JPS63165718A - Detector for abnormality in mass flowmeter - Google Patents

Abstract

PURPOSE:To prevent the outflow of a fluid due to the fatigue rupture of a conduit, by giving an alarm when a voltage value in the case of electromagnetic driving of the conduit exceeds a prescribed level. CONSTITUTION:A sine-wave signal being delivered from a pickup coil 8 and proportional to the speed in a conduit is integrated by an integrator 11, turned to be a mass signal by a phase difference detecting circuit 12 and passed through an amplifier circuit 13, and it is outputted as a flow rate signal from a terminal 14. Simultaneously, the signal of the coil 8 is subjected to linear amplification 20, and thereby a driving coil 4 is driven in sine through a driving circuit 16. A driving signal amplification control circuit 15 is composed of a comparator-amplifier comparing a direct-current signal obtained through a rectification of the signal of the integrator 11 with a reference voltage, and others, and it drives the circuit 16 on the basis of a difference signal of the direct-current signal and the reference voltage. While an input signal to the circuit 16 has a fixed value at a normal time when the conduit is not fatigued, accordingly, it becomes a signal enlarged by an increase in internal friction in the case when the friction is increased due to fatigue. Then, the reference voltage set in an amplitude limit value setting unit 17 is compared with an output signal of the circuit 15 by a comparator 18, and when the result of comparison exceeds a set value, an alarm signal is outputted from a terminal 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an abnormality detector for a mass flowmeter that uses the Coriolis force to detect an abnormality in a mass flowmeter and displays or warns about this abnormality.

Prior Art When vibration is applied to a fluid flow flowing through a conduit, a Coriolis force is generated in a direction perpendicular to the direction of the fluid flow and the vibration axis of the conduit. It is known that it is proportional to the mass flow rate, and
Japanese Patent Publication No. -52570 discloses a mass flowmeter that utilizes the Coriolis force. This prior art has a configuration in which a U-shaped conduit having an inlet and an outlet is fixed to a support member, and fluid passes through the inlet and flows out from the outlet. When a rotational vibration is applied in a direction perpendicular to the body surface of the U-shaped conduit with the fixed line corresponding to the fixed line as an axis, Coriolis force due to the fluid flowing through the U-shaped conduit acts, and the U-shaped shape perpendicular to the fixed line is applied. Since torsional vibrations proportional to the Coriolis force occur with respect to the axis of the conduit body, the flow rate is determined by determining the Coriolis force from the time difference in which the conduit passes through the reference plane. Also, JP-A-58-156813
In the publication, a conduit is supported between two points as a straight pipe to deform and vibrate, and the Coriolis force generated is determined from the time difference between signals detected by two AC output detectors.

In.

Mass flowmeters that utilize the Coriolis force are generally of the type that vibrates the conduit as described above. Further, the natural frequency of the conduit is selected as the vibration frequency when the conduit is vibrated. Coriolis force is extremely small compared to excitation force, so it is difficult to detect with high precision and is easily affected by noise from external vibrations.The magnitude of Coriolis force is small when the natural frequency is constant. is proportional to the amplitude.

In order to excite efficiently with a large amplitude, it is driven at the natural frequency of the conduit to improve the S/N ratio.

Furthermore, attempts have been made to increase the detection sensitivity by thinning the wall thickness of the conduit to reduce its bending rigidity, or by changing the shape of the conduit to increase the moment caused by the Coriolis force and increasing the time difference detection signal. . The above-mentioned measures to improve the detection sensitivity of the Coriolis force and attempts to improve reliability by increasing the fatigue strength of the conduit are contradictory, but it is possible to improve the detection sensitivity of the Coriolis force by increasing the fatigue strength of the conduit. Flowmeters that measure flow must prevent disasters such as fluid leakage due to fatigue rupture of conduits, but such preventive measures have not been taken in the past.

Means for Solving the Problem The present invention has been made for the purpose of detecting an abnormality in the above-mentioned Coriolis type mass flowmeter and issuing an alarm to prevent fluid outflow due to fatigue rupture of the conduit.

Corrosion-resistant stainless steel tubes are often used for the conduits through which fluid flows, and these conduits are driven with a constant amplitude of the natural vibration frequency, but if the conduits have a stable metal structure, the driving energy is constant, but when fatigue begins, the internal friction increases due to the progression of dislocations in the metal structure and slippage between dislocation surfaces, etc., and the energy required to drive with constant vibration increases. For example, an alarm is issued when the current or voltage value exceeds a predetermined level when electromagnetically driven.

