JP2952080B2 - Mass flow meter - Google Patents

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 for measuring a mass flow rate of a fluid using Coriolis force.

[0002] The mass of a fluid is desirably represented by a mass that is not affected by the type, physical properties (density, viscosity, etc.) of the fluid, and process conditions (temperature, pressure). As a mass flow meter that measures the mass flow rate of a fluid, for example, a so-called indirect mass flow meter that measures the volume flow rate of a fluid and converts the measured value to a mass flow rate and directly measures the mass flow rate of the fluid, There is a direct type mass flow meter that can measure with higher accuracy than the gauge.

[0003] As the direct type mass flow meter, there is a type in which a fluid is caused to flow in a vibrating sensor tube, and a mass flow rate is directly measured by utilizing the Coriolis force generated at this time.

[0004]

2. Description of the Related Art Conventionally, as a mass flow meter for measuring a mass flow rate using Coriolis force, a fluid is flowed through a pair of U-shaped sensor tubes, and the pair of sensor tubes are brought close to each other. 2. Description of the Related Art There has been known a device that measures a mass flow rate by vibrating in a separating direction and detecting displacement of a sensor tube caused by generation of a Coriolis force proportional to the mass flow rate.

In the mass flow meter configured to vibrate the sensor tube as described above, when the flow rate is zero, the displacement between the inflow side and the outflow side of the sensor tube coincides with each other so that no time difference occurs. However, in practice, there is a possibility that a deviation occurs between the inflow side and the outflow side of the sensor tube due to a processing error of a support portion supporting the sensor tube, a variation in dimensions of the sensor tube itself, a temperature, a pressure, and the like. In this case, the time difference between the inflow side and the outflow side is detected even though the flow rate is zero, and the displacement of the sensor tube causes a measurement error.

Therefore, conventionally, the time difference between signals detected by the inflow-side pickup and the outflow-side pickup for detecting the displacement of the sensor tube when the flow rate is zero is stored, and the time difference detected at the time of the flow rate measurement is determined as the zero flow rate. The correction was made based on the time difference.

Conventionally, when the zero point correction is performed, when the zero point correction switch is operated in a state of zero flow rate, the output signals of the inflow side pickup and the outflow side pickup for a fixed time (for example, 10 seconds) after the switch is operated. Is detected and the zero point is obtained from the average value of the time difference. Therefore, there is a problem that the user must wait a certain time from operating the zero point correction switch until the zero point is actually corrected. Therefore, for example, when a mass flow meter is provided in the middle of the production process, the flow rate cannot be measured until the zero point correction is performed and the flow rate can be measured, and the production line may be stopped during that time.

Accordingly, the present applicant has filed Japanese Patent Application No. 2-31653.
When the zero-point correction switch is operated according to No. 5, the zero-point correction can be performed based on the time difference between the output signal of the inflow-side pickup and the output signal of the outflow-side pickup stored in the memory before that. A proposed mass flowmeter was proposed.

[0009]

However, in the mass flow meter proposed above, when the zero point correction switch is operated in a state where the flow rate is zero, the inflow side is set for a predetermined time (for example, 10 seconds) before that. The time difference between the output signal from the pickup and the output signal from the outflow side pickup was detected, and the zero point was obtained from the average value of the time difference.The original valve was closed when the zero point correction switch was operated. Nevertheless, if the time difference is equal to or greater than a certain value, the determination circuit does not determine that the flow rate is zero, and the zero point correction process ends without executing the zero point correction.

Further, the zero point correction switch must be operated many times until the flow rate is determined to be zero by the determination circuit. During this time, the zero point correction processing remains suspended. However, even if the user operates the zero-point correction switch for the purpose of zero-point correction while changing the liquid type, the problem occurs that the zero-point correction is not executed within the liquid type switching time.

Accordingly, an object of the present invention is to provide a mass flow meter which has solved the above-mentioned problems.

[0012]

SUMMARY OF THE INVENTION The present invention provides a sensor tube through which a fluid to be measured flows, a vibrator for vibrating the sensor tube at a predetermined frequency, an inflow side of the sensor tube,
A pair of pickups for detecting the displacement on the outflow side, a zero point correction switch operated to output a zero point correction signal,
A memory for storing a time difference between the output signal of the inflow-side pickup and the output signal of the outflow-side pickup output from a predetermined time to the present, and a flow rate from the predetermined time to the present based on the time difference stored in the memory. Or, a determination means for determining whether or not the current flow rate is within a zero range, an averaging means for averaging the time difference stored in the memory and outputting a signal thereof, and holding an output of the averaging means. Latch means, timer means for continuously outputting a signal for a fixed time when the zero point correction signal is output from the zero point correction switch, and while the zero point correction switch is operated to output a signal from the timer means. Control means for controlling the latch means to cause the latch means to hold the output from the averaging means when the determination means determines that the flow rate is zero, A calculating means for calculating a mass flow rate from the average value of the time difference to be supplied the output signal of the serial inflow side pickup and the time difference between the output signal of the outflow-side pickup from said latch means, the more.

[0013]

When the zero point correction switch is operated, the determination means determines whether or not the flow rate is zero. If the flow rate is determined to be zero, the zero point is corrected at that time. Since the signal of the zero point correction switch is held for a certain period of time by the timer means, even if the flow rate is not determined to be zero when the zero point correction switch is operated, the determination means is output while the signal is output from the timer means. If the flow rate is determined to be zero, zero point correction is performed at that time.

