JPH08338750A - Converter of mass flowmeter - Google Patents

Abstract

PURPOSE: To obtain a stable time difference signal from sine wave signals having a phase difference which are generated by a Coriolis force acting on a flow tube. CONSTITUTION: Sine wave signals being proportional to a Coriolis force and having a frequency and an amplitude fixed, which are outputted from a velocity sensor fitted to a flow tube, are inputted to input terminals 1 and 1'. The sine wave input signals are converted into position signals by integrators 7 and 7' having a low-pass filter negative feedback circuit and are made trapezoidal wave signals by amplifiers 8 and 8' and outputted. The amplifiers 8 and 8' are clamped by Zener diodes ZD1 , ZD2 , ZD1 , and ZD2 making them amplifiable in active voltage regions of operational amplifiers 4 and 4', trapezoidal wave signals B and B' of a rise and a fall being always stable are obtained and compared with reference voltages set in accordance with the trapezoidal wave signals B and B', rectangular waves C and C' wherefrom a time difference signal can be taken out are determined and a time difference ΔT proportional to a mass flow rate is determined by an operational output unit 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flowmeter converter, and more specifically, in a Coriolis flowmeter, a Coriolis force acting on a flow tube is obtained as a symmetrical position time difference of the flow tube, and a mass flow rate proportional to the time difference is obtained. The present invention relates to a mass flowmeter converter for outputting.

[0002]

2. Description of the Related Art As is well known, Coriolis flowmeters support a flow tube in which a fluid having a mass flow rate m flows at both ends and apply a sine wave vibration at an angular velocity ω around a support point to the flow tube. It is based on the fact that Coriolis force F acting in proportion to the vector product of
It is based on the principle of measuring the Coriolis force F to obtain the mass flow rate. That is, the flow tube is deformed by this Coriolis force F, and a phase difference proportional to the Coriolis force is generated at a symmetrical position from the support point of the flow tube. It is possible to obtain the mass flow rate m by detecting as the time difference ΔT passing through. Furthermore, by selecting the angular velocity ω as the natural frequency ω ₀ around the support point, the fluid density ρ can be measured from the natural frequency ω ₀ . Japanese Patent Laid-Open No. 6-109515 discloses a mass flow rate measuring method as an example of the conventional measurement of the time difference ΔT.

FIG. 5 shows a conventional mass flowmeter conversion circuit. In the figure, 31, 31 'are coils, 32, 32' are integrators, 3
3, 33 'are amplifiers, 34, 34' are comparators, and 35 is a reading circuit.

In the mass flowmeter conversion circuit shown in FIG. 5, each sensor attached to the flow tube of the Coriolis flowmeter is of a speed conversion type composed of, for example, a magnet and a coil, and the sensor coil 31 is used. , 31 ', which are sinusoidal signals having different phases, are converted into rectangular waves having a time difference ΔT to obtain a mass flow rate proportional to the time difference ΔT. The coils 31 and 31 'include integrators 32 and 32' for converting a velocity signal into a position signal, and an integrator 3 respectively.
Amplifiers 33 and 33 'for amplifying the sine wave position signals output from the amplifiers 32 and 32' at a saturation level and converting them into trapezoidal wave signals;
In order to convert each trapezoidal wave signal with the output phase difference into a rectangular wave signal with a time difference ΔT proportional to the phase difference, it corresponds to the bias lines (+ a), (-a) of the trapezoidal wave signal. Are connected to comparators 34 and 34 'for comparing the reference voltages Va and Vb determined by the comparators 34 and 34'.
A reading circuit 35 for obtaining a time difference ΔT from the rectangular wave signals output from the amplifiers 33 and 33 ′ and outputting a mass flow rate proportional to the time difference ΔT is connected to the ′ ′.