However, Figure 2 is a prerequisite for detailed explanation of the present invention.
1 is a plan view showing an example of a Coriolis mass flowmeter having a U-shaped conduit 1, in which a U-shaped conduit 1 is attached to a support member 2 with an axis xx'
One end of the reciprocating member 3 extending in the direction of the axis xX' is fixed to the support member 2 . At the other end of this reciprocating member 3, a drive coil 4 is arranged which vibrates at a frequency substantially equal to the natural frequency of the conduit 1 around an axis YY' connecting the fixed points of the conduit 1. A magnet 5 is attached to the conduit 1 via a holding plate 6 on the axis of the drive coil 4, and is attracted and repelled by a drive source (not shown) in a direction perpendicular to the plane of the drawing, and as a result, the conduit 1 is moved along the axis YY'
is driven around.

As a result, a Coriolis force acts on the fluid flowing in the Q direction, and a rotational force is generated around the Xx' axis. This is a pickup coil 8 fixed symmetrically to both arms of the conduit 1.
Thus, the Coriolis force is determined as the time difference between the electric signals caused by the relative motion between the pickup coil 8 and the fixed magnet 7.

FIG. 1 is a block diagram illustrating the operation of the above-mentioned mass flowmeter from the aspect of signal flow in order to show an embodiment of the present invention. A sine wave signal proportional to the speed of the conduit 1 is output from 8, and this sine wave signal is integrated by an integrator 11 to convert it into a position signal, and a phase difference detection circuit 12 calculates a time difference to produce a mass signal, which is then sent to an amplifier circuit. A flow rate signal is output from the terminal 14 through the terminal 13. At the same time, the signal of the pickup coil 8 is amplified by the linear amplifier 20, and in response to this signal, the drive coil 4 is driven sinusoidally through the drive circuit 16, whereby the pickup coil 8 - linear amplifier 20 - drive circuit 16 - conduit 1 - reciprocating member 3 - drive coil 4 - magnet 5 - conduit 1 - pickup coil 8 A positive feedback loop causes sine vibration at a natural frequency.

The drive signal amplification control circuit 15 is an amplitude control circuit for suppressing the oscillation of the positive feedback loop and continuing vibration with a constant amplitude, and it combines a DC signal obtained by rectifying the signal from the integrator 11 with a constant vibration. It consists of a comparator amplifier (not shown), etc., which compares the base Q voltage corresponding to the value of the DC signal with the base Q voltage. The drive circuit 16 is driven by the difference signal from the lI voltage. Therefore, the input signal to the drive circuit 16 has a constant value under normal conditions when the density of the fluid to be measured is constant and the conduit 1 is not fatigued, but when the internal friction of the conduit 1 increases due to fatigue, The signal will be that much larger. In the present invention, focusing on the change in this signal, the reference voltage of the amplitude limit value setter 17 is set in consideration of the output signal from the drive signal amplitude control circuit 15 depending on the density range of the fluid to be measured. A comparator 18 compares the set value with the output signal of the drive signal amplitude control circuit 15, and when the set value is exceeded, an alarm signal is sent from a terminal 19 to issue a warning. The above description has been about the case where the present invention is applied to a Coriolis mass flowmeter having a U-shaped conduit 1. However, when the conduit is straight or has other shapes, the conduit can also be driven sinusoidally. If the system detects the Coriolis force generated by It is possible.

Effects As is clear from the above description, the present invention provides a Coriolis type mass flowmeter in which a conduit through which fluid flows is driven at a natural frequency of a constant amplitude. Based on the simple principle that the voltage or current value supplied for continuation increases by the internal loss of the conduit caused by fatigue of the conduit, abnormalities in the mass flow meter can be detected at low cost, and the conduit can be fatigue-ruptured and dangerous fluid can be released. Problems such as leakage can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an electrical block diagram for explaining an embodiment of the present invention, and FIG. 2 is a plan view showing an example of a Coriolis mass flowmeter. DESCRIPTION OF SYMBOLS 1... Conduit, 2... Support member, 3... Reciprocating member, 4... Drive coil, 5, 7... Magnet, 8... Pick-up coil, 15... Drive signal amplitude control circuit,
16... Drive circuit, 17... Amplitude limit value setter, 1
8... Comparator, 19... Alarm output terminal. Patent applicant Oval Equipment Industry Co., Ltd. Figure 1 Atsushi 21! lI! Y

Claims (1)

[Claims] a conduit through which fluid flows; a support means for supporting the conduit;
It consists of a driving means for driving the support section in a direction perpendicular to the pipe axis at a natural frequency of constant amplitude, and a detection means for detecting the Coriolis force generated by the driving of the driving means, and a mass flow rate proportional to the Coriolis force. In a mass flowmeter that seeks the following, the drive signal of the drive means is compared with a reference value determined as a specified value of the drive signal, and when the drive signal exceeds the reference value, an alarm is issued and/or the drive is stopped. An abnormality detector in a mass flow meter characterized by: