JPH02221818A - mass flow meter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a suspended flow meter, and more particularly to a mass flow meter that measures the mass flow rate of a fluid using the Coriolis force.

Conventional technology As described in Japanese Patent Application Laid-Open No. 54-525705'3, fluid is flowed through a vibrating U-shaped sensor tube and twisting of the sensor tube caused by the Coriolis force acting on the fluid is detected. However, there is a mass flow meter that measures the mass flow rate of fluid.

In the mass flowmeter described above, fluid is caused to flow through the pair of sensor tubes 1, and the pair of sensor tubes are vibrated in directions toward and away from each other. Since the Coriolis force acts in the direction of vibration of the sensor tube and is in opposite directions on the inlet and outlet sides, the sensor tube is twisted, and this twist angle is proportional to the mass flow rate. Therefore, a sensor for detecting vibration is provided at the twisting position on the inlet and outlet sides of a pair of sensor tubes, and the time difference between the output detection signals of both sensors is measured to measure the twist of the sensor tube, that is, the quality ω flow rate. are doing.

Problems to be Solved by the Invention In the conventional vibration control method of the sensor tube in the mass flowmeter described above, the sensor tube is forcibly vibrated by the electromagnetic force of the excitation coil of the vibrator (consisting of a magnet and an excitation coil). The sensor tube is vibrated in a resonant state at a frequency that provides the highest mechanical Q (inverse of the damping factor) in the direction. In this case, sensor 1-
The sensor tube vibrates in a resonant state as described above, not only when fluid is flowing inside the cylinder, but also when the fluid supply to the cylinder is stopped and there is no fluid in the sensor tube. was.

In this way, even during non-measurement when the measured fluid is not in the sensor tube, the excitation force applied to the sensor tube is applied in the same way as when the fluid is in the sensor tube, resulting in wasted energy. If this state continues for a long time, fatigue will accumulate in the sensor tube.

Furthermore, depending on the weight and shape of the sensor tube, when the sensor tube is vibrated without fluid in it, the vibration frequency of the sensor tube becomes about 1.5 to 2 times higher than in the state with fluid in it. In that case, unnecessary stress may be applied to the welded portion of the sensor tube, and the life of the sensor duplex may be shortened.

Therefore, an object of the present invention is to provide a mass flowmeter that solves the above problems.

Means for Solving the Problems The present invention provides, in the above-mentioned mass transfer 4, a frequency detection means for detecting the vibration frequency of the conduit by being supplied with a detection signal output from a vibration sensor, and a frequency detection means output from the frequency detection means. determining means for determining whether the value exceeds a predetermined frequency and outputting an abnormality detection signal when the value exceeds the predetermined frequency; or an abnormality processing means for issuing an alarm.

The vibration frequency of the vibrating pipe is detected, and when the frequency is higher than a predetermined value, it is assumed that there is some abnormality in the pipe and the vibration of the pipe is stopped or an alarm is issued.

Embodiment FIGS. 1 to 3 show an embodiment of the mass flowmeter of the present invention.

In each figure, the main body 1 of the mass flowmeter has 7 runs at both ends, 2 parts 1a.
, lb, the 7 flange portion 1a is connected to upstream piping (not shown), and the flange portion 1b is located downstream! (not shown).

The main body 1 is provided with an inlet for fluid to flow in (not visible separately in Fig. 1) and an outlet 2 for fluid to flow out, and the interior of the main body 1 is partitioned by partition plates 1c and id. ing. One end of each U-shaped channel 1-3.4 is connected to the inlet, and the other end is connected to the outlet 2. A magnet 5 and an excitation coil 6 for exciting the sensor tube 3.4 in the direction of arrow X are attached to the center position of the U-shaped curved portion between the sensor tubes 13.4.

Further, vibration sensors 7 and 8 are provided at both ends of the U-shaped curved portion between the sensor duplexes 3 and 4, respectively.

The vibration sensor 7 is connected to the sensor tube 3 as shown in FIG.
It is composed of a coil 7a held by a holding member 9 fixed to the sensor tube 4, and magnets 7b and 7c held by a holding member 10 fixed to the sensor tube 4. It is located in Here, when the sensor tube 3.4 is vibrated and relatively displaced in the direction of the arrow X, an electromotive force is generated in the coil 7a according to the relative speed, and this electromotive force is taken out as a detection signal. .

