CN111238586B - Electromagnetic flowmeter for measuring low conductivity and rate measuring method thereof - Google Patents
Electromagnetic flowmeter for measuring low conductivity and rate measuring method thereof Download PDFInfo
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- CN111238586B CN111238586B CN202010226334.6A CN202010226334A CN111238586B CN 111238586 B CN111238586 B CN 111238586B CN 202010226334 A CN202010226334 A CN 202010226334A CN 111238586 B CN111238586 B CN 111238586B
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- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
- G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
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Abstract
The invention belongs to the field of magnetic flowmeters, and discloses an electromagnetic flowmeter for measuring low conductivity, which comprises a sensor unit, a signal processing unit, a V/F conversion unit and an ARM module, wherein the sensor unit is connected with a working power supply; the sensor unit is connected with the signal processing unit, the signal processing unit is connected with the V/F conversion unit, and the V/F conversion unit is connected with the ARM module; the signal processing unit comprises a preceding-stage amplification module, a low-pass filtering module and a subsequent-stage amplification module. The invention also discloses a low conductivity measurement method by using the electromagnetic flowmeter. The electromagnetic flowmeter can effectively amplify weak flow signals through three-stage amplification, ensures the measurement accuracy of the electromagnetic flowmeter, and has the advantages of small misadjustment, small temperature drift, good linearity and stable and adjustable gain.
Description
Technical Field
The invention belongs to the field of electromagnetic flowmeters, and particularly relates to an electromagnetic flowmeter for measuring low conductivity and a measuring method thereof.
Background
The basic principle of electromagnetic flow meters is the faraday's law of electromagnetic induction. The excitation module of the electromagnetic flowmeter generates a magnetic field excitation intensity B, and when a conductive fluid flows in a pipeline with the diameter of D and the speed v, the induced potential E = kBVD, k between two measuring electrodes is a fixed coefficient, namely a sensor coefficient. Conventional electromagnetic flowmeters cannot measure liquids with conductivities below 10 mus/cm.
In the industrial production process, the flow rate is an extremely important thermal parameter and is one of important measurement parameters in the industrial and agricultural production process control. The electromagnetic flowmeter has the characteristics of high measuring accuracy, simple later maintenance, wide measuring range and the like. With the widespread adoption of electromagnetic flow meters in various fields, the research focus of researchers is more closely surrounding how to solve the problems and contradictions encountered in actual measurement.
At present, the accuracy of the electromagnetic flowmeter for measuring liquid with low conductivity is lower by one order of magnitude, which greatly limits the application range of the electromagnetic flowmeter.
Disclosure of Invention
The invention aims to provide an electromagnetic flowmeter for measuring low conductivity with high accuracy and convenient measurement and a method for measuring low conductivity by using the same.
In order to solve the technical problems, the invention provides the following technical scheme: the electromagnetic flowmeter for measuring the low conductivity comprises a sensor unit, a signal processing unit, a V/F conversion unit, an RS485 communication module and an ARM module, wherein the ARM module is connected with the RS485 communication module, and the sensor unit is connected with a working power supply; the signal output end of the sensor unit is connected with the signal input end of the signal processing unit, the signal output end of the signal processing unit is connected with the signal input end of the V/F conversion unit, and the signal output end of the V/F conversion unit is connected with the ARM module; the signal processing unit comprises a preceding-stage amplification module, a low-pass filtering module and a subsequent-stage amplification module, wherein the input end of the preceding-stage amplification module is connected with the signal output end of the sensor unit, the output end of the preceding-stage amplification module is connected with the in-phase input end of the low-pass filtering module, the output end of the low-pass filtering module is connected with the in-phase input end of the subsequent-stage amplification module, and the output end of the subsequent-stage amplification module is connected with the V/F conversion unit.
