Conductivity transmitter and use method

Abstract

The invention relates to the technical field of conductivity measurement, and discloses a conductivity transmitter and a use method thereof, the conductivity transmitter comprises a signal generation circuit, an electrode connection terminal and a signal processing module; the signal generation circuit is used for outputting an excitation signal; the electrode connecting terminal comprises a first connecting end, a second connecting end, a third connecting end and a fourth connecting end, a first short-circuit piece is arranged between the first connecting end and the second connecting end, a second short-circuit piece is arranged between the third connecting end and the fourth connecting end, and the first connecting end is connected with one end of the reference resistor unit; the signal processing module is used for receiving voltage output by the second connecting end and the third connecting end and / or voltage output by the first end and the second end of the reference resistor unit so as to output conductivity detection signals, and the conductivity detection circuit can be suitable for a double-wire conductivity electrode and a four-wire conductivity electrode and is convenient to use.

Description

Technical Field

[0001] The present invention relates to the technical field of conductivity measurement, and in particular to a conductivity transmitter and a use method thereof. Background Art

[0002] At present, commonly used conductivity electrodes include two types: two-electrode and four-electrode. The two types of electrodes are suitable for different scenarios. The conductivity transmitter is a device used to connect the conductivity electrode and convert the analog signal output by the conductivity electrode into a standard signal. Common conductivity electrodes and conductivity transmitters are used in pairs, that is, two-electrode or four-electrode conductivity electrodes correspond to different conductivity transmitters, and the conductivity transmitter cannot be adapted to two-electrode and four-electrode conductivity electrodes at the same time. This leads to the need to replace the conductivity electrode and the conductivity transmitter together in some scenarios where the conductivity electrode needs to be replaced, which brings great inconvenience. Summary of the invention

[0003] In view of this, the present invention provides a conductivity transmitter and a method of use to solve or partially solve the technical problem that the existing conductivity transmitter cannot be adapted to two-electrode and four-electrode conductivity electrodes at the same time and is inconvenient to use.

[0004] The technical solution proposed by the present invention is as follows:

[0005] A first aspect of the present invention provides a conductivity transmitter, comprising a signal generating circuit, an electrode connecting terminal and a signal processing module; the signal generating circuit is used to output an excitation signal; the electrode connecting terminal comprises a first connecting end, a second connecting end, a third connecting end and a fourth connecting end, a first short-circuit is provided between the first connecting end and the second connecting end, a second short-circuit is provided between the third connecting end and the fourth connecting end, the first short-circuit is used to switch the on-off state between the first connecting end and the second connecting end, the second short-circuit is used to switch the on-off state between the third connecting end and the fourth connecting end, the first connecting end is connected to a first end of a reference resistor unit, the second end of the reference resistor unit is connected to an output end of the signal generating circuit, the second connecting end and the third connecting end are respectively connected to corresponding signal output lines of the conductivity electrode, the second connecting end and the third connecting end are also respectively connected to two input ends of the signal processing module, the fourth connecting end is grounded, and the two ends of the reference resistor unit are respectively connected to the other two input ends of the signal processing module; the signal processing module is used to receive the voltage output by the second connecting end and the third connecting end and / or the voltage output by the first end and the second end of the reference resistor unit to output a conductivity detection signal.

[0006] Optionally, the signal generating circuit includes a first controllable switch chip and a first voltage follower, the control end of the first controllable switch chip is connected to a second control signal source for outputting a second control signal, the two input ends of the first controllable switch chip are respectively connected to a positive voltage signal source and a negative voltage signal source, the output end of the first controllable switch chip is periodically switched between the two input ends of the first controllable switch chip according to the second control signal, and the output end of the first controllable switch chip is connected to the input end of the first voltage follower.

[0007] Optionally, the conductivity transmitter further includes a range adjustment circuit, the range adjustment circuit includes a second controllable switch chip, the second controllable switch chip includes a first input terminal, a first control terminal, a second control terminal, a first output terminal, a second output terminal, a third output terminal and a fourth output terminal, the reference resistance unit includes a zeroth resistor, a first resistor, a second resistor and a third resistor connected in series in sequence, the first input terminal is connected to the output terminal of the signal generating circuit, the first control terminal and the second control terminal are respectively connected to a third control signal source for outputting a third control signal and a fourth control signal source for outputting a fourth control signal, the first output terminal is respectively connected to one end of the zeroth resistor and the signal processing circuit The module is connected to one of the other two input terminals of the module, the second output terminal is respectively connected to the other end of the zeroth resistor and one end of the first resistor, the third output terminal is respectively connected to the other end of the first resistor and one end of the second resistor, the fourth output terminal is respectively connected to the other end of the second resistor and one end of the third resistor, the other end of the third resistor is connected to the first connection terminal, and the other end of the third resistor is also connected to the other input terminal of the other two input terminals of the signal processing module. The second controllable switch chip controls the first input terminal to connect to any one of the first output terminal, the second output terminal, the third output terminal and the fourth output terminal according to the third control signal and the fourth control signal.

