CN102445245B - Flow rate measurement device based on bridge-type flow rate measurement and electromagnetic flow rate measurement - Google Patents

Abstract

The invention discloses a flow rate measurement device based on bridge-type flow rate measurement and electromagnetic flow rate measurement. The ARM microprocessor of the flow rate measurement device is connected with an excitation system, an A/D converter, a D/A convertor, an output display circuit, and a communication debugging circuit respectively; and one branch of an electromagnetic flow rate measurement sensor is connected with the excitation system and another branch is connected with the A/D converter through an electromagnetic signal processing circuit. The invention further comprises an oscillation drive circuit, a bridge-type flow rate measurement sensor, and a bridge-type signal processing circuit, wherein the bridge-type signal processing circuit is connected with the A/D converter; and the oscillation drive circuit is connected with the bridge-type signal processing circuit through the bridge-type flow rate measurement sensor. Bridge-type flow rate measurement is suitable for volumetric flow rate measurement of conducting liquid with a low flow velocity lower than 1m/s and a small flow rate; and when the flow velocity increases, the electromagnetic flow rate measurement excitation system is started and the bridge-type flow rate measurement system is closed to ensure measurement accuracy. The bridge-type flow rate measurement system in the device dispenses with an excitation coil, and has a simple structure and a low implementation cost.

Description

Flow measurement device based on bridge-type flow measurement and electromagnetic flow-measurement

Technical field

The present invention relates to a kind of flow measurement device, especially relate to a kind of flow measurement device based on bridge-type flow measurement and electromagnetic flow-measurement.

Background technology

Mainly adopt the electromagnetic flowmeter of electromagnetic flow-measurement technology at present to the conducting liquid volume flow measurement.Electromagnetic flow-measurement is according to Faraday's electromagnetic induction law, when conductor moves in magnetic field and during cutting magnetic line, the conductor two ends can produce induction electromotive force.Be located in the uniform magnetic field, perpendicular to magnetic field a diameter being arranged is the pipeline of D.Inner surface of pipeline has in the insulation village, when conducting medium flows in pipeline, and cutting magnetic line, thereby can the generation induction electromotive force vertical with magnetic field and flow direction.This induction electromotive force is detected by the pair of electrodes of measuring on the tube wall, and as shown in Figure 1, its value is:

$E=\mathrm{KB}\stackrel{\‾}{v}D---(1-1)$

In the formula: E---induction electromotive force, V;

B---magnetic induction density, T;

D---measuring tube internal diameter, m;

---mean flow rate, m/s;

K---meter constant;

$q_v=\frac{\mathrm{\π}}{4}{D}^2\stackrel{\‾}{v}---(1-2)$

q _v---volumetric flow rate, mL/s;

(1-1) formula substitution (1-2) formula,

$E=\frac{4}{\mathrm{\π}}\frac{B}{D}{q}_v---(1-3)$

Or $q_v=\frac{\mathrm{\π}}{4}D\frac{E}{B}---(1-4)$

Structurally, Electromagnetic Flow is formed in respect of electromagnetic flow transducer and electromagnetic flux converter two parts.Electromagnetic flow transducer mainly is made up of measuring tube, excitation system and pair of electrodes.It is installed on the industrial process pipeline, and its effect is that the liquid volume flow value in the flowing into pipeline is transformed into induced electromotive force linearly, and through transmission line this signal is transferred to converter.Converter is installed in from the not far place of sensor, effect be the flow signal that sends sensor amplify and the normalized current signal that changes into the 4-20mA that is directly proportional with the measured medium volumetric flow rate to show, to accumulate and to regulate control.

If the not high fluids of viscosity such as general industry pipeline transporting water, flow velocity generally designs between economic velocity 1.5～3m/s.Electromagnetic flowmeter is used on such pipeline, and optional electromagnet flow meter sensor bore is identical with caliber.The flow rate of liquid in electromagnetic flowmeter full scale when metering is in 1～10m/s scope, and the upper limit flow velocity of electromagnetic flowmeter but in actual the use, seldom surpasses 7m/s on principle and unrestricted usually, surpasses the more rare of 10m/s.Full scale flow velocity lower limit is generally 1m/s.

