CN109187657B - Water conductivity detection system and detection method - Google Patents
Water conductivity detection system and detection method Download PDFInfo
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- CN109187657B CN109187657B CN201811227574.7A CN201811227574A CN109187657B CN 109187657 B CN109187657 B CN 109187657B CN 201811227574 A CN201811227574 A CN 201811227574A CN 109187657 B CN109187657 B CN 109187657B
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Abstract
The invention discloses a water conductivity detection system and a detection method, which comprises a main control module, an impedance conversion module, a temperature detection module and a conductivity detection module, wherein the impedance conversion module is used for realizing automatic identification and switching of a conductivity detection range, the detection range is always kept to work in an ideal linear region, and the accuracy of water conductivity detection is improved; a temperature detection module is added, the temperature value detected by the temperature detection module is fused with the measurement amplitude of the conductivity measurement module, so that the automatic compensation of the conductivity measurement result in the variable temperature environment is realized, and the accuracy of the water quality conductivity measurement result is further improved; the power isolation module and the communication isolation module are used for isolating the peripheral circuit, so that the interference of the peripheral circuit on measurement is reduced, and the accuracy and stability of water conductivity measurement in a severe water environment are improved.
Description
Technical Field
The invention relates to the technical field of water quality monitoring, in particular to a water quality conductivity detection system and a detection method.
Background
The conductivity gamma is an electrical physical quantity for evaluating the conductivity performance of water quality, and is the reciprocal of resistivity rho, namely: γ is 1/ρ. In the field of water quality monitoring, the conductivity of water quality is an important index for measuring water quality, for example, measuring the conductivity of drinking water can reflect the concentration of electrolyte in outlet water, measuring the conductivity of underground water can reflect the pollution degree of the outlet water, and the like. Therefore, the accuracy and precision of water conductivity detection is very important. The measured temperature of the water conductivity is usually 25 degrees, and in actual measurement, the temperature of the water body to be measured usually changes, and the conductivity detection result changes along with the change of the temperature, so that the accuracy of the conductivity detection result is very critical to temperature correction.
Disclosure of Invention
The invention aims to provide a water conductivity detection system and a detection method, which aim to improve the detection precision of the existing water conductivity detection system.
In order to achieve the above object, the present invention provides a water conductivity detection system, which includes a main control module, an impedance conversion module, a temperature detection module and a conductivity detection module, wherein calibration coefficients of the conductivity detection module under different detection ranges are stored in the main control module, the impedance conversion module switches the detection range of the conductivity detection module to enable the conductivity detection module to detect the conductivity of a water body under an optimal detection range, and the main control module obtains the conductivity of the water body under a standard temperature according to a measurement amplitude of the conductivity detection module under the optimal detection range, the calibration coefficient corresponding to the optimal detection range and a temperature value detected by the temperature detection module.
Optionally, the calibration coefficient includes a gain coefficient GFxSystematic coefficient of misadjustment NosxAnd a conductivity correction factor CxObtaining the conductivity gamma' of the water body at the standard temperature according to the following formula:
γ＝(Nx-Nosx)×GFx
wherein N isxIs the measured amplitude of the conductivity detection module; t is a temperature value detected by the temperature detection module; gamma is measured conductivity; K. beta is the electrode coefficient and the conductance temperature constant of the conductivity detection module respectively.
Optionally, the water quality and conductivity detection system further comprises a communication isolation module and a power isolation module, the communication isolation module is located between an upper computer and the main control module and conducts communication isolation, and the power isolation module isolates voltage provided by a power conversion module and converts the voltage into working voltage to supply power to the main control module, the impedance conversion module, the temperature detection module, the conductivity detection module and the communication isolation module.
Optionally, the power conversion module includes a first-stage conversion circuit and a second-stage conversion circuit, the power isolation module includes a first-stage isolation module and a second-stage isolation module, the first-stage conversion circuit converts a direct-current voltage into a first voltage signal and a second voltage signal respectively with the second-stage conversion circuit, the first-stage isolation module converts the first voltage signal and the second voltage signal into a first isolation signal and a second isolation signal respectively with the second-stage isolation module.