[0008] Optionally, the signal processing module includes an input switching circuit and an instrumentation amplifier, the input switching circuit includes a third controllable switch chip, the third controllable switch chip includes a second input terminal, a third input terminal, a fourth input terminal, a fifth input terminal, a third control terminal, a fourth control terminal, a fifth output terminal and a sixth output terminal, the second input terminal, the third input terminal, the fourth input terminal and the fifth input terminal are respectively connected to the second connection terminal, the first terminal of the reference resistance unit, the third connection terminal and the second terminal of the reference resistance unit, the third control terminal and the fourth control terminal are both connected to a first control signal source for outputting a first control signal, the fifth output terminal and the sixth output terminal are respectively connected to two input terminals of the instrumentation amplifier, and the third controllable switch chip connects the second input terminal and the fourth input terminal to the fifth output terminal and the sixth output terminal respectively according to the first control signal, or connects the third input terminal and the fifth input terminal to the fifth output terminal and the sixth output terminal respectively.

[0009] Optionally, the instrumentation amplifier includes a second voltage follower, a third voltage follower and a differential amplifier, the input end of the second voltage follower and the input end of the third voltage follower are respectively connected to the fifth output end and the sixth output end of the input switching circuit, and the output end of the second voltage follower and the output end of the third voltage follower are respectively connected to the two input ends of the differential amplifier.

[0010] Optionally, the signal processing module also includes a rectifier circuit, which includes a fifth op amp, a sixth op amp, a first diode, a second diode, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, and a first capacitor. The reverse input terminal of the fifth op amp is connected to one end of the eighth resistor, the non-inverting input terminal of the fifth op amp is grounded, the anode of the first diode is connected to the output terminal of the fifth op amp, the cathode of the first diode is connected to the reverse input terminal of the fifth op amp, the cathode of the second diode is connected to the output terminal of the fifth op amp, the two ends of the tenth resistor are respectively connected to the anode of the second diode and the cathode of the first diode, the anode of the second diode is also connected to one end of the eleventh resistor, the two ends of the ninth resistor are respectively connected to the other end of the eleventh resistor and the other end of the eighth resistor, the other end of the eleventh resistor is respectively connected to the reverse input terminal of the sixth op amp, one end of the twelfth resistor and one end of the first capacitor, the output terminal of the sixth op amp is respectively connected to the other end of the twelfth resistor and the other end of the first capacitor, one end of the thirteenth resistor is connected to the non-inverting input terminal of the sixth op amp, and the other end of the thirteenth resistor is grounded.

[0011] Optionally, the signal processing module also includes a filtering circuit and a third diode, one end of the filtering circuit is connected to the output end of the rectifier circuit, the other end of the filtering circuit is connected to the anode of the third diode, and the cathode of the third diode is connected to a preset protection voltage source.

[0012] A second aspect of the present invention provides a method for using a conductivity transmitter, which is applied to the conductivity transmitter of the first aspect of the present invention and any one of the first aspects, including: determining the wiring system of the electrode to be connected; if the wiring system of the electrode to be connected is a four-wire system, disconnecting the path between the first connection end and the second connection end through a first short-circuit, disconnecting the path between the third connection end and the fourth connection end through a second short-circuit, and connecting the first connection end, the second connection end, the third connection end and the fourth connection end to the four electrode lead wires of the electrode to be connected respectively; if the wiring system of the electrode to be connected is a two-wire system, closing the path between the first connection end and the second connection end through the first short-circuit, closing the path between the third connection end and the fourth connection end through the second short-circuit, and connecting the second connection end and the third connection end to the two electrode lead wires of the electrode to be connected respectively.

[0013] It can be seen from the above technical solutions that the present invention has the following advantages:

[0014] The present invention provides a conductivity transmitter and a method of using the same. A first short-circuit is provided between a first connection end and a second connection end, and a second short-circuit is provided between a third connection end and a fourth connection end. If the wiring system of the electrodes to be connected is a four-wire system, the first short-circuit is used to disconnect the passage between the first connection end and the second connection end, and the second short-circuit is used to disconnect the passage between the third connection end and the fourth connection end. If the wiring system of the electrodes to be connected is a two-wire system, the first short-circuit is used to close the passage between the first connection end and the second connection end, and the second short-circuit is used to close the passage between the third connection end and the fourth connection end. When the electrodes to be connected are two-wire electrodes or four-wire electrodes, an excitation signal can be output for the conductivity electrode through a signal generating circuit. After the conductivity electrode is placed in the liquid to be tested, the signal processing module can receive the voltage output by the second connection end and the third connection end and / or the voltage output by the first end and the second end of the reference resistance unit, and then output a conductivity detection signal. The output conductivity detection signal includes the voltage difference between the second connection end and the third connection end, and the voltage difference between the two ends of the reference resistance unit. Since the access resistance of the reference resistance unit is known, the equivalent resistance of the liquid to be tested can be calculated by using the voltage division relationship between the equivalent resistance of the liquid to be tested and the access resistance of the reference resistance unit, and then the conductivity of the liquid to be tested can be obtained. Therefore, the conductivity electrode transmitter of the present invention is applicable to both two-wire conductivity electrodes and four-wire conductivity electrodes, and is easy to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly express the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 is a principle block diagram of a conductivity transmitter in an embodiment of the present invention;

[0017] Figure 2 1 is a circuit diagram of a conductivity transmitter according to an embodiment of the present invention;

[0018] Figure 3 is a circuit schematic diagram of a signal processing module in an embodiment of the present invention;

[0019] Figure 4 is an equivalent circuit diagram of a conductivity electrode when the conductivity electrode is a four-wire electrode type in an embodiment of the present invention;

[0020] Figure 5 is an equivalent circuit diagram of a conductivity electrode when the conductivity electrode is a two-wire electrode type in an embodiment of the present invention;

[0021] Figure 6 The figure is a flow chart of a method for using the conductivity transmitter in an embodiment of the present invention.