Electromagnetic flowmeter has lot of advantages: big like the measurement range degree; Measure the influence that the density do not receive fluid, temperature, pressure, viscosity, Reynolds number etc. change; Corrosion resistance and good; Measuring principle is linear, and measuring accuracy is high; Velocity flow profile is required low etc.

As shown in Figure 2, the graph of a relation of Kanex-Krohneanlagen Export GmbH's electromagnetic flowmeter measuring error and flow velocity under standard conditions.When flow velocity during less than 1m/s, measuring error obviously increases.Because detected signal is very faint with respect to undesired signal, be difficult to measure, therefore introduce the amplifier of high-amplification-factor.Yet so just make electromagnetic flowmeter receive the interference of external electromagnetic field especially easily, even very faint interference after amplifying through high power, also is huge to result's influence.Will certainly influence the accuracy of instrument so widely, stability, the reliability of control system also constituted very big hidden danger.On the low side like some engineering operation initial stage flow velocity, from measuring accuracy, the instrument bore should be used little caliber instead, is connected on the caliber with reducer pipe.Therefore, for minimum velocity, realize that on original pipeline the accurate measurement of flow is still a difficult problem at present.

Summary of the invention

The purpose of this invention is to provide a kind of flow measurement device based on bridge-type flow measurement and electromagnetic flow-measurement.On the basis of traditional electrical magnetic flow measurement excitation system, increase the bridge-type Flow Measuring System; The bridge-type flow measurement is for electromagnetic flow-measurement, and it does not need excitation system, and is simple in structure; The realization cost is low, and the excitation system of electromagnetic flow-measurement is not produced any influence.

The technical scheme that the present invention adopts is:

The present invention includes excitation system, electromagnetic flow-measurement sensor, electromagnetic signal treatment circuit, A/D converter, ARM microprocessor, D/A converter, output display circuit and communication debug circuit; The ARM microprocessor is connected with the communication debug circuit with excitation system, A/D change-over circuit device, D/A converter, output display circuit respectively; Electromagnetic flow-measurement sensor one tunnel is connected with excitation system, and another road is connected with A/D converter through the electromagnetic signal treatment circuit; It is characterized in that: also comprise oscillation drive circuit, bridge-type flow measuring sensor and bridge signal treatment circuit; Follower in the bridge signal treatment circuit is connected with A/D converter, and oscillation drive circuit is connected with amplifier in the bridge signal treatment circuit through the bridge-type flow measuring sensor; The bridge signal treatment circuit comprises amplifier, current rectifying and wave filtering circuit, zero point correction circuit and follower; One end of amplifier is connected with the bridge signal treatment circuit, and the other end of amplifier is connected with an end of follower behind current rectifying and wave filtering circuit and zero point correction circuit, and the other end of follower is connected with A/D converter.

Described bridge-type flow measuring sensor has two pairs of electrodes; The two pairs of electrodes are placed on the both sides of pair of electrodes of the electromagnetic flow-measurement sensor of measuring tube axial cross section respectively, and the two pairs of electrodes of bridge-type flow measuring sensor and the pair of electrodes of electromagnetic flow-measurement sensor are positioned at same axial cross section; Wheatstone bridge is formed in lumped parameter impedance between two pairs of electrodes of bridge-type flow measuring sensor; One group to a ground connection in the corner electrode; Another the 6th pin that meets oscillation drive circuit LM741 encourages, and another group connects the 10th, 5 pin of amplifier INA101 to corner electrode; The measuring tube inside surface has the insulation lining, and the both ends of the surface of measuring tube are connected with the two ends tested pipeline respectively through insulation spacer or politef sheet with flange.

Described oscillation drive circuit is core with LM741; One group of electrode to corner electrode of the 6th pin output terminal of LM741 and bridge-type flow measuring sensor joins; One group of another electrode grounding to corner electrode; Another of bridge-type flow measuring sensor organized the 5th pin that an electrode of corner electrode is met amplifier INA101, and another group of bridge-type flow measuring sensor connects the 10th pin of amplifier INA101 to another electrode of corner electrode.

In the described bridge signal treatment circuit; Low consumed power operational amplifier LM124 has four operational amplifier OP07; Wherein join as the 3rd pin of first operational amplifier OP07-1 of current rectifying and wave filtering circuit and the 8th pin of amplifier INA101, first the 1st pin of calculating amplifier OP07-1 joins with the 6th pin as second operational amplifier OP07-2 of zero point correction circuit; The 7th pin of second operational amplifier OP07-2 joins with the 10th pin as the 3rd operational amplifier OP07-3 of follower, and the 8th pin of the 3rd operational amplifier OP07-3 is through A/D converter input ARM microprocessor.

