CN1532529A - Phase difference detection circuit for coriolis'force mass flow meter - Google Patents

Abstract

The phase different measuring circuit for Coriolis' force mass flow meter includes the first measuring branch and the second measuring branch, each of which comprises magnetoelectric sensor, integrating circuit and phase measuring circuit, as well as phase difference measuring digital circuit connected two these two measuring branches. The integrating circuit includes the first operate-amplifier, an integrating branch with two resistors and one capacitor, and a star circuit with one capacitor and three resistors. The phase different measuring circuit has the advantages of no phase change with temperature and frequency in the integrating circuit, constant phase shift of 90 deg in the useful frequency range of the integrating circuit, and no influence of the DC drift in preceding circuit on phase measurement of signal.

Description

A kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter

Technical field

The present invention relates to a kind of metering circuit that is used for the Coriolis force mass flowmeter, particularly phase difference measuring circuit wherein.

Background technology

Existing Coriolis force mass flowmeter, mostly adopt the vibration tube-type structure, by measuring the vibration phase difference between the vibrating tube that causes by Coriolis force, come the mass rate in the measuring tube, mass rate is directly proportional with vibration phase difference between two vibrating tube.Magnetoelectric sensor generally is set on vibrating tube, in order to record the vibration velocity signal of vibrating tube, processing of circuit after testing then, and record phase differential between two paths of signals.

A kind of prior art scheme as shown in Figure 1, this figure select from Xiao Suqin, Han Houyi chief editor " mass flowmeter " (Sinopec publishing house, in March, 1999 first published, P77).Record the voltage sinusoidal signal that two row are represented the vibrating tube vibration velocity by the left and right side electromagnet-type detector.Phase difference detecting circuit and time integral device are delivered in processing such as the voltage signal of and arranged on left and right sides signal detector is through accurate integrator, amplifier and level detector amplifies, filtering, shaping, paraphase and phase shift together.When phase differential equals zero, no-output.When phase differential, pulse output is arranged, pulse width homophase potential difference is directly proportional, thereby obtains mass flow value.

In addition, the voltage signal of left-side signal detecting device also through driving amplifier, drive coil, constitutes a positive feedback loop, keeps the self-sustained oscillation of measuring tube vibrational system.

The existing circuit that AC signal is carried out integration as shown in Figure 2, A wherein ₁Be operational amplifier (after this will abbreviate operational amplifier as amplifier without exception), R1 is the integrating resistor that is connected on the amplifier inverting input, and C1 is an integrating capacitor, and R1 ' is a DC feedback resistance, R5 is the direct current biasing compensating resistance, is connected on the amplifier in-phase input end and with reference between the ground.

The problem that integrating circuit shown in Figure 2 exists is: 1, be subjected to device to change inconsistent the influence, the phase place of integrating circuit output signal varies with temperature and changes, and irregular following; 2, in available frequency band, the phase place of integrating circuit output signal changes with the variation of frequency.Above problem all can influence final Phase Difference Measuring Precision.

Existing phase measuring circuit is the positive input terminal that the output signal dividing potential drop of amplifier is fed back to amplifier as shown in Figure 3, carries out phase measurement as benchmark.Use this phase measuring circuit, the dc shift in the preorder metering circuit can equivalence be the phase change of signal, thereby produces than mistake in the phase difference measurement result.The output voltage drift of amplifier can change the comparing voltage value that feeds back, and also can cause error in the phase difference measurement result.

Summary of the invention

Purpose of the present invention is exactly in order to overcome the above problems, make integrating circuit overcome the defective of existing phase place with temperature and frequency change, and in available frequency band, keep the integrating circuit characteristic of phase shift 90 degree all the time, overcome the influence that preorder circuit DC-shift is measured signal phase simultaneously, so that a kind of high-precision Coriolis force mass flowmeter phase difference measuring circuit to be provided.

The present invention realizes the scheme of above-mentioned purpose: a kind of metering circuit that is used for the Coriolis force mass flowmeter comprises:

The first measurement branch road and second that comprises magnetoelectric transducer, integrating circuit, phase measuring circuit is respectively measured branch road, and measures the phase difference measurement digital circuit that branch road links to each other with above-mentioned first and second;

Above-mentioned integrating circuit comprises: first operational amplifier, be connected to first, five resistance of the first operational amplifier inverting input and normal phase input end, be connected the integration branch road that comprises first electric capacity between the first operational amplifier inverting input and the output terminal;

It is characterized in that described integrating circuit also comprises:

Second electric capacity and by second and third, the star circuit formed of four resistance, the other end of third and fourth resistance is connected with output terminal with the first operational amplifier inverting input respectively, the other end of the 5th resistance links to each other with ground, and second electric capacity and the 5th resistance are connected in parallel between stellate node and the ground.Also comprise at above-mentioned a kind of integrating circuit that is used for the phase difference measuring circuit of Coriolis force mass flowmeter: be connected in the 6th resistance in the above-mentioned integration branch road.In the phase measuring circuit of above-mentioned a kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter, comprise: second operational amplifier, the 7th, eight resistance, the 3rd electric capacity; The inverting input of second operational amplifier and normal phase input end connect an end of the 7th, eight resistance respectively, seven, the other end of eight resistance links to each other with the output terminal of above-mentioned amplifying circuit, and the 3rd electric capacity is connected between the normal phase input end and ground of second operational amplifier.

Adopt technique scheme, in conjunction with the following embodiment that will narrate, the technical progress that the present invention gives prominence to is:

1, in available frequency band, in the frequency characteristic, the DC feedback resistance value of equivalence is reduced at this integrating circuit of optimization, thereby reduced the dc shift error output of integrating circuit.

2, the drift of resistance, capacitance values diminishes to the influence of integrator characteristic in the integrating circuit, and the phase place of integrating circuit output signal no longer changes with temperature; In available frequency band, the phase place of integrating circuit output signal no longer changes with frequency.

3, overcome the influence that preorder circuit DC-shift is measured signal phase,

Description of drawings

Fig. 1 is the metering circuit block scheme that is used for the Coriolis force mass flowmeter of prior art;

Fig. 2 is the integrating circuit schematic diagram of prior art;

Fig. 3 is the phase measuring circuit schematic diagram of prior art;

Fig. 4 is the circuit square frame and the schematic diagram of technical scheme of the present invention;

Fig. 5 is the circuit square frame and the schematic diagram of Technological improvement plan of the present invention;

Fig. 6 is the integrating circuit schematic diagram of embodiments of the invention 2;

Fig. 7 is that the integrating circuit amplitude versus frequency characte of embodiments of the invention 2 compares synoptic diagram;

Fig. 8 is the phase measuring circuit schematic diagram of embodiments of the invention 3.

Embodiment

Embodiment 1

As shown in Figure 5, a kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter, comprise magnetoelectric transducer (5) (being equivalent to the detecting device in the background technology), integrating circuit (1) (being equivalent to the accurate integrator in the background technology), amplifying circuit (2) (being equivalent to the amplifier in the background technology), phase measuring circuit (3) (being equivalent to the level detector in the background technology) and phase differential digital measurement circuit (4) (being equivalent to the phase difference measuring circuit in the background technology), integrating circuit (1) comprises amplifier A1, be connected the integrating resistor R1 and the direct current biasing compensating resistance resistance R 5 that is connected amplifier A1 normal phase input end of amplifier A1 inverting input, the feedback network of integrating circuit (1) comprises resistance R 2, resistance R 3, resistance R 4, capacitor C 1 and capacitor C 2; The inverting input of capacitor C 1 one termination amplifier A1, the output terminal of another termination amplifier A1; Resistance R 2, resistance R 3 and resistance R 4 are pressed Y-connection, the inverting input of another termination amplifier A1 of resistance R 2, the output terminal of another termination amplifier A1 of resistance R 3, the public ground of another termination of resistance R 4; Capacitor C 2 is in parallel with resistance R 4.

In the present embodiment technical scheme, the star dc feedback network that constitutes with resistance R2, resistance R 3 and resistance R 4 replaces the DC feedback resistance R 1 ' in the prior art integrating circuit shown in Figure 2, and increasing frequency feedback building-out capacitor C2, C2 and resistance R 4 are connected in parallel.

Effect and the principle of integrating resistor R1, direct current biasing compensating resistance R5, identical with prior art integrating circuit shown in Figure 2.

Angle from circuit theory, present embodiment is to be a kind of special case of 0 o'clock with 6 values of the resistance R in the integrating circuit of following embodiment 2, method for designing described in the embodiment 2 and specificity analysis etc., also all be applicable to present embodiment, therefore corresponding method for designing of present embodiment and specificity analysis etc. see also embodiment 2.

