CN107014452A - The flow sensing circuit of constant difference thermal flow rate sensor - Google Patents
The flow sensing circuit of constant difference thermal flow rate sensor Download PDFInfo
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- CN107014452A CN107014452A CN201710247910.3A CN201710247910A CN107014452A CN 107014452 A CN107014452 A CN 107014452A CN 201710247910 A CN201710247910 A CN 201710247910A CN 107014452 A CN107014452 A CN 107014452A
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- G—PHYSICS
- 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
- G01F1/68—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 thermal effects
- G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
- G01F1/688—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
- G01F1/69—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element of resistive type
-
- G—PHYSICS
- 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
- G01F1/68—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 thermal effects
- G01F1/696—Circuits therefor, e.g. constant-current flow meters
Abstract
The invention discloses a kind of flow sensing circuit of constant difference thermal flow rate sensor, prior art is solved the problem of low discharge range signals accuracy of detection is not high.Detection circuit is connected to bridge circuit, the amplification of RC integral voltages, LPF and output circuit successively, and booster power supply circuit is that all circuits are powered.The fluid temperature difference detected is converted into voltage by temperature detecting resistance RS and the resistance RH that tests the speed in bridge circuit, control is generated by RC integral voltages amplifying circuit to test the speed the feedback voltages of resistance RH heating powers, simultaneously, low-pass filter circuit fluid flow signal is filtered processing, the relation curve of 0 recognizable 5V output voltages of output circuit generation other equipment, demarcation output voltage and flow calculates each moment fluid flow.The present invention can accurately determine the fluid flow in the range of low discharge, accuracy of detection height, fast response time, easy for installation, simple to operate, the flow detection for the low discharge scope such as medical, chemical industry in real time.
Description
Technical field
The invention belongs to medical and chemical industry fluid Automatic Measurement Technique field, the flow detection of fluid is related generally to, specifically
It is a kind of flow sensing circuit of constant difference thermal flow rate sensor, the real-time accurate survey for fluid flow in the range of low discharge
Amount.
Background technology
Thermal flow rate sensor detects fluid flow using calorifics principle, that is, utilizes the fluid in flowing and thermal source (fluid
In be used for heat object or measurement pipe external heat body) between heat exchange relationship carry out flow measurement.It is main electric by bridge-type
Road and output signal conditioning circuit composition.Flow-sensitive element is placed in flow conduit with temperature compensating element, with other resistance
Element constitutes bridge circuit, and the change of fluid flow is converted into the change of bridge arm output voltage, the detection of fluid flow is realized.
Thermal flow rate sensor it is most-often used have two classes：One class is to transmit heat using streaming flow, changes measurement pipe
The heat distribution formula flow sensor of wall temperature field distribution effect；Another kind of passed using the heat type flow quantity of the dissipation of heat (cooling) effect
Sensor.
Above-mentioned two classes thermal flow rate sensor is mainly used in a wide range of fluid stream of the range of flow more than more than 500ml/min
Amount detection, the fluid of detection mainly includes pure water and the liquid based on pure water and air mass flow detection.Current existing flow
Detection circuit is designed mainly for large-scale flow high precision test, and the precision of sensor can be met in big flow scope
Measurement accuracy requirement, but it is related to the less detection of flow detection scope, such as flow in for fields such as medical and chemical industry
Scope is typically not greater than 500ml/min, sometimes in 100ml/min, and sensor accuracy is difficult to meet high-precision requirement, therefore,
Design is needed for the flow sensing circuit of low discharge.Heat distribution formula flowmeter measures fluid by the detection to change of temperature field
Flow, it is sensitive to variation of ambient temperature, and need to ensure the Laminar Flow of fluid, circuit structure is complicated, is generally difficult to be applied to
The fluid flow detection of low discharge scope.