Described ARM microprocessor adopts 32 arm processor, and for the LPC2106 of Philips company is 32 ARM flush bonding processors of technical grade to Embedded Application that main CPU or Atmel company release, A/D converter adopts the AD7715 of ADI company; D/A converter adopts the output module AD421 chip of 4-20mA; The output display circuit adopts 12864 dot matrix band Chinese character Liquid Crystal Modules; The communication debug circuit comprises RS232 interface and RS485 interface; The shared above circuit of bridge-type flow measurement and electromagnetic flow-measurement.

The beneficial effect that the present invention has is:

1) the bridge-type flow measurement that increases newly is applicable to the low flow velocity below the 1m/s, the volume flow measurement of low discharge conducting liquid.This measurement mechanism has increased the bridge-type flow measurement on the basis of traditional electrical magnetic flow measurement, make this flow measurement device detect or when the engineering operation initial stage, flow velocity was on the low side, use the bridge-type Flow Measuring System that low discharge is measured at blank pipe.When flow velocity increases to a certain degree, open the electromagnetic flow-measurement excitation system, close the bridge-type Flow Measuring System, guarantee measuring accuracy.The high precision that this device has kept electromagnetic flow-measurement that the conducting liquid volume flow measurement is had on the one hand, the high accuracy characteristics have remedied under low flow velocity, low discharge state the characteristic that measuring accuracy is not high simultaneously.

2) adopt two cover control system, bridge-type Flow Measuring System and electromagnetic flow-measurement system are independent of each other.The bridge-type Flow Measuring System does not have any impact to traditional electrical magnetic flow excitation system.Bridge-type Flow Measuring System in this device does not need field coil, and is simple in structure, realizes that cost is low.

Description of drawings

Fig. 1 electromagnetic flowmeter principle of work synoptic diagram.

Fig. 2 is the graph of a relation of Kanex-Krohneanlagen Export GmbH's electromagnetic flowmeter measuring error and flow velocity under standard conditions.

Fig. 3 is a front view of the present invention.

Fig. 4 is the A-A cut-open view of Fig. 3.

Fig. 5 is the structural principle block diagram of electromagnetic flowmeter.

Fig. 6 is a structural principle block diagram of the present invention.

Fig. 7 is bridge-type flow measurement four electrode lumped parameter impedance net synoptic diagram of the present invention.

Fig. 8 is bridge signal treatment circuit figure of the present invention.

Fig. 9 is oscillation drive circuit figure of the present invention.。

Among the figure: 1, field coil, 2, flange, 3, electrode, 4, measuring tube, 5, the insulation lining.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is further specified.

Like Fig. 5, shown in Figure 6, the present invention includes excitation system, electromagnetic flow-measurement sensor, electromagnetic signal treatment circuit, A/D converter, ARM microprocessor, D/A converter, output display circuit, communication debug circuit; The ARM microprocessor is connected with the communication debug circuit with excitation system, A/D change-over circuit device, D/A converter, output display circuit respectively; Electromagnetic flow-measurement sensor one tunnel is connected with excitation system, and another road is connected with A/D converter through the electromagnetic signal treatment circuit; Also comprise oscillation drive circuit, bridge-type flow measuring sensor and bridge signal treatment circuit; Follower in the bridge signal treatment circuit is connected with A/D converter, and oscillation drive circuit is connected with amplifier in the bridge signal treatment circuit through the bridge-type flow measuring sensor; The bridge signal treatment circuit comprises amplifier, current rectifying and wave filtering circuit, zero point correction circuit and follower, and is as shown in Figure 6; One end of amplifier is connected with the bridge signal treatment circuit, and the other end of amplifier is connected with an end of follower behind current rectifying and wave filtering circuit and zero point correction circuit, and the other end of follower is connected with A/D converter.

Excitation system is to have constant current source to drive a H bridge circuit; Current waveform is that forms such as square wave, sine wave, three value ripples produce an alternating magnetic field; Conductive fluid is cutting magnetic line in magnetic field, on bridge-type flow measuring sensor two electrodes, induces extremely several millivolts alternating voltage signal of tens microvolts, joins through differential amplifier, low pass and Hi-pass filter, gain amplifier and A/D converter and ARM microprocessor; Realize the amplification denoising of signal, improve signal to noise ratio (S/N ratio).The communication debugging module comprises RS232 interface and RS485 interface; Select corresponding communication modes according to user's needs, convenient and host computer carries out communication, and the output module of 4-20mA is selected the AD421 chip for use; Can directly convert digital signal to current signal output, and reserve HART agreement communication interface.

Like Fig. 3, Fig. 4, shown in Figure 7; Described bridge-type flow measuring sensor has two pairs of electrodes 3; The two pairs of electrodes 3 are placed on the both sides of pair of electrodes of the electromagnetic flow-measurement sensor of measuring tube 4 axial cross sections respectively, and the two pairs of electrodes of bridge-type flow measuring sensor and the pair of electrodes of electromagnetic flow-measurement sensor are positioned at same axial cross section; Wheatstone bridge is formed in lumped parameter impedance between two pairs of electrodes of bridge-type flow measuring sensor; In the action of a magnetic field territory that these two pairs of electrodes need not produce at the field coil of excitation system; A ground connection among one group of diagonal angle electrode A, the D; Another the 6th pin that meets oscillation drive circuit LM741 encourages, and another group diagonal angle electrode B, C connect the 10th, 5 pin of amplifier INA101; Measuring tube 4 inside surfaces have insulation lining 5, and the flange 2 of the both ends of the surface of measuring tube is connected with the two ends tested pipeline respectively through insulation spacer or politef sheet, and the both sides up and down of the pair of electrodes of electromagnetic flow-measurement sensor are equipped with field coil 1 respectively.

Like Fig. 7, shown in Figure 9; Described oscillation drive circuit is core with LM741; One group of electrode A to corner electrode of the 6th pin output terminal of LM741 and bridge-type flow measuring sensor is joined; One group of another electrode D ground connection to corner electrode, another of bridge-type flow measuring sensor organized the 5th pin that an electrode C of corner electrode is met amplifier INA101, and another group of bridge-type flow measuring sensor connects the 10th pin of amplifier INA101 to another electrode B of corner electrode.The 3rd pin of resistance R 6 one termination LM741, other end ground connection.The 6th pin of line rheostat R5 one termination LM741, the 3rd of another termination LM741.Resistance R 4 is parallelly connected with capacitor C 2, an end ground connection, and the 2nd pin of another termination LM741, resistance R 3 is connected with capacitor C 1, the 6th pin of a termination LM741, the 2nd pin of a termination LM741.

As shown in Figure 8; In the described bridge signal treatment circuit; Low consumed power operational amplifier LM124 has four operational amplifier OP07; Wherein join as the 3rd pin of first operational amplifier OP07-1 of current rectifying and wave filtering circuit and the 8th pin of amplifier INA101, the 1st pin of first operational amplifier OP07-1 joins with the 6th pin as second operational amplifier OP07-2 of zero point correction circuit; The 7th pin of second operational amplifier OP07-2 joins with the 10th pin as the 3rd operational amplifier OP07-3 of follower, and the 8th pin of the 3rd operational amplifier OP07-3 is through A/D converter input ARM microprocessor.

