A conductivity measurement circuit

Abstract

The application provides a conductivity measurement circuit, which comprises a conductivity electrode, an excitation source circuit, a first operational amplifier, and a switch resistance circuit. The output end of the excitation source circuit is connected with one end of the conductivity electrode. The first input end of the first operational amplifier is connected with the other end of the conductivity electrode, the second input end of the first operational amplifier is grounded, and the output end of the first operational amplifier is used for outputting a voltage signal reflecting the resistance of the conductivity electrode. The switch resistance circuit comprises a switch and a plurality of resistances. The switch is used for controlling the connection of at least one of the plurality of resistances between the first input end and the output end of the first operational amplifier. The conductivity measurement circuit can select different amplification gains through the switch resistance circuit, so as to adjust the voltage signal of the resistance of the conductivity electrode, facilitate the measurement of the voltage signal of the resistance of the conductivity electrode, and improve the convenience of conductivity measurement.

Description

Technical Field

[0001] This invention relates to the field of conductivity measurement technology, and more particularly to a conductivity measurement circuit. Background Technology

[0002] Electrical conductivity is a physical quantity used to express the ability of a solution to conduct electric current. The conductivity increases when water contains inorganic acids, bases, salts, or charged organic colloids. Existing conductivity electrodes calculate the conductivity of the liquid being tested by measuring the resistance between two electrodes.

[0003] In existing technologies, the voltage signal of the resistance of a conductivity electrode is affected by the conductivity of the liquid being measured, and the voltage signal is easily too high or too low, which is not conducive to measurement.

[0004] Therefore, how to solve the problem that the voltage signal of the resistance of conductivity electrodes is not easy to measure in the existing technology remains an urgent problem to be solved in the field of conductivity measurement technology. Summary of the Invention

[0005] This invention provides a conductivity measurement circuit to address the deficiency in the prior art where the voltage signal of the resistance of conductivity electrodes is not easily measured.

[0006] This invention provides a conductivity measurement circuit, comprising:

[0007] Conductivity electrode;

[0008] An excitation source circuit, wherein the output terminal of the excitation source circuit is connected to one end of the conductivity electrode;

[0009] A first operational amplifier has its first input terminal connected to the other end of the conductivity electrode, its second input terminal grounded, and its output terminal used to output a voltage signal reflecting the resistance of the conductivity electrode.

[0010] A switched resistor circuit includes a switch and a plurality of resistors, wherein the switch is used to control the two ends of at least one of the plurality of resistors to be connected to the first input terminal and the output terminal of the first operational amplifier, respectively.

[0011] According to the present invention, a conductivity measurement circuit is provided, wherein the excitation source circuit includes:

[0012] A square wave oscillator circuit is used to output a square wave signal;

[0013] An amplitude limiting circuit is provided, the input of which is connected to the output of the square wave oscillation circuit. The amplitude limiting circuit is used to limit the amplitude of the square wave signal.

[0014] According to the present invention, a conductivity measurement circuit is provided, wherein the square wave oscillation circuit includes a first capacitor, a first resistor, a second resistor, a third resistor, and a second operational amplifier, and the output terminal of the square wave oscillation circuit is the output terminal of the second operational amplifier;

[0015] One end of the first capacitor is grounded, and the other end is connected to the first input terminal of the second operational amplifier.

[0016] The two ends of the first resistor are respectively connected to the first input terminal and the output terminal of the second operational amplifier;

[0017] One end of the second resistor is grounded, and the other end is connected to the second input terminal of the second operational amplifier;

[0018] The two ends of the third resistor are respectively connected to the second input terminal and the output terminal of the second operational amplifier.

[0019] According to a conductivity measurement circuit provided by the present invention, the limiting circuit includes a fourth resistor, a first limiting diode, and a second limiting diode;

[0020] One end of the fourth resistor serves as the input terminal of the limiting circuit, and the other end serves as the output terminal of the limiting circuit, which is connected to the anode of the first limiting diode and the cathode of the second limiting diode, respectively.

[0021] The cathode of the first limiting diode and the anode of the second limiting diode are grounded.