Compare with embodiment 2, the advantage of present embodiment is to have reduced by a resistive element, and shortcoming is that circuit characteristic is slightly not good enough.

Above-mentioned amplifying circuit also can be connected between magnetoelectric transducer and the integrating circuit.

In addition, the output signal at magnetoelectric transducer is strong, integrating circuit gains greatly or under the phase measuring circuit precision condition with higher, this phase difference measuring circuit also can not comprise amplifying circuit (as shown in Figure 4).

Embodiment 2

Present embodiment is the best way that realizes technical solution of the present invention, on the basis of embodiment 1, increase resistance R 6, with the integrating circuit partial design for as shown in Figure 6, resistance R 6 and capacitor C 1 series connection, the inverting input of one termination amplifier A1 of this series circuit, the output terminal of another termination amplifier A1 is present embodiment.

(such as 60Hz～110Hz) should be identical with the integrator of prior art, but that its DC current gain has become the amplitude versus frequency characte of present embodiment integrating circuit is lower in available frequency band; Gain maximum in the full frequency band is not more than the gain maximum of the integrator of prior art; (60Hz～110Hz), it is good more to spend near 90 more in available frequency band for phase-frequency characteristic; Avoid occurring the flex point of 180 degree in the full frequency band.The specific design method is:

(A), choose the integrator integral element according to the magnetoelectric sensor impedance.For the impedance discreteness that makes sensor and measure lead is kept to minimum to the influence of integrator, the impedance of getting input circuit resistance R 1 is 1500～2500 times of sensor impedance.

(B) according to the mechanical resonant frequency f (being about 75Hz) of vibrating tube, be chosen near the integration time constant of this resonance centre frequency (or claiming gain) and be about 5, it is as follows to calculate capacitor C 1 formula:

$\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">C</figure-callout>}1=\frac{1}{2\&times;\mathrm{\&pi;}\&times;f\&times;\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}1\&times;5}$

(C) according to following transport function F (f), R2, R3, R4, R6 and C2 are chosen in examination.For ease of choosing desirable R2=R3.

$F\left(f\right)=\frac{-\{(Z1\left(f\right)+R6)\&times;[(\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2+R3)\&times;Z2\left(f\right)\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}4+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2\&times;\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}3\&times;(Z2\left(f\right)+R4)\left]\right\}}{(Z0\left(f\right)+R1)\&times;[(Z1\left(f\right)+R6+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2+R3)\&times;Z2\left(f\right)\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}4+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2\&times;\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}3\&times;(Z2\left(f\right)+R4)]}$

In the formula: the f-frequency

Z0 (f)-electromagnetic sensor inside (L1) impedance

The impedance of Z1 (f)-capacitor C 1

The impedance of Z2 (f)-capacitor C 2

(D) amplitude-frequency and the phase-frequency characteristic curve of transport function F (f) in the calculation procedure (C).According to following criterion, whether R2, R3, R4, R6 and C2 that definite examination is chosen be feasible:

● self-sustained oscillation occurs for avoiding amplifier, 0 ° flex point can not appear in amplitude-versus-frequency curve;

● contain in the full frequency band of direct current, the gain maximum is no more than 220;

● in available frequency band, the phase-frequency characteristic curve is at 90 ° ^{+ 0.03 °} _{-0.01 °}

● in available frequency band, phase-frequency characteristic curve parallel with 90 ° (adjusting R6), the difference of maximal value and minimum value is less than 0.001 °.

(E) if do not meet above-mentioned four criterions, then turn back to step (C) and choose R2, R3, R4, R6 and C2 again.

(F) resistance R 5 is calculated as follows:

$\mathrm{<figure-callout\; id="5"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}5=\frac{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}1\&times;(\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}4+\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}3\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}4+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2\&times;R3)}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}1\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}4+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}4+\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}3\&times;\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}4+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}2\&times;\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="A0311968500151.png"\; state="\{\{state\}\}">R</figure-callout>}3}$

Fig. 7 is the phase-frequency characteristic comparison curves of present embodiment integrating circuit and prior art integrating circuit.Three amplitude-versus-frequency curves that curve is the prior art integrating circuit in top, correspondence with the element value among Fig. 2 is: R ₁=4.3K Ω, C ₁=0.1 μ F, R ₁'=1M Ω, R ₁"=R ₁//R ₁'=4.3K Ω.Three curves in top are respectively: the corresponding capacitor C of fx0 (f) ₀Change 0%; The corresponding capacitor C of fxl (f) ₀Change+5%; And the corresponding capacitor C of fx2 (f) ₀Change-5%.