Bridge signal treatment circuit figure is made up of amplifier, current rectifying and wave filtering circuit, zero point correction circuit and follower.Low consumed power operational amplifier LM124 has four operational amplifier OP07; Amplifier INA101 carries out one-level to output voltage and amplifies; The 9th pin and the positive supply of amplifier INA101 join; The 6th pin and the negative supply of amplifier INA101 join, and the 9th pin of positive supply and amplifier INA101 connects a high-frequency filter capacitor respectively between the 6th pin of negative supply and amplifier INA101.Meet a line rheostat R8 between the 1st, 4 pin of amplifier INA101 and be used for the gain of resonance-amplifier, the 10th pin of amplifier INA101 is a negative input end, and the 5th pin of amplifier INA101 is a positive input terminal.The 8th pin of amplifier INA101 is an output terminal.Current rectifying and wave filtering circuit is a core with first operational amplifier OP07-1; The 8th pin of one termination amplifier INA101 of resistance R 9; The 3rd pin of first operational amplifier of another termination OP07-1 of resistance R 9; Diode D1, D2 are reverse, the 2nd pin of first operational amplifier of termination OP07-1, the 1st pin of first operational amplifier of another termination OP07-1.The 1st pin of first operational amplifier OP07-1 is through resistance R 10 and capacitor C 5 parallelly connected ground connection.The zero point correction circuit is a core with second operational amplifier OP07-2; The 6th pin of second operational amplifier OP07-2 of resistance R 13 1 terminations, the 7th pin of second operational amplifier OP07-2 of another termination, the 1st pin of first operational amplifier of resistance R 14 1 terminations OP07-1; The 6th pin of second operational amplifier OP07-2 of another termination; The 7th pin of second operational amplifier OP07-2 is an output terminal, line rheostat R11 one termination positive supply, another termination negative supply; Join with resistance R 12 1 ends simultaneously and connect the 5th pin of second operational amplifier OP07-2 again; The 5th pin of second operational amplifier OP07-2 is through R15 ground connection, and the 7th pin of second operational amplifier OP07-2 joins through R16 and follower the 10th pin with the 3rd operational amplifier OP07-3, and the 8th pin of the 9th pin of the 3rd operational amplifier OP07-3 and the 3rd operational amplifier OP07-3 directly joins; Simultaneously, the 8th pin of the 3rd operational amplifier OP07-3 is an output terminal.

The present invention introduces the bridge-type Flow Measuring System, and there is electrochemical phenomena in metal electrode in fluid electrolyte.According to electrochemical principle, there is the interface electric field between electrode and fluid, the interface of electrode and fluid is that the electrostatic double layer of electrode and the alternate existence of fluid is caused.Electrode and fluid interface Study of Electric Field are found that molecule, atom and the ion of material have enrichment or poor adsorption phenomena at the interface; And find that most of inorganic anions are surface reactive materials; Have typical ionic adsorption rule, and the surfactivity of inorganic cation is very little.Because polarization impedance causes electric potential difference; If small-signal alternating current driver one group to corner electrode on; Two and half electromotive forces between this alternating voltage and two electrodes are superimposed; To another electrode, current density is subject to polarization impedance and the ohmage between two electrodes to ion in the fluid from an electrode stream simultaneously.In addition, if fluid be along the measuring channel direction from an electrode stream to another electrode, ion is along with fluid moves because the viscous force effect that velocity gradient produces, current density finally reaches mobile equilibrium.Therefore, polarization impedance is depended in interelectrode lumped parameter impedance, ohmage, the velocity gradient impedance of fluid.Be considered to constantly for fixing system's polarization impedance and ohmage, the velocity gradient of passing the pipeline fluid xsect depends on the speed of fluid.

As shown in Figure 7; Bridge-type flow measurement four electrode lumped parameter impedance nets; Suppose to have four lumped parameter impedances between the four symmetrical in twos electrodes of axial cross section, when conducting liquid is crossed the measuring channel of horizontal positioned with laminar flow low discharge state flow, suppose that it is not along diametric flow velocity unit; Therefore, the lumped parameter impedance Z between electrode A, the C ₁And the lumped parameter impedance Z between the electrode B, D ₃Be constant.Lumped parameter impedance Z between electrode A, the B ₂And the lumped parameter impedance Z between the electrode C, D ₄Change with the fluid velocity gradient.

Therefore, according to the Wheatstone bridge principle, two electrodes of a diagonal pass to constant alternating current, and another changes the output of the corner electrode flow velocity with conducting liquid.The alternating voltage Vs of fixed frequency is provided between electrode A, D, because metering circuit has high input impedance, bridge circuit voltage output signal V ₀For

$V_0=V_s\frac{(Z_2{Z}_4-Z_1{Z}_3)}{({\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="111102135307.png,111102135309.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1+Z_4)({\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="111102135307.png,111102135312.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2+Z_3)}---\left(1\right)$

For alternating voltage Vs and identical electrodes Z is arranged ₁=Z ₃, Z ₂=Z ₄

Suppose that flow is Q ₀Fluid, Z ₁=Z ₃=Z _C, Z ₂=Z ₄=Z ₀, be different from Q at another ₀Flow Q under, the lumped parameter impedance Z ₀Become Z _QZ _QTaylor series expansion do