[0022] Reference numerals:

[0023] 1-signal generating circuit; 2-range adjusting circuit; 3-signal processing module; 31-input switching circuit; 32-instrument amplifier; 33-rectifier circuit; 34-filter circuit; SW1-first controllable switch chip; IC1-second controllable switch chip; IC2-third controllable switch chip; AMP1-first op amp; AMP2-second op amp; AMP3-third op amp; AMP4-fourth op amp; AMP5-fifth op amp; AMP6-sixth op amp; R0-zeroth resistor; R1-first resistor; R2-second resistor; R3-third resistor; R4-fourth resistor; R5-fifth resistor; R6-sixth resistor; R7-seventh resistor; R8-eighth resistor; R9-ninth resistor; R 10-10th resistor; R11-11th resistor; R12-12th resistor; R13-13th resistor; R14-14th resistor; R15-15th resistor; D1-1st diode; D2-2nd diode; D3-3rd diode; C01-1st capacitor; C02-2nd capacitor; C03-3rd capacitor; L3-3rd inductor; L4-4th inductor; C1-1st connection terminal; C2-2nd connection terminal; C3-3rd connection terminal; C4-4th connection terminal; Z-1st input terminal; 3Y0-2nd input terminal; 3Y1-3rd input terminal; 2Y0-4th input terminal; 2Y1-5th input terminal; S0-1st control terminal; S1-2nd control terminal; S2-3rd control terminal; S3-4th control terminal;

[0024] Y0-first output terminal; Y1-second output terminal; Y2-third output terminal; Y3-fourth output terminal; 2Z-fifth output terminal; 3Z-sixth output terminal; Rx-equivalent resistance; MCU_D-first control signal source; MCU_A-second control signal source; MCU_B-third control signal source; MCU_C-fourth control signal source. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] The embodiment of the present invention provides a conductivity transmitter, which can be applicable to two different conductivity electrodes, namely, a two-wire system and a four-wire system, and provides convenience for flexible replacement of conductivity electrodes.

[0030] like Figure 1 , Figure 2 and Figure 3 As shown, an embodiment of the present invention provides a conductivity transmitter, including a signal generating circuit 1, an electrode connecting terminal and a signal processing module 3;

[0031] The signal generating circuit 1 is used for outputting an excitation signal;

[0032] The electrode connection terminal includes a first connection terminal C1, a second connection terminal C2, a third connection terminal C3 and a fourth connection terminal C4, which correspond one-to-one to four electrode lead wires of the four-wire electrode. A first short-circuit is provided between the first connection terminal C1 and the second connection terminal C2, and a second short-circuit is provided between the third connection terminal C3 and the fourth connection terminal C4. The first short-circuit is used to switch the on-off state between the first connection terminal C1 and the second connection terminal C2, and the second short-circuit is used to switch the on-off state between the third connection terminal C3 and the fourth connection terminal C4. The first connection terminal C1 is connected to a first end of a reference resistance unit, a second end of the reference resistance unit is connected to an output end of the signal generating circuit 1, the second connection terminal C2 and the third connection terminal C3 are respectively connected to corresponding signal output lines of the conductivity electrode, the second connection terminal C2 and the third connection terminal C3 are also respectively connected to two input ends of the signal processing module 3, the fourth connection terminal C4 is grounded, and both ends of the reference resistance unit are respectively connected to the other two input ends of the signal processing module 3;

[0033] The signal processing module 3 is used to receive the voltage outputted by the second connection terminal and the third connection terminal and / or the voltage outputted by the first terminal and the second terminal of the reference resistance unit to output a conductivity detection signal.

[0034] It should be understood that the excitation signal is a signal used to excite or drive the conductivity electrode to work. In one example, the excitation signal is a square wave signal with a peak-to-peak value of ±2.5 V. The signal generating circuit 1 can generate the excitation signal by a square wave generator or an analog controllable switch chip.

[0035] The first short-circuit and the second short-circuit can be devices such as switches or jumpers for controlling the on-off of the circuit. The on-off of the first connection terminal C1 and the second connection terminal C2 is controlled by the first short-circuit, and the on-off of the third connection terminal C3 and the fourth connection terminal C4 is controlled by the second short-circuit, which is convenient to operate.

[0036] The output end of the signal generating circuit 1 is connected to the first connection end C1 after passing through the reference resistor unit to excite the conductivity electrode, and the second connection end C2 and the third connection end C3 are used to connect to the signal output line of the conductivity electrode and are connected to the input end of the signal processing module 3, so as to output the output signal of the conductivity electrode to the signal processing module 3. The fourth connection end C4 is grounded, specifically, the fourth connection end C4 is grounded through the third inductor L3 to reduce current fluctuations.

[0037] At the same time, the output end of the signal generating circuit 1 is connected to the reference resistance unit. The signal processing module 3 has four input ends, two of which are connected to the second connection end C2 and the third connection end C3, respectively, and the remaining two input ends are connected to the two ends of the reference resistance unit. In one example, in order to reduce current fluctuations, a fourth inductor L4 can be connected in series between the first connection end C1 and the input end of the reference resistance unit.