Optionally, the impedance conversion module includes an impedance channel selection circuit and an amplification comparison circuit, and the impedance channel selection circuit is configured to switch the calibration access resistor and the measurement access channel, and input the impedance measurement signal of the conductivity detection module into the main control module through the amplification comparison circuit.
The invention also provides a water conductivity detection method, which comprises the following steps:
s1: providing the water quality and conductivity detection system;
s2: the main control module enters a calibration mode after receiving a calibration instruction, the impedance conversion module selects an impedance channel to switch a calibration access resistor under each measurement range, the resistance value of the calibration access resistor corresponds to the detection measurement range of the conductivity detection module, and the main control module obtains and stores the calibration coefficient of the conductivity detection module under each detection measurement range according to the measurement amplitude of the conductivity detection module under each detection range;
s3: the main control module enters a data acquisition mode after receiving a data acquisition instruction, the conductivity detection module detects the conductivity of the water body from small to large in the detection range until the measurement amplitude of the conductivity detection module does not overflow, and the detection range at the moment is used as the optimal detection range;
s4: the temperature detection module detects the temperature of the water body;
s5: the main control module obtains the conductivity of the water body at the standard temperature according to the measurement amplitude of the conductivity detection module at the optimal detection range, the calibration coefficient corresponding to the optimal detection range and the temperature value detected by the temperature detection module.
Optionally, the impedance conversion module includes an impedance channel selection circuit and an amplification comparison circuit, and the step of the main control module obtaining the calibration coefficient of the conductivity detection module under each detection range according to the measurement amplitude of the conductivity detection module under each detection range includes:
s21: the resistance value of the impedance channel selection circuit is R11The calibration access resistor is connected into a feedback channel of the amplifying and comparing circuit, and the resistance value is R21The calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YL1Measured amplitude of time NL1(ii) a Continuously setting the resistance value to R22The calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YH1Measured amplitude of time NH1To obtain the minimum detection range Q1The calibration coefficient of (a);
s22: will have a resistance value of R1xThe calibration access resistor is connected into a feedback channel of the amplifying and comparing circuit, and the resistance value is R2xThe calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YLxMeasured amplitude of time NLx(ii) a Continuously setting the resistance value to R2(x+1)The calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YH1Measured amplitude of time NH1To obtain the detection range QxThe calibration coefficient of (a);
s23: let x be (x +1) and execute step S22 until the calibration coefficients of all the detection ranges Q are acquired.
Optionally, the calibration coefficient includes a gain coefficient GFxSystematic coefficient of misadjustment NosxAnd a conductivity correction factor CxAnd, obtaining a calibration coefficient for each of the detection ranges by the following formula:
Nosx＝Nx-YHx/GFx；
optionally, resistance R1xAnd resistance value R2xEqual and resistance R1xAnd resistance value R2xBoth increase with increasing x.
Optionally, the precision of each calibrated access resistor is greater than or equal to one thousandth.
The invention has the following beneficial effects:
(1) the impedance conversion module is used for realizing automatic identification and switching of the detection range of the conductivity detection module, so that the detection range is always kept to work in an ideal linear region, and the accuracy of water quality conductivity detection is improved;
(2) a temperature detection module is added, the temperature value detected by the temperature detection module is fused with the measurement amplitude of the conductivity measurement module, so that the automatic compensation of the conductivity measurement result in the variable temperature environment is realized, and the accuracy of the water quality conductivity measurement result is further improved;
(3) a peripheral circuit is isolated through the power isolation module and the communication isolation module, so that the interference of the peripheral circuit on measurement is reduced, and the accuracy and stability of water conductivity measurement in a severe water environment are improved;
(4) the whole system adopts dual power supplies to supply power, and the distortion of water conductivity measurement and temperature measurement is reduced to the maximum extent.
Drawings
Fig. 1 is a schematic structural diagram of a water conductivity detection system according to an embodiment of the present invention;
fig. 2 is a schematic circuit diagram of a main control module and an impedance conversion module according to an embodiment of the present invention;
FIG. 3 is a schematic circuit diagram of a temperature detection module according to an embodiment of the present invention;
FIG. 4 is a schematic circuit diagram of a power isolation module according to an embodiment of the present invention;
fig. 5 is a schematic circuit diagram of a communication isolation module according to an embodiment of the present invention;
FIG. 6 is a flow chart of a water conductivity detection method according to an embodiment of the present invention;
FIG. 7 is a flowchart of a calibration mode provided by an embodiment of the present invention;
fig. 8 is a flowchart of a data collection mode according to an embodiment of the present invention.