$Z_Q={\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+{\left(\frac{\&PartialD;Z_Q}{\&PartialD;Q}\right)}_{{\mathrm{<figure-callout\; id="0"\; label="Q"\; filenames="111102135307.png"\; state="\{\{state\}\}">Q</figure-callout>}}_0}\mathrm{\&Delta;Q}+\frac{1}{2!}{\left(\frac{{\&PartialD;}^2{Z}_Q}{\&PartialD;Q^2}\right)}_{{\mathrm{<figure-callout\; id="0"\; label="Q"\; filenames="111102135307.png"\; state="\{\{state\}\}">Q</figure-callout>}}_0}\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="111102135307.png,111102135312.png"\; state="\{\{state\}\}">Q</figure-callout>}}^2+\&CenterDot;\&CenterDot;\&CenterDot;---\left(2\right)$

Flow velocity increment Delta Q=Q-Q wherein ₀, order

${\left(\frac{\&PartialD;Z_Q}{\&PartialD;Q}\right)}_{Q_O}=\mathrm{\&mu;},$ $\frac{1}{2!}{\left(\frac{{\&PartialD;}^2{Z}_Q}{\&PartialD;Q^2}\right)}_{{\mathrm{<figure-callout\; id="0"\; label="Q"\; filenames="111102135307.png"\; state="\{\{state\}\}">Q</figure-callout>}}_0}=\mathrm{\&beta;}$

So Z _Q=Z ₀+ μ Δ Q+ β Δ Q ²+ ... (3)

When laminar condition, β value the and more coefficient of higher order term is very little.Therefore, when Δ Q fluctuations in discharge is very little, Z _QBe expressed from the next

Z _Q＝Z ₀+μΔQ (4)

Z ₁=Z ₃=Z _C, Z ₂=Z ₄=Z _QSubstitution (1) formula, the bridge circuit output voltage did when flow was Q

${\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="111102135307.png"\; state="\{\{state\}\}">V</figure-callout>}}_0=V_S\left[\frac{(Z_Q-Z_C)}{(Z_Q+Z_C)}\right]---\left(5\right)$

Draw by (4) and (5) formula

${\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="111102135307.png"\; state="\{\{state\}\}">V</figure-callout>}}_0=V_S\left[\frac{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+\mathrm{\&mu;\; \&Delta;\; Q}-Z_C)}{(Z_C+{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+\mathrm{\&mu;\; \&Delta;\; Q})}\right]$ Perhaps

${\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="111102135307.png"\; state="\{\{state\}\}">V</figure-callout>}}_0=[\left(\frac{Z_0-{\mathrm{<figure-callout\; id="0"\; label="Z\; C\; Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_C}{Z_{}}\right)+\frac{2Z_C\mathrm{\&mu;}}{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C)}\mathrm{\&Delta;Q}-\frac{{\mathrm{\&mu;}}^2}{{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C)}^2}\mathrm{\&Delta;}{Q}^2]V_S$

V ₀＝K ₁+K ₂ΔQ-K ₃ΔQ ² (6)

Wherein

${\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="111102135307.png,111102135309.png"\; state="\{\{state\}\}">K</figure-callout>}}_1=\left(\frac{Z_0-{\mathrm{<figure-callout\; id="0"\; label="Z\; C\; Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_C}{Z_{}}\right)V_S---\left(7\right)$

${\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="111102135307.png,111102135312.png"\; state="\{\{state\}\}">K</figure-callout>}}_2=\frac{2\mathrm{\&mu;}{Z}_C}{{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C)}^2}{V}_S---\left(8\right)$

${\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="111102135307.png,111102135312.png"\; state="\{\{state\}\}">K</figure-callout>}}_3=\frac{{\mathrm{\&mu;}}^2}{{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C)}^2}{V}_S---\left(9\right)$

When laminar condition, COEFFICIENT K ₃Value be considered to very for a short time, ignore.Therefore, when Δ Q fluctuations in discharge was very little, (6) formula was expressed as

V ₀＝K ₁+K ₂ΔQ (10)

Or do

V ₀＝K ₁+K ₂(Q-Q ₀) (11)

Find out that thus under laminar condition, bridge circuit output voltage and fluctuations in discharge amount are linear.When no liquid flows through pipeline, flow Q ₀=0, equate Z along the duct orientation inter-electrode impedance with the radial electrode impedance ₀=Z _CThis moment K ₁=0, (11) formula is reduced to