The sensor unit comprises an excitation generating circuit, a measuring pipeline and an excitation control circuit, wherein the excitation generating circuit comprises a first coil and a second coil, the first coil and the second coil are respectively arranged above and below the measuring pipeline, two electrodes are vertically connected in the measuring pipeline, and voltage between the two electrodes is transmitted to the signal processing unit; the excitation control circuit comprises a first comparator, a second comparator, a first solid-state relay, a second solid-state relay, a third solid-state relay and a fourth solid-state relay, wherein the non-inverting input ends of the first comparator and the second comparator are connected with a direct-current power supply, and the inverting input ends of the first comparator and the second comparator are respectively connected with a first coil and a second coil through sampling resistors; the output end of the first comparator is respectively connected with the trigger ends of the first solid-state relay and the second solid-state relay, and the power supply ends of the first comparator and the second comparator are connected with a direct-current power supply; the positive electrode of the working power supply is connected with the first end of the first solid-state relay, the second end of the first solid-state relay is connected with the first coil, meanwhile, the second end of the first solid-state relay is also connected with the first end of the third solid-state relay, and the second end of the third solid-state relay is connected with the negative electrode of the direct-current power supply; the positive pole of working power supply still connects the first end of second solid state relay, and the second end of second solid state relay connects the first end of fourth solid state relay, and the first end of fourth solid state relay still connects the second coil, and the second end of fourth solid state relay connects DC power supply's negative pole.
RS485 communication module includes the MAX485 chip, and 3 signal output part of ARM module are respectively through optical coupling connection MAX485 chip's receiver output, driver input and driver work enable end, and MAX485 chip's receiver output enable end connects the driver work enable end of MAX485 chip.
The preceding stage amplification module comprises the following models: the first amplifier, low pass filter module of IMA332 comprises model number: the second amplifier of the OPA705, the post-amplification module comprises the type: a second amplifier of the OPA705, wherein a first resistor is connected between two gain ends of the first amplifier, an output end of the first amplifier is connected with a non-inverting input end of the second amplifier, and an inverting input end of the second amplifier is connected with an output end of the second amplifier; the output end of the second amplifier is also connected with the non-inverting input end of the third amplifier, the inverting input end of the third amplifier is connected with the output end of the third amplifier through a fifth resistor, and the inverting input end of the third amplifier is also grounded through a fourth resistor.
The device is characterized by further comprising an empty pipe detection unit, the empty pipe detection unit comprises a voltage following module, a comparator module and a trigger module, the signal input end of the voltage following module is connected with the signal output end of the sensor unit, the signal output end of the voltage following module is connected with the signal input end of the comparator module, the signal output end of the comparator module is connected with the signal input end of the trigger module, the signal output end of the trigger module is connected with a buzzer circuit, and the signal output end of the trigger module is further connected with the signal input end of the ARM module.
The voltage following module comprises a third amplifier, the comparator module comprises a fourth amplifier, the trigger module comprises a trigger, the non-inverting input end of the third amplifier is connected with the signal output end of the sensor unit, the inverting input end of the third amplifier is connected with the output end of the third amplifier, the output end of the third amplifier is connected with the inverting input end of the fourth amplifier through a seventh resistor, the non-inverting input end of the fourth amplifier is grounded through a ninth resistor, and the non-inverting input end of the fourth amplifier is also connected with a direct-current power supply through an eighth resistor; the output end of the fourth amplifier is connected with the first trigger end of the trigger, the output end of the fourth amplifier is also connected with a first diode, the output end of the fourth amplifier is connected with the cathode of the first diode, and the anode of the first diode is grounded; the second trigger end and the third trigger end of the trigger are connected with a direct-current power supply; the external timing capacitor end of the trigger is sequentially connected with a direct current power supply through a first capacitor and a tenth resistor; the external timing resistor end of the trigger is connected with a direct-current power supply through a tenth resistor; the output end of the trigger is connected with the base electrode of the triode, the collector electrode of the triode is connected with the anode of the second diode, the cathode of the second diode is connected with the direct-current power supply, and a buzzer is connected between the collector electrode of the triode and the direct-current power supply; the emitter of the triode is grounded.
The V/F conversion unit comprises a V/F conversion chip and a level conversion chip, and a first power supply end of the level conversion chip is connected with a 3.3V direct-current power supply; an input clock pin of the level conversion chip is connected with a 6M clock; the second power end of the level conversion chip is connected with a 5V direct-current power supply; an output clock pin of the level conversion chip is connected with a clock pin of the V/F conversion chip; the input end of the V/F conversion chip is connected with the output end of the third amplifier; the output end of the V/F conversion chip is connected with a 5V direct-current power supply through a sixth resistor; the output end of the V/F conversion chip is also connected with the input end of the ARM module.
A low conductivity measurement method using the above-described electromagnetic flowmeter for measuring low conductivity, the method comprising the steps of:
(1) the conductive liquid flows through the sensor and the sensor to generate induced electromotive force;
(2) detecting the induction potential in an empty pipe manner, if the phenomenon of empty pipe occurs, displaying a digital hold in the previous second, otherwise, performing the step (3);
(3) carrying out three-stage amplification on the induced potential;
(4) converting the amplified potential into a digital signal;
(5) transmitting the converted digital signal to an ARM module;
(6) and displaying the signal transmitted to the ARM module.