The difference controlled according to mode of heating, the thermal flow rate sensor based on the dissipation of heat (cooling) effect can be divided into perseverance again
Streaming is measured and the measurement of constant temperature differential.Prior art generally carries out flow measurement using constant temperature differential measuring method, by simple
Whiston bridge circuit and scaling circuit composition flow sensing circuit carry out flow detection, when carrying out low discharge detection,
The small-signal detected is easily by noise jamming, and noise includes ambient noise and circuit inner noise.On the other hand, it is traditional
Whiston bridge circuit sensitivity is not high, and the small-signal produced to low discharge is insensitive, in the output of low discharge range signals
Precision is not high, it is impossible to real-time and accurately measure fluid flow.
The content of the invention
It is an object of the invention to for above-mentioned the deficiencies in the prior art there is provided a kind of low discharge accuracy of detection it is higher, letter
Number fast response time, the flow sensing circuit of constant temperature differential heat-flow sensor easy for installation.
To achieve the above object, the present invention is adopted the following technical scheme that：A kind of flow of constant difference thermal flow rate sensor
Detect circuit, it is characterised in that：Direction of transfer according to flow detecting signal is connected with bridge circuit, voltage amplification electricity in turn
Road, low-pass filter circuit, output circuit and power circuit, provided with LPF electricity between voltage amplifier circuit and output circuit
Road；In described bridge circuit, temperature detecting resistance RS is film metal RTD PT1000, the RTD and precision resistance R1, electricity
Position device R2 and precision resistance R3 series connection, constitutes first bridge arm of bridge circuit, and temperature detecting resistance RS is located under first bridge arm
Bridge arm end, the resistance RH that tests the speed is film metal RTD PT50, and RTD RH connects with resistance R4, the of composition bridge circuit
Two bridge arms, the resistance RH that tests the speed is located at the lower bridge arm end of second bridge arm；Described voltage amplifier circuit is in operational amplifier list
RC integrating circuit are additionally arranged in member, RC integral voltage amplifying circuits, the input termination bridge of RC integral voltage amplifying circuits is formd
Formula circuit output, the output feedback of RC integral voltage amplifying circuits is connected to the triode Q1 base stages positioned at bridge circuit top, uses
Tested the speed resistance RH heating powers in control；Described low-pass filter circuit is connected on RC integral voltage amplification circuit output ends, to RC
The flow detecting signal of integral voltage amplifying circuit processing output carries out low-pass filtering treatment, removes high-frequency signal and external noise
Flow detecting signal is carried out isolation point by interference, the input of the output termination output circuit of low-pass filter circuit, output circuit
The recognizable 0-5V analog voltages of other equipment are obtained after pressure processing；Power circuit is booster power supply circuit, and electricity is constituted to be all
Road provides the 16V supply voltages needed for work.
Compared with prior art, the present invention has the advantages that：
1. the flow sensing circuit in the present invention keeps the resistance RH and temperature detecting resistance RS that tests the speed using whiston bridge circuit
Between the temperature difference it is constant, the resistance RH that tests the speed uses film metal RTD using film metal RTD PT50, temperature detecting resistance RS
PT1000, resistance and the temperature of two metal RTDs have good linear relationship, it is ensured that difference variation is accurately converted to electricity
Buckling；Metal RTD PT50 and PT1000 is sensitive to temperature change, sets the electricity of other precision resistances in resistance bridge
Resistance, accurately detects the changes in flow rate in the range of low discharge, it is ensured that flow sensing circuit has higher in the range of low discharge
Accuracy of detection；
2. the flow sensing circuit of the present invention uses constant difference mode, put in the voltage for amplifying and feeding back temperature signal
RC integrating circuit are additionally arranged in big circuit, RC integral voltage amplifying circuits are formed, steady quickly constant difference control is realized, so that
Ensure that flow sensing circuit detects fluid flow real-time；
3. the flow sensing circuit composition of the present invention is simple in construction, using the less component of encapsulation, integrated circuit volume
Small, in the absence of movable part, circuit output analog voltage signal is easy to connect with other external equipments, easy for installation.