Detailed Description
The following describes in more detail embodiments of the present invention with reference to the schematic drawings. Advantages and features of the present invention will become apparent from the following description and claims. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
Please refer to fig. 1, which is a schematic structural diagram of a water conductivity detection system provided in this embodiment, as shown in fig. 1, the water conductivity detection system comprises a main control module 1, an impedance conversion module 2, a temperature detection module 4 and a conductivity detection module 3, the main control module 1 stores calibration coefficients of the conductivity detection module 3 under different detection ranges, the impedance conversion module 2 switches the detection range of the conductivity detection module 3 so that the conductivity detection module 3 detects the conductivity of a water body under the optimal detection range, and the main control module 1 obtains the conductivity of the water body at the standard temperature according to the measurement amplitude of the conductivity detection module 3 at the optimal detection range, the calibration coefficient corresponding to the optimal detection range and the temperature value detected by the temperature detection module 4.
Specifically, as shown in fig. 2, the main control module 1 may include a microprocessor 11, a reference power supply 12 (for example, a TL431 chip), a reset circuit 13 (for example, a MAX809SD chip), a system clock, and the like, and the main control module 1 may perform communication and signal conversion with the upper computer 7 to implement mode switching of startup, standby, calibration, detection, and uploading of the water quality and conductivity detection system, for example, a startup command is sent to the microprocessor 11 by the upper computer 7, and the microprocessor 11 is awakened from a standby sleep mode to a working mode; the standby command is sent to the microprocessor 11 by the upper computer 7, and the microprocessor enters a low-power-consumption standby sleep mode from a working mode; the calibration instruction is sent to the microprocessor 11 by the upper computer 7, the microprocessor 11 executes a calibration mode, and controls the impedance conversion module 2 to complete gain coefficient calculation, system offset coefficient calculation, conductance correction coefficient calculation and data storage of each detection range; a data acquisition instruction is sent to the microprocessor 11 by the upper computer 7, and after the microprocessor 11 enters a data acquisition mode, the conductivity detection module 3 and the temperature acquisition module 4 are respectively controlled to complete the acquisition of the conductivity and the temperature of the water body, and complete the conductivity compensation correction calculation and result output; in the data uploading mode, the microprocessor 11 uploads the measurement result (measured conductivity, temperature value, conductivity at standard temperature) to the upper computer 7. In this embodiment, the microprocessor 11 uses an STM32F407VET6 chip.
Further, the impedance conversion module 2 mainly includes an impedance channel selection circuit 21 and an amplification comparison circuit 22, and the impedance conversion module 2 is connected to the microprocessor 11 through an excitation amplification circuit 23, and the impedance channel selection circuit 21 is configured to switch a calibration access resistor and a measurement access channel, and input a measurement signal of the conductivity detection module 3 into the microprocessor 11 through the amplification comparison circuit 22. In this embodiment, the impedance conversion module 2 selectively accesses 3 calibration access resistors with a precision greater than or equal to 1% to the reverse input channel and 2 calibration access resistors with a precision greater than or equal to 1% to the feedback channel, and obtains 2 sets of calibration coefficients under the detection range respectively.
