CN111537569A - Distributed water conductivity detection circuit and key module thereof - Google Patents
Distributed water conductivity detection circuit and key module thereof Download PDFInfo
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Abstract
The invention discloses a distributed water conductivity detection circuit and a key module thereof, belonging to the technical field of electronic measurement; the circuit consists of an excitation source characteristic program-controlled setting circuit, a program-controlled alternating-current precise constant current source circuit, a conductivity measurement electrode selection circuit and a conductivity measurement signal acquisition circuit, wherein the excitation source characteristic program-controlled setting circuit consists of an edge crystal oscillator, a double-four-bit binary counter, an analog switch, an operational amplifier chip, a reference chip, a resistor and a capacitor; the program-controlled alternating-current precise constant-current source circuit consists of an operational amplifier chip, a switch diode and a plurality of precise low-temperature drift resistors; the conductivity measuring electrode selection circuit consists of an analog multiplexer and a connector; the conductivity measurement signal acquisition circuit consists of a displacement buffer, a programmable instrument amplifier, a precise operational amplifier, a converter, a 24-bit ADC, a switch diode and a plurality of resistance capacitors; the invention has the technical advantages of adjustable excitation source frequency, selectable amplitude, low development cost, strong measurement stability and strong real-time property.
Description
Technical Field
The invention discloses a distributed water conductivity detection circuit and a key module thereof, belonging to the technical field of electronic measurement.
Background
Water resources are indispensable in people's life and industrial production. In the daily domestic water of residents and industrial water for manufacturing, processing, cooling, air conditioning, washing, boilers and the like, the conductivity is an important detection index for measuring the water quality condition according to the water quality detection standard of China. Water quality detection is related to water safety problems, and in industries such as air conditioners, washing, boilers and the like, the over-high concentration of electric ions corrodes instruments and equipment, so that the safety problems are caused. In addition, domestic and industrial wastewater is discharged through water purification treatment, and then water quality detection is carried out, otherwise, problems such as environmental pollution and the like are caused.
Firstly, the widely used conductivity detection method is generally that a pair of electrodes performs single-point measurement on the conductivity of the whole conductivity cell solution, and the single-point measurement can only reflect the change of the conductivity of the solution with time. However, in special applications such a detection method causes large errors, for example in the feed water and the outlet water of a boiler, the electrical conductivity of which changes at different points at the same time. Resulting in inaccurate detection results. Secondly, a conductivity detection hardware circuit is arranged, and the key point of conductivity detection is to overcome the influence of polarization effect and capacitance effect on the measurement result to the maximum extent. In general engineering, an alternating current excitation source is adopted to weaken polarization reaction, and solutions in different application occasions show inconsistent resistance states, sometimes show a low-resistance state and sometimes show a high-resistance state, so that the influence of capacitance effect is different. However, the conventional conductivity detection instrument generally has the following problems;
firstly, the single fixed frequency excitation source is adopted, and the detection error of the conductivity of the solution with different resistance states is larger.
Secondly, the excitation source with fixed amplitude is adopted, and the detection can be only carried out within a certain range.
Thirdly, the stability is poor, for example, the measurement result is greatly influenced by the fluctuation of the power supply sometimes.
Fourth, the hardware cost is high, for example, the bridge method has high measurement accuracy and wide measurement range, but the hardware cost of the required electronic balancer is high.
Fifth, the measurement method which is used in industrial fields in large scale at present has poor timeliness, besides the bridge method, a pulse measurement method is also adopted, the pulse method is that a measurement signal is stable after a period of time, and then measurement is repeated, so that a relatively stable measurement signal can be obtained, and the target of real-time detection cannot be achieved.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a distributed water conductivity detection circuit and a key module thereof, wherein the distributed water conductivity detection circuit comprises an excitation source characteristic program control setting circuit, a program control alternating current precision constant current source circuit, a conductivity measurement electrode selection circuit and a conductivity measurement signal acquisition circuit; the circuit has the technical advantages of adjustable excitation source frequency, selectable amplitude, low development cost, strong measurement stability and strong real-time property.
The purpose of the invention is realized as follows:
a distributed water conductivity detection circuit comprises an excitation source characteristic program control setting circuit, a program control alternating current precise constant current source circuit, a conductivity measurement electrode selection circuit and a conductivity measurement signal acquisition circuit;
the excitation source characteristic program control setting circuit is composed of 1 active crystal oscillator, 1 double four-bit binary counter SN74LS393, 1 analog switch 74HC4051, 1 analog switch 74HC4053, 2 double precision operational amplifier chips OPA2277, 1 reference chip ADR4525, a plurality of resistors and capacitors;
an active crystal oscillator generates an alternating current signal with a fixed frequency of 32.768kHz, VCC analog voltage is 5V, a double four-bit binary counter divides the frequency to generate CK 0-CK 7, and bits SET0, SET1 and SET2 are controlled by an analog switch U3 to select and output FCLK in a program control mode; the control bit SET3 enables the bit to control the U3 to work; r17 is a common resistor with a size of 1K omega; the U5 reference chip outputs +2.5V reference voltage VREF, and the chip has a bypass capacitor to the ground; VREF is defined as NREF is-2.5V voltage through U6A impedance transformation and filtering, R1 and R2 are proportional resistors, and 10 ppm/DEG C low-temperature drift and high-precision resistors with the size of 10K omega are selected; u4 is an analog switch, and XO, X1, Y0, Y1, Z0 and Z1 outputs are selected by control bits FCLK, SET4 and SET 5; selecting and outputting three gears, namely SUQH, SQUM and SQUL; SQUH selects square wave with output amplitude of +/-2.5V through VREF and NREF; the SUQM is defined by R3, R4 and U7B through impedance transformation and filtering, and R3 and R4 respectively select 10 ppm/DEG C low-temperature drift and high-precision resistance with the sizes of 9K omega and 1K omega; SQUM is square wave of + -0.25V; SQUL obtains square waves of +/-0.025V through low temperature drift of 10 ppm/DEG C and high-precision resistance impedance transformation of R5 and R6 with the size of 9K omega and 1K omega; SQHM is square wave of + -2.5V and + -0.25V directly selected and output by SQUH and SQUM; SQU is the + -2.5V, + -0.25V, + -0.025V square wave of SQHM and SQUL selection output, wherein SQU follows the output through U6B;
the program-controlled alternating-current precise constant current source circuit is composed of 1 double-precise operational amplifier chip OPA2277, 1 switching diode BAV199 and a plurality of precise low-temperature drift resistors;
the SQU selects square waves with different amplitudes to be output, the constant current source IOUT outputs driving currents with different magnitudes, and R7, R8, R9, R10, R12, R13, R14 and R15 select 10 ppm/DEG C low-temperature drift and high-precision resistance with the magnitude of 10K omega, or: r12, R13, R14 and R15 adopt accurate resistor network chips matched with temperature characteristics, so that the output working current has extremely low temperature drift characteristics; r11 adopts a resistor of 1K omega; the switching diode D1 carries out overcurrent protection on the circuit, and prevents the damage of the subsequent circuit caused by the excessive current;
the conductivity measurement electrode selection circuit consists of 4 single-chip CMOS analog multiplexers ADG5208 and two connectors;
JX and JY are 2 connectors to represent two groups of X and Y conductivity measuring electrodes, XA, XB, XC, XD, XE, YA, YB, YC, YD and YE respectively represent two groups of different electrodes; each electrode is composed of two wires; the 4 single-chip CMOS analog multiplexers are all controlled by 3-bit binary address lines SET8, SET9 and SET10 to output, one of XA, XB, XC, XD, XE, YA, YB, YC, YD and YE8 is selected to be switched to a common output D, and SET11 controls the enabling of a chip; wherein AGND is analog ground, and the power supply voltage is +/-9V, which is the power supply voltage of the analog circuit; the common outputs of U9 and U10 are IOUT and AGND, respectively; u11 and U12 are voltage input ends, which are respectively input with two ends VIH and VIL of the differential voltage to be measured;
the conductivity measurement signal acquisition circuit consists of 2 displacement buffers 74HC595, 1 programmable and programmable instrument amplifier AD8253, 1 precision operational amplifier AD8512, 1 RMS-DC converter LTC1968, 1 24bit ADC LTC2400, 1 switch diode BAV199 and a plurality of resistance capacitors;
u13 provides +2.5V reference voltage from VREF, VIH and VIL are input ends for measuring conductivity differential signals, and RMSIN is a measurement signal of an output end to the ground; SET12 and SET13 are 2-bit address lines, and can SET the amplification of output signals to be 1, 10, 100 and 1000 times in a programmable manner; d2 switching the diode between +5V and GND; the signal RMSIN is followed by a resistor R16 and a precision operational amplifier U14A; u15 is RMS-DC converter for true effective value conversion, two input signal channels IN1, IN2, IN2 input reference voltage VREF, U15 output signal ADIN is sent to U16, 24bit ADC collects, ADC reference voltage VREF is provided by reference chip, MSCK, MSDI, ADCS are clock line, data line, chip select line respectively; requiring electrical isolation to exchange information with the microprocessor.
A distributed water conductivity detection circuit key module is a program control setting circuit for excitation source characteristics, and comprises 1 active crystal oscillator, 1 double four-bit binary counter SN74LS393, 1 analog switch 74HC4051, 1 analog switch 74HC4053, 2 double precision operational amplifier chips OPA2277, 1 reference chip ADR4525, a plurality of resistors and capacitors;
an active crystal oscillator generates an alternating current signal with a fixed frequency of 32.768kHz, VCC analog voltage is 5V, a double four-bit binary counter divides the frequency to generate CK 0-CK 7, and bits SET0, SET1 and SET2 are controlled by an analog switch U3 to select and output FCLK in a program control mode; the control bit SET3 enables the bit to control the U3 to work; r17 is a common resistor with a size of 1K omega; the U5 reference chip outputs +2.5V reference voltage VREF, and the chip has a bypass capacitor to the ground; VREF is defined as NREF is-2.5V voltage through U6A impedance transformation and filtering, R1 and R2 are proportional resistors, and 10 ppm/DEG C low-temperature drift and high-precision resistors with the size of 10K omega are selected; u4 is an analog switch, and XO, X1, Y0, Y1, Z0 and Z1 outputs are selected by control bits FCLK, SET4 and SET 5; selecting and outputting three gears, namely SUQH, SQUM and SQUL; SQUH selects square wave with output amplitude of +/-2.5V through VREF and NREF; the SUQM is defined by R3, R4 and U7B through impedance transformation and filtering, and R3 and R4 respectively select 10 ppm/DEG C low-temperature drift and high-precision resistance with the sizes of 9K omega and 1K omega; SQUM is square wave of + -0.25V; SQUL obtains square waves of +/-0.025V through low temperature drift of 10 ppm/DEG C and high-precision resistance impedance transformation of R5 and R6 with the size of 9K omega and 1K omega; SQHM is square wave of + -2.5V and + -0.25V directly selected and output by SQUH and SQUM; SQU is a 2.5V, + -0.25V, + -0.025V square wave of the SQHM and SQUL selection output, where the SQU follows the output via U6B.