Brief description of the drawings
Fig. 1 constitutes block diagram for the circuit of the present invention；
Fig. 2 is flow sensing circuit schematic diagram of the invention；
Fig. 3 is bridge circuit figure of the present invention；
Fig. 4 is the relation curve between actual test flow of the present invention and output voltage.
Embodiment
The present invention is described in detail with embodiment below in conjunction with the accompanying drawings.
Thermal flow rate sensor detects fluid flow using calorifics principle, existing based on designed by thermal flow rate sensor
Flow sensing circuit mainly for the high precision test of big flow scope, the precision of sensor is in fluid flow more than 500ml/
During min, measurement can be met and apply required required precision, but be related to flow detection scope in the fields such as medical and chemical industry
In less flow detection, the sufferer infusion under such as medical environment, if being continuing with original flow sensing circuit, its
Precision is difficult to meet high-precision requirement, therefore, objectively needs design for the flow sensing circuit of low discharge scope.
Embodiment 1
It is related to for prior art in the fields such as medical and chemical industry in the less flow detection of flow detection scope, essence
The problem of degree is difficult to meet high-precision requirement, the present invention proposes a kind of flow sensing circuit of constant difference thermal flow rate sensor,
Direction of transfer according to flow detecting signal is connected with bridge circuit, voltage amplifier circuit, low-pass filter circuit, output electricity in turn
Road and power circuit, referring to Fig. 1 and Fig. 2, the present invention is provided with low-pass filter circuit between voltage amplifier circuit and output circuit；
The present invention is in bridge circuit, and temperature detecting resistance RS uses film metal RTD PT1000, the RTD and precision resistance R1, electricity
Position device R2 and precision resistance R3 series connection, constitutes first bridge arm of bridge circuit, and temperature detecting resistance RS is located under first bridge arm
Bridge arm end, the resistance RH that tests the speed is connected using film metal RTD PT50, RTD RH with resistance R4, constitutes bridge circuit
Second bridge arm, the resistance RH that tests the speed is located at the lower bridge arm end of second bridge arm, and the resistance RH and temperature detecting resistance RS that tests the speed is installed in
On the measurement pipeline of fluid, it will directly detect that obtained fluid flow detection signal is converted into temperature signal from measurement pipeline,
The temperature signal is directly entered A, 2 points of B in detection circuit, and the present invention is converted to unbalanced voltage signal by bridge circuit,
From the A of bridge circuit, 2 points of B is exported to follow-up signal modulate circuit.Temperature detecting resistance selects metal RTD in the present invention
PT1000, the resistance that tests the speed selects metal RTD PT50, and resistance and the temperature of two metal RTDs have good linear pass
System, and it is sensitive to temperature change, whiston bridge circuit is accurately detected the changes in flow rate in the range of low discharge, it is ensured that stream
Amount detection circuit has higher accuracy of detection in the range of low discharge.
The present invention is improved on the basis of conventional proportional amplifying circuit, and RC products are additionally arranged in operational amplifier unit
Parallel circuit, realizes the heating power of steady rapidly feedback control bridge circuit, and RC integrating circuit and operational amplifier unit are common
With RC integral voltage amplifying circuits are formd, the input termination bridge circuit output of RC integral voltage amplifying circuits receives bridge-type
The voltage signal of 2 points of output of circuit A, B, the output feedback of RC integral voltage amplifying circuits is connected to positioned at bridge circuit top
Triode Q1 base stages, by bridge circuit A, the unbalance voltage signal of 2 points of outputs of B is amplified, control triode Q1 unlatching
And closing, change the electric current for adding bridge circuit, so that the heating power for the resistance RH that controls to test the speed.The RC integral voltages of the present invention
Amplifying circuit is during fluid flow changes, it is ensured that the steady control of the constant temperature difference between temperature detecting resistance and the resistance that tests the speed.