The vibration sensor 8 also has exactly the same structure.

Here, the current flowing through the excitation coil 6 is set to sensor antenna 1-3.4.
When the vibrations are varied at their respective natural frequencies, the attraction and repulsion of the excitation coil 6 and magnet 5 cause
vibrate close to and apart from each other in the direction of arrow X.

When fluid flows through the vibrating Senridges 1-13 and 4, a Coriolis force is generated. The direction of the first force is the direction of movement of the fluid and the vibration direction (angular velocity) of the sensor tube 3.4.
is the direction of the vector product of , and the magnitude of the Coriolis force is
to the mass and velocity of the fluid.

Proportional.

Since the amplitude of the sensor tube 3.4 increases toward the center of the U-shaped curved portion, positive acceleration is applied to the fluid at the position of the vibration sensor 7 on the inflow side, and the vibration sensor +
At position J8, negative acceleration is applied to the fluid. Therefore, on the inflow side, Coriolis force acts to damp vibrations, and on the outflow side, Coriolis force acts to increase vibrations, causing twisting in each of the sensor tubes 3 and 4. Since this torsional deformation is proportional to the quality of the fluid ffi, the time difference τ caused by the torsional deformation of the detection signals of the vibration sensors 7 and 8 is
is proportional to the fluid quality II flow rate.

In FIG. 1, the excitation coil 6 and the vibration sensor 7.8 are each connected to an outflow measurement control device 11, and the ia measurement control device 11 has a configuration roughly shown in FIG. 3. That is,
The flow rate measurement control IIA device 11 includes a drive circuit 12 that supplies current to the excitation coil 6 that vibrates the sensor tubes 3 and 4 as described above, and detection from the vibration sensor 7.8 that detects the displacement of the sensor tube 3.4. It has a time difference detection circuit 13 which receives the signals a and b and detects the time difference between the rain detection signals a and b which are proportional to the flow rate. Zarani, flow rate measurement control bag H1
1 includes a frequency detection circuit 14 as a frequency detection means that receives a detection signal from the vibration sensor 8 and detects the vibration frequency f1 of the sensor tubes 3 and 4, and a sensor tube 3 detected by the frequency detection circuit 14. .4 frequency f1
A determination circuit 15 is provided as a determination means for determining whether the value is within a predetermined range or outside the predetermined range.

Further, the drive circuit 12 receives a detection signal (velocity signal) b from the vibration sensor 8, and changes the current flowing through the excitation coil 6 at the natural frequency of the sensor tube 3.4. The frequency detection circuit 14 shapes the detection signal of the vibration sensor 8 into a pulsed rectangular wave, counts the number of pulses per unit time, and detects the frequency f1 of the senna tube 3.4. The determination circuit 15 determines the maximum allowable frequency f wa during flow rate measurement centered around the natural frequency of the sensor tube 3.4.
x and the minimum frequency f win are set in advance.

It should be noted that the allowable range (fmax~f
5 in) includes variations in the vibration frequency of the sensor tube 3.4 that varies within the density range of the treated fluid and the ambient temperature range, with frequencies outside the usable range being filtered out. Further, this allowable range may be set by setting only the upper limit 1' IIax.

In the determination circuit 15, the frequency detection circuit 14
The frequency f from , and the set reference frequency f■ ax, f
Compare with gin.

The determination circuit 15 has a built-in timer, and continuously determines f, >f■aX or f, for a predetermined time set by the timer.
<rain, it is assumed that an abnormality has occurred in the sensor tubes 3 and 4, and an abnormality detection signal C is output to the drive circuit 12 and alarm device 16 as abnormality processing means.

The alarm device 16 is installed, for example, in a control room that manages the FFI Ill III system, and when the detection signal C from the judgment circuit 15 is input, it blinks a lamp or sounds a buzzer (or a warning device that is installed in a pipe). inform the person that something is wrong.

During normal flow measurement, the sensor tube 3.4 vibrates at its natural frequency, so the frequency f1 is flax >f'
, >f'min, and normal flow rate measurement is being performed.