[0022] According to the conductivity measurement circuit provided by the present invention, the excitation source circuit further includes:

[0023] A first follower, the input of which is connected to the output of the limiting circuit, and the output of which serves as the output of the excitation source circuit.

[0024] The conductivity measurement circuit provided by the present invention further includes:

[0025] A rectifier circuit, wherein the input terminal of the rectifier circuit is connected to the output terminal of the first operational amplifier.

[0026] According to the present invention, a conductivity measurement circuit is provided, wherein the rectifier circuit includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a third operational amplifier, a fourth operational amplifier, a first diode, and a second diode;

[0027] One end of the fifth resistor is connected to the output terminal of the first operational amplifier, and the other end is connected to one end of the sixth resistor, the first input terminal of the third operational amplifier, and one end of the ninth resistor, respectively.

[0028] The other end of the sixth resistor is connected to one end of the seventh resistor and the anode of the first diode, respectively;

[0029] The cathode of the first diode is connected to the anode of the second diode, the cathode of the second diode is connected to the other end of the ninth resistor and the second input terminal of the fourth operational amplifier, and the second input terminal of the third operational amplifier is grounded;

[0030] The other end of the seventh resistor is connected to one end of the eighth resistor and the first input terminal of the fourth operational amplifier, and the other end of the eighth resistor is connected to the output terminal of the fourth operational amplifier.

[0031] The output terminal of the fourth operational amplifier is the output terminal of the rectifier circuit.

[0032] The conductivity measurement circuit provided by the present invention further includes:

[0033] A signal conditioning circuit, wherein the input terminal of the signal conditioning circuit is connected to the output terminal of the rectifier circuit, and the signal conditioning circuit is used to output a conductivity sampling signal.

[0034] According to the present invention, a conductivity measurement circuit is provided, wherein the signal conditioning circuit comprises:

[0035] A low-pass filter, wherein the input terminal of the low-pass filter is connected to the output terminal of the rectifier circuit;

[0036] The second follower is connected to the output of the low-pass filter.

[0037] According to the present invention, a conductivity measurement circuit is provided, wherein the output terminal of the signal conditioning circuit is used to connect to the analog-to-digital conversion port of a processing device.

[0038] The present invention provides a conductivity measurement circuit that can select different amplification gains through a switching resistor circuit, thereby adjusting the voltage signal of the resistance of the conductivity electrode, making the voltage signal of the resistance of the conductivity electrode easy to measure and improving the convenience of conductivity measurement. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the conductivity measurement circuit provided by the present invention;

[0041] Figure 2 This is one of the structural schematic diagrams of the excitation source circuit provided by the present invention;

[0042] Figure 3 This is the second schematic diagram of the excitation source circuit provided by the present invention;

[0043] Figure 4 This is a schematic diagram of the rectifier circuit provided by the present invention;

[0044] Figure 5 This is a schematic diagram of the signal conditioning circuit provided by the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] The terms "first," "second," etc., used in the specification and claims of this invention are used to distinguish similar objects and are not used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and that the objects distinguished by "first," "second," etc., are generally of the same class.

[0047] The Conductivity Temperature Depth (CTD) meter is the most fundamental instrument for measuring environmental information in marine dynamic environmental elements. Marine surveys begin with investigating the distribution and variation of seawater temperature and salinity with depth. All marine observation and monitoring platforms integrate and utilize CTD meters; related measuring instruments are widely used in stations, ships, buoys, moorings, bottom-mounted, towed, and underwater moving platforms.

[0048] This invention provides a conductivity measurement circuit that can be applied in a temperature, salinity, and depth (TDT) instrument. It can sample conductivity and calculate the voltage signal of the resistance of the conductivity electrode according to a formula, which is an important part of the production and design of a TDT instrument.

[0049] Figure 1 This is a schematic diagram of the conductivity measurement circuit provided by the present invention, as shown below. Figure 1 As shown, the circuit includes:

[0050] Conductivity electrode P1;

[0051] An excitation source circuit 110, the output terminal of which is connected to one end of the conductivity electrode P1;

[0052] The first operational amplifier U1 has its first input terminal connected to the other end of the conductivity electrode P1, its second input terminal grounded, and its output terminal used to output a voltage signal reflecting the resistance of the conductivity electrode P1.