The low-pass filter circuit of the present invention is connected on the output end of RC integral voltage amplifying circuits, and electricity is amplified to RC integral voltages
The flow detecting signal of road processing output carries out low-pass filtering treatment, removes high-frequency signal and external noise to flow sensing circuit
The influence of measurement accuracy, the input of the output termination output circuit of low-pass filter circuit, output circuit is by low-pass filter circuit
The flow detecting signal of processing output carries out obtaining the recognizable 0-5V analog voltages of other equipment, output after isolation voltage division processing
Circuit power taking resistance R11 and resistance R12 concatenation point is output end, and 2.54mm contact pins are reserved in output end, and other external equipments lead to
Cross Du Pont's line conveniently can connect with output end.Flow detection has been completed to this.Detection stream body is obtained by conversion and calculating
The real-time measurement values of flow.Existing flow sensing circuit is detected that the signal detected is compared to height for big flow scope
Frequency signal and external noise signals, signal power are bigger, and noise influences small to measurement result, without filter circuit.Carry out rill
During amount detection, the weak output signal detected, power is small, it is easier to by noise jamming, is that this present invention specially sets up low pass filtered
Wave circuit, removes high-frequency signal and external noise, it is ensured that detection signal is undistorted, realizes the accurate detection of low discharge scope.
Other external equipments are made up of SCM system or dsp system, are drawn by the A/D conversions of single-chip microcomputer or dsp chip
Pin can obtain the output voltage signal of flow sensing circuit, realize simple.Output voltage and flow are obtained by curve matching
Relation curve, real-time flow value is calculated by the curve fitted.
Power circuit is the 16V supply voltage needed for all composition circuit offer work, it is ensured that flow detection of the invention
Circuit can realize the flow detection of small range flow rate zone.
The present invention employs the measurement of constant temperature differential on the whole, compared to constant current mode measurement, constant temperature differential measurement response speed
Faster, circuit constitutes simple, realization of being more convenient for.
The flow sensing circuit of the present invention keeps testing the speed between resistance RH and temperature detecting resistance RS using whiston bridge circuit
The temperature difference it is constant, the change of fluid flow causes difference variation, and it is complete that temperature signal is converted to voltage signal by flow sensing circuit
Into flow measurement, difference variation is fed back to whiston bridge circuit by RC integral voltages amplifying circuit, changes resistance bridge electricity
The heating voltage on road makes the temperature difference keep constant.Potentiometer R2 value is adjusted, changes the size of current for adding the resistance RH that tests the speed, so that
Change the heating power for the resistance RH that tests the speed, the sensitivity that bridge circuit is detected to low discharge is improved, while by rationally setting favour
The resistance value of other precision resistances in this electric bridge, makes whiston bridge circuit accurately to detect the flow in the range of low discharge
Change, it is ensured that flow sensing circuit has higher accuracy of detection in the range of low discharge.The circuit that the present invention is designed can be just
Really, the fluid flow in the range of low discharge, and operation automatic convenience, signal fast response time, operating efficiency are accurately determined
It is high.
Embodiment 2
The overall of the flow sensing circuit of constant difference thermal flow rate sensor constitutes be the same as Example 1, RC integrations of the invention
Voltage amplifier circuit includes operational amplifier unit and RC integrating circuit.Wherein, operational amplifier IC1 output end and anti-phase defeated
Enter and resistance R8 is serially connected between holding, positive input and power end are serially connected with resistance R7, form operational amplifier unit, and computing is put
Big that electric capacity C1 is serially connected between device output end and inverting input, reverse input end and bridge output are terminated with resistance R5, formed
RC integrating circuit, operational amplifier unit and RC integrating circuit are collectively forming RC integral voltage amplifying circuits.RC integral voltages are put
The input of big circuit and the output end of bridge circuit are connected, and output terminates to the triode Q1 bases positioned at bridge circuit top
Pole, forms the Voltage Feedback for changing the resistance RH heating powers that tested the speed in bridge circuit.RC integrating circuit test the speed resistive dissipation and
Stable constant difference control is realized in the dynamic equilibrium for rising heat.
Excessive RC values will cause to respond slowly, have a strong impact on constant difference control, too small RC values can cause constant difference control
Unstable, the response speed and stability of influence flow sensing circuit output signal of system, can adjust in actually measurement and determine.