[0038] The conductivity detection signal includes the voltage difference between the second connection terminal and the third connection terminal, and the voltage difference between the two ends of the reference resistance unit. The control end of the signal processing module 3 is connected to the first control signal source MCU_D to receive the first control signal, and the input voltage signal is differentially operated based on the first control signal to obtain the voltage difference between the second connection terminal and the third connection terminal, and the voltage difference between the two ends of the reference resistance unit. The signal processing module 3 can selectively perform differential operations on the voltage signals of two of the four inputs to obtain the voltage divided by the connected reference resistance unit and the voltage across the equivalent resistance Rx (hereinafter referred to as the resistance to be measured) of the liquid to be measured, and complete the measurement of the resistance value of the resistance to be measured according to the proportional relationship between the resistance value of the connected reference resistance unit and the equivalent resistance Rx and the relationship between the voltage division, thereby obtaining the conductivity of the liquid to be measured.

[0039] Among them, the measurement of the resistance value of the resistor to be measured is completed according to the proportional relationship between the resistance value of the connected reference resistor unit and the equivalent resistance Rx and the voltage division relationship, and then the calculation step of the conductivity of the measured liquid can be achieved through the control unit. The control unit also has a first control signal source MCU_D, a second control signal source MCU_A, a third control signal source MCU_B and a fourth control signal source MCU_C, which are used to output corresponding control signals.

[0040] In a conductivity transmitter according to an embodiment of the present invention, a first short-circuit is provided between a first connection terminal C1 and a second connection terminal C2, and a second short-circuit is provided between a third connection terminal C3 and a fourth connection terminal C4. If the wiring system of the electrode to be connected is a four-wire system, the passage between the first connection terminal C1 and the second connection terminal C2 is disconnected by the first short-circuit, and the passage between the third connection terminal C3 and the fourth connection terminal C4 is disconnected by the second short-circuit. If the wiring system of the electrode to be connected is a two-wire system, the passage between the first connection terminal C1 and the second connection terminal C2 is closed by the first short-circuit, and the passage between the third connection terminal C3 and the fourth connection terminal C4 is closed by the second short-circuit. When the electrode to be connected is a two-wire electrode or a four-wire electrode, the signal generating circuit 1 can be used to generate a conductivity transmitter. The conductivity electrode outputs an excitation signal. After the conductivity electrode is placed in the liquid to be tested, the signal processing module can receive the voltage output by the second connection terminal and the third connection terminal and / or the voltage output by the first end and the second end of the reference resistance unit, and then output a conductivity detection signal. The output conductivity detection signal includes the voltage difference between the second connection terminal C2 and the third connection terminal C3, and the voltage difference between the two ends of the reference resistance unit. Since the access resistance of the reference resistance unit is known, the equivalent resistance Rx of the liquid to be tested can be calculated by using the voltage division relationship between the equivalent resistance Rx of the liquid to be tested and the access resistance of the reference resistance unit, and then the conductivity of the liquid to be tested can be obtained. Therefore, the conductivity electrode transmitter of the present invention can be applicable to both two-wire conductivity electrodes and four-wire conductivity electrodes, and is easy to use.

[0041] In some embodiments, the signal generating circuit 1 includes a first controllable switch chip SW1 and a first voltage follower, the control end of the first controllable switch chip SW1 is connected to a second control signal source MCU_A for outputting a second control signal, the two input ends of the first controllable switch chip SW1 are respectively connected to a positive voltage signal source and a negative voltage signal source, the output end of the first controllable switch chip SW1 is periodically switched between the two input ends of the first controllable switch chip SW1 according to the second control signal, and the output end of the first controllable switch chip SW1 is connected to the input end of the first voltage follower.

[0042] Specifically, the first controllable switch chip SW1 has two input terminals and one output terminal, and the absolute values ​​of the voltages provided by the positive voltage signal source and the negative voltage signal source are equal. For example, the voltages provided by the positive voltage signal source and the negative voltage signal source are +2.5V voltage signal and -2.5V voltage signal respectively.

[0043] The second control signal is a square wave signal, which regards a high level as "1" and a low level as "0". When the second control signal = 1, the input end and the output end of the +2.5V voltage signal are connected. When the second control signal = 0, the input end and the output end of the -2.5V voltage signal are connected.

[0044] The first voltage follower is mainly composed of a first operational amplifier AMP1, the in-phase input terminal of the first operational amplifier AMP1 is connected to the output terminal of the first controllable switch chip SW1, and the reverse input terminal of the first operational amplifier AMP1 is connected to the output terminal of the first operational amplifier AMP1 to realize the voltage following function.

[0045] Therefore, the signal generating circuit 1 can output a square wave voltage with positive and negative amplitudes of ±2.5V respectively, that is, an output excitation signal.

[0046] The excitation signal is generated and outputted through the first controllable switch chip SW1 and the first voltage follower, which facilitates the control of the output of the excitation signal and improves the stability of the excitation signal.

[0047] In some embodiments, the conductivity transmitter also includes a range adjustment circuit 2, the input end of the range adjustment circuit 2 is connected to the output end of the signal generating circuit 1, the output end of the range adjustment circuit 2 is connected to the reference resistance unit, and the range adjustment circuit 2 is used to adjust the resistance value between the reference resistance unit connected to the excitation signal and one of the other two input ends of the signal processing module 3.