Specifically, as shown in fig. 2, the impedance channel selection circuit 21 employs an ADG715 chip (U2), the amplification comparison circuit 22 is composed of a reverse comparator (U5B), the excitation amplification circuit 23 is composed of an amplifier (U5A), the 33 rd pin of the microprocessor 11 generates an excitation signal to the 3 rd pin of the U5A chip, and the excitation signal is amplified by the U5A chip and then output to the 12 th pin, the 13 th pin, the 15 th pin, the 17 th pin and the 19 th pin of the ADG715 chip through the 1 st pin, and the ADG715 chip implements 3-way calibration access resistors (R11-R13, R14-R16, where R13 is a reserved calibration access resistor) access selection and measurement access channel access selection; the measurement signal of the conductivity detection module 3 is output to the 61 st pin of the microprocessor 11 through the 7 th pin after being selected by the impedance channel and reversely amplified by the U5B chip, the microprocessor 11 completes the analysis and calculation of the access impedance characteristic by using the on-chip DSP, and the calculation result can be output to the upper computer 7. Under a data acquisition mode, a 65 th pin and a 66 th pin of a microprocessor 11 send acquisition commands to a 1 st pin and a 3 rd pin of an ADG715 chip, the 20 th pin and a 19 th pin of the ADG715 chip are controlled to be conducted, the 6 th pin is sequentially conducted with the 5 th pin, the 61 st pin of the microprocessor 11 outputs a sine excitation signal to the 3 rd pin of a U5A chip, the U5A chip amplifies the sine signal 1:1, the output voltage of the 1 st pin of the U5A chip always follows the 3 rd pin of the U5A chip, and conductivity detection in a uS-mS detection range is completed (the resistance values of R11-R13 are respectively 100 omega, 1K omega and 10K omega, and the resistance values of R14-R16 are respectively 100 omega, 1K and 10K omega); if the detection result (measurement amplitude) exceeds the range, the microprocessor 11 continues to send a data acquisition command to the ADG715 chip, controls the conduction of the 1 st pin and the 3 rd pin, the conduction of the 20 th pin and the 19 th pin, and the conduction of the 6 th pin and the 7 th pin of the ADG715 chip, obtains the detection result (measurement amplitude) in the detection range from mS to S, and completes the switching of the detection range. It can be understood that in this embodiment, the conductivity detection module 3 only sets two detection ranges of uS to mS, mS to S, and sets the number and the resistance value of the calibration access resistor accordingly, but actually, the conductivity detection module 3 may also have more than two detection ranges, and may set the number and the resistance value of the calibration access resistor through a corresponding conversion formula, which is not illustrated here.
As shown in fig. 3, the temperature detecting module 4 and the conductivity detecting module 3 are respectively used for detecting the temperature and the conductivity of the water body, in this embodiment, the temperature detection module 4 comprises a temperature sensor 41, a signal amplification circuit 42 and a voltage following circuit 43, the temperature sensor 41 directly contacts with the water body to detect the temperature of the water body, and outputs a tiny voltage analog signal, which is amplified in phase by the signal amplifying circuit 42 and output to the voltage follower circuit 43, the 2 nd pin of the reverse input end of the U3A chip in the voltage follower circuit 43 is directly connected with the 1 st pin of the output end to form a voltage follower, so that the output voltage always follows the voltage of the non-inverting input terminal, the output voltage signal of the 1 st pin of the U3A chip is connected with the 97 th pin of the microprocessor 11, so as to input the measurement information to the microprocessor 11, and the microprocessor 11 converts the temperature analog quantity value into an actual measurement temperature value through on-chip high-precision AD conversion. When the conductivity of the water body needs to be acquired, the microprocessor 11 generates a sinusoidal signal with fixed frequency, the sinusoidal signal is amplified by the excitation amplification module 23 and then applied to one end of the electrode of the conductivity detection module 3, so that the water body between the two electrodes of the conductivity detection module 3 generates an alternating electric field, the impedance conversion module 2 acquires a current signal from the other end of the electrode of the conductivity detection module 3, and the current signal is further converted into voltage and amplified and transmitted to the microprocessor 11; the microprocessor 11 completes the impedance analysis and calculation, and the calculation result is transmitted to the communication conversion module 8 through the communication isolation module 51 and then transmitted to the upper computer 7. Optionally, the temperature sensor 6 is an LM35DZ sensor, the signal amplification circuit 42 is an AD623 chip for a U1 chip, and the voltage follower circuit 43 is an OP07 chip for a U3A chip.
Further, as shown in fig. 4 and 5, the water quality and conductivity detection system further includes a communication isolation module 51 and a power isolation module 52, the communication isolation module 51 is located between the upper computer 7 and the main control module 1 and performs communication isolation, and the power isolation module 52 isolates a voltage provided by the power conversion module 6 and converts the voltage into a working voltage to supply power to the main control module 1, the impedance conversion module 2, the temperature detection module 4, the conductivity detection module 3, and the communication isolation module 51.
