JPH04130227A - Mass flowmeter - Google Patents

Abstract

PURPOSE:To detect the abnormal vibration generated in sensor tubes quickly and to prevent breakdown by detecting the difference between voltages generated in shakers in response to the amplitude changes in a pair of the sensor tubes, and comparing the output corresponding to the difference with a threshold value. CONSTITUTION:Under the normal conditions, the amplitudes of sensor tubes are approximately equal. Resonance is generated at the natural frequency determined by the spring constant of the connecting part of the sensor tubes through a loop constituted of the sensor tubes, pickup 18 and 19, a driving circuit 9 and shakers 20 and 21. When the vibration is stopped or the amplitude is decreased due to the stagnation of bubbles and the like in one sensor tube, the change in inductive electromotive force occurs in a coil part 20a or 21a of the shaker 20 or 21 of the sensor tube. a third differential amplifier 3 detects the voltage difference between first and second differential amplifiers 1 and 2 based on the change. The output voltage corresponding to the voltage difference is compared with a threshold voltage in a comparing circuit 5. Thus, the difference exceeding a certain level can be detected as the abnormality of the sensor tube.

Description

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

BACKGROUND OF THE INVENTION It is desirable that the flow rate of a fluid be expressed in terms of mass that is not affected by the type of fluid, physical properties (density, viscosity, etc.), and process conditions (temperature, pressure). Examples of mass flowmeters that measure the mass flow rate of a fluid include a so-called indirect mass flowmeter that measures the volumetric flow rate of a fluid and converts this measured value into a mass flow rate;
There is a direct mass flowmeter that directly measures the mass flow rate of a fluid with higher accuracy than an indirect mass flowmeter.

Some direct mass flow meters directly measure the mass flow rate by flowing fluid through a vibrating sensor tube and utilizing the Coriolis force generated at this time.

In this type of Coriolis mass flowmeter, as described in Japanese Patent Application Laid-Open No. 54-4168, fluid is caused to flow through a pair of U-shaped sensor tubes, and the pair of sensor tubes are placed close to each other. Vibrate in the direction of separation. Coriolis force acts in the direction of vibration of each sensor tube,
Since the inlet and outlet sides are in opposite directions, the sensor tube is twisted, and this twist angle is proportional to the mass flow rate. Therefore, a sensor is provided at the inlet and outlet sides of a pair of sensor tubes to detect the displacement of the sensor tube due to the twist, and the time difference between the output detection signals of both sensors is measured to detect the twist of the sensor tube. , that is, the mass flow rate is being measured.

Problems to be Solved by the Invention In the conventional Coriolis mass flowmeter as described above, a pair of sensor tubes is shifted in phase to create a resonance state.
Moreover, the sensor tubes are vibrated so that the relative amplitude between these sensor tubes is constant. However, if one of the pair of sensor tubes becomes clogged or damaged, resulting in an abnormal fluid flow and one sensor tube no longer vibrates, the amplitude of the other sensor tube will return to the normal amplitude.
The vibration is doubled, resulting in abnormal vibration. This abnormal vibration caused problems such as damage to the sensor tube.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a mass flow meter that detects an abnormality when abnormal vibration occurs in a sensor tube and prevents damage to the sensor tube.

Means for Solving the Problems The present invention provides a first pipe line vibrated by a first excitation means, and a second pipe line vibrated by a second excitation means synchronized with the first excitation means. The first and second pipes are deformed by the Coriolis force generated by flowing the fluid, and the first and second pipes are deformed on the inflow and outflow sides of the first and second pipes, respectively. In a mass flowmeter that detects vibration relative to a second pipe line and measures the mass flow rate of the fluid based on the time difference between the detection signals, the first a first detection circuit that detects a voltage generated in the excitation means; a second detection circuit that detects a voltage generated in the second excitation means in response to vibration of the second conduit; and the first detection circuit. circuit and the second above
a differential amplifier for outputting the difference between the output signals of the detection circuit; threshold setting means for setting a threshold that defines an allowable range of the level of the output signal from the differential amplifier; and a comparison circuit that compares it with the threshold value set by the threshold value setting means and outputs a signal according to the relative relationship, and determines the vibration state of the first and second pipes based on the output signal of the comparison circuit. It is characterized by

Further, in order to deal with the fact that the output signals of the first and second detection circuits are affected by the temperature of the fluid, the relative speed between the first and second pipe lines is detected. It is equipped with a speed detection means, or a temperature detection means for detecting the temperature of a component of the mass flowmeter or the fluid, and the threshold value setting means is configured to respond to an output signal from the speed detection means or the temperature detection means. Set the threshold value.