[0005]

In the Coriolis flowmeter, as described above, the Coriolis force generated in the flow tube is applied to the symmetry point of the flow tube by vibrating the flow tube in a sine wave shape with a constant amplitude and a constant frequency. Is detected as a time difference ΔT passing through the reference line, and a mass flow rate proportional to the time difference ΔT is obtained, but the Coriolis force is a minute amount. That is, the phase difference signal proportional to the Coriolis force with respect to the vibration amplitude of the flow tube is minute, and therefore the time difference ΔT is also a minute time, and this time difference ΔT is detected with an accuracy commensurate with the accuracy of the Coriolis flowmeter. In order to achieve this, firstly, a clock pulse oscillator (not shown) that oscillates a clock pulse used for time measurement is stable and highly accurate.
Is the condition. Also, the integrators 32 and 32 'and the amplifier 3
The second condition is that the circuit elements of the mass flowmeter converter, such as 3, 33 'and the comparators 34, 34', operate stably and a stable and highly accurate rectangular wave pulse signal is input to the readout circuit 35. Becomes

In the conventional mass flowmeter converter shown in FIG. 5, the integrators 32 and 32 'and the comparators 34 and 34' operate in the operating region, but the amplifiers 33 and 33 'are input. The waveform converter that converts the sine wave signal into the trapezoidal wave signal is amplified in the saturation region to increase the amplification factor. But,
Amplifying the amplifiers 33 and 33 'to the saturation region tends to make the timing unstable when the output trapezoidal signal rises and falls, and thus does not satisfy the second condition.

FIG. 6 is a diagram for explaining an example of a trapezoidal wave signal amplified in a saturation region, in which a sine wave signal is amplified by amplifiers 33 and 33 'driven at a saturation level of a power supply voltage ± Ecc. The obtained trapezoidal wave signal A having a half cycle τ is exaggeratedly shown. The trapezoidal wave signal A has a peak value of a low voltage ΔE due to the internal resistance of the amplifiers 33 and 33 ′ when amplified at the saturation level. Signal (amplifier is CMOS (Complement
ary metal oxide semiconductor), △ E ≒ 2V
When Ecc is ± 15 V, the peak value of the trapezoidal wave signal A is ± (1
3 to 15) V range. ), As shown by broken lines Aa and Ab, the start-up and the fall are unstable with respect to the trapezoidal wave signal A indicated by the solid line which is the reference of the time difference measurement, and the rise and fall timings are unstable. . As a result, when the trapezoidal wave signals are input to the comparators 34 and 34 'and converted into rectangular wave signals, the pulse widths of the rectangular wave signals become unstable, and the rectangular wave signals having the phase difference are obtained. The time difference ΔT, which is proportional to the phase difference, becomes unstable and the accuracy is poor, and a time measurement error is likely to occur. For example, in the time difference measurement of a straight tube type Coriolis flowmeter with a low detection sensitivity and a small time difference ΔT in the flow rate measurement range, the measurement error of the time difference ΔT is large and the measurement accuracy cannot be improved.

According to the present invention, amplifiers 33 and 33 'for converting a sine wave signal in which the Coriolis force is detected into a trapezoidal wave signal are shown in FIG.
Aims to provide a mass flowmeter converter from the sine wave signal is operated in the active region of ± E _D and an amplifier which can be converted into a stable trapezoidal wave signal shown by the solid line indicated by a broken line in Is.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention drives a flow tube supported by two points separated from each other by a sine wave with a constant amplitude and a constant frequency to act on the flow tube. Of the symmetric points from the supporting points are detected as a time difference of passing a reference line connecting the supporting points, and a mass flow rate computing unit for obtaining a mass flow rate proportional to the time difference is detected. An integrator connected to a sensor for detecting the velocity of the flow tube, which negatively feeds back a low-pass filter that passes a low-frequency signal component lower than the signal frequency of the sensor, and outputs a sine wave signal of a constant level. An amplifier that is connected to the integrator and that converts the sine wave signal into a trapezoidal wave signal by providing a clamper for amplifying the sine wave signal within an operation level range; A first comparator for outputting a first square wave signal compared serial to one of the trapezoidal wave signal positive reference voltage,
The time difference between the second comparator for outputting the second rectangular wave signal by comparing the other trapezoidal wave signal with the negative reference voltage equal to the positive reference voltage and the pulse width of the first rectangular wave signal is calculated. And a time difference detector that outputs a mass flow rate proportional to the obtained time difference.

[0010]

The amplifier for amplifying the sine wave signal of the constant amplitude detected from the flow tube of the Coriolis flowmeter into a trapezoidal wave signal is provided with a clamper, and the trapezoidal wave signal is amplified and output in a stable manner in the operation area of the amplifier.