Specifically, as shown in fig. 4, the power conversion module 6 includes a first-stage conversion circuit 61 and a second-stage conversion circuit 62, and is configured to convert a dc voltage within a range of 5 to 36V into a first voltage signal and a second voltage signal, in this embodiment, the first voltage signal is 5V, the second voltage signal is 3.3V, and the power isolation module 52 includes a first-stage isolation module 522 and a second-stage isolation module 521, and is configured to convert the second voltage signal of 3.3V into a first isolation signal of 3.3V and a second isolation signal of 3.3V. As shown in fig. 4, in the present embodiment, the dc power supply is configured to generate a dc voltage within a range of 5 to 36V, an anode of the dc power supply is connected to a 7 th pin of a U1 chip in the primary conversion circuit 61, a cathode of the power supply is connected to a pin marked by an electrical symbol GND in fig. 4, a 16 th pin of a U4 chip in the primary isolation module 522 outputs an isolation voltage of 3.3V, a 1 st pin of a U3 chip in the secondary isolation module 521 outputs an isolation voltage of-3.3V, and supplies power to the impedance conversion module 2, the temperature detection module 4, the microprocessor 11 and the communication isolation module 51, for example, the microprocessor 11 needs a working voltage of 3.3V to provide an isolation voltage of 3.3V for the microprocessor 11, and the temperature detection module 4 needs a working voltage of 5V to provide an isolation voltage of 5V for the temperature detection module 4, which is not limited thereto.
The power conversion module 6 has the characteristics of small instability voltage and small ripple voltage, and the power isolation module 52 has excellent isolation performance, so that the impedance analysis precision is improved to the maximum extent. Optionally, a chip U1 in the power conversion module 6 is a TPS5430 chip, a chip U2 in the power conversion module 6 is an ASM1117-3.3 chip, a chip U3 in the power isolation module 52 is a TPS60400DBVT chip, and a chip U4 in the power isolation module 52 is an ADuM5000 chip.
Next, as shown in fig. 5, the communication isolation module 51 includes a magnetic communication isolation chip (U1), and the signal output by the microprocessor 11 is isolated and output to a communication conversion module 8 through the communication isolation module 51 and is transmitted to the upper computer 7. In the circuit for connecting the communication isolation module 51 with the upper computer 7, the 16 th pin of the magnetic communication isolation chip is connected with the 2 nd pin of the U2 chip in the power conversion circuit 6, and the 5 th pin and the 6 th pin of the magnetic communication isolation chip are connected with the communication conversion module 8 to form a communication isolation side A; in the circuit for connecting the communication isolation module 51 with the microprocessor 11, the 1 st pin of the magnetic communication isolation chip is connected with the 16 th pin of the U4 chip in the power isolation module 52, the 5 th pin, the 6 th pin, the 3 rd pin and the 4 th pin of the magnetic communication isolation chip are respectively connected with the 85 th pin, the 86 th pin, the 87 th pin and the 88 th pin of the microprocessor 11 to form a communication isolation side B, the communication isolation side B receives the communication signal of the microprocessor 11 and isolates and outputs the communication signal to a communication isolation side A, the communication isolation side A receives the communication signal of the upper computer 7 and isolates and outputs the communication signal to the communication isolation side B, therefore, communication isolation is realized, interference of an interference signal of the upper computer 7 to the microprocessor 11 through the communication interface is prevented, the electrical isolation performance of the impedance conversion module 2 and a peripheral circuit can be improved to the maximum extent, and the interference of the peripheral circuit to the impedance conversion module 2 is reduced. Optionally, the communication isolation chip is an ADM2486 chip. The communication conversion module 8 adopts a USB-to-485 communication converter.