[0053] The switched resistor circuit SW includes a switch and a plurality of resistors. The switch is used to control the connection of at least one of the plurality of resistors to the first input terminal and the output terminal of the first operational amplifier U1, respectively.

[0054] Specifically, the conductivity measurement circuit includes a conductivity electrode P1, an excitation source circuit 110, a first operational amplifier U1, and a switching resistor circuit SW.

[0055] In the conductivity measurement circuit, the conductivity needs to be sampled when measuring conductivity. During the sampling process, the conductivity electrode P1 needs to be stimulated by an excitation signal. This excitation signal is generated by the excitation source circuit 110. Generally, the frequency of the excitation signal is between 1Hz and 10kHz, and the amplitude of the excitation signal is less than 1V. The output terminal of the excitation source circuit is connected to one end of the conductivity electrode P1, that is, the output terminal of the excitation source circuit 110 is connected to port 1 of the conductivity electrode P1.

[0056] The first operational amplifier U1 refers to operational amplifier U1. Its first input terminal is connected to the other end of the conductivity electrode P1, that is, the first input terminal of operational amplifier U1 is connected to port 2 of the conductivity electrode P1. Here, the first input terminal is the inverting input terminal. The second input terminal of operational amplifier U1 is grounded, and here, the second input terminal is the non-inverting input terminal. The output terminal of operational amplifier U1 can be used to output a voltage signal reflecting the resistance of the conductivity electrode.

[0057] Here, through the connection relationship between the excitation source circuit 110, the conductivity electrode P1 and the first input terminal of the first operational amplifier U1, it can be understood that the voltage signal output by the excitation source circuit 110 as a voltage source is input to the first input terminal of the first operational amplifier U1 after passing through the conductivity electrode P1, which can be regarded as a resistor.

[0058] A switched resistor circuit SW is used to adjust the magnitude of the voltage signal that characterizes the resistance of the conductivity electrode, so as to facilitate conductivity measurement. The switched resistor circuit SW includes a switch and multiple resistors. For example, the switched resistor circuit SW includes one switch and multiple resistors. The resistors connected to the conductivity measurement circuit are switched by turning the switch on and off. Another example is that the switched resistor circuit SW includes multiple resistors and a number of switches equal to the number of resistors. The switches and resistors are in one-to-one correspondence. Each switch controls whether the corresponding resistor is connected to the conductivity measurement circuit. The embodiments of the present invention do not make specific limitations in this regard.

[0059] Since the principle of measuring conductivity is to measure the resistance R of the water between conductivity electrodes P1, conductivity can be converted from electrode constant. The formula for electrode constant is as follows:

[0060]

[0061] Where EC is the electrode ratio and R is the resistance of the water between the measuring electrodes.

[0062] The first operational amplifier U1 and the feedback resistor of the conductivity measurement circuit connected in the switched resistor circuit SW can form an RV conversion linear circuit, thereby converting the resistance R of the water between the conductivity electrodes into a voltage signal. The switch can select different amplification gains, and the voltage signal V... 电压信号 The formula is as follows:

[0063]

[0064] Among them, V 激励源信号 That is, the voltage value of the excitation signal output by the excitation source circuit 110. For example, if the excitation signal is a square wave signal with an amplitude of 0.2V, then V 激励源信号 =0.2V.

[0065] From the above equation, we can see that V 电压信号 Proportional to The conductivity EC is also proportional to Therefore, V 电压信号 It is also proportional to the conductivity EC.

[0066] Therefore, by measuring the voltage signal V 电压信号 The conductivity EC can be measured.

[0067] In the above formula, in V 激励源信号 Under the premise that R is not adjustable, the resistance value R of the feedback resistor 反馈电阻 It can regulate V 电压信号 The effect of the magnitude, that is, by adjusting the resistance value R of the feedback resistor. 反馈电阻 Choose different amplification gains. For example, in the current output V 电压信号 If the value of R is too low, resulting in low measurement accuracy, you can increase R. 反馈电阻In V 电压信号 If the value is too high and exceeds the measurement threshold, R can be reduced. 反馈电阻 Understandably, R 反馈电阻 That is, the resistor connected to the conductivity measurement circuit through the switched resistor circuit SW. The switch in the switched resistor circuit SW makes the resistance value of the specific resistor adjustable, thereby allowing different amplification gains to be selected.

[0068] The present invention provides a conductivity measurement circuit that can select different amplification gains through a switching resistor circuit, thereby adjusting the voltage signal of the resistance of the conductivity electrode, making the voltage signal of the resistance of the conductivity electrode easy to measure and improving the convenience of conductivity measurement.

[0069] Based on the above embodiments, Figure 2 This is one of the structural schematic diagrams of the excitation source circuit provided by the present invention, such as... Figure 2 As shown, the excitation source circuit 110 includes:

[0070] Square wave oscillator circuit 111 is used to output a square wave signal;

[0071] A limiting circuit 112 is provided, the input terminal of which is connected to the output terminal of the square wave oscillation circuit. The limiting circuit is used to limit the amplitude of the square wave signal.

[0072] Specifically, the excitation source circuit includes a square wave oscillation circuit 111 and a limiting circuit 112, which are used to generate the excitation signal that needs to be applied during the sampling process of the conductivity electrode P1.

[0073] The square wave oscillator circuit 111 is used to output a square wave signal. This circuit consists of a capacitor, multiple resistors, and an operational amplifier. The square wave amplitude generated by the oscillator circuit 111 may be too large, for example, close to 5V. Since an excessively large square wave amplitude makes it inconvenient to measure the voltage signal of the resistance of the conductivity electrode, a limiting circuit 112 is needed to limit the amplitude of the square wave generated by the oscillator circuit 111. The input terminal of the limiting circuit 112 is connected to the output terminal of the square wave oscillator circuit 111.

[0074] Based on the above embodiments, Figure 3 This is a second schematic diagram of the excitation source circuit provided by the present invention, as shown below. Figure 3 As shown, the square wave oscillator circuit 111 includes a first capacitor C1, a first resistor R1, a second resistor R2, a third resistor R3, and a second operational amplifier U2. The output terminal of the square wave oscillator circuit is the output terminal of the second operational amplifier.

[0075] One end of the first capacitor C1 is grounded, and the other end is connected to the first input terminal of the second operational amplifier U2;

[0076] The two ends of the first resistor R1 are connected to the first input terminal and the output terminal of the second operational amplifier U2, respectively;

[0077] One end of the second resistor R2 is grounded, and the other end is connected to the second input terminal of the second operational amplifier U2;

[0078] The two ends of the third resistor R3 are connected to the second input terminal and the output terminal of the second operational amplifier U2, respectively.

[0079] Specifically, such as Figure 3 As shown, the square wave oscillator circuit 111 includes a first capacitor C1, a first resistor R1, a second resistor R2, a third resistor R3, and a second operational amplifier U2. Here, the second operational amplifier refers to the operational amplifier U2, and the output terminal of the square wave oscillator circuit 111 is the output terminal of the operational amplifier U2.

[0080] The formula for the frequency of the square wave generated by the square wave oscillator circuit 111 is as follows:

[0081]

[0082] Where R1 is the first resistor, C1 is the first capacitor, R2 is the second resistor, R3 is the third resistor, and T is the square wave frequency generated by the square wave oscillator circuit.

[0083] like Figure 3 As shown, one end of the first capacitor C1 is grounded, that is, the first capacitor C1 is connected to GND, and the other end is connected to the first input terminal of the second operational amplifier, that is, the other end of the first capacitor C1 is connected to the first input terminal of the operational amplifier U2. Here, the first input terminal is the inverting input terminal.

[0084] The two ends of the first resistor R1 are connected to the first input terminal and the first output terminal, respectively;

[0085] One end of the second resistor R2 is grounded, that is, one end of the second resistor R2 is connected to GND, and the other end is connected to the second input terminal of the second operational amplifier, that is, the other end of the second resistor R2 is connected to the second input terminal of the operational amplifier U2. Here, the second input terminal is the non-inverting input terminal.

[0086] The two ends of the third resistor R3 are connected to the second input terminal and the output terminal of the operational amplifier U2, respectively. The second input terminal here is the non-inverting input terminal.

[0087] Based on the above embodiments, such as Figure 3 As shown, the limiting circuit 112 includes a fourth resistor R4, a first limiting diode D1, and a second limiting diode D2;

[0088] One end of the fourth resistor R4 serves as the input terminal of the limiting circuit 112, and the other end serves as the output terminal of the limiting circuit 112, which is connected to the anode of the first limiting diode D1 and the cathode of the second limiting diode D2, respectively.

[0089] The cathode of the first limiting diode D1 and the anode of the second limiting diode D2 are grounded.

[0090] Specifically, in the limiting circuit 112, one end of the fourth resistor R4 serves as the input terminal of the limiting circuit 112, and the other end serves as the output terminal of the limiting circuit 112, which is connected to the anode of the first limiting diode D1 and the cathode of the second limiting diode D2 respectively.

[0091] The cathode of the first limiting diode D1 and the anode of the second limiting diode D2 are grounded, meaning the cathode of the first limiting diode D1 and the anode of the second limiting diode D2 are connected to GND. Here, the two limiting diodes can be Schottky diodes. By connecting the two limiting diodes in reverse parallel, bidirectional limiting can be achieved, for example, limiting the amplitude of the output voltage signal to ±0.2V.

[0092] Based on the above embodiments, the excitation source circuit 110 further includes:

[0093] A first follower, the input of which is connected to the output of the limiting circuit, and the output of which serves as the output of the excitation source circuit.

[0094] Specifically, such as Figure 3 As shown, the first follower consists of resistor R16 and operational amplifier U6. The input terminal of the first follower is connected to the output terminal of the limiting circuit, that is, the input terminal of the first follower is connected to the anode of the first limiting diode D1 and the cathode of the second limiting diode D2. The output terminal of the first follower serves as the output terminal of the excitation source circuit. By using the first follower, the load-carrying capacity of the excitation source circuit can be improved.

[0095] Based on the above embodiments, the conductivity measurement circuit further includes:

[0096] A rectifier circuit, wherein the input terminal of the rectifier circuit is connected to the output terminal of the first operational amplifier.

[0097] Specifically, the conductivity measurement circuit also includes a rectifier circuit, which converts the AC voltage signal into a DC voltage signal to facilitate the measurement of the voltage signal of the resistance of the conductivity electrode. The input terminal of the rectifier circuit is connected to the output terminal of the operational amplifier U1.

[0098] Based on the above embodiments, Figure 4 This is a schematic diagram of the rectifier circuit provided by the present invention, as shown below. Figure 4As shown, the rectifier circuit includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a third operational amplifier U3, a fourth operational amplifier U4, a first diode D3, and a second diode D4.

[0099] One end of the fifth resistor R5 is connected to the output terminal of the first operational amplifier U1, and the other end is connected to one end of the sixth resistor R6, the first input terminal of the third operational amplifier U3, and one end of the ninth resistor R9, respectively.

[0100] The other end of the sixth resistor R6 is connected to one end of the seventh resistor R7 and the anode of the first diode D3, respectively.

[0101] The cathode of the first diode D3 is connected to the anode of the second diode D4. The cathode of the second diode D4 is connected to the other end of the ninth resistor R9 and the second input terminal of the fourth operational amplifier U4. The second input terminal of the third operational amplifier U3 is grounded.

[0102] The other end of the seventh resistor R7 is connected to one end of the eighth resistor R8 and the first input terminal of the fourth operational amplifier U4, and the other end of the eighth resistor R8 is connected to the output terminal of the fourth operational amplifier U4.

[0103] The output terminal of the fourth operational amplifier U4 is the output terminal of the rectifier circuit.