[0011]

2A and 2B are views for explaining an example of a Coriolis flowmeter to which the present invention is applied. FIG. 2A is a sectional view in the flow direction, and FIG. 2B is FIG. 2A. 2 is a cross-sectional view taken along the line BB of FIG. 1, in which 21 is an outer cylinder, 22 is a flow tube, 2
3 is a counter balance, 24 is a drive unit, 25 and 26 are sensors, and 27 is a double tube.

When the fluid to be measured flows through the Coriolis flowmeter shown in FIG. 2 and the flow tube 22 of the double pipe 27 is resonantly driven by the drive unit 24 at a constant amplitude and a constant frequency with the counter balance 23, the flow tube is driven. A Coriolis force is generated at the velocity sensor 25, and a sine wave signal having a phase difference proportional to the Coriolis force is generated at the speed sensors 25 and 26.

FIG. 1 shows a mass flowmeter converter according to the present invention, in which 1,1 'is an input terminal and 2,2', 3,3 '.
4, 4'5 and 5'are operational amplifiers, 6 is an operational output device, 7,
Reference numeral 7'denotes an integrator, 8, 8'denotes an amplifier, and 9 and 9'denotes a comparator.

The mass flowmeter converter shown in FIG. 1 comprises integrators 7 and 7 ', amplifiers 8 and 8', comparators 9 and 9 ', and an operation output circuit 6, and integrators 7 and 7'and amplifier 8 are provided. Since and 8'are the same circuit, only one of them will be described. A sine wave signal having a constant amplitude from the coil of one sensor 25 is input to the input terminal 1 and is connected to an integrator 7 including an integration time constant resistor R ₁ , a capacitor C ₁ and an operational amplifier 2. Further, from the output P ₂ of the integrator 7 to the input P ₁ , low frequency filters R ₃ and C ₂ which pass a noise component frequency lower than the input sine wave signal are impedance-converted by the amplifier 3 and the resistor R ₄ is connected. Negative feedback is performed via the sine wave signal A to output low frequency noise-free sine wave signal A.

The amplifier 8 is a sine wave output from the sensor.
Created in the operating area for inputting a signal and converting it into a trapezoidal signal.
The operational amplifier 4 is an amplifier having a clamp function to move
Mainly the input terminal P of the operational amplifier 4₃Output of the integrator 7
Power P₂Input resistance R connected to _FiveBut the input end P_FourType in
P₁And resistance R_Four, R₆And capacitor C₃Low-pass fill consisting of
Input / output P₃And P_FiveTse connected in reverse between
Nar diode Z_D1, Z_D2Clamp voltage and resistance R₇of
The parallel circuit is negatively fed back. Zener diode
Z_D1, Z_D2Is a voltage lower than the power supply voltage Ecc, and
The gate voltage E can be sufficiently controlled within the active region of the operational amplifier 4.
It is selected so that the voltage value is effective.

The comparator 9 comprises an operational amplifier 5 for inputting a trapezoidal wave signal B and a reference voltage at point P ₆ to be compared with the trapezoidal wave signal B. The reference voltage at point P ₆ is the reference voltage Es.
Is divided by resistors R ₈ and R ₉ . Therefore, the output of the comparator 9 is a rectangular wave signal C that is turned on when the trapezoidal wave signal B falls and turned off when it rises.

The operation output device 6 obtains a time difference ΔT based on the difference between the pulse widths of the rectangular pulses C and C ′ output from the comparators 5 and 5 ′, and outputs a mass flow rate proportional to the time difference ΔT. Circuit. Hereinafter, the amplifiers 8 and 8'and the comparators 9 and 9
According to the output waveforms B, B'and C, C'of '
The operation output circuit 6 for obtaining T will be described with reference to FIGS.

FIG. 3 is a time chart of waveforms for explaining the time difference when the flow rate is zero. FIG. 3 (a) is a trapezoidal wave signal, and FIG. 3 (b) is a comparator 9, 9'and an operation output circuit. 6
3 shows a pulse train for explaining the time difference ΔT calculated in.