Based on this, the embodiment further provides a water conductivity detection method, including:
s1: providing the water quality conductivity detection system;
s2: the main control module enters a calibration mode after receiving a calibration instruction, the impedance conversion module selects an impedance channel to switch a calibration access resistor under each measurement range, the resistance value of the calibration access resistor corresponds to the detection measurement range of the conductivity detection module, and the main control module obtains and stores the calibration coefficient of the conductivity detection module under each detection measurement range according to the measurement amplitude of the conductivity detection module under each detection range;
s3: the main control module enters a data acquisition mode after receiving a data acquisition instruction, the conductivity detection module detects the conductivity of the water body from small to large in the detection range until the measurement amplitude of the conductivity detection module does not overflow, and the detection range at the moment is used as the optimal detection range;
s4: the temperature detection module detects the temperature of the water body;
s5: the main control module obtains the conductivity of the water body at the standard temperature according to the measurement amplitude of the conductivity detection module at the optimal detection range, the calibration coefficient corresponding to the optimal detection range and the temperature value detected by the temperature detection module.
Specifically, referring to fig. 6, first, after the temperature detection module 4 and the conductivity detection module 3 enter the water body, the power supply is turned on; and the microprocessor 11 executes communication initialization, judges whether a starting instruction sent by the upper computer 7 is received or not, sends a starting response instruction to the upper computer 7 if the starting instruction is received, enables the microprocessor 11 to execute temperature and conductivity acquisition initialization, and enters a standby mode to wait if the starting instruction is not received.
The microprocessor 11 executes temperature and conductivity acquisition initialization, the microprocessor 11 judges whether a calibration instruction of the upper computer 7 is received, if so, the calibration mode is entered, and if not, the standby mode is still entered.
In the calibration mode, the microprocessor 11 obtains the calibration coefficient of the conductivity detection module 3 under each detection range according to the measurement amplitude of the conductivity detection module 3 under each detection range, and the specific steps are as follows:
as shown in FIG. 2 and FIG. 7, the microprocessor 11 controls the impedance channel selection circuit 21 to have a resistance R by using the IIC communication interface11(R11 in fig. 2, with a resistance of 100 Ω) is connected to the feedback path of the amplifying and comparing circuit 22, and the calibration access resistor with a resistance of R21(R14 in fig. 2, with a resistance value of 100 Ω) calibration access resistor is connected to the reverse input channel of the amplification and comparison circuit 22, and the conductivity detection module 3 obtains a reference signal YL1Measured amplitude of time NL1(ii) a Continuously setting the resistance value to R22(R15 in fig. 2, the resistance value is 1k Ω) calibration access resistor is connected into the reverse input channel of the amplification comparison circuit, and the conductivity detection module 3 obtains a reference signal YH1Measured amplitude of time NH1To obtain the minimum detection range Q1Calibration coefficients of (uS-mS);
then, the resistance is R12(R12 in FIG. 2, with a resistance of 1k Ω) is connected to the feedback path of the amplifying and comparing circuit 22, and the calibration access resistor with a resistance of R22(FIG. 2)R15 with a resistance value of 1k Ω) is connected to the reverse input channel of the amplifying and comparing circuit 22, and the conductivity detection module 3 obtains a reference signal YL2Measured amplitude of time NL2(ii) a Continuously setting the resistance value to R23(R17 in fig. 2, with a resistance of 10k Ω) calibration access resistor is connected to the reverse input channel of the amplification and comparison circuit 22, and the conductivity detection module 3 obtains a reference signal YH2Measured amplitude of time NH2To obtain the detection range Q2The microprocessor 11 obtains the calibration coefficient according to the following calculation formula:
and after the automatic calibration is completed, the calibration coefficients GF1, GF2, Nos1, Nos2, C1 and C2 corresponding to the two detection ranges are stored in the Flash on the chip of the microprocessor 11.
It is understood that if the conductivity detection module 3 has more than two detection ranges, calibration coefficients for other detection ranges can be found according to the above method, for example: will have a resistance value of R1xThe calibration access resistor is connected into a feedback channel of the amplifying and comparing circuit, and the resistance value is R2xThe calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YLxMeasured amplitude of time NLx(ii) a Continuously setting the resistance value to R2(x+1)The calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YH1Measured amplitude of time NH1To pass throughObtaining the detection range QxThe calibration coefficient of (a);
Nosx＝Nx-YHx/GFx； (5)
and (x +1) and executing the steps in a circulating mode until the calibration coefficients of all the detection ranges Q are acquired. Wherein the resistance value R1xAnd resistance value R2xEqual and resistance R1xAnd resistance value R2xBoth increase with increasing x.