Operation The first and second pipes vibrate with the same amplitude under normal conditions, but when an abnormality occurs in either of the first or second pipes, the amplitude changes. The change in amplitude is the first and second
The voltage generated in the first and second excitation means for vibrating the pipe line is changed. Since the probability that both the first and second conduits will be in an abnormal state at the same time is very small and can be ignored, the differential amplifier detects the voltage in the first and second detection circuits. By detecting the difference between the respective output signals and comparing the output signal corresponding to this difference with the threshold value set by the threshold value setting means in the comparison circuit, the difference above a certain level is detected as an abnormality in the pipe line. be able to.

The respective pressure signals from the first and second detection circuits are
Due to changes in resistance values of the first and second excitation means due to temperature, the actual amplitudes of the first and second pipes deviate from each other. Therefore, the speed detection means detects the natural frequency of the pipe line, which changes in response to the temperature of the excitation means, as the relative speed between the first pipe line and the second pipe line, and the threshold value setting means By inputting the signal from the speed detection means and correcting the threshold value by the amount of deviation, the comparison circuit can determine an abnormality without being affected by temperature.

Further, instead of the speed detecting means, the temperature detecting means directly detects the temperature of a component of the mass flowmeter or the fluid corresponding to the temperature of the excitation means, and the threshold setting means receives a signal from the temperature detecting means. By correcting the threshold value in the same manner as above, the comparator circuit can determine an abnormality without being affected by temperature.

Embodiment FIG. 1 shows a configuration diagram of a sensor tube abnormality detection circuit 10 applied to a first embodiment of a mass flowmeter according to the present invention.

In the figure, l is a first differential amplifier which is a first detection circuit;
2 is the second differential amplifier which is the second detection circuit; 3 is the first differential amplifier;
a third differential amplifier for calculating the difference between the output from the differential amplifier and the output from the second differential amplifier; 4 is the first absolute value circuit; 5 is the comparison circuit; 6 is the speed detection circuit; 8 represents a second absolute value circuit, 8 represents a threshold value setting circuit, and 9 represents a drive circuit.

Here, the configuration of the Coriolis mass flowmeter will be explained.

As shown in FIGS. 2 to 6, the mass flow meter 30 has a pair of sensor tubes 11 and 12 attached to the manifold 13. The manifold 13 has an inflow pipe 14 and an outflow pipe 1
5 and connected to the inflow pipe 14.
3a and an outflow path 13b connected to the outflow pipe 15.

Note that, as shown in FIGS. 2 to 4, the inflow passage 13a communicates with connection ports 13a+ and 13a of the manifold 13, which branch to the left and right. The outflow path 13b is also the inflow path 13a.
Similarly, the branched connection port 13b of the manifold 13,
and 13b.

One sensor tube 11 is connected to the connection port 1 of the inflow path 13a.
3a, which extends in the piping direction; a straight pipe part 11b, which is connected to the connection port 13bl of the outflow path 13b and extends in the piping direction; It consists of a U-shaped connection part lie that connects the bent part 11c and the lid.

The other sensor tube 12 is the sensor tube 11
The straight pipe portion 12a is formed in the same shape as the straight pipe portion 12a.

12b is installed symmetrically with the sensor tube 11 so that it is parallel to the straight pipe portions 11a and llb. Note that the connecting portions 11e and 12e of the sensor tube 11.12 are brackets 16a fixed to a ring 16c that loosely fits around the outflow pipe 15.

16b.

Straight pipe portions 11a, ll of a pair of sensor tubes 11.12
b, 12a, 12b pass through the support plate 17, and the support plate 17
Each connection port 13a of the manifold 13 is fixed to the manifold 13 at its end by welding.

13az, 13k)+, and 13b2 are fixedly connected. A hole 17a is bored in the center of the support plate 17, and the outflow pipe 15 passes through this hole 17a.

As shown in FIGS. 3 to 6, the straight pipe section 11a on the inflow side
and 12a, and straight pipe portions 11b and 12b on the outflow side.
A pickup 18°19 is provided between the two. Pickups 18 and 19 have the aforementioned detection coil on one straight pipe! 2a.

12b and a magnet interposed in the detection coil is fixed to the other straight pipe portion 11a, llb. 20.
Reference numeral 21 denotes an exciter (excitation means), which is provided between the tips of the straight tube sections 11a and llb and between the tips of the straight sections 12a and 12b.

Here, a method of vibration using the vibrators 20 and 21 will be explained. Since the vibrators 20 and 21 have the same structure as an electromagnetic solenoid, when the coil parts 20a and 21a are energized, an attractive or repulsive force is generated between the coil parts 20a and 21a and the magnet parts 20b and 21b. Sensor tube 11
When the current to the coil portion 20a is changed at the natural frequency of
The part connected to 1 becomes the node of vibration.

In addition, the coil portion 21 is
When the current of a is changed, the straight pipe parts 12a and 12b of the sensor tube 12 vibrate facing each other like a tuning fork, and the connected part of the support plate 17 and the sensor tube 12 becomes a node of vibration. . At this time, the sensor tube 11 and the sensor tube 12 are alternately vibrated so that their proximity and separation are reversed, and a relative amplitude is generated between the sensor tubes 11 and 12.

The pickups 18 and 19 are straight pipe portions 11a.

The vibrations of 11b, 12a, and 12b are measured as changes in the speed of a detection coil placed in a magnetic field.

Therefore, from the signals of pickups 1B and 19, straight pipe section 1
If the currents to the coil parts 20a and 21a are determined and supplied so that the relative amplitudes of the coils 1a, llb, 12a and 12b are constant, the sensor tubes 11 and 12 can be vibrated with the minimum current.

When fluid flows through the sensor tubes 11, 12, Coriolis is generated due to the action of the fluid flow and vibrations. The direction of this Coriolis is the direction of fluid movement and the sensor tube 11.
In the direction of the vector product of the vibration directions (angular velocity) exciting 12, the magnitude of Coriolis is proportional to the mass of the fluid flowing through the sensor tube 11.12 and its velocity. In the straight pipe portions 11a and 12a on the inflow side, acceleration in the vibration direction is given to the fluid due to the large amplitude at the tips thereof, and in the straight pipe portions 11b and 12b on the outflow side, the fluid returns to the manifold 13 side. As the amplitude decreases, a negative acceleration is given.

As a result, the straight pipe portion 11a on the inflow side.

In the straight pipe portions 11b and 12b on the outflow side, Coriolika acts to suppress vibrations, and in the straight pipe portions 11b and 12b, Coriolika acts to accelerate vibrations. Therefore, the fluid flows into the sensor tube 1.
1.12, Coriolis acts in a direction that twists the sensor tube 11.12. Since this deformation is proportional to the mass flow rate of the fluid flowing into the sensor tubes 11 and 12, the output signals of the pickup 18, which is a vibration sensor installed on the inflow side, and the pickup 19, which is a vibration sensor installed on the outflow side, are proportional to the mass flow rate. A proportional time difference τ (phase difference) is generated. Then, by measuring this time difference, the mass flow rate can be determined.

In FIG. 1, the coil portions 20a of the vibrators 20 and 21,
21a are connected in series and supplied with current from the drive circuit 9. The speed detection circuit 6 detects the relative speed of the sensor tube 11.12 from the two pickups 18.19, and the drive circuit 9 integrates it so that the maximum value of the relative amplitude of the sensor tube 11.12 is a constant value. A current is supplied to the coil portions 20a and 21a such that

The first differential amplifier 1 is connected to both ends of the coil section 20a, and measures the voltage across the coil section 20a.