A distributed water conductivity detection circuit key module is a program-controlled alternating current precise constant current source circuit and is composed of 1 double-precise operational amplifier chip OPA2277, 1 switch diode BAV199 and a plurality of precise low-temperature drift resistors;
the SQU selects square waves with different amplitudes to be output, the constant current source IOUT outputs driving currents with different magnitudes, and R7, R8, R9, R10, R12, R13, R14 and R15 select 10 ppm/DEG C low-temperature drift and high-precision resistance with the magnitude of 10K omega, or: r12, R13, R14 and R15 adopt accurate resistor network chips matched with temperature characteristics, so that the output working current has extremely low temperature drift characteristics; r11 adopts a resistor of 1K omega; the switching diode D1 carries out overcurrent protection on the circuit, and prevents the damage of the subsequent circuit caused by excessive current.
A distributed water conductivity detection circuit key module is a conductivity measurement electrode selection circuit and consists of 4 single-chip CMOS analog multiplexers ADG5208 and two connectors;
JX and JY are 2 connectors to represent two groups of X and Y conductivity measuring electrodes, XA, XB, XC, XD, XE, YA, YB, YC, YD and YE respectively represent two groups of different electrodes; each electrode is composed of two wires; the 4 single-chip CMOS analog multiplexers are all controlled by 3-bit binary address lines SET8, SET9 and SET10 to output, one of XA, XB, XC, XD, XE, YA, YB, YC, YD and YE8 is selected to be switched to a common output D, and SET11 controls the enabling of a chip; wherein AGND is analog ground, and the power supply voltage is +/-9V, which is the power supply voltage of the analog circuit; the common outputs of U9 and U10 are IOUT and AGND, respectively; u11 and U12 are voltage inputs to which are input terminals VIH and VIL, respectively, of the differential voltage to be measured.
A distributed water conductivity detection circuit key module comprises a conductivity measurement signal acquisition circuit, a data acquisition circuit and a data acquisition circuit, wherein the conductivity measurement signal acquisition circuit consists of 2 displacement buffers 74HC595, 1 programmable instrumentation amplifier AD8253, 1 precision operational amplifier AD8512, 1 RMS-DC converter LTC1968, 1 24bit ADC LTC2400, 1 switch diode BAV199 and a plurality of resistor capacitors;
u13 provides +2.5V reference voltage from VREF, VIH and VIL are input ends for measuring conductivity differential signals, and RMSIN is a measurement signal of an output end to the ground; SET12 and SET13 are 2-bit address lines, and can SET the amplification of output signals to be 1, 10, 100 and 1000 times in a programmable manner; d2 switching the diode between +5V and GND; the signal RMSIN is followed by a resistor R16 and a precision operational amplifier U14A; u15 is RMS-DC converter for true effective value conversion, two input signal channels IN1, IN2, IN2 input reference voltage VREF, U15 output signal ADIN is sent to U16, 24bit ADC collects, ADC reference voltage VREF is provided by reference chip, MSCK, MSDI, ADCS are clock line, data line, chip select line respectively; requiring electrical isolation to exchange information with the microprocessor.
The invention has the following beneficial effects:
firstly, because a method of selecting multiple excitation sources by adopting single fixed frequency division is adopted, different frequencies can be selected to detect the conductivity solutions with different resistance states, and the detection error is reduced.
Secondly, because the method of reference selection transformation is adopted, excitation sources with different amplitudes can be selected to carry out detection in a wide range, and the detection range is expanded.
Thirdly, the method for measuring the reference conversion of the driving current by adopting the conductivity is irrelevant to the power supply voltage, the power supply fluctuation is irrelevant to the reference voltage generated by the reference chip, and the stability is strong.
Fourthly, because the method of current method measurement with adjustable amplitude frequency is adopted, the adjustable amplitude frequency is realized by the combination of analog switches, and the generated drive current for measuring the conductivity is generated by the proportional transformation of the resistance, expensive components are not needed, and the cost is lower.
And fifthly, as the technology of time-sharing detection scanning is adopted, the measured conductivity is automatically switched to ID detection scanning, and data can be sent to the microprocessor in real time, so that the real-time property is strong.