The trapezoidal wave signal B of symmetrical shape with the peak value ± E _D with respect to the reference voltage O level in the flow "0", B
There is no phase difference and they match. Therefore, the trapezoidal signals B and B'are turned on between the voltage levels M and Q of (+ E),
Between the rectangular wave signal C obtained by turning it off and the rectangular wave signal C ′ obtained by turning it on and off between the voltage levels N and P of (−E), the rectangular wave signals C, C ′ The pulse width T between rising edges is the pulse width T between falling edges of the rectangular wave signals C and C '.
It is equal to ′ and T−T ′ = 0.

FIG. 4 is a diagram for explaining the time difference when the flow rate flows. FIG. 4 (a) is a trapezoidal wave signal B, B'having a phase difference, and FIG. 4 (b) is a comparator 9, 9 shows a pulse train for explaining the time difference ΔT calculated by 9 ′ and the calculation output device 6.

There is a time difference ΔT between the trapezoidal wave signals B and B'when a flow rate flows. Therefore, looking at the output rectangular wave signal C having the pulse width MQ of the comparator 9 compared with the voltage (+ E) and the output rectangular wave signal C ′ having the pulse width N′P ′ of the comparator 9 ′, Square wave signal C and square wave signal C ′
The pulse obtained by each start-up is (T + ΔT)
Have a time range of. This can be understood by the fact that the quadrilateral MNN'M 'is a parallelogram. Similarly, the pulse obtained by the fall of each of the rectangular wave signal C and the rectangular wave signal C ′ has a time width of (T−ΔT), and the output calculator 6 (T + ΔT) − (T -ΔT) is calculated to calculate a time difference corresponding to 2ΔT, and a mass flow rate proportional to the time difference ΔT is output. Therefore, the rectangular wave signals C ₁ , C ₂
Is an important factor in measuring the time difference ΔT.

[0022]

As described above, according to the present invention, in the process of converting a sine wave signal having a phase difference due to the Coriolis force acting on the flow tube of the Coriolis flowmeter into a rectangular wave signal that can be digitally processed, For an amplifier that converts a signal into a trapezoidal wave signal, the voltage can be forcibly clamped so that the operation of the amplifier can be controlled by the voltage in the active region, and the variations in the rising and falling timings of the trapezoidal waveform can be suppressed. Therefore, the rise and fall timings are correctly maintained, and the stable time difference ΔT proportional to the Coriolis force is accurately measured. Therefore, the present invention can be applied to a straight pipe type Coriolis flowmeter having a particularly low sensitivity.

[Brief description of drawings]

FIG. 1 is a mass flow meter converter according to the present invention.

FIG. 2 is a diagram for explaining an example of a Coriolis flowmeter to which the present invention is applied.

FIG. 3 is a time chart of waveforms for explaining a time difference when the flow rate is zero.

FIG. 4 is a diagram for explaining a time difference when there is a flow rate.

FIG. 5 is a conventional mass flow meter converter circuit.

FIG. 6 is a diagram for explaining an example of a trapezoidal wave signal amplified at a saturation level.

[Explanation of symbols]

1, 1 '... input terminals, 2, 2', 3, 3 ', 4, 4',
5, 5 '... Operational amplifier, 6 ... Operational output device, 7, 7' ... Integrator, 8, 8 '... Amplifier, 9, 9' ... Comparator, 21 ... Outer cylinder, 22 ... Flow tube, 23 ... Counter balance,
24 ... Drive unit, 25, 26 ... Sensor, 27 ... Heavy horn.

Claims (1)

[Claims] 1. A flow tube supported at two points separated from each other is driven by a sine wave with a constant amplitude and a constant frequency, and Coriolis force acting on the flow tube is symmetric with respect to the support point. A trapezoid is obtained by inputting the sine wave signals output from the sensors provided at the respective symmetry points in a mass flow rate calculator that detects the time difference of passing through the reference line connecting the two and calculates the mass flow rate proportional to the time difference. An amplifier having a clamp function for operating in an active region for converting into a wave signal, and comparing each of the one trapezoidal wave signals output from the amplifier with a positive reference voltage, and comparing the first rectangular wave signal with the first rectangular wave signal. A first comparator for outputting, a second comparator for comparing the other trapezoidal wave signal with a negative reference voltage equal to a positive reference voltage, and outputting a second rectangular wave signal, and the first rectangular wave signal And the second rectangular wave And a time difference detector that outputs a mass flow rate proportional to the time difference of the pulse widths of the signal and the mass flowmeter converter.