The method for detecting the induction potential by empty pipe comprises the following steps: comparing the electromotive force transmitted in the step (1) with a set value, if the electromotive force exceeds the set value, triggering a trigger to enable the trigger to act, and simultaneously outputting a signal to an ARM module, wherein the ARM module outputs the signal to enable display numbers on a display screen to be kept unchanged; the set value is a voltage value of 2.5V.
When the empty pipe phenomenon occurs, the ARM module outputs signals to enable the display numbers on the display screen to keep 5S unchanged.
Through the technical scheme, the invention has the beneficial effects that:
the electromagnetic flowmeter can effectively amplify weak flow signals through three-stage amplification, ensures the measurement accuracy of the electromagnetic flowmeter, and has the advantages of small misadjustment, small temperature drift, good linearity and stable and adjustable gain. This electromagnetic flowmeter has empty pipe and detects the function, reports to the police when the sensor detects the bubble to regard the empty pipe as not having the flow to flow, gather the velocity of flow that the signal catastrophe was former simultaneously and replace current velocity of flow, effectively reduced the influence of empty pipe to measuring result. Compared with the prior art, the electromagnetic flowmeter enlarges the range of the measured liquid, improves the measurement precision of the traditional electromagnetic flowmeter and effectively controls the signal interference of an empty pipe.
The measuring method has high measuring accuracy, is easy to realize the measurement of the low-conductivity liquid, can detect the empty pipe, and effectively controls the signal interference of the empty pipe.
Drawings
FIG. 1 is a schematic frame of the present invention;
FIG. 2 is a schematic diagram of a sensor unit structure;
FIG. 3 is a schematic diagram of a signal processing unit;
FIG. 4 is a schematic diagram of a V/F conversion unit;
FIG. 5 is a schematic diagram of an empty pipe detection unit;
FIG. 6 is a schematic diagram of an LCD display module;
fig. 7 is a schematic diagram of an RS485 communication module.
Detailed Description
The electromagnetic flowmeter for measuring the low conductivity comprises a sensor unit, a signal processing unit, a V/F conversion unit, an ARM module, an empty pipe detection unit, an LCD display module and an RS485 communication module, wherein the sensor unit is connected with a working power supply, and the working power supply provides basic voltage for the work of the sensor unit, as shown in figures 1-7.
The signal output end of the sensor unit is connected with the signal input end of the signal processing unit, the signal output end of the signal processing unit is connected with the signal input end of the V/F conversion unit, the signal output end of the V/F conversion unit is connected with the ARM module, the ARM module is connected with the LCD display module and the RS485 communication module, the signal output end of the sensor unit is further connected with the empty pipe detection unit, and the signal output end of the empty pipe detection unit is connected with the signal input end of the ARM module.
Wherein the conductive fluid in the measuring pipe of the sensor unit is measured at a flow rateVWhen passing through, an induced potential is generatedEInduced electric potentialEThe two electrode outputs of the sensor unit are connected to a signal processing unit which outputs signalsX0To a V/F conversion unit for converting the converted digital signalL1Inputting into ARM module for processing to generate flow signalL2Flow rate signalL2And displayed by the display module.
Simultaneously, this electromagnetic flowmeter can carry out 485 communications through RS485 communication module to flow signal transmission goes out.
The ARM module includes ARM processor U9 (model is LPC 2106) and ARM processor U9's minimum system, and ARM processor U9's minimum system is ripe prior art, includes power supply circuit, reset circuit and clock circuit, and no longer redundance in this embodiment.
The sensor unit comprises an excitation generating circuit, a measuring pipeline and an excitation control circuit.
The excitation generating circuit comprises a first coil X1 and a second coil X2, wherein the first coil X1 is positioned above the measuring pipeline, and a magnetic field parallel to the width direction of the measuring pipeline is formed in the measuring pipeline. Second coil X2 is located the measurement pipeline below, also forms the magnetic field that is on a parallel with measurement pipeline width direction in the measurement pipeline, and two magnetic fields superpose each other, improve measurement accuracy.
Two electrodes J are vertically connected in the measuring pipeline and are respectively positioned at the upper inner part and the lower inner part of the measuring pipeline. The two electrodes are connected with a signal processing unit through a first sampling resistor RC.