[0048] Specifically, the range adjustment circuit 2 includes a second controllable switch chip IC1, the second controllable switch chip IC1 includes a first input terminal Z, a first control terminal S0, a second control terminal S1, a first output terminal Y0, a second output terminal Y1, a third output terminal Y2 and a fourth output terminal Y3, the reference resistance unit includes a zeroth resistor R0, a first resistor R1, a second resistor R2 and a third resistor R3 connected in series in sequence, the first input terminal Z is connected to the output end of the signal generating circuit 1, the first control terminal S0 and the second control terminal S1 are respectively connected to a third control signal source MCU_B for outputting a third control signal and a fourth control signal source MCU_C for outputting a fourth control signal, the first output terminal Y0 is respectively connected to one end of the zeroth resistor R0 and the signal processing module 3 The second controllable switch chip IC1 controls the first input terminal Z to connect to any one of the other two input terminals of the signal processing module 3, the second output terminal Y1 is respectively connected to the other end of the zeroth resistor R0 and one end of the first resistor R1, the third output terminal Y2 is respectively connected to the other end of the first resistor R1 and one end of the second resistor R2, the fourth output terminal Y3 is respectively connected to the other end of the second resistor R2 and one end of the third resistor R3, the other end of the third resistor R3 is connected to the first connection terminal C1, and the other end of the third resistor R3 is also connected to the other input terminal of the other two input terminals of the signal processing module 3, and the second controllable switch chip IC1 controls the first input terminal Z to connect to any one of the first output terminal Y0, the second output terminal Y1, the third output terminal Y2 and the fourth output terminal Y3 according to the third control signal and the fourth control signal.

[0049] The switching logic of the second controllable switch chip IC1 is as follows:

[0050] When the third control signal = 0 and the fourth control signal = 0, the first input terminal Z and the first output terminal Y0 are connected;

[0051] When the third control signal = 1 and the fourth control signal = 0, the first input terminal Z and the second output terminal Y1 are connected;

[0052] When the third control signal = 0 and the fourth control signal = 1, the first input terminal Z and the third output terminal Y2 are connected;

[0053] When the third control signal=1 and the fourth control signal=1, the first input terminal Z and the fourth output terminal Y3 are connected.

[0054] Therefore, by controlling the third control signal and the fourth control signal to output different levels, the first input terminal Z and one of the first output terminal Y0 to the fourth output terminal Y3 can be controlled to be conductive.

[0055] Further, the resistances of the zeroth resistor R0 , the first resistor R1 , the second resistor R2 , and the third resistor R3 decrease in sequence. In one example, R0 : R1 : R2 : R3 = 1000 : 100 : 10 : 1.

[0056] By controlling the first input terminal Z and one of the first output terminal Y0 to the fourth output terminal Y3 to be turned on, the proportional relationship between the total resistance value of the voltage divider connected in the reference resistance unit and the equivalent resistance Rx of the liquid to be measured is changed, thereby achieving the measurement range adjustment of the conductivity electrode.

[0057] In some embodiments, the signal processing module 3 includes an input switching circuit 31 and an instrumentation amplifier 32, the input switching circuit 31 includes a third controllable switch chip IC2, the third controllable switch chip IC2 includes a second input terminal 3Y0, a third input terminal 3Y1, a fourth input terminal 2Y0, a fifth input terminal 2Y1, a third control terminal S2, a fourth control terminal S3, a fifth output terminal 2Z and a sixth output terminal 3Z, the second input terminal 3Y0, the third input terminal 3Y1, the fourth input terminal 2Y0 and the fifth input terminal 2Y1 are respectively connected to the second connection terminal C2, the first terminal of the reference resistor unit, the first terminal of the reference resistor unit, and the second terminal of the reference resistor unit. The third connection terminal C3 is connected to the second end of the reference resistance unit, the third control terminal S2 and the fourth control terminal S3 are both connected to the first control signal source MCU_D for outputting the first control signal, the fifth output terminal 2Z and the sixth output terminal 3Z are respectively connected to the two input terminals of the instrument amplifier 32, and the third controllable switch chip IC2 connects the second input terminal 3Y0 and the fourth input terminal 2Y0 to the fifth output terminal 2Z and the sixth output terminal 3Z respectively according to the first control signal, or connects the third input terminal 3Y1 and the fifth input terminal 2Y1 to the fifth output terminal 2Z and the sixth output terminal 3Z respectively.

[0058] Among them, the switching logic of the third controllable chip is as follows:

[0059] When the first control signal = 1, the fifth input terminal 2Y1 is connected to the fifth output terminal 2Z, and the third input terminal 3Y1 is connected to the sixth output terminal 3Z;

[0060] When the first control signal=0, the fourth input terminal 2Y0 and the fifth output terminal 2Z are connected, and the second input terminal 3Y0 and the sixth output terminal 3Z are connected.

[0061] Through the first control signal, the voltage between the two output terminals of the first controllable chip can be the voltage divided by the total resistance value of the voltage divider connected in the reference resistance unit or the voltage of the equivalent resistance Rx of the liquid to be measured.

[0062] Furthermore, the instrumentation amplifier 32 includes a second voltage follower, a third voltage follower and a differential amplifier, the input end of the second voltage follower and the input end of the third voltage follower are respectively connected to the fifth output end 2Z and the sixth output end 3Z of the input switching circuit 31, and the output end of the second voltage follower and the output end of the third voltage follower are respectively connected to the two input ends of the differential amplifier.

[0063] Specifically, in the instrumentation amplifier 32, the second voltage follower is mainly composed of the second op amp AMP2, and the third voltage follower is mainly composed of the third op amp AMP3. The in-phase input terminal of the second op amp AMP2 is connected to the sixth output terminal 3Z, and the inverting input terminal of the second op amp AMP2 is connected to the output terminal of the second op amp AMP2. The in-phase input terminal of the third op amp AMP3 is connected to the fifth output terminal 2Z, and the inverting input terminal of the third op amp AMP3 is connected to the output terminal of the third op amp AMP3.

[0064] The differential amplifier is mainly composed of a fourth op amp AMP4, an inverting input terminal of the fourth op amp AMP4 is connected to the output terminal of the second op amp AMP2 through a fourth resistor R4, a non-inverting input terminal of the fourth op amp AMP4 is connected to the output terminal of the third op amp AMP3 through a fifth resistor R5, a sixth resistor R6 is connected in series between the non-inverting input terminal of the fourth op amp AMP4 and the ground, and a seventh resistor R7 is connected between the inverting input terminal of the fourth op amp AMP4 and the output terminal of the fourth op amp AMP4.

[0065] By collecting the voltage signal at the output end of the differential amplifier, the voltage obtained by dividing the total resistance value of the reference resistance unit or the voltage of the equivalent resistance Rx of the liquid to be measured can be obtained, and the resistance value of the equivalent resistance Rx is obtained by analysis by the control unit to obtain the conductivity. The first control signal, the second control signal, the third control signal and the fourth control signal can all be output through the corresponding signal output pins in the control unit.

[0066] Differential amplification is achieved by cooperating with the second voltage follower, the third voltage follower and the differential amplifier, which can ensure signal stability when performing differential amplification of voltage signals and make signal acquisition more accurate.

[0067] In some embodiments, the signal processing module 3 further includes a rectifier circuit 33 , and the rectifier circuit 33 is used to rectify the output voltage of the instrumentation amplifier 32 .

[0068] Specifically, the rectifier circuit 33 includes a fifth op amp AMP5, a sixth op amp AMP6, a first diode D1, a second diode D2, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, and a first capacitor C01. The inverting input terminal of the fifth op amp AMP5 is connected to one end of the eighth resistor R8, the in-phase input terminal of the fifth op amp AMP5 is grounded, the anode of the first diode D1 is connected to the output terminal of the fifth op amp AMP5, the cathode of the first diode D1 is connected to the inverting input terminal of the fifth op amp AMP5, the cathode of the second diode D2 is connected to the output terminal of the fifth op amp AMP5, and the tenth resistor R1 Two ends of a ninth resistor R9 are connected to the other end of the eleventh resistor R11 and the other end of the eighth resistor R8, respectively. The other end of the eleventh resistor R11 is connected to the inverting input end of the sixth operational amplifier AMP6, one end of the twelfth resistor R12 and one end of the first capacitor C01, respectively. The output end of the sixth operational amplifier AMP6 is connected to the other end of the twelfth resistor R12 and the other end of the first capacitor C01, respectively. One end of the thirteenth resistor R13 is connected to the non-inverting input end of the sixth operational amplifier AMP6, and the other end of the thirteenth resistor R13 is grounded.

[0069] The rectifier circuit 33 uses the fifth operational amplifier AMP5, the first diode D1 and the second diode D2 to achieve rectification. The circuit structure is simple and convenient for collecting signals. The collected signals can be directly input into the processor for processing.

[0070] In some embodiments, the signal processing module 3 also includes a filtering circuit 34 and a third diode D3, one end of the filtering circuit is connected to the output end of the rectifier circuit, the other end of the filtering circuit is connected to the positive electrode of the third diode, and the negative electrode of the third diode is connected to a preset protection voltage source.

[0071] Specifically, the filtering circuit 34 includes a fourteenth resistor R14, a fifteenth resistor R15, a second capacitor C02 and a third capacitor C03. The output end of the sixth operational amplifier AMP6 is connected in series with the fourteenth resistor R14, the fifteenth resistor R15 and the third diode D3 in sequence and then connected to a preset protection voltage source. One end of the second capacitor C02 is connected to the output end of the sixth operational amplifier AMP6, the other end of the second capacitor C02 is connected to one end of the third capacitor C03 and is grounded, and the other end of the third capacitor C03 is connected to the series connection point between the fourteenth resistor R14 and the fifteenth resistor R15.

[0072] Specifically, the preset protection voltage source is used to output a +2.5V voltage. The conductivity detection signal is collected between the fifteenth resistor R15 and the third diode D3 and output to the A / D converter, and is output to the control unit through the A / D converter for conductivity calculation. When the voltage between the fifteenth resistor R15 and the third diode D3 does not exceed the +2.5V voltage, the third diode D3 is cut off, and the collected voltage directly enters the A / D converter. When the voltage between the fifteenth resistor R15 and the third diode D3 exceeds the +2.5V voltage, the third diode D3 is turned on, so that the collected voltage is maintained at a maximum of +2.5V, thereby avoiding excessive voltage input to the A / D converter to protect the A / D converter.

[0073] The embodiment of the present invention also provides a method for using a conductivity transmitter, which is applied to the conductivity transmitter in the above embodiment. Figure 6 As shown, the method comprises the following steps:

[0074] Step S101, determining the wiring system of the electrodes to be connected;

[0075] Step S102, if the connection system of the electrode to be connected is a four-wire system, disconnect the path between the first connection terminal C1 and the second connection terminal C2 through the first short-circuit, disconnect the path between the third connection terminal C3 and the fourth connection terminal C4 through the second short-circuit, and connect the first connection terminal C1, the second connection terminal C2, the third connection terminal C3 and the fourth connection terminal C4 to the four electrode lead wires of the electrode to be connected respectively;

[0076] Step S103, if the wiring system of the electrode to be connected is a two-wire system, the passage between the first connection terminal C1 and the second connection terminal C2 is closed by the first short-circuit component, the passage between the third connection terminal C3 and the fourth connection terminal C4 is closed by the second short-circuit component, and the second connection terminal C2 and the third connection terminal C3 are respectively connected to the two electrode lead wires of the electrode to be connected.