According to the output response speed of flow sensing circuit, RC values are adjusted by actual test, a larger RC initial value is set first,
Then progressively reduce RC values, until flow sensing circuit output signal is shaken, then incrementally increase RC values, until circuit is defeated
Go out concussion to disappear, it is determined that drawing effective RC values.
The present invention uses constant difference mode, and RC is additionally arranged in the voltage amplifier circuit for amplifying and feeding back temperature signal
Integrating circuit, forms RC integral voltage amplifying circuits, steadily quick constant difference can control, it is ensured that flow sensing circuit is real-time
It is quickly detected from fluid flow.
Embodiment 3
The overall of the flow sensing circuit of constant difference thermal flow rate sensor constitutes be the same as Example 1-2, and the present invention is in RC products
Low-pass filter circuit is provided between component voltage amplifying circuit and output circuit, low-pass filter circuit is by operational amplifier and its periphery
Circuit is constituted, wherein, operational amplifier IC2 output end is connected with reverse input end, and in-phase input end is grounded by electric capacity C3,
Meanwhile, operational amplifier IC2 in-phase input end is sequentially connected in series resistance R9, R10 to the output of RC integral voltage amplifying circuits again
End, resistance R9 and resistance R10 concatenation point are connected by electric capacity C2 and operational amplifier IC2 output end, power end connection 16V
Supply voltage, GND ends ground connection, forms low-pass filter circuit, the input and RC integral voltage amplifying circuits of low-pass filter circuit
Connection, output end is connected with output circuit.
The low-pass filter circuit of the present invention is active low-pass filter circuit, and it is substantially active frequency selection circuit, it
Allow the signal of designated frequency band to pass through, and the signal in remaining frequency range is suppressed or makes its sharp-decay.Filter circuit is adopted
Constituted with operational amplifier and RC network, its performance is better than passive filter, between the input, output in filter circuit not
Impedance matching is needed, with good buffer action；Because without inductance element, anti-electromagnetic interference capability is strong.Low-pass filter circuit
Low-pass filtering treatment is carried out to the flow detecting signal of RC integral voltages amplifying circuit processing output, high-frequency signal and outside is removed
Noise jamming, prevents interference of the external signal to output signal, it is ensured that low-frequency flow detecting signal is not attenuated.
Embodiment 4
The overall of the flow sensing circuit of constant difference thermal flow rate sensor constitutes be the same as Example 1-5, referring to Figures 1 and 2,
In the bridge circuit of the present invention, for detection low discharge small-signal, temperature detecting resistance RS uses film metal RTD PT1000.Adjust
The heating power of the whole resistance that tests the speed, changes output voltage values.The resistance RH that tests the speed uses film metal RTD PT50, as RH* (R1
+ R2)=R4* (R3+RS) when, A, 2 voltages of B are equal, bridge circuit be in poised state.
The RC integral voltages amplifying circuit of the present invention receives 2 points of bridge circuit A, B voltage signal, by A, the electricity that B at 2 points
Feedback control tests the speed resistance RH heating powers after pressure signal amplification, and the output of RC integral voltage amplifying circuits is believed as feedback voltage
The directly control of bridge circuit top number is connected to test the speed the regulation of resistance heating power.
The low-pass filter circuit of the present invention is connected on RC integral voltage amplification circuit output ends, to RC integral voltage amplifying circuits
The flow detecting signal of processing output carries out low-pass filtering treatment, removes noise jamming.The output circuit of the present invention examines flow
Survey signal and carry out isolation voltage division processing；Power circuit uses booster power supply circuit, it is ensured that the resistance that tests the speed obtains enough heating work(
Rate, has high sensitivity in the range of low discharge, improves the stability of circuit.A more detailed specific example is given below
Son, the present invention is further described.