Drawings
FIG. 1 is a general block diagram of a distributed water conductivity detection circuit of the present invention.
Fig. 2 is a schematic diagram of a circuit for program-controlled setting of characteristics of an excitation source in a distributed water conductivity detection circuit according to the present invention.
FIG. 3 is a schematic diagram of a program-controlled alternating-current precise constant current source circuit in the distributed water conductivity detection circuit of the invention.
FIG. 4 is a schematic diagram of a conductivity measurement electrode selection circuit in the distributed water conductivity detection circuit of the present invention.
FIG. 5 is a schematic diagram of a conductivity measurement signal acquisition circuit in the distributed water conductivity detection circuit of the present invention.
Fig. 6 is a schematic diagram of electrode placement of the distributed water conductivity detection circuit of the present invention.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Detailed description of the invention
The following is a specific implementation of the distributed water conductivity detection circuit.
The overall block diagram of the distributed water conductivity detection circuit in the embodiment is shown in fig. 1, and the distributed water conductivity detection circuit is composed of an excitation source characteristic program control setting circuit, a program control alternating current precise constant current source circuit, a conductivity measurement electrode selection circuit and a conductivity measurement signal acquisition circuit;
the excitation source characteristic program control setting circuit is shown in fig. 2, and is composed of 1 active crystal oscillator, 1 double four-bit binary counter SN74LS393, 1 analog switch 74HC4051, 1 analog switch 74HC4053, 2 double precision operational amplifier chips OPA2277, 1 reference chip ADR4525, a plurality of resistors and capacitors;
an active crystal oscillator generates an alternating current signal with a fixed frequency of 32.768kHz, VCC analog voltage is 5V, a double four-bit binary counter divides the frequency to generate CK 0-CK 7, and bits SET0, SET1 and SET2 are controlled by an analog switch U3 to select and output FCLK in a program control mode; the control bit SET3 enables the bit to control the U3 to work; r17 is a common resistor with a size of 1K omega; the U5 reference chip outputs +2.5V reference voltage VREF, and the chip has a bypass capacitor to the ground; VREF is defined as NREF is-2.5V voltage through U6A impedance transformation and filtering, R1 and R2 are proportional resistors, and 10 ppm/DEG C low-temperature drift and high-precision resistors with the size of 10K omega are selected; u4 is an analog switch, and XO, X1, Y0, Y1, Z0 and Z1 outputs are selected by control bits FCLK, SET4 and SET 5; selecting and outputting three gears, namely SUQH, SQUM and SQUL; SQUH selects square wave with output amplitude of +/-2.5V through VREF and NREF; the SUQM is defined by R3, R4 and U7B through impedance transformation and filtering, and R3 and R4 respectively select 10 ppm/DEG C low-temperature drift and high-precision resistance with the sizes of 9K omega and 1K omega; SQUM is square wave of + -0.25V; SQUL obtains square waves of +/-0.025V through low temperature drift of 10 ppm/DEG C and high-precision resistance impedance transformation of R5 and R6 with the size of 9K omega and 1K omega; SQHM is square wave of + -2.5V and + -0.25V directly selected and output by SQUH and SQUM; SQU is the + -2.5V, + -0.25V, + -0.025V square wave of SQHM and SQUL selection output, wherein SQU follows the output through U6B;
the program-controlled alternating-current precise constant current source circuit is shown in fig. 3 and comprises 1 double-precise operational amplifier chip OPA2277, 1 switching diode BAV199 and a plurality of precise low-temperature drift resistors;
the SQU selects square waves with different amplitudes to be output, the constant current source IOUT outputs driving currents with different magnitudes, and R7, R8, R9, R10, R12, R13, R14 and R15 select 10 ppm/DEG C low-temperature drift and high-precision resistance with the magnitude of 10K omega, or: r12, R13, R14 and R15 adopt accurate resistor network chips matched with temperature characteristics, so that the output working current has extremely low temperature drift characteristics; r11 adopts a resistor of 1K omega; the switching diode D1 carries out overcurrent protection on the circuit, and prevents the damage of the subsequent circuit caused by the excessive current;
the conductivity measurement electrode selection circuit is shown in fig. 4 and consists of 4 single-chip CMOS analog multiplexers ADG5208 and two connectors;
JX and JY are 2 connectors to represent two groups of X and Y conductivity measuring electrodes, XA, XB, XC, XD, XE, YA, YB, YC, YD and YE respectively represent two groups of different electrodes; each electrode is composed of two wires; the 4 single-chip CMOS analog multiplexers are all controlled by 3-bit binary address lines SET8, SET9 and SET10 to output, one of XA, XB, XC, XD, XE, YA, YB, YC, YD and YE8 is selected to be switched to a common output D, and SET11 controls the enabling of a chip; wherein AGND is analog ground, and the power supply voltage is +/-9V, which is the power supply voltage of the analog circuit; the common outputs of U9 and U10 are IOUT and AGND, respectively; u11 and U12 are voltage input ends, which are respectively input with two ends VIH and VIL of the differential voltage to be measured;
the conductivity measurement signal acquisition circuit is shown in fig. 5, and the conductivity measurement signal acquisition circuit is composed of 2 displacement buffers 74HC595, 1 programmable instrumentation amplifier AD8253, 1 precision operational amplifier AD8512, 1 RMS-DC converter LTC1968, 1 24bit adc LTC2400, 1 switching diode BAV199 and a plurality of resistor capacitors;
u13 provides +2.5V reference voltage from VREF, VIH and VIL are input ends for measuring conductivity differential signals, and RMSIN is a measurement signal of an output end to the ground; SET12 and SET13 are 2-bit address lines, and can SET the amplification of output signals to be 1, 10, 100 and 1000 times in a programmable manner; d2 switching the diode between +5V and GND; the signal RMSIN is followed by a resistor R16 and a precision operational amplifier U14A; u15 is RMS-DC converter for true effective value conversion, two input signal channels IN1, IN2, IN2 input reference voltage VREF, U15 output signal ADIN is sent to U16, 24bit ADC collects, ADC reference voltage VREF is provided by reference chip, MSCK, MSDI, ADCS are clock line, data line, chip select line respectively; requiring electrical isolation to exchange information with the microprocessor.