The sampling resistor RC collects the voltage between the two motors and transmits the collected voltage value to the signal processing unit, which is a mature prior art. The method specifically comprises the following steps: the first end of the first sampling resistor RC is connected with one electrode, the second end of the first sampling resistor RC is connected with the other electrode, the voltage value flowing through the measuring pipeline is equal to the voltage values at the two ends of the first sampling resistor RC, and the second end of the first sampling resistor RC is connected with the signal input end of the signal processing unit.
The excitation control circuit comprises a first comparator U19 (with the model being LM 393), a second comparator U20 (with the model being LM 393), a first solid-state relay U14, a second solid-state relay U15, a third solid-state relay U16 and a fourth solid-state relay U17, the non-inverting input ends of the first comparator U19 and the second comparator U20 are connected with a direct-current power supply, and the inverting input ends of the first comparator U19 and the second comparator U20 are respectively connected with the voltage values of a first coil X1 and a second coil X2. The sampling method of the voltage values of the first coil X1 and the second coil X2 is mature prior art, and only one sampling resistor needs to be connected in parallel to the first coil X1 and the second coil X2 respectively, and the voltage values at two ends of the sampling resistor can be measured.
The output end of the first comparator U19 is respectively connected with the trigger ends of the first solid-state relay U14 and the second solid-state relay U15, and the power supply ends of the first comparator U19 and the second comparator U20 are connected with a direct-current power supply.
The positive pole of working power supply connects the first end of first solid state relay U14, and the second end of first solid state relay U14 connects first coil X1, and the second end of first solid state relay U14 still connects the first end of third solid state relay U16 simultaneously, and the second end of third solid state relay U16 connects the negative pole of DC power supply.
The positive electrode of the working power supply is also connected with the first end of a second solid-state relay U15, the second end of a second solid-state relay U15 is connected with the first end of a fourth solid-state relay U17, the first end of the fourth solid-state relay U17 is also connected with a second coil X2, and the second end of a fourth solid-state relay U17 is connected with the negative electrode of the direct-current power supply.
The sources of the direct current power supply in the excitation control circuit are as follows: the excitation control circuit further comprises a voltage stabilizing chip U18 (model is L7805), the input end of the voltage stabilizing chip U18 is connected with a 5V direct-current power supply, the output end of the voltage stabilizing chip U18 is connected with a first voltage dividing resistor and a second voltage dividing resistor, the first voltage dividing resistor is grounded through the second voltage dividing resistor, a 1V direct-current power supply is connected to a joint of the first voltage dividing resistor and the second voltage dividing resistor, and the 1V direct-current power supply is the direct-current power supply connected to the non-inverting input ends of the first comparator U19 and the second comparator U20.
The working process of the excitation control circuit is as follows: the voltage stabilizing chip U18 provides 5V stabilized voltage, after voltage division, 1V voltage is provided for the first comparator U20 and the second comparator U20, through two-way analog control signals, voltage comparison between the voltage on the first coil X1 and the voltage on the second coil X2 and the 1V voltage is realized, when the voltage on the first coil X1 is larger than 1V, the first comparator U19 outputs low level, the first solid-state relay U14 and the fourth solid-state relay U17 are cut off, the second solid-state relay U16 and the third solid-state relay U16 are conducted, current flows to the first coil X1 from the second coil X2, baseline drift is overcome, and the stabilized magnetic field and the power are lower. When the four solid-state relays work, currents flow through the first coil and the second coil, so that a superposed magnetic field is formed in the measuring pipeline, and the accuracy of a detection result is improved.
The signal processing unit is used for amplifying the weak signal of the sensor unit, so that the electromagnetic flowmeter can measure low-conductivity liquid.
The signal processing unit comprises a pre-stage amplification module, a low-pass filtering module and a post-stage amplification module, wherein the in-phase input end of the pre-stage amplification module is connected with the signal output end of the sensor unit, the output end of the pre-stage amplification module is connected with the in-phase input end of the low-pass filtering module, the output end of the low-pass filtering module is connected with the in-phase input end of the post-stage amplification module, and the output end of the post-stage amplification module is connected with the V/F conversion unit.
The preceding stage amplification module comprises the following models: the first amplifier U1 of IMA332, the low pass filtering module comprises model numbers: the second amplifier U2 of OPA705, the post-amplification module includes model: a first resistor R1 is connected between the two gain terminals of the second amplifier U2 and the first amplifier U1 of the OPA 705.