[0077] Specifically, when the conductivity electrode is a four-wire electrode type, its equivalent circuit is as follows: Figure 4 shown.

[0078] When the first control signal output by the processor outputs a high level to the third control terminal S2 and the fourth control terminal S3, the fifth input terminal 2Y1 of the third controllable switch chip IC2 is connected to the fifth output terminal 2Z, the third input terminal 3Y1 is connected to the sixth output terminal 3Z, the fifth output terminal 2Z and the sixth output terminal 3Z are connected to the instrument amplifier 32, the third input terminal 3Y1 inputs an excitation signal, and the input voltage of the fifth input terminal 2Y1 is the voltage divided by the conductivity electrode. Therefore, the differential signal obtained by the instrument amplifier 32 at this time is the voltage divided by the excitation signal at the zeroth resistor R0 to the third resistor R3. By switching the level type of the first control signal output, the voltage representing the excitation signal divided at the zeroth resistor R0 to the third resistor R3 and the voltage divided by the excitation signal at the equivalent resistor Rx can be obtained at different times. Since the resistance values ​​of the zeroth resistor R0, the first resistor R1, the second resistor R2 and the third resistor R3 are known and are all precision resistors, the resistance value of the corresponding equivalent resistor Rx of the liquid to be measured can be obtained, and then the conductivity can be calculated.

[0079] When the conductivity electrode is a double electrode, its equivalent circuit is as follows: Figure 5 As shown:

[0080] Rx is the equivalent resistance Rx of the liquid to be measured between the two electrodes. The two signal lead wires of the dual-electrode conductivity electrode are respectively connected to the first connection terminal C1 and the fourth connection terminal C4 of the conductivity transmitter. The second connection terminal C2 is short-circuited with the first connection terminal C1 through the first short-circuit component, and the third connection terminal C3 and the fourth connection terminal C4 are short-circuited through the second short-circuit component. At this time, when the first control signal outputs a low level to the third control terminal S2 and the fourth control terminal S3, the second input terminal 3Y0 is connected to the first connection terminal C1, and the fourth input terminal 2Y0 is connected to the fourth connection terminal C4. Therefore, the differential signal obtained by the instrument amplifier 32 is still the voltage divided across the equivalent resistance Rx of the liquid to be measured. When the first control signal of the processor outputs a high level to the third control terminal S2 and the fourth control terminal S3, the fifth input terminal 2Y1 of the third controllable switch chip IC2 is connected to the fifth output terminal 2Z, the third input terminal 3Y1 is connected to the sixth output terminal 3Z, the fifth output terminal 2Z and the sixth output terminal 3Z are connected to the instrument amplifier 32, the third input terminal 3Y1 inputs an excitation signal, and the input voltage of the fifth input terminal 2Y1 is the voltage divided by the conductivity electrode. Therefore, the differential signal obtained by the instrument amplifier 32 at this time is the voltage divided by the excitation signal at the zeroth resistor R0 to the third resistor R3. By switching the level type output by the first control signal, the voltage representing the excitation signal divided at the zeroth resistor R0 to the third resistor R3 and the voltage divided by the excitation signal at the equivalent resistor Rx can be obtained at different times. Since the resistance values ​​of the zeroth resistor R0 to the third resistor R3 are known and are all precision resistors, the resistance value of the corresponding equivalent resistor Rx of the liquid to be measured can be obtained, and then the conductivity can be calculated.

[0081] In summary, the embodiments of the present invention can make the conductivity electrode transmitter applicable to both two-wire conductivity electrodes and four-wire conductivity electrodes. The short-circuit can be a switch or a jumper cap or other device for controlling the on-off of the circuit, which is easy to operate.

[0082] Although example embodiments and their advantages have been described in detail, those skilled in the art may make various changes, substitutions and modifications to these embodiments without departing from the spirit and defined scope of the present invention, and such modifications and variations are all within the defined scope.

Claims

1. A conductivity transmitter, characterized in that: It includes a signal generating circuit, an electrode connecting terminal and a signal processing module; The signal generating circuit is used to output an excitation signal; The electrode connection terminal includes a first connection end, a second connection end, a third connection end and a fourth connection end, a first short-circuit is provided between the first connection end and the second connection end, a second short-circuit is provided between the third connection end and the fourth connection end, the first short-circuit is used to switch the on-off state between the first connection end and the second connection end, and the second short-circuit is used to switch the on-off state between the third connection end and the fourth connection end, the first connection end is connected to the first end of the reference resistance unit, the second end of the reference resistance unit is connected to the output end of the signal generating circuit, the second connection end and the third connection end are respectively connected to the corresponding signal output lines of the conductivity electrode, the second connection end and the third connection end are also respectively connected to the two input ends of the signal processing module, the fourth connection end is grounded, and the two ends of the reference resistance unit are respectively connected to the other two input ends of the signal processing module; The signal processing module is used to receive the voltage output by the second connection terminal and the third connection terminal and / or the voltage output by the first terminal and the second terminal of the reference resistance unit to output a conductivity detection signal.

2. The conductivity transmitter according to claim 1, characterized in that: The signal generating circuit includes a first controllable switch chip and a first voltage follower, the control end of the first controllable switch chip is connected to a second control signal source for outputting a second control signal, the two input ends of the first controllable switch chip are respectively connected to a positive voltage signal source and a negative voltage signal source, the output end of the first controllable switch chip is periodically switched between the two input ends of the first controllable switch chip according to the second control signal, and the output end of the first controllable switch chip is connected to the input end of the first voltage follower.

3. The conductivity transmitter according to claim 1, characterized in that: The range adjustment circuit also includes a range adjustment circuit, the range adjustment circuit includes a second controllable switch chip, the second controllable switch chip includes a first input terminal, a first control terminal, a second control terminal, a first output terminal, a second output terminal, a third output terminal and a fourth output terminal, the reference resistance unit includes a zeroth resistor, a first resistor, a second resistor and a third resistor connected in series in sequence, the first input terminal is connected to the output terminal of the signal generating circuit, the first control terminal and the second control terminal are respectively connected to a third control signal source for outputting a third control signal and a fourth control signal source for outputting a fourth control signal, the first output terminal is respectively connected to one end of the zeroth resistor and one of the other two input terminals of the signal processing module. The first input terminal is connected to the second controllable switch chip, the second output terminal is respectively connected to the other end of the zero resistor and one end of the first resistor, the third output terminal is respectively connected to the other end of the first resistor and one end of the second resistor, the fourth output terminal is respectively connected to the other end of the second resistor and one end of the third resistor, the other end of the third resistor is connected to the first connection terminal, and the other end of the third resistor is also connected to the other input terminal of the other two input terminals of the signal processing module, and the second controllable switch chip controls the first input terminal to connect to any one of the first output terminal, the second output terminal, the third output terminal and the fourth output terminal according to the third control signal and the fourth control signal.

4. The conductivity transmitter according to claim 1, characterized in that: The signal processing module includes an input switching circuit and an instrumentation amplifier. The input switching circuit includes a third controllable switch chip. The third controllable switch chip includes a second input terminal, a third input terminal, a fourth input terminal, a fifth input terminal, a third control terminal, a fourth control terminal, a fifth output terminal and a sixth output terminal. The second input terminal, the third input terminal, the fourth input terminal and the fifth input terminal are respectively connected to the second connection terminal, the first terminal of the reference resistance unit, the third connection terminal and the second terminal of the reference resistance unit. The third control terminal and the fourth control terminal are both connected to a first control signal source for outputting a first control signal. The fifth output terminal and the sixth output terminal are respectively connected to two input terminals of the instrumentation amplifier. The third controllable switch chip connects the second input terminal and the fourth input terminal to the fifth output terminal and the sixth output terminal respectively according to the first control signal, or connects the third input terminal and the fifth input terminal to the fifth output terminal and the sixth output terminal respectively.

5. The conductivity transmitter according to claim 4, characterized in that: The instrumentation amplifier includes a second voltage follower, a third voltage follower and a differential amplifier, the input end of the second voltage follower and the input end of the third voltage follower are respectively connected to the fifth output end and the sixth output end of the input switching circuit, and the output end of the second voltage follower and the output end of the third voltage follower are respectively connected to the two input ends of the differential amplifier.

6. The conductivity transmitter according to claim 4, characterized in that: The signal processing module also includes a rectifier circuit, which includes a fifth op amp, a sixth op amp, a first diode, a second diode, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, and a first capacitor. The inverting input terminal of the fifth op amp is connected to one end of the eighth resistor, the in-phase input terminal of the fifth op amp is grounded, the anode of the first diode is connected to the output terminal of the fifth op amp, the cathode of the first diode is connected to the inverting input terminal of the fifth op amp, the cathode of the second diode is connected to the output terminal of the fifth op amp, the two ends of the tenth resistor are connected to the first capacitor, and the cathode of the second diode is connected to the output terminal of the fifth op amp. The anode of the second diode is connected to the cathode of the first diode, the anode of the second diode is also connected to one end of the eleventh resistor, the two ends of the ninth resistor are respectively connected to the other end of the eleventh resistor and the other end of the eighth resistor, the other end of the eleventh resistor is respectively connected to the reverse input end of the sixth op amp, one end of the twelfth resistor and one end of the first capacitor, the output end of the sixth op amp is respectively connected to the other end of the twelfth resistor and the other end of the first capacitor, one end of the thirteenth resistor is connected to the non-inverting input end of the sixth op amp, and the other end of the thirteenth resistor is grounded.

7. The conductivity transmitter according to claim 6, characterized in that: The signal processing module also includes a filtering circuit and a third diode, one end of the filtering circuit is connected to the output end of the rectifier circuit, the other end of the filtering circuit is connected to the anode of the third diode, and the cathode of the third diode is connected to a preset protection voltage source.

8. A method for using a conductivity transmitter, applied to the conductivity transmitter according to any one of claims 1 to 7, characterized in that: include: Determine the wiring system of the electrodes to be connected; If the connection system of the electrode to be connected is a four-wire system, the path between the first connection end and the second connection end is disconnected by the first short-circuit, the path between the third connection end and the fourth connection end is disconnected by the second short-circuit, and the first connection end, the second connection end, the third connection end and the fourth connection end are respectively connected to the four electrode lead wires of the electrode to be connected; If the wiring system of the electrode to be connected is a two-wire system, the passage between the first connection end and the second connection end is closed by the first short-circuit component, the passage between the third connection end and the fourth connection end is closed by the second short-circuit component, and the second connection end and the third connection end are respectively connected to the two electrode lead wires of the electrode to be connected.

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