The second differential amplifier 2 is connected to both ends of the coil section 21a, and measures the voltage across the coil section 21a.

The third differential amplifier 3 is connected to the output sides of the first and second differential amplifiers 1.2 and detects the difference in voltage between them.

Therefore, this third differential amplifier 3 includes the coil section 20a,
This means that the difference in amplitude of 21a is detected. This third
The output of the differential amplifier 3 is a sine wave output that changes with the vibration of the sensor tubes 11 and 12, and when input to the first absolute value circuit 4, it becomes a signal proportional to the peak value of the sine wave.

The pickups 18, 19 have a pair of sensor tubes 11.
The speed detection circuit 6 detects the relative speed of the sensor tube 12, and the speed detection circuit 6 transmits the signal obtained by the pickup 18 and 19 to the sensor tube 1 of the pair.
1. Change to a voltage signal proportional to the relative speed of 12. This signal is supplied to the drive circuit 9 and the second absolute value circuit 7, respectively. The second absolute value circuit 7 is a circuit that detects the absolute value of the input voltage and calculates the amplitude of the input voltage such as the peak value.

The output of the second absolute value circuit 7 is the sensor tube 11°12
A signal proportional to the maximum speed of is obtained.

The output of the second absolute value circuit 7 is input to a threshold value setting circuit 8. The output of the threshold setting circuit 8 is sent to the second absolute value circuit 7.
The output voltage is determined by multiplying the output signal by a certain coefficient. This coefficient is used to reduce the output voltage of the second absolute value circuit 7 so that the output voltage of the second absolute value circuit 7 can be compared with the output voltage of the first absolute value circuit 4 in the comparator circuit 5. In reality, the coefficient is about 10%.

The output voltage of the threshold value setting circuit 8 is input to the terminal (plus input) for setting the upper limit of the comparator circuit 5, and
The output of is input to the input terminal (minus input) of the comparator circuit 5. When the output voltage of the threshold value setting circuit 8 is higher than the output voltage of the first absolute value circuit 4, the output of the comparison circuit 5 becomes a level of 1.

Conversely, the output voltage of the threshold value setting circuit 8 is the same as that of the first absolute value circuit 4.
When the output voltage is lower than the output voltage of the output voltage, it becomes low level.

The output of the comparator circuit 5 is supplied to a warning device 25, and the warning device 25 issues a warning when the output of the comparator circuit 5 becomes low level to notify the outside of the occurrence of an abnormality in the sensor tubes 11 and 12.

Next, the operation of the sensor tube abnormality detection circuit 10 will be explained.

First, under normal conditions, the amplitudes of the sensor tubes 11 and 12 are almost the same;
12, pickups 18, 19, drive circuit 8, and vibrators 20, 21 resonate at a natural frequency determined by the spring constant of the connecting portion of sensor tubes 11 and 12.

Here, the first differential amplifier 1 and the second differential amplifier 2
Consider the input of

A coil portion 2 is provided at both ends of each of the coil portions 20a and 21a.
0a, 21a and the magnet part 20b.

Since 21b is moving relatively, an induced electromotive force is generated according to Lenz's law. This induced electromotive force is proportional to the relative speed of the coil parts 20a, 21a and the magnet parts 20b, 21b, so if the amplitude of the exciter 20 and the amplitude of the exciter 21 are the same, approximately the same induced electromotive force will be generated. .

Therefore, the voltage across the coil parts 20a, 21a is the sum of the voltage drop determined from the resistance value of the coil parts 20a, 21a and the flowing current, and the induced electromotive force generated by the relative speed of the coil and the magnet. Become something. And the coil part 20a.