And then, entering a data acquisition mode, accessing the conductivity detection module 3 into a measurement access channel, and sequentially detecting the conductivity of the water body from the small value to the large value of the detection range Q by the conductivity detection module 3 until the measurement amplitude of the conductivity detection module 3 does not overflow, and taking the detection range as the optimal detection range.
Specifically, as shown in fig. 8, the microprocessor 11 executes temperature and conductivity acquisition, the temperature detection module 11 obtains the water temperature value t, and the microprocessor 11 controls the impedance channel selection circuit 21 to connect the two electrodes of the conductivity detection module 3 to the reverse input end of the amplification comparison circuit 22 by using the IIC communication interface, and switches the two electrodes to Q1The detection range is detected, and the conductivity detection module 3 obtains the measurement amplitude N1Judgment of N1Whether the uS-mS detection range overflows or not, if so, the detection range is switched to Q2Measuring range (will Q)2The detection range is taken as the optimal detection range), and the measurement amplitude N under the mS-S range is obtained2(ii) a If there is no overflow, then only Q needs to be added1The detection range is used as the optimal detection range, and the microprocessor 11 measures the measurement amplitude N corresponding to the optimal detection rangexConverted into the measured conductivity gamma according to the formula (7), and the calculation result is stored in an internal Flash of the microprocessor 11.
γ＝(Nx-Nosx)×GFx (7)
Finally, the microprocessor 11 combines the electrode coefficient K, the conductance temperature constant beta and the conductance correction coefficient C of the conductance detection module 3 corresponding to the optimal detection range according to the acquired water body temperature value t and the measured conductance gammaxAnd (3) calculating the conductivity gamma' at the standard temperature (25 ℃) according to a formula (8), and outputting the measurement result to an upper computer 7.
In summary, the water conductivity detection system and the detection method provided by the embodiment of the invention comprise a main control module, an impedance conversion module, a temperature detection module and a conductivity detection module, wherein the impedance conversion module is used for realizing automatic identification and switching of the conductivity detection range, so that the detection range is always kept to work in an ideal linear region, and the accuracy of water conductivity detection is improved; a temperature detection module is added, the temperature value detected by the temperature detection module is fused with the measurement amplitude of the conductivity measurement module, so that the automatic compensation of the conductivity measurement result in the variable temperature environment is realized, and the accuracy of the water quality conductivity measurement result is further improved; a peripheral circuit is isolated through the power isolation module and the communication isolation module, so that the interference of the peripheral circuit on measurement is reduced, and the accuracy and stability of water conductivity measurement in a severe water environment are improved;
the above description is only a preferred embodiment of the present invention, and does not limit the present invention in any way. It will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (9)
1. A water quality and conductivity detection system is characterized by comprising a main control module, an impedance conversion module, a temperature detection module and a conductivity detection module, wherein calibration coefficients of the conductivity detection module under different detection ranges are stored in the main control module, the impedance conversion module switches the detection range of the conductivity detection module to enable the conductivity detection module to detect the conductivity of a water body under the optimal detection range, and the main control module obtains the conductivity of the water body under the standard temperature according to the measurement amplitude of the conductivity detection module under the optimal detection range, the calibration coefficient corresponding to the optimal detection range and the temperature value detected by the temperature detection module;
the calibration coefficients comprise gain coefficients GFxSystematic coefficient of misadjustment NosxAnd a conductivity correction factor CxObtaining the conductivity gamma' of the water body at the standard temperature according to the following formula:
γ＝(Nx-Nosx)×GFx
wherein N isxMeasuring an amplitude value for the water quality conductivity of the conductivity detection module; t is a water quality temperature value detected by the temperature detection module; gamma is measured conductivity; K. beta is the electrode coefficient and the conductance temperature constant of the conductivity detection module respectively.
2. The water quality conductivity detection system of claim 1, further comprising a communication isolation module and a power isolation module, wherein the communication isolation module is located between an upper computer and the main control module and performs communication isolation, and the power isolation module isolates a voltage provided by a power conversion module and converts the voltage into a working voltage to supply power to the main control module, the impedance conversion module, the temperature detection module, the conductivity detection module and the communication isolation module.
