JPH04236330A - Mass flowmeter - Google Patents

Abstract

PURPOSE:To vibrate a sensor tube of a mass flowmeter efficiently with reducing the power consumption. CONSTITUTION:Speed detecting circuits 7, 8 output a speed signal of a sensor tube to a time difference detecting circuit 9 and also to an amplitude detecting circuit 14, a speed value detecting circuit 16 and a speed direction detecting circuit 17. A multivibrator 18 generates a triangular wave based on the difference between the set value output from an amplitude judging circuit 15 and the amplitude. When the output of the triangular wave reaches a signal value of the speed value detecting circuit 16, a comparator 26 resets a flipflop 20 and turns the output of an operational amplifier to zero. An exciting circuit 19 turns ON and OFF the transistors 32, 33 by the combination of the signals from the speed direction detecting circuit 17 and the flipflop 20, so that a voltage corresponding to the vibrating direction of the sensor tubes 2, 3 is intermittently supplied to the exciting coils 11a, 12a. The feeding time of the voltage to the exciting coils 11a, 12a is determined by the amplitude of the triangular wave.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter, and more particularly to a mass flow meter that detects displacement of a sensor tube due to Coriolis force proportional to flow rate.

0002

2. Description of the Related Art As one type of mass flow meter, a pair of sensor tubes is vibrated at the natural frequency in a state where the inside is filled with fluid for measurement, and the fluid is caused to flow through the sensor tubes. There is a mass flow meter that measures the flow rate of a liquid by detecting the time difference between vibrations of a sensor tube caused by the Coriolis force generated in the liquid flowing inside the sensor tube.

In order to stably perform measurements in this mass flowmeter, it is important that the sensor tube vibrate stably at the above-mentioned natural frequency.

[0004] Therefore, in the Coriolis mass flowmeter,
The amplitude of the sensor tube is detected based on the detection signal from the pickup that detects the displacement of the sensor tube, and the voltage value supplied to the excitation coil of the exciter that vibrates the sensor tube is controlled, so that the sensor tube resonates. It is made to vibrate at a certain frequency.

[0005]

[Problems to be Solved by the Invention] However, in a mass flowmeter configured to vibrate the sensor tube and measure the flow rate using the Coriolis force as described above, as the amplitude of the sensor tube increases, the external Vibration (noise)
On the other hand, when the sensor tube vibrates, stress is concentrated near the fixed part that serves as a fulcrum, and the sensor tube may be damaged. In order to prevent such damage to the sensor tube, the mass flowmeter incorporates an amplitude control circuit that keeps the amplitude of the vibrating sensor tube at a constant value that will not cause damage.

In order to excite the sensor tube at its own resonant frequency, the speed signal from the pickup is positively fed back to drive the exciter (excitation coil), and a multiplier is used to adjust the voltage supplied to the excitation coil. The value was controlled.

By the way, when considering a case where the mass flowmeter is installed on site, power is supplied to the circuit from an external or internal battery. In this case, a voltage of 24 V, for example, is applied to the circuit, but the output voltage of the multiplier is about 5 V, and this voltage difference is consumed by elements such as transistors of the multiplier. Therefore, the amount of power consumed for purposes other than excitation increases, which causes the capacity of the external power source to increase and the life of the battery to shorten.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a mass flowmeter that solves the above problems by suppressing power consumption supplied to components other than the vibrator.

[0009]

[Means for Solving the Problems] The present invention provides a mass flow rate system having a vibrator that vibrates a sensor tube through which a fluid to be measured flows, and a pickup that detects displacement of the sensor tube due to the generation of a Coriolis force proportional to the flow rate. The sensor includes means for changing the application time of the voltage supplied to the vibrator in accordance with changes in the amplitude of the sensor tube.

0010

[Operation] By controlling the application time of the voltage supplied to the vibrator, the sensor tube is excited to a resonance state and the amplitude of the sensor tube is maintained at a constant amplitude, thereby reducing power consumption.