Embodiment 5
The overall of the flow sensing circuit of constant difference thermal flow rate sensor constitutes be the same as Example 1-6, reference picture 2, this hair
Bright RC integral voltages amplifying circuit is made up of operational amplifier unit and RC integrating circuit.The operational amplifier selected in this example
IC1 model TLV27L2, operational amplifier IC1 1 pin connecting resistance R8 a pin, operational amplifier IC1 2 pin connect electricity
R8 another pin is hindered, an operational amplifier IC1 3 pin connecting resistance R7 pin, resistance R7 another pin connects fortune
Amplifier IC1 8 pin are calculated, operational amplifier IC1 4 pin ground connection, the partial circuit connects to form operational amplifier unit；Computing
Amplifier IC1 1 pin connects an electric capacity C1 pin, and operational amplifier IC1 2 pin connect electric capacity C1 another pin, resistance
A R5 pin connects operational amplifier IC1 2 pin, and resistance R5 another pin connects the B points of bridge circuit, the partial circuit
Connection forms RC integrating circuit, and RC integrating circuit are collectively forming RC integral voltage amplifying circuits, RC products with operational amplifier unit
The input of component voltage amplifying circuit and the output end of bridge circuit are connected, and output is terminated to positioned at three poles on bridge circuit top
Test the speed the heating voltage of resistance in pipe Q1 base stages, feedback control bridge circuit.
Referring to Fig. 2, low-pass filter circuit of the invention includes operational amplifier IC2, resistance R9, resistance R10, electric capacity C2 and
Electric capacity C3.The operational amplifier IC1 model OPA2188, operational amplifier IC2 that are selected in this example 1 pin and 2 pin are connected, 3 pin
The pin with resistance R10 and electric capacity C3 is connected respectively, and electric capacity C3 another pin ground connection, 8 pin connect 16V power supplys, and resistance R10's is another
Pin connects an electric capacity C2 pin, and electric capacity C2 another pin connects operational amplifier IC2 1 pin, and a resistance R9 pin connects electric capacity C2 and electricity
R10 tie point is hindered, another pin connects the output end of RC integral voltage amplifying circuits, i.e. operational amplifier IC1 1 pin.
Referring to Fig. 2, output circuit of the invention is made up of voltage follower circuit and bleeder circuit.The fortune selected in this example
Calculation Amplifier Model is OPA2188, an operational amplifier IC3 1 pin connecting resistance R11 pin, operational amplifier IC3 2 pin and 1
Pin is connected, and its 3 pin connects the output end of low-pass filter circuit, and its 4 pin ground connection, its 8 pin connects 16V power supplys, forms voltage follower electricity
Road；Resistance R11 another pin connecting resistance R12, resistance R12 another pin ground connection, form bleeder circuit.Voltage follower circuit and
Bleeder circuit is collectively forming output circuit.The present invention power circuit include DC booster converter IC4, electric capacity C4, electric capacity C5,
The DC booster converter model selected in inductance L1, resistance R13, resistance R14 and Xiao Jite diode Q2, this example
SX1308.DC booster converter IC4 1 pin connects Xiao Jite diodes Q2 positive pole, and DC booster converter IC4 2 pin connect
Ground, DC booster converter IC4 3 pin are grounded by resistance R14, and DC booster converter IC4 4 pin connect 5V power supplys, direct current
Booster converter IC4 5 pin connect 5V power supplys, and DC booster converter IC4 6 pin are hanging, and an electric capacity C4 pin connects DC boosting
Converter IC4 5 pin, its another pin ground connection, an inductance L1 pin connects DC booster converter IC4 5 pin, and its another pin meets Xiao
Base spy's diode Q2 positive pole, a resistance R13 pin connects Xiao Jite diodes Q2 negative pole, its another pin connecting resistance R14, electric capacity
A C5 pin connects Xiao Jite diodes Q2 negative pole, its another pin ground connection.