In a normal state where the resistance value of 21a is equal and the relative speed is equal, the voltages at both ends of the coil parts 20a and 21a are equal, so the first differential amplifier 1 is connected to the second differential amplifier 2.
A voltage equivalent to the input voltage is input. Therefore, the output of the third differential amplifier 3, which detects the difference between the first differential amplifier 1 and the second differential amplifier 2, becomes a voltage of Ov, and the input to the comparator circuit 5 also becomes Ov. Become.

On the other hand, the output voltage of the speed detection circuit 6 is a voltage of a predetermined value because the pair of sensor tubes 11 and 12 are vibrating normally, and the output voltage of the second absolute value circuit 7 is also a voltage signal of a predetermined value. It is. Therefore, the output voltage of the threshold value setting circuit 8 is multiplied by the above coefficients and becomes a positive voltage, although it becomes smaller, and is compared with the output voltage of the first absolute value circuit 4 of 0. As a result, the output voltage of the comparison circuit 5 becomes a positive voltage. The output becomes high level. In this manner, when the sensor tubes 11 and 12 are vibrating normally, the output of the comparator circuit 5 is at a high level.

Here, either one of the sensor tubes 11 or 12
Air bubbles may remain in the sensor tube or solid matter may precipitate therein, causing a change in the natural frequency, and the vibration of either sensor tube 11 or 12 may stop or its amplitude may decrease. Think about the state of being put away. In this case, the drive circuit 9 is connected to the sensor tube 1
1. Coil part 2 so as to keep the relative amplitude of 12 constant.
0a.

Since the current to 21a is increased, the amplitude of the sensor tube ti or 12 whose vibration has not stopped becomes twice that of the normal one. On the other hand, the coil portion 20a.

Since the magnet portions 20b and 21b are brought close to and separated from each other by the vibration of the sensor tube 11.12, an induced electromotive force is generated according to Lenz's law. Since its magnitude is proportional to the relative motion, the coil section 20 of the vibrator 20 or 21 of the stopped sensor tube
No induced electromotive force is generated in a or 21a. On the contrary, twice the induced electromotive force is generated in the coil portion 20a or 21a of the vibrator 20 or 21 of the sensor tube that is vibrating.

In this state, although the respective voltage drops due to the resistance bones of the coil parts 20a and 21a remain the same, a large difference appears in the induced electromotive force as described above, so the coil parts 20a and 21a
The voltages across the terminal 21a are not uniform. Therefore, as described above, the voltage equivalent to that of the second differential amplifier 2 is no longer input to the first differential amplifier 1, and as described above, the voltage equivalent to that of the second differential amplifier 2 is The output voltage of the third differential amplifier 3, which detects the difference between the output voltages of Ov, has a value larger than Ov. The output voltage of the first absolute value circuit 4 also has a certain magnitude.

On the other hand, as described above, even if one sensor tube 11 or 12 stops, the relative amplitude between the pair of sensor tubes 11 and 12 does not change, and the output of the speed detection circuit 6 does not change. That is, the threshold value set by the dark value setting circuit 8 does not change. Therefore, when the output voltage of the first absolute value circuit 4 becomes so large as to exceed the threshold value, the comparison circuit 5
The output becomes low level, and the warning device 25 is activated to notify of an abnormality in the sensor tubes 11 and 12. As a result, it is possible to prevent the pipeline from operating for a long period of time with abnormal vibrations, which could damage the pipeline.
It is also possible to prevent erroneous measurement values from being read in a state of abnormal vibration.

Next, the influence of the temperature of the fluid on the abnormality detection operation of the sensor tubes 11 and 12 described above will be explained.

The voltage across the coil parts 20a, 21a of the vibrator 20.21 is determined by the voltage drop caused by the resistance bones of the coil parts 20a, 21a, the coil parts 20a, 21a and the magnet parts 20b, 2.
It was explained on the previous page that it is the sum of the induced electromotive force generated at the relative speed of 1b.

Let us now consider the influence of temperature on the induced electromotive force and resistance value.

In this embodiment, as described above, the sensor tubes 11 and 12
The vibrations of the sensor tubes 11 and 12 are controlled so that the relative amplitude at the pickups 18 and 19 becomes a predetermined value. Therefore, the amplitude of the sensor tubes 11, 12 remains constant regardless of changes in the temperature of the fluid (changes in the temperature of the fluid change the temperature of the entire mass flow meter).

Therefore, the coil parts 20a, 21a and the magnet part 20b
, 21b does not change, the induced electromotive force according to Lenz's law remains a constant value even if the temperature of the fluid changes. However, the resistance value that causes a voltage drop across the coil parts 20a, 21a is a value that changes in response to the temperature of the coil parts 20a, 21a, which changes as the temperature of the fluid is transmitted.

When the temperature of the fluid actually rises, although the induced electromotive force remains the same, the voltage drop increases, and the coil portions 20a, 21
It can be observed that the voltage across a decreases.

In the case of an abnormal state where one of the sensor tubes 11 and 12 stops vibrating, an induced electromotive force twice as large as normal is generated in the vibrating coil portion 20a or 21a as described above. , the third differential amplifier 3 is connected to the first and second differential amplifiers.
Differential amplifier 1. A large voltage difference is detected between the two.

Then, check the sensor tube 11 or 12 that caused the abnormality.
Even if the amplitude of the coil part 20a is not completely zero,
A difference definitely appears between the induced electromotive force of the coil portion 21a and the third differential amplifier 3 detects the voltage difference.

Then, a first differential amplifier 1 and a second differential amplifier that create the voltage difference are provided.
As described above, the output voltage of the differential amplifier 2 is
Since this includes the voltage drop due to the resistance of the coil parts 20a and 21a, for example, if the temperature of the coil parts 20a and 21a is 200°
In the output voltage when the temperature is C, the ratio of the voltage drop to the induced electromotive force is larger than that when the temperature is 0°C.

Therefore, even if the abnormal states of the sensor tubes 11 and 12 are the same, the voltage difference is smaller at 200°C than at 0°C. That is, even when the sensor tubes 11 and 12 are vibrating with the same vibration difference, the output voltage of the third differential amplifier 3 (first absolute value circuit 4
The output voltage of the coil parts 20a and 21 also corresponds to this.
When the temperature of a changes from 0° C. to 200° C., it decreases, resulting in a state where the measurement sensitivity is decreased.

As described above, since the comparator circuit 5 compares the output voltage of the first absolute value circuit 4 with the threshold value, if the output voltage of the first absolute value circuit 4 slightly exceeds the threshold value, If the output voltage of the first absolute value circuit 4 decreases, it will fall within the range of the above-mentioned threshold value, and there will be cases where an abnormality cannot be detected even though it has occurred.

Here, the influence of the temperature of the fluid in the speed detection circuit 6 will be considered.

In the normal state of the sensor tubes 11, 12, the amplitudes of the sensor tubes 11, 12 are almost the same, and the sensor tubes 11, 12 are composed of the sensor tubes 11, 12, pickups 18, 19, drive circuit 9, and exciter 20°21. The loop resonates at a natural frequency determined by the spring constant of the connecting portion of the sensor tubes 11,12.

If the temperature of the vibrators 20 and 21 is o'C and the temperature of the sensor tube 11.12 is also 0C, the sensor tube 11.12 resonates at the natural frequency N at 0C. In general, it is known that the elastic modulus of a spring body changes depending on the temperature, so that the natural frequency of the spring body decreases as the temperature of the spring body increases. Therefore, for example 20”
When measuring a high temperature fluid of C, the sensor tube 11.1
2 also becomes a value close to 200° C., and the elastic coefficient of the sensor tube changes. Therefore, the natural frequency N2 at which the sensor tube 11, 12 resonates has a value slightly decreased from the natural frequency N1.

The speed detection circuit 6 detects this change in the natural frequency as a change in the relative speed of the sensor tubes 11 and 12, and outputs a signal to the second absolute value circuit 7. In this way, the speed detection circuit 6 detects the natural frequency of the sensor tube 11, 12.
The output voltage corresponds to the temperature of the fluid to be measured, and is a value that decreases as the temperature increases.

Therefore, the threshold value set in the threshold value setting circuit 8 by multiplying by a coefficient that is a constant value also becomes a value that decreases as the temperature of the fluid increases, and the above-mentioned first absolute value that similarly decreases as the temperature of the fluid increases. Since the change is the same as the output voltage of the circuit 4, the comparator circuit 5 can accurately detect an abnormality in the sensor tube 11.1.2 without being affected by the temperature of the fluid.

In fact, the rate at which the above voltage difference changes depending on temperature is that when the coil material is Cu, the resistance value is +4000 ppm/''
Since it has a temperature coefficient of C, the resistance value changes by 1.8 times between 0°C and 200°C. Therefore, if the speed detection circuit 6 and the second absolute value circuit 7 are configured so that the output voltage of the second absolute value circuit 7, which is the basis of the threshold value, is 1/1.8, the temperature will change in the same abnormal state. (The comparator circuit 5 operates at the same timing.)

FIG. 7 shows a configuration diagram of a sensor tube abnormality detection circuit 4o as a second embodiment of the present invention.

In the figure, 26 indicates a temperature detection circuit that detects the temperature of the coil portion 20a of the vibrator 2o, and 27 indicates a threshold value setting circuit. In addition, in the same figure, the coil part 20a.

First and second differential amplifiers 1 connected to both ends of 21a
．． The circuits from 2 to the warning device 25 via the comparison circuit 5 have the same configuration as the circuit of the first embodiment described above, and therefore are given the same reference numerals and a description thereof will be omitted.

The temperature detection circuit 26 detects the temperature of the coil portion 20a with a temperature sensor 26a, and a conversion circuit 26b converts the current signal of the temperature sensor 26a into a voltage signal. This signal is a signal proportional to the temperature of the coil portion 20a, that is, the temperature of the fluid serving as the temperature transmission source, and is output to the threshold value setting circuit 27 instead of the speed detection circuit 6 in the first embodiment. .

The threshold setting circuit 27 has a configuration in which the threshold setting circuit 8 of the first embodiment is further provided with an arithmetic circuit, and generates a signal that is the reciprocal of the voltage signal input from the temperature detection circuit 26, and further calculates the above-mentioned coefficients. The threshold value is set by combining the multiplications. This coefficient is a value determined corresponding to the magnitude of the output voltage of the temperature detection circuit 26 so that the threshold value to be set can be compared with the output voltage of the absolute value circuit 4 in the comparator circuit 5, and is not necessarily the first value. It is not the same value as in the example. The output of the threshold value setting circuit 27 is then output from the comparator circuit 5.
is connected to the terminal that sets the upper limit level.

The drive circuit 9 is directly connected to the pickup 18.19, which detects the relative amplitude of the sensor tube 11.12, and applies current to the coil portion 20a so that the maximum amplitude thereof becomes a constant value.

21a.

Next, the operation of the sensor tube abnormality detection circuit 40 having the above configuration will be explained.

The first and second differential amplifiers 1.2 are connected to coil sections 20a and 2.
A third differential amplifier 3 detects the difference between these output voltages, and inputs the output to an input terminal of a comparison circuit 5 via an absolute value circuit 4. The operation of the above circuit in the normal and abnormal states of the sensor tubes 11 and 12, and the effects on this circuit when the temperature of the coil parts 20a and 21a changes, have been explained in detail in the first embodiment, so they will not be explained here. omitted.

The temperature detection circuit 26 outputs a voltage signal corresponding to the temperature of the coil portion 20a to the threshold absolute value circuit 27 as described above. This voltage signal is a signal that increases as the temperature of the coil portion 20a increases. In the threshold value setting circuit 27, this input signal is first input to an arithmetic circuit, and is converted into a signal whose voltage decreases when the temperature of the coil section 20a increases. Then, the converted signal is multiplied by the above-mentioned coefficient and the threshold value is input to the comparator circuit 5. The threshold set in this way is
Since the above coefficient is a constant value, it becomes a value that decreases in inverse proportion to the temperature of the coil portion 20a. That is, the threshold value set in this embodiment changes in the same manner as the threshold value set based on the output of the speed detection circuit 6 in the first embodiment with respect to temperature changes of the coil portions 20a and 21a.

Therefore, as described above in the first embodiment, the voltage difference caused by the difference in the amplitude of the sensor tubes 11 and 12 is reduced due to the influence of the temperature rise of the coil parts 20a and 21a. , the above-mentioned threshold value is similarly decreased and inputted to the comparator circuit 5, so in this embodiment as well, abnormality detection of the sensor tube can be accurately performed without being affected by the temperature of the fluid, as in the first embodiment. You will be able to do this.

Note that the temperature sensor 26a is not limited to the coil part 20a of the vibrator 20 as in the above embodiment;
1.12 or the temperature of the fluid itself may be detected.

Effects of the Invention As described above, according to the present invention, the voltages generated in the excitation means of a pair of pipes in accordance with the amplitude of the pipes are detected respectively, and the abnormal vibrations occurring in the pipes are detected by determining the difference between these values. This can prevent the pipeline from operating for a long period of time with abnormal vibrations, which could damage the pipeline, and also prevent the reading of incorrect measurement values when abnormally vibrating. .

Furthermore, the functions of the speed detection means and temperature detection means can eliminate malfunctions in detecting abnormal vibrations caused by changes in resistance due to temperature of the excitation means, and improve the reliability of detecting abnormalities in pipelines. Cultivate.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a sensor tube abnormality detection circuit applied to the first embodiment of the mass flowmeter according to the present invention, Fig. 2 is a perspective view of the mass flowmeter, and Figs. 3 and 4 are mass flow rate The plan view, side view, and Figures 5 and 6 are taken along lines X-X and Y- in Figure 3.
FIG. 7, a sectional view taken along the Y line, is a configuration diagram of a second embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... 1st differential amplifier, 2... 2nd differential amplifier, 3... 3rd differential amplifier, 4... 1st absolute value circuit, 5... Comparator circuit , 6... speed detection circuit, 7...
- Second absolute value circuit, 8... Threshold value setting circuit, 9...
Drive circuit, 10.40...Sensor tube abnormality detection circuit, 11°12...Sensor tube, 18.19
... Pickup, 20.21 ... Vibrator, 20a
, 21a... Coil part, 20b, 21b... Magnet part, 25... Warning device, 26... Temperature detection circuit, 30... Mass flow meter. Patent applicant: Tokico Co., Ltd.

Claims (3)

[Claims] (1) It is generated by flowing a fluid through a first pipe line vibrated by a first excitation means and a second pipe line vibrated by a second excitation means synchronized with the first excitation means. The first and second pipes are deformed by Coriolis force, and the first pipe and the second pipe are relative to each other on the inflow side and the outflow side of the first and second pipes, respectively. In a mass flowmeter that detects vibrations of the fluid and measures the mass flow rate of the fluid from the time difference of the detection signals, the voltage generated in the first excitation means in response to the vibrations of the first pipe line is detected. a first detection circuit; a second detection circuit that detects a voltage generated in the second excitation means in response to vibrations of the second conduit; and a first detection circuit and a second detection circuit. a differential amplifier that outputs a difference between output signals; a threshold setting means that sets a threshold that defines an allowable range of the level of the output signal from the differential amplifier; and a threshold setting means that outputs the output signal of the differential amplifier. a comparison circuit that compares with the set threshold value and outputs a signal according to the relative relationship, and determines the vibration state of the first and second pipes based on the output signal of the comparison circuit. Features of mass flowmeter. (2) comprising a speed detection means for detecting the relative speed of the first conduit and the second conduit, and the threshold value setting means is configured to detect a relative speed of the first conduit and the second conduit; The mass flowmeter according to claim 1, characterized in that a threshold value is set. (3) It is characterized by comprising a temperature detection means for detecting the temperature of a component of the mass flow meter or the fluid, and the threshold value setting means sets a threshold value according to an output signal from the temperature detection means. 2. The mass flowmeter according to claim 1.