3. The water quality conductivity detection system of claim 2, wherein the power conversion module comprises a primary conversion circuit and a secondary conversion circuit, the power isolation module comprises a primary isolation module and a secondary isolation module, the primary conversion circuit and the secondary conversion circuit respectively convert a direct current voltage into a first voltage signal and a second voltage signal, and the primary isolation module and the secondary isolation module respectively convert the first voltage signal and the second voltage signal into a first isolation signal and a second isolation signal.
4. The water conductivity detection system of claim 1, wherein the impedance conversion module comprises an impedance channel selection circuit and an amplification comparison circuit, the impedance channel selection circuit is used for switching the calibration access resistor and the measurement access channel, and the amplification comparison circuit inputs the impedance measurement signal of the conductivity detection module into the main control module.
5. A water conductivity detection method is characterized by comprising the following steps:
s1: providing a water quality conductivity detection system as claimed in any one of claims 1 to 4;
s2: the main control module enters a calibration mode after receiving a calibration instruction, the impedance conversion module selects an impedance channel to switch a calibration access resistor under each measurement range, the resistance value of the calibration access resistor corresponds to the detection measurement range of the conductivity detection module, and the main control module obtains and stores the calibration coefficient of the conductivity detection module under each detection measurement range according to the measurement amplitude of the conductivity detection module under each detection range;
s3: the main control module enters a data acquisition mode after receiving a data acquisition instruction, the conductivity detection module detects the conductivity of the water body from small to large in the detection range until the measurement amplitude of the conductivity detection module does not overflow, and the detection range at the moment is used as the optimal detection range;
s4: the temperature detection module detects the temperature of the water body;
s5: the main control module obtains the conductivity of the water body at the standard temperature according to the measurement amplitude of the conductivity detection module at the optimal detection range, the calibration coefficient corresponding to the optimal detection range and the temperature value detected by the temperature detection module.
6. The method for detecting water conductivity according to claim 5, wherein the impedance conversion module comprises an impedance channel selection circuit and an amplification comparison circuit, and the step of the main control module obtaining the calibration coefficient of the conductivity detection module in each detection range according to the measurement amplitude of the conductivity detection module in each detection range comprises:
s21: the resistance value of the impedance channel selection circuit is R11The calibration access resistor is connected into a feedback channel of the amplifying and comparing circuit, and the resistance value is R21The calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YL1Measured amplitude of time NL1(ii) a Continuously setting the resistance value to R22The calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YH1Measured amplitude of time NH1To obtain the minimum detection range Q1The calibration coefficient of (a);
s22: will have a resistance value of R1xThe calibration access resistor is connected into a feedback channel of the amplifying and comparing circuit, and the resistance value is R2xThe calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YLxMeasured amplitude of time NLx(ii) a Continuously setting the resistance value to R2(x+1)The calibration access resistor is connected into a reverse input channel of the amplification comparison circuit, and the conductivity detection module obtains a reference signal YHxMeasured amplitude of time NHxTo obtain the detection range QxThe calibration coefficient of (a);
s23: let x be (x +1) and execute step S22 until the calibration coefficients of all the detection ranges Q are acquired.
7. The method of claim 6, wherein the calibration factor comprises a gain factor GFxSystematic coefficient of misadjustment NosxAnd a conductivity correction factor CxAnd, obtaining a calibration coefficient for each of the detection ranges by the following formula:
Nosx＝Nx-YHx/GFx；
Nxthe measured amplitude value corresponding to the optimal detection range.
8. The method of claim 6, wherein the resistance R is1xAnd resistance value R2xEqual and resistance R1xAnd resistance value R2xBoth increase with increasing x.
9. The method according to claim 8, wherein the accuracy of each calibrated access resistor is greater than or equal to one thousandth.
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| CN110658237A (en) * | 2019-10-25 | 2020-01-07 | 南宁学院 | Automatic milk conductivity detection system |
| CN112014434A (en) * | 2020-07-29 | 2020-12-01 | 桂林优利特医疗电子有限公司 | Water quality real-time detection method and detection device for biochemical immunoassay analyzer |
| CN113295196A (en) * | 2021-05-28 | 2021-08-24 | 东华大学 | Three-in-one device for filtering equipment and calibration method thereof |
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