Temperature detecting resistance RS in reference picture 3, described bridge circuit chooses film metal RTD PT1000, resistance position
In the upstream of measurement pipeline, for measuring fluid self-temperature, in order that its own does not produce heat, with ensure measurement temperature with
Fluid temperature (F.T.) is equal, and by the necessary very little of its electric current, therefore temperature detecting resistance resistance is larger；The resistance RH that tests the speed chooses film metal
RTD PT50, the resistance is located at the downstream of measurement pipeline, passes through larger current self-heating a to perseverance for being higher than fluid thereon
Constant temperature degree is heated for fluid, while measuring the temperature of fluid at this；Triode Q1 electrification stream amplifications.When circuit connects electricity
During source, resistance R6 conductings are powered to bridge circuit.When fluid flow changes, the balance of bridge circuit is destroyed, A, B in Fig. 3
Voltage at 2 points is unequal, and unbalanced voltage signal is input to bridge circuit after the amplification of RC integral voltages amplifying circuit
Triode Q1 base stage, triode is opened, and is added in the voltage increase on electric bridge, so that by the electric current increase for the resistance RH that tests the speed,
The resistance RH resistance of testing the speed becomes big, meanwhile, the voltage increase of IC1 end of oppisite phase, as RH* (R1+R2)=R4* (R3+RS), A, B
2 voltages are equal, and electric bridge reaches dynamic balance state again.
The flow sensing circuit composition of the present invention is simple in construction, using the less component of encapsulation, circuit overall volume
Small, in the absence of movable part, circuit output analog voltage signal is easy to connect with other external equipments, easy for installation.
Below by the technique effect of the actual measurement explanation present invention
Embodiment 6
The overall of the flow sensing circuit of constant difference thermal flow rate sensor constitutes be the same as Example 1-7, what the present invention was designed
The flow sensing circuit of constant difference thermal flow rate sensor is applied to be related to low discharge detection model in the fields such as medical and chemical industry
The fluid flow detection enclosed, the relation curve of output voltage and flow is calibrated by actual test, is surveyed altogether in actual test
Examination obtains six groups of test curves and a class mean curve.
Test condition is as follows：Environment temperature is 24 degrees Celsius, and test fluid is physiological saline, and test fluid temperature (F.T.) 23 is Celsius
Degree, ambient humidity 36%, air pressure size is standard atmospheric pressure, determines range of flow 0-15ml/min.During actual test,
14 flow detection calibration points are set in the range of flow measurement, after (etc. after the output voltage stabilization of each flow rate test calibration point
Treat time about 30s), output voltage values now are recorded, after all test calibration points are measured, are obtained by curve matching
The relation curve of output voltage and flow, real-time flow value is calculated by the curve fitted.Test result reference picture
4。
Reference picture 4, is the data that obtain under the test conditions above of the present invention from 7 empirical curves in Fig. 4, can be with
Find out, the output voltage of flow sensing circuit of the invention increases with the increase of flow, single tests curve of output in flow
The linearity is good in range of flow more than 1.6ml/min, and all experiment output voltages are approximately straight line；Single test is bent
Line output voltage is steady, no big ups and downs, test for each time output voltage identical flow rate test point compared with average difference compared with
It is small；Each time test curve output voltage tendency is identical, and curve of output is largely focused near Mean curve, and repeatability is good.
The present invention takes the relation curve that Mean curve is final output voltage and flow, and calculating fluid flow by curve proves, this
Invention can determine the fluid flow in the range of low discharge precisely in real time.
In brief, the flow sensing circuit of a kind of constant difference thermal flow rate sensor disclosed by the invention, according to flow
The direction of transfer of detection signal is connected with bridge circuit, RC integral voltages amplifying circuit, low-pass filter circuit, output circuit in turn
And power circuit.In described bridge circuit, temperature detecting resistance RS is film metal RTD PT1000, positioned at first bridge arm
Lower bridge arm end, the resistance RH that tests the speed is film metal RTD PT50, positioned at the lower bridge arm end of second bridge arm；The RC integrations electricity
Pressure amplifying circuit is additionally arranged RC integrating circuit in operational amplifier unit, forms RC integral voltage amplifying circuits.Meanwhile, it is low
Bandpass filter circuit is filtered processing, the recognizable 0-5V output electricity of output circuit generation other equipment to flow detecting signal
Pressure.