[0011]

Embodiment FIGS. 1 and 2 show an embodiment of a mass flowmeter according to the present invention.

In both figures, a mass flowmeter 1 vibrates sensor tubes 2 and 3 (shown in FIG. 2) through which fluid flows, and measures the flow rate by detecting the displacement of the sensor tubes 2 and 3 due to the Coriolis force caused by the vibration. It has a flow rate measurement circuit 4 (shown in FIG. 1) that performs the measurement.

[0013] The flow rate measurement circuit 4 includes sensor tubes 2 and 3.
The detection coils 5a of the pickups 5 and 6 detect the displacement of
, 6a, and a time difference detection circuit 9 that detects the time difference between the output signals output from the speed detection circuits 7 and 8. The flow rate calculation circuit 10 calculates the mass flow rate by multiplying the time difference by a certain coefficient.

Furthermore, the mass measurement circuit 4 has a drive circuit 13 that drives vibrators 11 and 12 that excite the sensor tubes 2 and 3. As will be described later, this drive circuit 13 sends a pulsed current having a pulse width corresponding to the speed signals from the speed detection circuits 7 and 8 to the excitation coils 11a and 12a of the vibrators 11 and 12, so that the sensor tube 2, 3 is configured to vibrate at a predetermined resonant frequency.

That is, the drive circuit 13 roughly includes an amplitude detection circuit 14, an amplitude judgment circuit 15, a speed value detection circuit 16, a speed direction detection circuit 17, a multivibrator 18, an excitation circuit 19, a flip-flop 20, and an oscillator 21. .

When the output signals from the speed detection circuits 7 and 8 are input, the amplitude detection circuit 14 calculates the amplitude of the sensor tubes 2 and 3, that is, it integrates once and calculates the absolute value of the value or the average of the absolute values. Output the value. Further, the amplitude determining circuit 15 compares the output signal from the amplitude detecting circuit 14 with a set value inputted in advance, and determines how much the amplitudes of the sensor tubes 2 and 3 differ from the set value.

When the output signal from the amplitude detection circuit 14 is larger than the set value, the amplitude judgment circuit 15 outputs a negative voltage that approaches 0V as the difference increases; Outputs a negative voltage that is further away from 0V as it is smaller than the value. That is, the output of the amplitude judgment circuit 15 varies from approximately -0.1V to -5.0V depending on the magnitude of the output signal from the amplitude detection circuit 14, for example.
It changes linearly between V. The multivibrator 18 is a circuit that determines the pulse width, and causes the flip-flop 20 to generate a pulse signal whose pulse width is varied according to the magnitude of the output from the amplitude determination circuit 15. This multivibrator 18 includes a triangular wave generation circuit 34 consisting of a resistor 22, an analog switch 23, a capacitor 24, and an operational amplifier 25, and a comparator 2 that compares the output signal B output from the operational amplifier 25 with the output signal from the speed value detection circuit 16.
6. Note that the output signal C from the comparator 26
is input to the R terminal of the flip-flop 20, a signal is output from the Q terminal to the analog switch 23, which is the inverted output of the Q signal output from the Q terminal of the flip-flop 20. Switch 23 is turned on.

The oscillator 21 turns off the analog switch 23 via the flip-flop 20, and starts the output of the multivibrator 18 at regular intervals.

Furthermore, the output signal A from the speed detection circuits 7 and 8
is supplied not only to the amplitude circuit 14 but also to a speed value detection circuit 16 and a speed direction detection circuit 17.

The excitation circuit 19 includes an inverter 27 and a NAND
Gate 28, AND gate 29, resistors 30, 31, PN
It consists of a P-type transistor 32 and an NPN-type transistor 33. The excitation circuit 19 operates to cause a current in the forward direction or a current in the reverse direction to flow through the excitation coils 11 and 12 according to the output of the speed direction detection circuit 17, as will be described later.