V ₀＝K ₂Q (12)

Drawn by formula (12), under laminar flow low discharge state, the bridge circuit output voltage is directly proportional with flow.Under the relatively big state of turbulent flow flow velocity, (3) formula is expressed as

Z _Q＝Z ₀+μΔQ+βΔQ ²

Getting bridge circuit voltage by formula (5) does

${\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="111102135307.png"\; state="\{\{state\}\}">V</figure-callout>}}_0=\frac{(Z_0-Z_C+\mathrm{\&mu;\&Delta;Q}+\mathrm{\&beta;}{\mathrm{\&Delta;Q}}^2)}{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+\mathrm{\&mu;\&Delta;Q}+\mathrm{\&beta;\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="Q"\; filenames="111102135307.png,111102135312.png"\; state="\{\{state\}\}">Q</figure-callout>}}^2+Z_C)}{V}_S---\left(13\right)$

Therefore, under the turbulence state, the bridge circuit output voltage becomes non-linear with flow increment.Suppose Z ₀+ Z _C＞＞μ Δ Q+ β Δ Q ²Output voltage is expressed as

${\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="111102135307.png"\; state="\{\{state\}\}">V</figure-callout>}}_0=\frac{Z_0-Z_C+\mathrm{\&mu;\; \&Delta;\; Q}+\mathrm{\&beta;\; \&Delta;}{Q}^2}{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C}[1-\frac{\mathrm{\&mu;\; \&Delta;\; Q}+\mathrm{\&beta;\; \&Delta;}{Q}^2}{{\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C}]$ Or do

V ₀＝K ₁+K ₂ΔQ+K ₃′ΔQ ²-K ₄ΔQ ³-K ₅ΔQ ⁴ (14)

Wherein

${{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="111102135307.png,111102135312.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^{\&prime;}=\frac{{2Z}_C\mathrm{\&beta;}-{\mathrm{\&mu;}}^2}{{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C)}^2}{V}_S---\left(15\right)$

${\mathrm{<figure-callout\; id="5"\; label="K"\; filenames="111102135307.png,111102135324.png"\; state="\{\{state\}\}">K</figure-callout>}}_5=\frac{{\mathrm{\&beta;}}^2}{{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C)}^2}{V}_S---\left(16\right)$

${\mathrm{<figure-callout\; id="5"\; label="K"\; filenames="111102135307.png,111102135324.png"\; state="\{\{state\}\}">K</figure-callout>}}_5=\frac{{\mathrm{\&beta;}}^2}{{({\mathrm{<figure-callout\; id="0"\; label="Z"\; filenames="111102135307.png"\; state="\{\{state\}\}">Z</figure-callout>}}_0+Z_C)}^2}{V}_S---\left(17\right)$

Because of μ and β are very little, K ₄And K ₅Can ignore, (14) formula is reduced to so

V ₀＝K ₁+K ₂ΔQ+K ₃′ΔQ ² (18)

Initial flow is Q ₀, under transition or turbulence state, the equation of front becomes

V ₀＝K ₁+K ₂(Q-Q ₀)+K ₃′(Q-Q ₀) ² (19)

Therefore, under turbulence state, bridge circuit output voltage and flow increment can think have certain non-linear.The theoretical foundation of bridge-type flow measurement technology that Here it is.

Described ARM microprocessor adopts 32 arm processor, and for the LPC2106 of Philips company is 32 ARM flush bonding processors of technical grade to Embedded Application that main CPU or Atmel company release, A/D converter adopts the AD7715 of ADI company; D/A converter adopts the output module AD421 chip of 4-20mA; The output display circuit adopts 12864 dot matrix band Chinese character Liquid Crystal Modules; The communication debug circuit comprises RS232 interface and RS485 interface; The shared above circuit of bridge-type flow measurement and electromagnetic flow-measurement.