Fig. 6 shows a schematic diagram of a distributed water conductivity detection circuit in this embodiment, which is installed when detecting the water conductivity. X groups of measuring electrodes and Y groups of measuring electrodes are arranged in the conductance cell, each group of electrodes respectively comprises XA, XB, XC, XD, XE, YA, YB, YC, YD and YE, 5 measuring electrodes are arranged in the conductance cell in parallel at different spatial positions, the electrodes belonging to the same group are arranged at different depths of the conductance cell, the comparison consistency of measured conductivity parameters is ensured, and the spatial distribution characteristics of the electric ions in the conductance cell are more scientifically and accurately reflected.
The invention uses ARM as microprocessor, the interface resource is limited, there are not many peripherals in the circuit, and the analog switch is used in the circuit, so the invention cascades 2 displacement buffers to expand output. Saves the interface of the microprocessor, can adapt to different microprocessor systems, and is suitable for measuring the conductivity in different occasions
According to the principle of conductivity measurement, the measurement accuracy is mainly related to the accuracy of true effective value conversion, the maximum conversion error is not more than 1%, so the error of not more than 2% is theoretically consistent with the invention. The temperature drift additional error is related to the applied electromotive force of the solution in the conductivity cell and the measured working current. The proportional resistors of the invention all use 10 ppm/DEG C low temperature drift and high precision resistors. The double-precision operational amplifier chip is selected, the temperature drift of the reference chip is also very small, and therefore the total temperature drift coefficient is theoretically small.
The signal transmission process is as follows:
through the introduction of the hardware circuit, the following describes the approximate transmission process of signals, U3 selects square wave frequency to generate signal FCLK, U4 selects three gears of SUQH, SQUM and SQUL for square wave amplitude, selects measuring electrode after selecting proper square wave frequency and amplitude according to the impedance of measuring solution, then generates electric conductivity measuring working current IOUT to obtain electric conductivity measuring differential signals VIH and VIL, the differential signals are amplified by U13 program control, the U15 true effective value is converted, and the signals are transmitted to U1624bit ADC for collection and transmission to microprocessor and displayed on the touch screen by program control.
The temperature compensation coefficient calibration process is as follows:
after the software and hardware functions of the detection circuit are debugged, a problem needs to be noticed, and three factors which have great influence on the conductivity measurement result include a polarization effect, a capacitance effect and temperature. The first two influencing factors are improved by a hardware circuit method, and the temperature is corrected by software.
Under the existing standard, the conductivity measurement is carried out at 25 ℃ as a reference, solutions at different temperatures are required to be converted into standard temperatures, temperature compensation coefficients are determined according to different requirements of actual measurement conditions to correct measurement results, and a formula for solving the temperature compensation coefficients is shown as follows;
K1＝K0[1+1(T1-25)+2(T1-25)2]
T1wherein is the temperature, K1Is the conductivity of the solution at temperature, K0Is the conductivity of the solution at a temperature of 25 c,1and2two temperature compensation coefficients. When the conductivity solution is measured, the algorithm process is started, the temperature is compensated, and the conductivity of the measured solution is obtained through recalculation.
The conductivity detection method and the detection circuit can scientifically and accurately detect the conductivity of daily domestic water and industrial water of residents and different resistance state solutions.
Detailed description of the invention
The following is a specific embodiment of the stimulus characteristic programmed setting circuit.