[0104] Specifically, such as Figure 4 As shown, the rectifier circuit includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, an operational amplifier U3, an operational amplifier U4, a first diode D3, and a second diode D4.

[0105] Among them, one end of the fifth resistor R5 is connected to the output terminal of the operational amplifier U1, and the other end is connected to one end of the sixth resistor R6, the first input terminal of the operational amplifier U3 and one end of the ninth resistor R9 respectively. Here, the first input terminal is the inverting input terminal.

[0106] The other end of the sixth resistor R6 is connected to one end of the seventh resistor R7 and the anode of the first diode D3, respectively.

[0107] The cathode of the first diode D3 is connected to the anode of the second diode D4. The cathode of the second diode D4 is connected to the other end of the ninth resistor R9 and the second input terminal of the operational amplifier U4. The second input terminal here is the non-inverting input terminal.

[0108] Furthermore, the second input terminal of operational amplifier U3 is grounded, meaning that the non-inverting input terminal of operational amplifier U3 is connected to GND;

[0109] The other end of the seventh resistor R7 is connected to one end of the eighth resistor R8 and the first input terminal of the operational amplifier U4, that is, the other end of the seventh resistor R7 is connected to one end of the eighth resistor R8 and the inverting input terminal of the operational amplifier U4, and the other end of the eighth resistor R8 is connected to the output terminal of the operational amplifier U4.

[0110] Furthermore, the output of operational amplifier U4 is the output of the rectifier circuit.

[0111] Based on the above embodiments, the conductivity measurement circuit further includes:

[0112] A signal conditioning circuit, wherein the input terminal of the signal conditioning circuit is connected to the output terminal of the rectifier circuit, and the signal conditioning circuit is used to output a conductivity sampling signal.

[0113] Specifically, the conductivity measurement circuit also includes a signal conditioning circuit, which is used to output a conductivity sampling signal, and the input terminal of the signal conditioning circuit is connected to the output terminal of the rectifier circuit.

[0114] Based on the above embodiments, Figure 5 This is a schematic diagram of the signal conditioning circuit provided by the present invention, as shown below. Figure 5 As shown, the signal conditioning circuit includes:

[0115] A low-pass filter, wherein the input terminal of the low-pass filter is connected to the output terminal of the rectifier circuit;

[0116] The second follower is connected to the output of the low-pass filter.

[0117] Specifically, such as Figure 5 As shown, the signal conditioning circuit includes a low-pass filter and a second follower. The low-pass filter consists of a resistor R14 and a capacitor C4, and the input terminal of the low-pass filter is connected to the output terminal of the rectifier circuit, that is, the input terminal of the low-pass filter is connected to the output terminal of the operational amplifier U4.

[0118] The second follower includes operational amplifier U5, and its input is connected to the output of the low-pass filter.

[0119] Based on the above embodiments, the output terminal of the signal conditioning circuit is used to connect to the analog-to-digital conversion port of the processing device.

[0120] Specifically, the output of the signal conditioning circuit is used to connect to the analog-to-digital conversion port of the processing device. The analog-to-digital conversion port of the processing device can be a microcontroller AD (analog-to-digital conversion) pin or an AD sampling chip. This embodiment of the invention does not specifically limit this.

[0121] Therefore, the voltage signal of the resistance of the conductivity electrode can be measured, and the value range of the voltage signal of the resistance of the conductivity electrode is 0 to 3.3V, which makes it convenient to measure the voltage signal of the resistance of the conductivity electrode.

[0122] Based on the above embodiments, this embodiment of the invention generates the excitation signal required by the conductivity measurement circuit through an excitation source circuit composed of a square wave oscillator circuit, a limiting circuit, and a first follower. The signal then passes sequentially through a switched resistor circuit, a first operational amplifier, a rectifier circuit, and a signal conditioning circuit. Different amplification gains can be selected through the switched resistor circuit to adjust the voltage signal of the conductivity electrode's resistance. Finally, the output of the signal conditioning circuit is connected to the analog-to-digital conversion port of the processing device, thereby facilitating the measurement of the voltage signal of the conductivity electrode's resistance and improving the convenience of conductivity measurement.

[0123] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0124] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A conductivity measurement circuit, characterized in that, include: Conductivity electrode; An excitation source circuit, wherein the output terminal of the excitation source circuit is connected to one end of the conductivity electrode; A first operational amplifier has its first input terminal connected to the other end of the conductivity electrode, its second input terminal grounded, and its output terminal used to output a voltage signal reflecting the resistance of the conductivity electrode. A switched resistor circuit includes a switch and multiple resistors. The switch controls the connection of at least one of the multiple resistors to a first input terminal and an output terminal of a first operational amplifier, respectively. The switched resistor circuit is used to adjust the magnitude of a voltage signal that characterizes the resistance of an electrode representing conductivity, so as to facilitate conductivity measurement. The excitation source circuit includes: A square wave oscillator circuit is used to output a square wave signal; A limiting circuit is provided, wherein the input terminal of the limiting circuit is connected to the output terminal of the square wave oscillation circuit, and the limiting circuit is used to limit the amplitude of the square wave signal. The square wave oscillation circuit includes a first capacitor, a first resistor, a second resistor, a third resistor, and a second operational amplifier. The output terminal of the square wave oscillation circuit is the output terminal of the second operational amplifier. One end of the first capacitor is grounded, and the other end is connected to the first input terminal of the second operational amplifier. The two ends of the first resistor are respectively connected to the first input terminal and the output terminal of the second operational amplifier; One end of the second resistor is grounded, and the other end is connected to the second input terminal of the second operational amplifier; The two ends of the third resistor are respectively connected to the second input terminal and the output terminal of the second operational amplifier; The limiting circuit includes a fourth resistor, a first limiting diode, and a second limiting diode; One end of the fourth resistor serves as the input terminal of the limiting circuit, and the other end serves as the output terminal of the limiting circuit, which is connected to the anode of the first limiting diode and the cathode of the second limiting diode, respectively. The cathode of the first limiting diode and the anode of the second limiting diode are grounded; The excitation source circuit further includes: A first follower, the input of which is connected to the output of the limiting circuit, and the output of which serves as the output of the excitation source circuit.

2. The conductivity measuring circuit according to claim 1, characterized in that, Also includes: A rectifier circuit, wherein the input terminal of the rectifier circuit is connected to the output terminal of the first operational amplifier.

3. The conductivity measuring circuit according to claim 2, characterized in that, The rectifier circuit includes a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a third operational amplifier, a fourth operational amplifier, a first diode, and a second diode; One end of the fifth resistor is connected to the output terminal of the first operational amplifier, and the other end is connected to one end of the sixth resistor, the first input terminal of the third operational amplifier, and one end of the ninth resistor, respectively. The other end of the sixth resistor is connected to one end of the seventh resistor and the anode of the first diode, respectively; The cathode of the first diode is connected to the anode of the second diode, the cathode of the second diode is connected to the other end of the ninth resistor and the second input terminal of the fourth operational amplifier, and the second input terminal of the third operational amplifier is grounded; The other end of the seventh resistor is connected to one end of the eighth resistor and the first input terminal of the fourth operational amplifier, and the other end of the eighth resistor is connected to the output terminal of the fourth operational amplifier. The output terminal of the fourth operational amplifier is the output terminal of the rectifier circuit.

4. The conductivity measuring circuit according to claim 2, characterized in that, Also includes: A signal conditioning circuit, wherein the input terminal of the signal conditioning circuit is connected to the output terminal of the rectifier circuit, and the signal conditioning circuit is used to output a conductivity sampling signal.

5. The conductivity measuring circuit according to claim 4, characterized in that, The signal conditioning circuit includes: A low-pass filter, wherein the input terminal of the low-pass filter is connected to the output terminal of the rectifier circuit; The second follower is connected to the output of the low-pass filter.

6. The conductivity measuring circuit according to claim 4, characterized in that, The output of the signal conditioning circuit is used to connect to the analog-to-digital conversion port of the processing device.

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