As shown in FIG. 2, in the mass flow meter 1, a pair of sensor tubes 2 are bent into a J-shape when viewed from above.
, 3 are arranged symmetrically on both sides of the outflow pipe 35, and the base ends of the sensor tubes 2, 3 are connected to a manifold 36. Therefore, the fluid flowing in from the inflow pipe 37 passes through the sensor tubes 2 and 3 and flows out from the outflow pipe 35.

[0022] Then, when measuring the flow rate, the sensor tubes 2 and 3
is the inflow side straight pipe part of the pair of sensor tubes 2 and 3,
It is excited in the X direction by excitation coils 11a and 12a of vibrators 11 and 12 provided between the straight pipe sections on the outflow side. When fluid flows through the vibrating sensor tubes 2 and 3, a Coriolis force proportional to the flow rate is generated, and the sensor tube 2
, 3, the outputs of the pickups 5 and 6 provided between the pickups 5 and 3 lead in phase on the inflow side and lag in phase on the outflow side. Since this phase difference is proportional to the flow rate, the flow rate can be determined based on the phase difference.

[0023] Here, the operation of the flow rate measurement circuit 4 during the flow rate measurement as described above will be explained.

When measuring the flow rate, as described above, the drive circuit 1
3 supplies current to the excitation coils 11a and 12a, and the straight pipe portions of the sensor tubes 2 and 3 are excited. The speed detection circuits 7, 8 are connected to the sensor tube 2, as shown in FIG. 3(A).
3, and the drive circuit 13 integrates this speed signal so that the maximum amplitude of the sensor tubes 2 and 3 becomes a constant value, that is, so that the input to the amplitude judgment circuit 15 matches the set value. By changing the output width (pulse width) of the multivibrator 18, the sensor tubes 2 and 3 are
A pulsed current having a pulse width corresponding to the speed of the excitation coils 11a and 12a is supplied to the excitation coils 11a and 12a.

Consider now the case where the amplitudes of the sensor tubes 2 and 3 are smaller than the set value. In this case, the output of the amplitude determining circuit 15 becomes close to 0V, and the slope of the triangular wave (shown in FIG. 3(B)) generated by the triangular wave generating circuit 34 described above becomes small.

That is, the current value of the triangular wave is detected by the speed value detection circuit 1.
As a result, the output signal from the comparator 26 (Fig. 3 (C
) is output to the flip-flop 20, that is, the time until reset is extended.

When the flip-flop 20 is set by inputting pulses at regular intervals from the oscillator 21, the output of the Q terminal becomes H and the output of the *Q terminal becomes L. Further, when the output signal C from the comparator 26 is input to the R terminal, it is reset, the output of the Q terminal is switched to L, and the output of the *Q terminal becomes H.

In the triangular waveform generation circuit 34, the *Q terminal is set to H.
When this happens, the analog switch 23 is turned on, the capacitor 24 is discharged, and the signal B becomes 0V. Comparator 26
The output signal B remains at 0V from when the signal C is output from the oscillator 21 until the signal from the oscillator 21 is output. Therefore,
After the signal is output from the oscillator 21, the comparator 26
The time it takes for the signal C to be output from the input signal C becomes the output width of the triangular wave, and if the amplitude is smaller than the set value, the output width of the triangular wave increases.

NAND gate 28 and A of excitation circuit 19
The signal D having the output width of the triangular wave is input to the ND gate 29 . Therefore, the time period for which the current is supplied to the excitation coils 11a and 12a is determined according to the output width of the triangular wave.

Accordingly, the driving force of the excitation coils 11a, 12a for exciting the sensor tubes 2, 3 increases, and the sensor tubes 2, 3 are driven in the direction of increasing the amplitude. In the excitation circuit 19, in order to apply a voltage according to the displacement direction of the sensor tubes 2 and 3 to the excitation circuits 11a and 12a, the transistors 32 and 33 are connected to the forward direction (H) or reverse direction (L) from the speed direction detection circuit 17. Turns on and off based on the signal.