The output end of the first amplifier U1 is connected to the non-inverting input end of the second amplifier U2 through a second resistor R2, and the non-inverting input end of the second amplifier U2 is further connected to a first filter capacitor C1 for filtering.
The inverting input end of the second amplifier U2 is connected with the output end of the second amplifier U2; the output terminal of the second amplifier U2 is connected to the inverting input terminal of the third amplifier U3 through a third resistor R3, the non-inverting input terminal of the third amplifier U3 is connected to the output terminal of the third amplifier U3 through a fifth resistor R5, and the non-inverting input terminal of the third amplifier U3 is also connected to ground through a fourth resistor R4.
The empty pipe detection unit comprises a voltage following module, a comparator module and a trigger module, wherein the signal input end of the voltage following module is connected with the signal output end of the sensor unit, the signal output end of the voltage following module is connected with the signal input end of the comparator module, the signal output end of the comparator module is connected with the signal input end of the trigger module, and the signal output end of the trigger module is connected with a buzzer circuit.
The voltage following module comprises a third amplifier U6, the comparator module comprises a fourth amplifier U7, and the trigger U8 module comprises a trigger U8.
The non-inverting input terminal of the third amplifier U6 is connected to the signal output terminal of the sensor unit, and in particular to the second terminal of the first sampling resistor R1. The inverting input terminal of the third amplifier U6 is connected to the output terminal of the third amplifier U6, the output terminal of the third amplifier U6 is connected to the inverting input terminal of the fourth amplifier U7 through a seventh resistor, the non-inverting input terminal of the fourth amplifier U7 is connected to ground through a ninth resistor R9, and the non-inverting input terminal of the fourth amplifier U7 is also connected to a dc power supply through an eighth resistor R8.
The output end of the fourth amplifier U7 is connected with a first trigger end (pin A1) of the flip-flop U8, the output end of the fourth amplifier U7 is also connected with a first diode D1, the output end of the fourth amplifier U7 is connected with the cathode of a first diode D1, and the anode of the first diode D1 is grounded; the second trigger end (pin A2) and the third trigger end (pin B) of the trigger U8 are connected with a direct-current power supply; an external timing capacitor end (pin cext) of the trigger U8 is connected with a direct-current power supply through a first capacitor C1 and a tenth resistor R10 in sequence; an external timing resistor end (pin rext) of the trigger U8 is connected with a direct-current power supply through a tenth resistor R10; a first output end (pin Q1) of the trigger U8 is connected with a base electrode of a triode Q1, a collector electrode of the triode Q1 is connected with an anode of a second diode D2 through a twelfth resistor R12, a cathode of the second diode D2 is connected with a direct-current power supply, and a buzzer B is also connected between the collector electrode of the triode Q1 and the direct-current power supply; the emitter of transistor Q1 is connected to ground.
A second output (pin Q2) of the flip-flop U8 is connected to a signal input of the ARM processor.
The voltage following module in this embodiment is used for keeping apart detection circuitry and other circuits of instrument, prevents that detection circuitry from producing the influence to measuring flow signal.
The non-inverting input end of the comparator module is divided by two resistors and connected with 2.5V voltage, and when the sensor pipeline is not an empty pipe, 6.25Hz positive and negative alternating rectangular waves are output. The maximum value of the signal is not more than 0.4V, and the output of the comparator module is always high level. When the sensor pipeline is an empty pipe, the amplitude of the interference signal is larger than 5V, and the comparator module outputs a series of square wave signals.
When the tube is full, the comparator module outputs high level, at the moment, three trigger ends of the trigger U8 module are all high level, the output signal of the trigger U8 module is low level, the triode is cut off, no current passes through the buzzer, and no alarm is given.
In the idle pipe, interference signals in the system are mainly co-frequency interference of 50 Hz. At this time, the comparator module outputs a square wave signal with the frequency of 50 Hz. The square wave signal is input to the A1 end of the trigger U8 module, when A2 and B are both at high level, the falling edge of A1 triggers, under the condition that the pulse width Tw of triggering is more than or equal to 20ms, the square wave signal output by the comparator module triggers the trigger U8 again before the output signal of the trigger U8 module is converted into low level, so that the high level is output in an empty tube state all the time, the high level enables the triode to be conducted, current flows through the buzzer, and empty tube alarming is realized.
Meanwhile, the empty pipe detection unit transmits the detected empty pipe information to the ARM module.
The V/F conversion unit is used for converting an analog signal into a digital signal, and the V/F conversion has the advantages of being strong in anti-interference capability compared with the A/D conversion. The V/F conversion unit comprises a V/F conversion chip U5 (model number is AD 7741) and a level conversion chip U4 (model number is 74LVC1T 45), and a first power supply end of the level conversion chip U4 is connected with a 3.3V direct-current power supply; an input clock pin of the level conversion chip U4 is connected with a 6M clock; the second power supply end of the level conversion chip U4 is connected with a 5V direct-current power supply; an output clock pin of the level conversion chip U4 is connected with a clock pin of the V/F conversion chip U5; the input end of the V/F conversion chip U5 is connected with the output end of the third amplifier U6; the output end of the V/F conversion chip U5 is connected with a 5V direct-current power supply through a sixth resistor R6; the output end of the V/F conversion chip U5 is also connected with the input end of the ARM module.
The signal output end of the ARM processor U9 is connected with an LCD display module, so that the flow signal is displayed, and data loss is prevented. The LCD display module comprises an LCD display screen U10 (the model is LM 016L), and the signal output end of the ARM processor U9 is connected with the signal input end (pins D0-D7) of the LCD display screen U10.
As a conversion of this embodiment, in order to prevent the loss of the number, the LCD display module further includes a latch U11 (model 74HC 373), the input terminal (pins D0-D7) of the latch U11 is connected to the signal output terminal (pins PO.0-PO.7) of the ARM processor U9; the output terminals (pins Q0-Q7) of the latch U11 are connected to the signal input terminals (pins D0-D7) of the LCD screen U10.
The flow signal is buffered by the latch and then displayed by the LCD display screen, so that the data can be stabilized and kept unchanged for a period of time until the new data is replaced by the new data, and competition and dangerous phenomena caused by inconsistent arrival time of all bits of the input signal and data loss can be avoided.
The RS485 communication module is used for realizing that the electromagnetic flowmeter can be in 485 communication with other equipment with the RS485 communication module.
Wherein, RS485 communication module includes MAX485 chip (the model is 75175), and 3 signal output part of ARM treater connect the receiver output (pin R) of MAX485 chip, driver input (pin D) and driver work enable end (pin DE) through opto-coupler U12 (the model is TIL 117) respectively, and the driver work enable end (pin DE) of MAX485 chip is connected to the receiver output enable end (pin RE) of MAX485 chip.
The receiver non-reverse output end (pin A) of the MAX485 chip is connected with a direct current power supply through a thirteenth resistor R13, and the receiver non-reverse output end (pin A) of the MAX485 chip is also connected with a sixteenth resistor R16; the reverse output end (pin B) of the receiver is grounded by being connected with a fifteenth resistor R15; a fourteenth resistor R14 is also connected between the receiver non-inverting output (pin a) and the receiver non-inverting output (pin a) of the MAX485 chip. The reverse output end (pin B) of the receiver is also connected with a seventeenth resistor R17; the other ends of the sixteenth resistor R16 and the seventeenth resistor R17 are used as communication terminals to send signals to other MAX485 chips.
In order to ensure the working effect, a first voltage-stabilizing diode D3 and a second voltage-stabilizing diode D4 are further connected between the sixteenth resistor R16 and the seventeenth resistor R17, and the anode of the first voltage-stabilizing diode D3 is connected with a sixteenth resistor R16; the cathode of the first zener diode D3 is connected to the cathode of the second zener diode D4, and the anode of the second zener diode D4 is connected to the seventeenth resistor R17.
The working process is as follows: signals generated by the sensor unit are subjected to three-stage amplification of signal processing and then subjected to analog-to-digital conversion of the V/F conversion unit, converted digital signals are sent to the ARM module to generate flow signals, the flow signals are displayed through the display module, and meanwhile, the numbers in the ARM module are communicated through the RS485 communication module. In addition, when the work is carried out, the empty pipe detection unit detects the received data, when the empty pipe is found, a signal is sent to the ARM module, and meanwhile, the buzzer sends out an alarm sound.
The electromagnetic flowmeter can effectively amplify weak flow signals through three-stage amplification, ensures the measurement accuracy of the electromagnetic flowmeter, and has the advantages of small misadjustment, small temperature drift, good linearity and stable and adjustable gain.
