is connected to the third voltage divider terminal 63, and amplifier output 52 is connected to a third switch terminal 23.

[0053] The first resistor R1 and the second resistor R2 are chosen such that the signal reaching the first amplifier 50 via the voltage divider 60 is not too high for the first amplifier 50. In other words, the voltage divider 60 is at least matched to the test signal PS. The first resistor R1 is, for example, several times larger than the second resistor R2. For example, the first resistor R1 is in the megaohm range, while the second resistor R2 is, for example, in the kiloohm range.

[0054] According to one embodiment (not shown), compatible with the further embodiments described herein, a filter capacitor is connected between the second control terminal 42 and the first voltage divider terminal 61 of the voltage divider 60. The filter capacitor is adapted to filter the DC component. This results in the test signal PS being free of a DC component.

[0055] According to one embodiment, compatible with the further embodiments described herein, a second amplifier 70 is disposed between the first coil terminal 11 and the first control terminal 41. The second amplifier 70 is preferably an I / U converter. The second amplifier 70 has a first amplifier input 71, a second amplifier input 72, and an amplifier output 73. The first amplifier input 71 is connected to the first coil terminal 11. The second amplifier input 72 is connected to the amplifier output 73 via a fourth resistor R4, and the amplifier output 73 is connected to the first control terminal 41. The fourth resistor R4 is selected such that it provides appropriate amplification for the circuit. The fourth resistor R4 serves as the feedback resistor for the second amplifier 70, i.e., the I / U converter.

[0056] According to one embodiment (not shown), which is compatible with the further embodiments described herein, the second amplifier 70 has a capacitor located between the first amplifier input 71 and the amplifier output 73. Since this capacitor is arranged in parallel with the second amplifier 70, an EMC protection circuit is implemented.

[0057] According to one embodiment, compatible with the further embodiments described herein, a third resistor R3 is disposed between the first coil terminal 11 and the first control terminal 41. The third resistor R3 is preferably suited for placement in an explosive area. The control unit 40 is protected from excessive current via the third resistor R3. The resistance of the third resistor R3 is, for example, between 100 ohms and 1 kiloohm. The third resistor R3 allows the measurement signal MS from the secondary coil 10 to be limited in terms of current.

[0058] According to one embodiment, compatible with the further embodiments described herein, the control unit 40 has a filter 43 for analog signal processing. The filter 43 is, for example, a passive filter. The advantage of a passive filter is that it does not oscillate independently of the signal to be filtered. The filter 43 is, for example, an RC element. The filter 43 is, for example, a bandpass filter produced by a combination of passive and active components.

[0059] In one possible embodiment, filter 43 is an active filter. The advantage of an active filter is that a high filter arrangement can therefore be achieved and frequency selectivity is thus possible.

[0060] In one possible embodiment, the amplification of filter 43 is adjustable. The advantage of this is that the filter signal can therefore be adapted to the analog-to-digital converter present in control unit 40. Control unit 40 preferably has an analog-to-digital converter (not shown) at the first control terminal 41.

[0061] The method for operating the above-described circuit 1 of the inductive conductivity sensor 100 is discussed below.

[0062] In the first step, the circuit 1 described above is provided. Circuit 1 is preferably arranged in the inductive conductivity sensor 100, or at least partially arranged in the inductive conductivity sensor 100.

[0063] Circuit 1 is preferably used to detect measurement signals, and is therefore located at the secondary coil 10 of the inductive conductivity sensor 100.

[0064] like Figure 1 As indicated by the double arrows and as mentioned above regarding the primary coil 110, the control unit 40 is preferably also adapted to control the primary coil 110. This means that the stimulation signal ST applied to the primary coil 110 is generated, for example, by the control unit 40. The stimulation signal ST is affected by the measurement medium and is applied to the secondary coil 10. The primary coil 110 can be controlled completely independently of the secondary coil 10.

[0065] The method also includes the step of measuring the measurement signal MS using circuit 1. This measurement step includes controlling switch 20 via control unit 40 such that switch 20 is placed in its first position P1. If switch 20 is in its first position P1, circuit 1 is in measurement mode. The measurement step also includes evaluating the measurement signal MS detected in secondary coil 10 via control unit 40.

[0066] The method also includes a step of testing circuit 1. This testing step includes controlling switch 20 via control unit 40 such that switch 20 is placed in its second position P2. If switch 20 is in its second position P2, circuit 1 is in test mode. This testing step also includes transmitting a test signal PS at a second control terminal 42 via control unit 40. By transmitting the test signal PS at the second control terminal 42, the test signal PS passes through several circuit components between the second control terminal 42 and the first control terminal 41 of control unit 40, depending on the embodiment of circuit 1. Specifically, the test signal PS thus passes through voltage divider 60, first amplifier 50, switch 20, secondary coil 10, third resistor R3, second amplifier 70, and filter 43 arranged in control unit 40. Preferably, the test signal PS is output by control unit 40 several times, wherein preferably, the frequency of the test signal PS changes with each test pass. For example, various test criteria or certain components in circuit 1 can be tested via frequency changes.

[0067] In this respect, it should be noted that measurement and testing steps can be interchanged and / or repeated separately as needed.

[0068] The test step also includes evaluating the test response PA generated by the test signal PS via the control unit 40. The test response PA is therefore a modification of the test signal PS by the test signal PS through the circuit components.

[0069] The steps for evaluating the test response PA include comparing the test response PA with the test signal PS, i.e., evaluating the differences between the test signal PS and the test response PA. Specifically, this involves analyzing changes in phase shift and / or amplitude and / or amplification or attenuation between the test signal PS and the test response PA, and / or shape differences between the test signal PS and the test response PA. For example, in the step of evaluating the test response PA, periodic signals such as square wave signals are particularly evaluated, and the edges of the square wave signal are specifically evaluated.

[0070] The step of evaluating the test response PA includes comparing the test signal PS with the test response PA to infer, for example, the impedance of the circuit component through which the test signal PS passes, and then comparing the determined impedance with a reference impedance stored in the control unit 40.

[0071] If the result of the step of evaluating the test response PA is that the test response PA is less than the threshold, for example, equal to zero, then the secondary coil 10 must be defective.

[0072] The test signal PS is preferably an AC voltage signal or an AC current signal. An AC voltage signal has the advantage that only one AC signal reaches the filter 43, especially in the bandpass case. The AC voltage signal is, for example, a sinusoidal signal, a square wave signal, a triangular signal, or an AC voltage signal of different shapes. Preferably, the frequency of the AC voltage signal is set such that it corresponds to the measurement frequency (bandpass frequency). Preferably, the amplitude of the AC voltage signal is set such that the AC voltage signal is optimally matched to the circuit components of circuit 1.

[0073] According to an alternative embodiment, a DC voltage signal or a DC current signal is selected as the test signal PS.

[0074] In a further step, the output of a status log via circuit 1 occurs after the testing step. Preferably, the output of the status log includes indications of which circuit components are defect-free or defective. In particular, the output indicates whether there is an inter-turn fault or open circuit in the secondary coil 10. As mentioned above, if the evaluation of the test response PA thus notices that it drops below a limit value, and therefore equals zero, then there must be an open circuit in the secondary coil 10. In this case, for example, the output notification contains the message: "Note: An interruption exists in the secondary coil!"

[0075] Due to the circuit and the test method described, a defect-free test circuit assembly is achieved. Furthermore, this test method allows for testing the function of the secondary coil 10 without the need for a conductor loop. Therefore, a reference resistor is not required, and the signal quality of the signal measured in measurement mode is not distorted by the conductor loop.

[0076] Thanks to the circuit and the measurement method described, better measurement quality is achieved. In particular, due to the circuit, the sensitive circuitry on the receiving side is independent of the transmitting side.

[0077] Because of the circuit and the test method described, the impedance of the transmission path, specifically the impedance between the first control terminal 41 and the second control terminal 42 of the control unit 40, can be further determined. Therefore, abnormalities in the components of the transmission path are also detectable. If an abnormality is detected in the transmission path, for example, a warning message will be output to the user, and a potentially defective component will be identified based on the abnormality.

[0078] List of reference numerals

[0079] 1. Circuit

[0080] 10 secondary coils

[0081] 11 First coil terminal

[0082] 12 Second coil terminal

[0083] 20 Switches

[0084] 21 First switch terminal

[0085] 22 Second switch terminal

[0086] 23 Third switch terminal

[0087] 30 First Potential Terminal

[0088] 31 Second Potential Terminal

[0089] 40 Control Unit

[0090] 41 First control terminal

[0091] 42 Second control terminal

[0092] 43 Filter

[0093] 50 First Amplifier

[0094] 51 Amplifier Input

[0095] 52 Amplifier Output

[0096] 60 voltage divider

[0097] 61 First voltage divider terminal

[0098] 62 Second voltage divider terminal

[0099] 63 Third voltage divider terminal

[0100] 70 Second Amplifier

[0101] 71 First Amplifier Input

[0102] 72 Second Amplifier Input

[0103] 73 Amplifier Output

[0104] 100 Inductive Conductivity Sensor

[0105] 110 Primary coil

[0106] R1 is the first resistor.

[0107] R2 is the second resistor.

[0108] R3 is the third resistor.