Three phase-frequency characteristics that curve is the present embodiment integrating circuit that straight lines coincide are spent with 90 in the below, and corresponding one group of resistance capacitance value and result of calculation are: R1=4.3K Ω, R2=R3=180K Ω, R4=140K Ω, R6=10 Ω, C1=0.1 μ F, C2=0.68 μ F, R5=4.3K Ω.Corresponding capacitor C 1 and C2 change simultaneously be respectively ± 5% and 0%.

As can be seen, adopt the integrating circuit technical scheme of present embodiment, the phase-frequency characteristic of circuit is in the more approaching desirable integrator characteristic of available frequency band internal ratio prior art integrating circuit, and the drift of components and parts numerical value is littler to the influence of phase-frequency characteristic.

Embodiment 3

On the basis of embodiment 1 or embodiment 2, with phase measuring circuit employing phase measuring circuit technical scheme as shown in Figure 8, further reduce the phase difference measurement error, promptly constitute

Embodiment 3.

In the described phase measuring circuit (3) of present embodiment, comprise amplifier A2, resistance R 8 and capacitor C 3; The end of the input end while connecting resistance R8 of amplifier A2 and an end of capacitor C 3, the other end of resistance R 8 is accepted input signal, the public ground of another termination of capacitor C 3; Another input end of amplifier A2 directly or by a resistance R 7 is accepted input signal.

The phase measurement comparator circuit of forming by A2 etc. in the present embodiment, resistance R 8 and capacitor C 3 play the low-pass filtering effect, the DC voltage of taking-up front stage circuits output is level as a comparison, and this level changes with the direct current of front stage circuits zero point, has played the effect of anti-front stage circuits DC-shift.

Claims (5)

1, a kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter comprises:

The first measurement branch road and second that comprises magnetoelectric transducer (5), integrating circuit (1), phase measuring circuit (3) is respectively measured branch road, and measures the phase difference measurement digital circuit (4) that branch road links to each other with above-mentioned first and second;

Above-mentioned integrating circuit comprises: first operational amplifier (A1), be connected to first, five resistance (R1, R5) of first operational amplifier (A1) inverting input and normal phase input end, be connected the integration branch road that comprises first electric capacity (C1) between first operational amplifier (A1) inverting input and the output terminal;

It is characterized in that described integrating circuit also comprises:

Second electric capacity (C2) and by second and third, the star circuit formed of four resistance (R2, R3, R4), the other end of third and fourth resistance (R2, R3) is connected with output terminal with first operational amplifier (A1) inverting input respectively, the other end of the 5th resistance (R5) links to each other with ground, and second electric capacity (C2) and the 5th resistance (R2) are connected in parallel between stellate node and the ground.

2, a kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter as claimed in claim 1, it is characterized in that the described first measurement branch road and the second measurement branch road also comprise amplifying circuit (2) respectively, and this amplifying circuit (2) is connected between described magnetoelectric transducer (5) and the described integrating circuit (1).

3, a kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter as claimed in claim 1, it is characterized in that the described first measurement branch road and the second measurement branch road also comprise amplifying circuit (2) respectively, and this amplifying circuit (2) is connected between described integrating circuit (1) and the described phase measuring circuit (3).

4, as claim 2 or the described a kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter of claim 3, it is characterized in that also comprising in the described integrating circuit: be connected in the 6th resistance (R6) in the above-mentioned integration branch road.

5, a kind of phase difference measuring circuit that is used for the Coriolis force mass flowmeter as claimed in claim 4 is characterized in that described phase measuring circuit (3) comprising: second operational amplifier (A2), the 7th, eight resistance (R7, R8), the 3rd electric capacity (C3); The inverting input of second operational amplifier (A2) and normal phase input end connect the end of the 7th, eight resistance (R7, R8) respectively, seven, the other end of eight resistance (R7, R8) links to each other with the output terminal of described amplifying circuit (2), and the 3rd electric capacity (C3) is connected between the normal phase input end and ground of second operational amplifier (A2).

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