When the Q terminal of the flip-flop 20 is at the H level and the output of the speed direction detection circuit 17 is at the H level, the output of the NAND gate 28 is at the L level. On the other hand, A.N.
The output of the D gate 29 becomes L because the output H of the speed direction detection circuit 17 becomes L by the inverter 27. In this way, when the outputs of the NAND gate 28 and the AND gate 29 both become L, the transistor 32 is turned on and the transistor 33 is turned off. As a result, a positive voltage is output from E to the excitation coils 11a and 12a.

Further, when the output of the speed direction detection circuit 17 is L, the output of the NAND gate 28 becomes H, and the output of the AND gate 29 also becomes H. In this case, transistor 32
is turned off and transistor 33 is turned on. Therefore, a negative voltage is output from E to the excitation coils 11a and 12a.

[0033] Also, contrary to the above, the flip-flop 20
When the output of the Q terminal becomes L, the output of the NAND gate 28 becomes H and the output of the AND gate 29 becomes L, regardless of whether the output of the speed direction detection circuit 17 is H or L. Therefore, since both transistors 32 and 33 are turned off, no current flows through the excitation coils 11a and 12a, and the sensor tubes 2 and 3 are not excited.

Therefore, from E to the excitation coils 11a, 12a
The voltage output to is output in a pulse-like waveform corresponding to the pulse width of the triangular waveform as shown in FIG. That is, the excitation coils 11a and 12a have 1
Since the voltage of 5V will be supplied intermittently and the voltage application time is determined by the pulse width of the triangular waveform based on the difference between the amplitude of sensor tubes 2 and 3 and the set value, set sensor tubes 2 and 3. The sensor tubes 2 and 3 can be stably excited at the natural resonance frequency without the amplitude exceeding the value.

Here, since the transistors 32 and 33 in the excitation circuit 19 only perform on/off switching driving, the voltage loss is almost zero. Therefore, most of the power supplied from the power supply is used by the excitation coil 11a,
12a, which efficiently excites the sensor tubes 2 and 3.

[0036] Therefore, the power consumption is lower than when a multiplier is used as in the conventional mass flowmeter, and the battery life can be extended, especially in the case of a battery-driven system.

In the above embodiment, the excitation coils 11a, 1
Although the triangular wave generation circuit 34 is used as a method for modulating the pulse width of the voltage output to 2a, the method is not limited to this, and the pulse width may be changed digitally using a combination of a counter circuit and a clock pulse generation circuit. good.

Furthermore, the excitation circuit may be constructed using a field effect transistor (FET), an analog switch, a relay, or the like instead of the above transistor.

[0039]

As described above, the mass flowmeter according to the present invention changes the application time of the voltage supplied to the vibrator that vibrates the sensor tube depending on the magnitude of the amplitude of the sensor tube. There is no need to reduce the voltage to supply the transistor, reducing power consumption and enabling efficient vibration of the sensor tube. Therefore, in the case of an external power supply or battery-powered type, such as a field-installed type, it has the advantage of suppressing power consumption, extending battery life, and eliminating the need to consider drops caused by a power cable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a flow rate measurement circuit of an embodiment of a mass flowmeter according to the present invention.

FIG. 2 is a perspective view of a mass flow meter.

FIG. 3 is an output waveform diagram of points A to E of the flow rate measurement circuit.

[Explanation of symbols]

1 Mass flow meter 2, 3 Sensor tube 4 Flow rate measurement circuit 5,6 Pickup 7, 8 Speed detection circuit 11,12 Vibrator 13 Drive circuit 14 Amplitude detection circuit 15 Amplitude judgment circuit 16 Speed value detection circuit 17 Speed direction detection circuit 18 Multivibrator 19 Excitation circuit 20 Flip-flop 21 Oscillator 34 Triangular wave generation circuit

Claims (1)

[Claims] 1. A mass flowmeter comprising: an exciter that vibrates a sensor tube through which a fluid to be measured flows; and a pickup that detects displacement of the sensor tube due to the generation of a Coriolis force proportional to the flow rate. A mass flowmeter comprising means for changing the application time of the supplied voltage in accordance with changes in the amplitude of the sensor tube.