This Flow Measuring System detects or when the engineering operation initial stage, flow velocity was on the low side, can stop the electromagnetic flow-measurement system at blank pipe, switches to the bridge-type Flow Measuring System.Electromagnetic flow transducer and field coil and electromagnetic signal treatment circuit are not worked, and realize bridge-type flow measurement completely.When flow velocity arrival economic velocity is above; Stop the bridge-type Flow Measuring System; Switch to the electromagnetic flow-measurement system, electromagnetic flow transducer and field coil and electromagnetic signal treatment circuit are all started working, and bridge-type flow measuring sensor, oscillation drive circuit and bridge signal treatment circuit then quit work; The intrinsic advantage of performance electromagnetic flow-measurement on the conducting liquid volume flow measurement realizes high precision, high accuracy measurement.

Claims (2)

1. the flow measurement device based on bridge-type flow measurement and electromagnetic flow-measurement comprises excitation system, electromagnetic flow-measurement sensor, electromagnetic signal treatment circuit, A/D converter, ARM microprocessor, D/A converter, output display circuit and communication debug circuit; The ARM microprocessor is connected with excitation system, A/D converter, D/A converter, output display circuit and communication debug circuit respectively; Electromagnetic flow-measurement sensor one tunnel is connected with excitation system, and another road is connected with A/D converter through the electromagnetic signal treatment circuit; It is characterized in that: also comprise oscillation drive circuit, bridge-type flow measuring sensor and bridge signal treatment circuit; Amplifier in the bridge signal treatment circuit, current rectifying and wave filtering circuit, zero point correction circuit link to each other with follower successively; Follower in the bridge signal treatment circuit is connected with A/D converter, and oscillation drive circuit is connected with amplifier in the bridge signal treatment circuit through the bridge-type flow measuring sensor;

Described bridge-type flow measuring sensor has two pairs of electrodes; The two pairs of electrodes are placed on the both sides of pair of electrodes of the electromagnetic flow-measurement sensor of measuring tube axial cross section respectively, and the two pairs of electrodes of bridge-type flow measuring sensor and the pair of electrodes of electromagnetic flow-measurement sensor are positioned at same axial cross section; Wheatstone bridge is formed in lumped parameter impedance between two pairs of electrodes of bridge-type flow measuring sensor; One group to a ground connection in the corner electrode (A, D); Another the 6th pin that meets oscillation drive circuit LM741 encourages, and another group connects the 10th, 5 pin of the amplifier INA101 in the bridge signal treatment circuit to corner electrode (B, C); The measuring tube inside surface has the insulation lining, and the both ends of the surface of measuring tube are connected with the two ends tested pipeline respectively through insulation spacer or politef sheet with flange;

Described oscillation drive circuit is core with LM741; One group of electrode (A) to corner electrode of the 6th pin output terminal of LM741 and bridge-type flow measuring sensor joins; One group of another electrode (D) ground connection to corner electrode; Another of bridge-type flow measuring sensor organized the 5th pin that an electrode (C) of corner electrode is met the amplifier INA101 in the bridge signal treatment circuit, and another group of bridge-type flow measuring sensor connects the 10th pin of the amplifier INA101 in the bridge signal treatment circuit to another electrode (B) of corner electrode;

In the described bridge signal treatment circuit; Low consumed power operational amplifier LM124 has four operational amplifier OP07; Wherein join as the 3rd pin of first operational amplifier OP07-1 of current rectifying and wave filtering circuit and the 8th pin of the amplifier INA101 in the bridge signal treatment circuit, the 1st pin of first operational amplifier OP07-1 joins with the 6th pin as second operational amplifier OP07-2 of zero point correction circuit; The 7th pin of second operational amplifier OP07-2 joins with the 10th pin as the 3rd operational amplifier OP07-3 of follower, and the 8th pin of the 3rd operational amplifier OP07-3 is through A/D converter input ARM microprocessor.

2. a kind of flow measurement device according to claim 1 based on bridge-type flow measurement and electromagnetic flow-measurement; It is characterized in that: described ARM microprocessor adopts 32 arm processor; For the LPC2106 of Philips company is 32 ARM flush bonding processors of technical grade to Embedded Application that main CPU or Atmel company release, A/D converter adopts the AD7715 of ADI company; D/A converter adopts the output module AD421 chip of 4-20mA; The output display circuit adopts 12864 dot matrix band Chinese character Liquid Crystal Modules; The communication debug circuit comprises RS232 interface and RS485 interface; The shared ARM microprocessor of bridge-type flow measurement and electromagnetic flow-measurement, A/D converter, D/A converter, output display circuit and communication debug circuit.

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