It is of the invention can in real time, the accurate fluid flow determined in the range of low discharge, accuracy of detection is higher, fast response time,
It is easy for installation, simple to operate, available for the less field of flow detection of the range of flows such as medical, chemical industry.
Claims (3)
1. a kind of flow sensing circuit of constant difference thermal flow rate sensor, it is characterised in that：Biography according to flow detecting signal
Pass direction and be connected with bridge circuit, voltage amplifier circuit, low-pass filter circuit, output circuit and power circuit, output electricity in turn
Low-pass filter circuit is provided with before road；In described bridge circuit, temperature detecting resistance RS is film metal RTD PT1000, the platinum
Resistance RS connects with precision resistance R1, potentiometer R2 and precision resistance R3, constitutes first bridge arm of bridge circuit, temperature detecting resistance
RS is located at the lower bridge arm end of first bridge arm, and the resistance RH that tests the speed is film metal RTD PT50, RTD RH and resistance R4
Series connection, constitutes second bridge arm of bridge circuit, and the resistance that tests the speed is located at the lower bridge arm end of second bridge arm；The voltage amplification electricity
Road is RC integral voltage amplifying circuits, and RC integrating circuit are additionally arranged in operational amplifier unit, RC integral voltages is formd and puts
Big circuit, the input termination bridge circuit output of RC integral voltage amplifying circuits, the output feedback of RC integral voltage amplifying circuits
The triode Q1 base stages positioned at bridge circuit top are connected to, the heating power for the resistance RH that tested the speed for control；Described low pass filtered
Wave circuit is connected on RC integral voltage amplification circuit output ends, and the input of the output termination output circuit of low-pass filter circuit is defeated
Go out circuit to carry out flow detecting signal to obtain the recognizable 0-5V analog voltages of other equipment after isolation voltage division processing；Power supply electricity
Road is booster power supply circuit, for the 16V supply voltages needed for all composition circuit offer work.
2. the flow sensing circuit of constant difference thermal flow rate sensor as claimed in claim 1, it is characterised in that：Described RC
Integral voltage amplifying circuit includes operational amplifier unit and RC integrating circuit, wherein, operational amplifier IC1 output ends and anti-phase
Resistance R8 is serially connected between input, positive input and power end are serially connected with resistance R7, form operational amplifier unit, computing
Electric capacity C1 is serially connected between amplifier out and inverting input, reverse input end and bridge output are terminated with resistance R5, shape
Into RC integrating circuit, operational amplifier unit and RC integrating circuit are collectively forming RC integral voltage amplifying circuits, RC integral voltages
The input of amplifying circuit and the output end of bridge circuit are connected, and output terminates to the triode Q1 bases positioned at bridge circuit top
Pole, forms the Voltage Feedback for changing the resistance RH heating powers that tested the speed in bridge circuit.
3. the flow sensing circuit of constant difference thermal flow rate sensor as claimed in claim 1, it is characterised in that：Described is low
Bandpass filter circuit, is made up of operational amplifier and its peripheral circuit, wherein, operational amplifier IC2 output end and reversely input
End is connected, and in-phase input end is grounded by electric capacity C3, and operational amplifier IC2 in-phase input end is sequentially connected in series resistance R9, R10 again
To the output end of RC integral voltage amplifying circuits, resistance R9 and resistance R10 concatenation point pass through electric capacity C2 and operational amplifier IC2
Output end connection, formed low-pass filter circuit, low-pass filter circuit input and RC integral voltages amplifying circuit connection, it is defeated
Go out end to be connected with output circuit, the flow detecting signal of RC integral voltages amplifying circuit processing output is carried out at LPF
Reason, removes high-frequency signal and external noise interference.
Priority Applications (1)
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| CN111595402A (en) * | 2020-05-29 | 2020-08-28 | 合肥工业大学 | Constant-temperature difference type thermal gas mass flow meter |
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