The embodiment also discloses a low conductivity measurement method based on the electromagnetic flow meter for measuring low conductivity, which comprises the following steps:
(1) the conductive liquid flows through the measuring pipeline of the sensor unit, and the sensor unit generates induced electromotive force. The first coil and the second coil on the measuring pipeline of the sensor unit form a mixed direct-current pulse excitation circuit, and the excitation mode can overcome baseline drift, stabilize a magnetic field and has low power.
(2) And (4) carrying out empty pipe detection on the induced potential, if an empty pipe phenomenon occurs, displaying digital hold in the previous second, and otherwise, carrying out the step (3).
The method for detecting the induction potential by the empty pipe comprises the following steps: comparing the electromotive force transmitted in the step (1) with a set value, if the electromotive force exceeds the set value, triggering the trigger U8 to enable the trigger U8 to act, meanwhile, outputting a signal to the ARM module, and enabling the display number on the display screen to be kept unchanged by the ARM module outputting the signal.
In addition, the set values are: a voltage value of 2.5V.
(3) Carrying out three-stage amplification on the induced potential;
(4) converting the amplified potential into a digital signal;
(5) transmitting the converted digital signal to an ARM module;
(6) and displaying the signal transmitted to the ARM module.
In the embodiment, when the empty pipe phenomenon occurs, the ARM module outputs signals to enable the display numbers on the display screen to keep 5S unchanged, and the detection of the empty pipe signal fault is achieved.
The measuring method has high measuring accuracy, is easy to realize the measurement of the low-conductivity liquid, can detect the empty pipe, and effectively controls the signal interference of the empty pipe.
Claims (9)
1. An electromagnetic flowmeter capable of measuring low conductivity, characterized by: the system comprises a sensor unit, a signal processing unit, a V/F conversion unit, an RS485 communication module and an ARM module, wherein the ARM module is connected with the RS485 communication module, and the sensor unit is connected with a working power supply; the signal output end of the sensor unit is connected with the signal input end of the signal processing unit, the signal output end of the signal processing unit is connected with the signal input end of the V/F conversion unit, and the signal output end of the V/F conversion unit is connected with the ARM module; the signal processing unit comprises a pre-stage amplification module, a low-pass filtering module and a post-stage amplification module, wherein the input end of the pre-stage amplification module is connected with the signal output end of the sensor unit, the output end of the pre-stage amplification module is connected with the in-phase input end of the low-pass filtering module, the output end of the low-pass filtering module is connected with the in-phase input end of the post-stage amplification module, the output end of the post-stage amplification module is connected with the V/F conversion unit, and the sensor unit comprises an excitation generation circuit, a measurement pipeline and an excitation control circuit; the excitation control circuit comprises a first comparator, a second comparator, a first solid-state relay, a second solid-state relay, a third solid-state relay and a fourth solid-state relay, wherein the non-inverting input ends of the first comparator and the second comparator are connected with a direct-current power supply, and the inverting input ends of the first comparator and the second comparator are respectively connected with a first coil and a second coil through sampling resistors; the output end of the first comparator is respectively connected with the trigger ends of the first solid-state relay and the second solid-state relay, and the power supply ends of the first comparator and the second comparator are connected with a direct-current power supply; the positive electrode of the working power supply is connected with the first end of the first solid-state relay, the second end of the first solid-state relay is connected with the first coil, meanwhile, the second end of the first solid-state relay is also connected with the first end of the third solid-state relay, and the second end of the third solid-state relay is connected with the negative electrode of the direct-current power supply; the positive pole of working power supply still connects the first end of second solid state relay, and the second end of second solid state relay connects the first end of fourth solid state relay, and the first end of fourth solid state relay still connects the second coil, and the second end of fourth solid state relay connects DC power supply's negative pole.
2. The electromagnetic flowmeter capable of measuring low conductivity of claim 1, wherein: the excitation generating circuit comprises a first coil and a second coil, the first coil and the second coil are respectively arranged above and below the measuring pipeline, two electrodes are vertically connected in the measuring pipeline, and voltage between the two electrodes is transmitted to the signal processing unit.