However, the frequency of the sensor tube 3.4 may become abnormally high. In this case, the frequency f1 detected by the frequency detection circuit 14 is equal to the frequency f wa set by the determination circuit 15.
It will exceed x.

It is believed that such a phenomenon occurs when, for example, no fluid enters the sensor tube 3.4. Further, depending on the shape of the sensor tube 3.4, the frequency f+ may become as loud as 1.5 to 2 times the natural frequency.

When this state continues for a predetermined period of time, the determination circuit 15 outputs the detection signal C to the drive circuit 12 and the alarm device 16. As a result, the drive circuit 12 stops supplying current to the coil 6 and stops the sensor tube 3.4. At the same time, the alarm device 16 issues an alarm.

This can prevent fatigue from accumulating in the sensor tube 3.4, or unnecessary stress acting on the connecting portions of the sensor tube 3.4, thereby preventing damage. Also,
It is also possible to eliminate the waste of vibrating the sensor tube 3.4 without fluid in it.

Also, the frequency f1 of the sensor tube 3.4 is determined by the determination circuit 15.
If the value is lower than 1n and continues for a predetermined period of time, for example, a fluid with a mass exceeding the measurement limit has flowed into the sensor tube 3.4, or an external load has been applied to the sensor tube 3.4. In this case as well, the determination circuit 15 outputs the detection signal C to the drive circuit 12 and the alarm device 16. Therefore, the drive circuit 12 stops excitation of the sensor tube 3.4. At the same time, the alarm device 16 issues an alarm.

Furthermore, −temporal dfl>f'1llaX or fI<f
gain may occur when measuring the flow rate, so even if there is a temporal frequency abnormality, the determination circuit 15 determines that the detection signal C
However, the tines in the determination circuit 15 may be unnecessary if the device is such that the above-mentioned phenomenon does not occur.

In the above embodiment, the sensor tube 3.4 formed in a 0-shape was explained as an example, but the sensor tube 3.4
The shape of the sensor is not limited to this, but it can also be a sensor with a different shape.
- Can also be applied to In that case, since the natural frequencies of the sensor tubes are different, it is sufficient to set a permissible frequency range (fmax to fWin) in the determination circuit 15 according to each shape.

In addition, in the frequency detection circuit 14, after shaping the input detection signal into a rectangular pulse wave, the time from the rise of the pulse wave to the rise of the next pulse wave is determined, and the frequency is determined based on this. can also be used for sieving.

Effects of the Invention As described above, the mass flowmeter according to the present invention can stop the vibration of the pipe by determining that the vibration frequency of the pipe through which fluid has exceeded a predetermined frequency. This eliminates the waste of vibrating the pipe when no fluid is in the pipe, and it also prevents excessive stress from being applied to the connecting parts of the pipe, reducing the burden on the pipe. This can extend the life of the conduit.

Furthermore, since the pipe does not vibrate when the frequency of vibration of the pipe exceeds the set value of the determination circuit, it has the advantage that it is also possible to detect the occurrence of an abnormality.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of a mass flowmeter according to the present invention;
FIG. 2 is a front view of a vibration sensor that detects displacement of the sensor duplex, and FIG. 3 is a block diagram of the flow rate measurement control device. 1...Main body, 3.4...Sensor tube, 6...
Coil, 7, 8... Vibration sensor, 11... Flow measurement control device, 12... Drive circuit, 13... Time difference detection circuit, 14... Frequency detection circuit, 15... Judgment circuit, 16...Alarm device. Patent applicant Tokiko Co., Ltd.

Claims (1)

[Claims] A conduit is vibrated in a resonant state by an exciter, and the conduit is deformed by the Coriolis force generated by flowing fluid through the vibrating conduit. In a mass flowmeter that detects vibration with a vibration sensor on each outflow side and measures the mass flow rate of the fluid from the time difference between the detection signals, the vibration frequency of the pipe is supplied with the detection signal output from the vibration sensor. a frequency detection means for detecting; a determination means for determining whether or not a frequency detection value outputted from the frequency detection means exceeds a predetermined frequency, and outputting an abnormality detection signal when the frequency detection value outputted from the frequency detection means exceeds the predetermined frequency; A mass flowmeter comprising: abnormality processing means for stopping vibration by the vibrator or issuing an alarm upon receiving an abnormality detection signal from the means.