The excitation source characteristic program control setting circuit in the embodiment can be implemented independently and can be applied to a distributed water conductivity detection circuit. The excitation source characteristic program control setting circuit is shown in fig. 2 and comprises 1 active crystal oscillator, 1 double four-bit binary counter SN74LS393, 1 analog switch 74HC4051, 1 analog switch 74HC4053, 2 double precision operational amplifier chips OPA2277, 1 reference chip ADR4525, a plurality of resistors and capacitors;
an active crystal oscillator generates an alternating current signal with a fixed frequency of 32.768kHz, VCC analog voltage is 5V, a double four-bit binary counter divides the frequency to generate CK 0-CK 7, and bits SET0, SET1 and SET2 are controlled by an analog switch U3 to select and output FCLK in a program control mode; the control bit SET3 enables the bit to control the U3 to work; r17 is a common resistor with a size of 1K omega; the U5 reference chip outputs +2.5V reference voltage VREF, and the chip has a bypass capacitor to the ground; VREF is defined as NREF is-2.5V voltage through U6A impedance transformation and filtering, R1 and R2 are proportional resistors, and 10 ppm/DEG C low-temperature drift and high-precision resistors with the size of 10K omega are selected; u4 is an analog switch, and XO, X1, Y0, Y1, Z0 and Z1 outputs are selected by control bits FCLK, SET4 and SET 5; selecting and outputting three gears, namely SUQH, SQUM and SQUL; SQUH selects square wave with output amplitude of +/-2.5V through VREF and NREF; the SUQM is defined by R3, R4 and U7B through impedance transformation and filtering, and R3 and R4 respectively select 10 ppm/DEG C low-temperature drift and high-precision resistance with the sizes of 9K omega and 1K omega; SQUM is square wave of + -0.25V; SQUL obtains square waves of +/-0.025V through low temperature drift of 10 ppm/DEG C and high-precision resistance impedance transformation of R5 and R6 with the size of 9K omega and 1K omega; SQHM is square wave of + -2.5V and + -0.25V directly selected and output by SQUH and SQUM; SQU is a 2.5V, + -0.25V, + -0.025V square wave of the SQHM and SQUL selection output, where the SQU follows the output via U6B.
Detailed description of the invention
The following is a specific implementation of the program-controlled ac precision constant current source circuit.
The program-controlled alternating-current precise constant-current source circuit in the embodiment can be implemented independently and can also be applied to a distributed water conductivity detection circuit. The program-controlled alternating-current precise constant current source circuit is shown in fig. 3 and comprises 1 double-precise operational amplifier chip OPA2277, 1 switching diode BAV199 and a plurality of precise low-temperature drift resistors;
the SQU selects square waves with different amplitudes to be output, the constant current source IOUT outputs driving currents with different magnitudes, and R7, R8, R9, R10, R12, R13, R14 and R15 select 10 ppm/DEG C low-temperature drift and high-precision resistance with the magnitude of 10K omega, or: r12, R13, R14 and R15 adopt accurate resistor network chips matched with temperature characteristics, so that the output working current has extremely low temperature drift characteristics; r11 adopts a resistor of 1K omega; the switching diode D1 carries out overcurrent protection on the circuit, and prevents the damage of the subsequent circuit caused by excessive current.
Detailed description of the invention
The following is a specific embodiment of the conductivity measurement electrode selection circuit.
The conductivity measurement electrode selection circuit in the embodiment can be implemented independently and can be applied to a distributed water conductivity detection circuit. The conductivity measurement electrode selection circuit is shown in fig. 4 and is composed of 4 single-chip CMOS analog multiplexers ADG5208 and two connectors;
JX and JY are 2 connectors to represent two groups of X and Y conductivity measuring electrodes, XA, XB, XC, XD, XE, YA, YB, YC, YD and YE respectively represent two groups of different electrodes; each electrode is composed of two wires; the 4 single-chip CMOS analog multiplexers are all controlled by 3-bit binary address lines SET8, SET9 and SET10 to output, one of XA, XB, XC, XD, XE, YA, YB, YC, YD and YE8 is selected to be switched to a common output D, and SET11 controls the enabling of a chip; wherein AGND is analog ground, and the power supply voltage is +/-9V, which is the power supply voltage of the analog circuit; the common outputs of U9 and U10 are IOUT and AGND, respectively; u11 and U12 are voltage inputs to which are input terminals VIH and VIL, respectively, of the differential voltage to be measured.
Detailed description of the invention
The following are specific embodiments of the conductivity measurement signal acquisition circuit.
The conductivity measurement signal acquisition circuit in the embodiment can be implemented independently and can be applied to a distributed water conductivity detection circuit. The conductivity measurement signal acquisition circuit is shown in fig. 5 and comprises 2 displacement buffers 74HC595, 1 programmable instrumentation amplifier AD8253, 1 precision operational amplifier AD8512, 1 RMS-DC converter LTC1968, 1 24bit adc LTC2400, 1 switching diode BAV199 and a plurality of resistance capacitors;
u13 provides +2.5V reference voltage from VREF, VIH and VIL are input ends for measuring conductivity differential signals, and RMSIN is a measurement signal of an output end to the ground; SET12 and SET13 are 2-bit address lines, and can SET the amplification of output signals to be 1, 10, 100 and 1000 times in a programmable manner; d2 switching the diode between +5V and GND; the signal RMSIN is followed by a resistor R16 and a precision operational amplifier U14A; u15 is RMS-DC converter for true effective value conversion, two input signal channels IN1, IN2, IN2 input reference voltage VREF, U15 output signal ADIN is sent to U16, 24bit ADC collects, ADC reference voltage VREF is provided by reference chip, MSCK, MSDI, ADCS are clock line, data line, chip select line respectively; requiring electrical isolation to exchange information with the microprocessor.
It should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A distributed water conductivity detection circuit is characterized by comprising an excitation source characteristic program control setting circuit, a program control alternating current precise constant current source circuit, a conductivity measurement electrode selection circuit and a conductivity measurement signal acquisition circuit;
the excitation source characteristic program control setting circuit is composed of 1 active crystal oscillator, 1 double four-bit binary counter SN74LS393, 1 analog switch 74HC4051, 1 analog switch 74HC4053, 2 double precision operational amplifier chips OPA2277, 1 reference chip ADR4525, a plurality of resistors and capacitors;
an active crystal oscillator generates an alternating current signal with a fixed frequency of 32.768kHz, VCC analog voltage is 5V, a double four-bit binary counter divides the frequency to generate CK 0-CK 7, and bits SET0, SET1 and SET2 are controlled by an analog switch U3 to select and output FCLK in a program control mode; the control bit SET3 enables the bit to control the U3 to work; r17 is a common resistor with a size of 1K omega; the U5 reference chip outputs +2.5V reference voltage VREF, and the chip has a bypass capacitor to the ground; VREF is defined as NREF is-2.5V voltage through U6A impedance transformation and filtering, R1 and R2 are proportional resistors, and 10 ppm/DEG C low-temperature drift and high-precision resistors with the size of 10K omega are selected; u4 is an analog switch, and XO, X1, Y0, Y1, Z0 and Z1 outputs are selected by control bits FCLK, SET4 and SET 5; selecting and outputting three gears, namely SUQH, SQUM and SQUL; SQUH selects square wave with output amplitude of +/-2.5V through VREF and NREF; the SUQM is defined by R3, R4 and U7B through impedance transformation and filtering, and R3 and R4 respectively select 10 ppm/DEG C low-temperature drift and high-precision resistance with the sizes of 9K omega and 1K omega; SQUM is square wave of + -0.25V; SQUL obtains square waves of +/-0.025V through low temperature drift of 10 ppm/DEG C and high-precision resistance impedance transformation of R5 and R6 with the size of 9K omega and 1K omega; SQHM is square wave of + -2.5V and + -0.25V directly selected and output by SQUH and SQUM; SQU is the + -2.5V, + -0.25V, + -0.025V square wave of SQHM and SQUL selection output, wherein SQU follows the output through U6B;
the program-controlled alternating-current precise constant current source circuit is composed of 1 double-precise operational amplifier chip OPA2277, 1 switching diode BAV199 and a plurality of precise low-temperature drift resistors;
the SQU selects square waves with different amplitudes to be output, the constant current source IOUT outputs driving currents with different magnitudes, and R7, R8, R9, R10, R12, R13, R14 and R15 select 10 ppm/DEG C low-temperature drift and high-precision resistance with the magnitude of 10K omega, or: r12, R13, R14 and R15 adopt accurate resistor network chips matched with temperature characteristics, so that the output working current has extremely low temperature drift characteristics; r11 adopts a resistor of 1K omega; the switching diode D1 carries out overcurrent protection on the circuit, and prevents the damage of the subsequent circuit caused by the excessive current;
the conductivity measurement electrode selection circuit consists of 4 single-chip CMOS analog multiplexers ADG5208 and two connectors;
JX and JY are 2 connectors to represent two groups of X and Y conductivity measuring electrodes, XA, XB, XC, XD, XE, YA, YB, YC, YD and YE respectively represent two groups of different electrodes; each electrode is composed of two wires; the 4 single-chip CMOS analog multiplexers are all controlled by 3-bit binary address lines SET8, SET9 and SET10 to output, one of XA, XB, XC, XD, XE, YA, YB, YC, YD and YE8 is selected to be switched to a common output D, and SET11 controls the enabling of a chip; wherein AGND is analog ground, and the power supply voltage is +/-9V, which is the power supply voltage of the analog circuit; the common outputs of U9 and U10 are IOUT and AGND, respectively; u11 and U12 are voltage input ends, which are respectively input with two ends VIH and VIL of the differential voltage to be measured;
the conductivity measurement signal acquisition circuit consists of 2 displacement buffers 74HC595, 1 programmable and programmable instrument amplifier AD8253, 1 precision operational amplifier AD8512, 1 RMS-DC converter LTC1968, 1 24bit ADC LTC2400, 1 switch diode BAV199 and a plurality of resistance capacitors;
u13 provides +2.5V reference voltage from VREF, VIH and VIL are input ends for measuring conductivity differential signals, and RMSIN is a measurement signal of an output end to the ground; SET12 and SET13 are 2-bit address lines, and can SET the amplification of output signals to be 1, 10, 100 and 1000 times in a programmable manner; d2 switching the diode between +5V and GND; the signal RMSIN is followed by a resistor R16 and a precision operational amplifier U14A; u15 is RMS-DC converter for true effective value conversion, two input signal channels IN1, IN2, IN2 input reference voltage VREF, U15 output signal ADIN is sent to U16, 24bit ADC collects, ADC reference voltage VREF is provided by reference chip, MSCK, MSDI, ADCS are clock line, data line, chip select line respectively; requiring electrical isolation to exchange information with the microprocessor.
2. A distributed water conductivity detection circuit key module is characterized in that a circuit is set for program control of excitation source characteristics, and the circuit is composed of 1 active crystal oscillator, 1 double four-bit binary counter SN74LS393, 1 analog switch 74HC4051, 1 analog switch 74HC4053, 2 double precision operational amplifier chips OPA2277, 1 reference chip ADR4525, a plurality of resistors and capacitors;
an active crystal oscillator generates an alternating current signal with a fixed frequency of 32.768kHz, VCC analog voltage is 5V, a double four-bit binary counter divides the frequency to generate CK 0-CK 7, and bits SET0, SET1 and SET2 are controlled by an analog switch U3 to select and output FCLK in a program control mode; the control bit SET3 enables the bit to control the U3 to work; r17 is a common resistor with a size of 1K omega; the U5 reference chip outputs +2.5V reference voltage VREF, and the chip has a bypass capacitor to the ground; VREF is defined as NREF is-2.5V voltage through U6A impedance transformation and filtering, R1 and R2 are proportional resistors, and 10 ppm/DEG C low-temperature drift and high-precision resistors with the size of 10K omega are selected; u4 is an analog switch, and XO, X1, Y0, Y1, Z0 and Z1 outputs are selected by control bits FCLK, SET4 and SET 5; selecting and outputting three gears, namely SUQH, SQUM and SQUL; SQUH selects square wave with output amplitude of +/-2.5V through VREF and NREF; the SUQM is defined by R3, R4 and U7B through impedance transformation and filtering, and R3 and R4 respectively select 10 ppm/DEG C low-temperature drift and high-precision resistance with the sizes of 9K omega and 1K omega; SQUM is square wave of + -0.25V; SQUL obtains square waves of +/-0.025V through low temperature drift of 10 ppm/DEG C and high-precision resistance impedance transformation of R5 and R6 with the size of 9K omega and 1K omega; SQHM is square wave of + -2.5V and + -0.25V directly selected and output by SQUH and SQUM; SQU is a 2.5V, + -0.25V, + -0.025V square wave of the SQHM and SQUL selection output, where the SQU follows the output via U6B.
3. A distributed water conductivity detection circuit key module is characterized in that the module is a program-controlled alternating-current precise constant-current source circuit and comprises 1 double-precise operational amplifier chip OPA2277, 1 switch diode BAV199 and a plurality of precise low-temperature drift resistors;
the SQU selects square waves with different amplitudes to be output, the constant current source IOUT outputs driving currents with different magnitudes, and R7, R8, R9, R10, R12, R13, R14 and R15 select 10 ppm/DEG C low-temperature drift and high-precision resistance with the magnitude of 10K omega, or: r12, R13, R14 and R15 adopt accurate resistor network chips matched with temperature characteristics, so that the output working current has extremely low temperature drift characteristics; r11 adopts a resistor of 1K omega; the switching diode D1 carries out overcurrent protection on the circuit, and prevents the damage of the subsequent circuit caused by excessive current.
4. A distributed water conductivity detection circuit key module is characterized in that the module is a conductivity measurement electrode selection circuit and consists of 4 single-chip CMOS analog multiplexers ADG5208 and two connectors;
JX and JY are 2 connectors to represent two groups of X and Y conductivity measuring electrodes, XA, XB, XC, XD, XE, YA, YB, YC, YD and YE respectively represent two groups of different electrodes; each electrode is composed of two wires; the 4 single-chip CMOS analog multiplexers are all controlled by 3-bit binary address lines SET8, SET9 and SET10 to output, one of XA, XB, XC, XD, XE, YA, YB, YC, YD and YE8 is selected to be switched to a common output D, and SET11 controls the enabling of a chip; wherein AGND is analog ground, and the power supply voltage is +/-9V, which is the power supply voltage of the analog circuit; the common outputs of U9 and U10 are IOUT and AGND, respectively; u11 and U12 are voltage inputs to which are input terminals VIH and VIL, respectively, of the differential voltage to be measured.
5. A distributed water conductivity detection circuit key module is characterized in that a conductivity measurement signal acquisition circuit consists of 2 displacement buffers 74HC595, 1 programmable and programmable instrument amplifier AD8253, 1 precision operational amplifier AD8512, 1 RMS-DC converter LTC1968, 1 24bit ADC LTC2400, 1 switch diode BAV199 and a plurality of resistance capacitors;
u13 provides +2.5V reference voltage from VREF, VIH and VIL are input ends for measuring conductivity differential signals, and RMSIN is a measurement signal of an output end to the ground; SET12 and SET13 are 2-bit address lines, and can SET the amplification of output signals to be 1, 10, 100 and 1000 times in a programmable manner; d2 switching the diode between +5V and GND; the signal RMSIN is followed by a resistor R16 and a precision operational amplifier U14A; u15 is RMS-DC converter for true effective value conversion, two input signal channels IN1, IN2, IN2 input reference voltage VREF, U15 output signal ADIN is sent to U16, 24bit ADC collects, ADC reference voltage VREF is provided by reference chip, MSCK, MSDI, ADCS are clock line, data line, chip select line respectively; requiring electrical isolation to exchange information with the microprocessor.
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