3. The electromagnetic flowmeter capable of measuring low conductivity of claim 2, wherein: the preceding stage amplification module comprises the following models: the first amplifier, low pass filter module of IMA332 comprises model number: the second amplifier of the OPA705, the post-amplification module comprises the type: a second amplifier of the OPA705, wherein a first resistor is connected between two gain ends of the first amplifier, an output end of the first amplifier is connected with a non-inverting input end of the second amplifier, and an inverting input end of the second amplifier is connected with an output end of the second amplifier; the output end of the second amplifier is also connected with the non-inverting input end of the third amplifier, the inverting input end of the third amplifier is connected with the output end of the third amplifier through a fifth resistor, and the inverting input end of the third amplifier is also grounded through a fourth resistor.
4. The electromagnetic flowmeter capable of measuring low conductivity of claim 3, wherein: the device is characterized by further comprising an empty pipe detection unit, the empty pipe detection unit comprises a voltage following module, a comparator module and a trigger module, the signal input end of the voltage following module is connected with the signal output end of the sensor unit, the signal output end of the voltage following module is connected with the signal input end of the comparator module, the signal output end of the comparator module is connected with the signal input end of the trigger module, the signal output end of the trigger module is connected with a buzzer circuit, and the signal output end of the trigger module is further connected with the signal input end of the ARM module.
5. The electromagnetic flowmeter capable of measuring low conductivity of claim 4, wherein: the voltage following module comprises a third amplifier, the comparator module comprises a fourth amplifier, the trigger module comprises a trigger, the non-inverting input end of the third amplifier is connected with the signal output end of the sensor unit, the inverting input end of the third amplifier is connected with the output end of the third amplifier, the output end of the third amplifier is connected with the inverting input end of the fourth amplifier through a seventh resistor, the non-inverting input end of the fourth amplifier is grounded through a ninth resistor, and the non-inverting input end of the fourth amplifier is also connected with a direct-current power supply through an eighth resistor; the output end of the fourth amplifier is connected with the first trigger end of the trigger, the output end of the fourth amplifier is also connected with a first diode, the output end of the fourth amplifier is connected with the cathode of the first diode, and the anode of the first diode is grounded; the second trigger end and the third trigger end of the trigger are connected with a direct-current power supply; the external timing capacitor end of the trigger is sequentially connected with a direct current power supply through a first capacitor and a tenth resistor; the external timing resistor end of the trigger is connected with a direct-current power supply through a tenth resistor; the output end of the trigger is connected with the base electrode of the triode, the collector electrode of the triode is connected with the anode of the second diode, the cathode of the second diode is connected with the direct-current power supply, and a buzzer is connected between the collector electrode of the triode and the direct-current power supply; the emitter of the triode is grounded.
6. The electromagnetic flowmeter capable of measuring low conductivity of claim 5, wherein: the V/F conversion unit comprises a V/F conversion chip and a level conversion chip, and a first power supply end of the level conversion chip is connected with a 3.3V direct-current power supply; an input clock pin of the level conversion chip is connected with a 6M clock; the second power end of the level conversion chip is connected with a 5V direct-current power supply; an output clock pin of the level conversion chip is connected with a clock pin of the V/F conversion chip; the input end of the V/F conversion chip is connected with the output end of the third amplifier; the output end of the V/F conversion chip is connected with a 5V direct-current power supply through a sixth resistor; the output end of the V/F conversion chip is also connected with the input end of the ARM module.
7. The method of measuring a measurable low conductivity electromagnetic flowmeter based on the measurable low conductivity electromagnetic flowmeter of claim 1, wherein: the method comprises the following steps:
(1) the conductive liquid flows through the sensor and the sensor to generate induced electromotive force;
(2) detecting the induction potential in an empty pipe manner, if the phenomenon of empty pipe occurs, displaying a digital hold in the previous second, otherwise, performing the step (3); the method for detecting the induction potential by empty pipe comprises the following steps: comparing the electromotive force transmitted in the step (1) with a set value, if the electromotive force exceeds the set value, triggering a trigger to enable the trigger to act, and simultaneously outputting a signal to an ARM module, wherein the ARM module outputs the signal to enable display numbers on a display screen to be kept unchanged;
(3) carrying out three-stage amplification on the induced potential;
(4) converting the amplified potential into a digital signal;
(5) transmitting the converted digital signal to an ARM module;
(6) and displaying the signal transmitted to the ARM module.
8. The method of measuring a measurable low conductivity electromagnetic flowmeter of claim 7 wherein: when the empty pipe phenomenon occurs, the ARM module outputs signals to enable the display numbers on the display screen to keep 5S unchanged.
9. The method of measuring a measurable low conductivity electromagnetic flowmeter of claim 8 wherein: the set value is a voltage value of 2.5V.
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