[0109] R4, the fourth resistor

[0110] PS test signal

[0111] P1 First Position

[0112] P2 Second Position

[0113] PA Test Response

[0114] MS measurement signal

[0115] ST stimulation signal

Claims

1. A circuit (1) for an inductive conductivity sensor (100), comprising: - Secondary coil (10), the secondary coil having a first coil terminal (11) and a second coil terminal (12). - A switch (20) having a first switch terminal (21), a second switch terminal (22), and a third switch terminal (23). - First potential terminal (30). - Control unit (40), the control unit having a first control terminal (41) and a second control terminal (42). The first coil terminal (11) is connected to the first control terminal (41), the second coil terminal (12) is connected to the first switch terminal (21), the second switch terminal (22) is connected to the first potential terminal (30), and the third switch terminal (23) is connected to the second control terminal (42). The control unit (40) is adapted to switch the switch (20) between a first position (P1) and a second position (P2), wherein in the first position, the first switch terminal (21) is connected to the second switch terminal (22), and in the second position, the first switch terminal (21) is connected to the third switch terminal (23). The control unit (40) is adapted to issue a test signal (PS) at the second control terminal (42), and the control unit (40) is adapted to receive and evaluate the test signal (PS) as a test response (PA) at the first control terminal (41). The test signal (PS) is transmitted through several circuit components between the second control terminal (42) and the first control terminal (41) of the control unit (40). The secondary coil (10) is adapted to detect a measurement signal (MS) emitted by the primary coil (110) as a stimulus signal (ST) and altered by the measurement medium, and the control unit (40) is adapted to receive and evaluate the measurement signal (MS) at the first control terminal (41).

2. The circuit (1) according to claim 1, wherein, A first amplifier (50) and a voltage divider (60) are arranged between the second control terminal (42) and the third switch terminal (23). The voltage divider (60) has a first resistor (R1) and a second resistor (R2). The voltage divider (60) has a first voltage divider terminal (61) connected to the first resistor (R1) and the second control terminal (42), and a second voltage divider terminal (62) connected to the second resistor (R2) and the second potential terminal (31). The voltage divider (60) also has a third voltage divider terminal (63) arranged between the first resistor (R1) and the second resistor (R2). The first amplifier (50) has an amplifier input (51) connected to the third voltage divider terminal (63) and an amplifier output (52) connected to the third switch terminal (23).

3. The circuit (1) according to claim 1, wherein, A second amplifier (70) is arranged between the first coil terminal (11) and the first control terminal (41); wherein the second amplifier (70) has a first amplifier input (71), a second amplifier input (72) and an amplifier output (73); wherein the first amplifier input (71) is connected to the first coil terminal (11), the second amplifier input (72) is connected to the amplifier output (73) via a fourth resistor (R4), and the amplifier output (73) is connected to the first control terminal (41).

4. The circuit (1) according to any one of claims 1 to 3, wherein, A third resistor (R3) is arranged between the first coil terminal (11) and the first control terminal (41).

5. The circuit (1) according to any one of claims 1 to 3, wherein, The control unit (40) includes a filter (43) for analog signal processing.

6. An inductive conductivity sensor (100), comprising: - Primary coil (110). - The circuit (1) according to any one of claims 1 to 5. The primary coil (110) is connected to the control unit (40), and the control unit (40) is adapted to send a stimulation signal (ST) to the primary coil (110) in order to detect a measurement signal (MS) in the secondary coil (10).

7. A method for operating a circuit (1) for an inductive conductivity sensor (100), the method comprising the steps of: - Provide a circuit (1) according to any one of claims 1 to 5. - Measuring a measurement signal (MS), wherein the measurement includes controlling the switch (20) by the control unit (40) to place the switch (20) in its first position (P1), and the measurement also includes evaluating the measurement signal (MS) detected in the secondary coil (10) by the control unit (40). - Test the circuit (1), wherein the test includes controlling the switch (20) by the control unit (40) to place the switch (20) in its second position (P2), and the test also includes transmitting a test signal (PS) at the second control terminal (42) by the control unit (40), wherein the test signal (PS) passes through several circuit components between the second control terminal (42) of the control unit (40) and the first control terminal (41), and the test also includes evaluating the test response (PA) generated by the test signal (PS) at the first control terminal (41).

8. The method according to claim 7, wherein, The test signal (PS) is an AC voltage signal.

9. The method according to claim 7, wherein, The test steps include comparing the test signal (PS) with the test response (PA) via the control unit (40).

10. The method according to any one of claims 7 to 9, wherein, The method also includes the step of outputting a status log of the circuit (1).

11. A method for testing a circuit (1) for an inductive conductivity sensor (100), the method comprising the steps of: - Provide a circuit (1) according to any one of claims 1 to 5. - Test the circuit (1), wherein the test includes controlling the switch (20) by the control unit (40) to place the switch (20) in its second position (P2), and the test also includes transmitting a test signal (PS) at the second control terminal (42) by the control unit (40), and the test also includes evaluating the test response (PA) generated by the test signal (PS) at the first control terminal (41).

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