[0014]

1 and 2 show an embodiment of a mass flow meter according to the present invention.

[0015] In both figures, a mass flow meter 1 and the inflow-side flange 1a of the inlet port 1a ₁ is open at its center, between the outlet side flange 1b of the outlet (not shown) is opened, the pair Manifold 4 to which sensor tubes 2 and 3 are connected
And a box-shaped cover 1c that accommodates and protects the sensor tubes 2 and 3.

The pair of sensor tubes 2 and 3 extend in the horizontal direction from the manifold 4 and are arranged symmetrically in the horizontal direction through a vertical surface that stands up and down. One sensor tube 2 is connected and fixed to a connection port on the inflow side of the manifold 4 by brazing or the like, and has a first straight pipe portion 2 a extending in the pipe direction and a base end connected to the manifold 4.
And a second straight pipe portion 2b extending in parallel with the first straight pipe portion 2a and a base end side of the first and second straight pipe portions 2a and 2b. The curved portions 2c and 2d are bent so as to be folded back, and a U-shaped connecting portion 2e connecting the curved portions 2c and 2d.

The other sensor tube 3 is formed in the same shape as the sensor tube 2, and is symmetrical with the sensor tube 2 so that the straight pipe portions 3a and 3b are parallel to the outflow pipe 6 and the straight pipe portions 2a and 2b. It is arranged in. The connection portions 2e and 3e of the sensor tubes 2 and 3 are connected by a holding member 8 and are mutually held.

The holding member 8 is not in contact with the outflow pipe 6, so that the piping vibration of the outflow pipe 6 is not directly transmitted to the sensor tubes 2 and 3.

In the pair of sensor tubes 2 and 3, pickups 9 and 10 are disposed between the straight pipes 2a and 3a on the inflow side and between the straight pipes 2b and 3b on the outflow side. ing.

Since the pickups 9 and 10 have the same configuration, only one pickup 9 will be described.

The pickup 9 comprises a coil portion held by the straight tube portion 2a of the sensor tube 2, and a magnet provided on the straight tube portion 3a of the sensor tube 3 so as to face the coil portion in the left and right directions.

Therefore, when the sensor tubes 2 and 3 vibrate, the coil portion provided in the straight tube portion 3a is relatively displaced between the magnets in the direction of the arrow X. Therefore, an electromotive force corresponding to the relative displacement of the straight pipe sections 2a and 3a is generated in the coil section, and the pickup 9 detects the displacement of the straight pipe section 3a from the voltage of the coil section.

Reference numerals 11 and 12 denote vibrators, which are straight pipe portions 2a and 2b.
And between the ends of the straight pipe sections 3a and 3b.

The vibrator 11 has substantially the same configuration as that of the electromagnetic solenoid, and includes a coil portion attached to the inflow side straight tube portion 2a and a magnet attached to the outflow side straight tube portion 2b and fitted into the coil portion. Department. Therefore, the shaker 11
When the coil section is energized, the straight pipe sections 2a and 2b
Vibrates in the directions (up, down).

Since the vibrator 12 has the same configuration as the vibrator 11, its description is omitted.

Next, the measuring operation of the mass flow meter 1 having the above configuration will be described.

At the time of flow measurement, a pair of sensor tubes 2 and 3
Is vibrated by the operation of the vibrators 11 and 12 while a fluid is flowing inside. Manifold 4 from inflow pipe 5
The measured fluid that has flowed into the sensor tubes is divided into sensor tubes 2 and 3
Flows into the straight pipe portions 2a, 3a below the curved portions 2c, 3c,
After passing through the connecting portions 2e, 3e and the curved portions 2d, 3d, it reaches the upper straight pipe portions 2b, 3b, merges in the outflow passage (not shown) of the manifold 4, and flows out of the outflow pipe 6.

The sensor tubes 2 and 3 are connected to the vibrator 11,
12, the sensor tubes 2, 3
It vibrates in the direction of the arrow X (vertical direction) at the natural number of revolutions determined by the spring constant and the flow rate flowing through the sensor tubes 2 and 3.

The Coriolis force acts in the direction of vibration of the sensor tubes 2 and 3 and acts in opposite directions on the inflow side and the outflow side, so that the straight pipe portions 2a, 2b and 3 of the sensor tubes 2 and 3
The twist occurs in a and 3b, and the twist angle is proportional to the mass flow rate. The pickups 9 and 10 measure the relative displacement due to the torsion of the sensor tubes 2 and 3 as a time difference of the output signal to measure the mass flow rate.

FIG. 2 shows a flow rate measuring section 13 of the mass flow meter 1.
It is a block diagram of. In the figure, reference numeral 14 denotes a time difference detection circuit, which is a time difference (phase difference) between an output signal from the pickup 9 on the inflow side and an output signal from the pickup 10 on the outflow side.
Is detected. The signal from the time difference detection circuit 14 is
5 (arithmetic means), the arithmetic unit 15 obtains the flow rate from the time difference, and displays the flow rate on the display unit 16.

Numeral 17 denotes a zero point correction unit, which is a memory 18, an averaging unit 19 (averaging unit), a latch unit 20, a judgment circuit 21 (judgment unit), a switch circuit 22, and a timer circuit 23 (timer unit). Means) and a latch unit control circuit 24. The memory 18 stores the time difference obtained within a predetermined time (for example, about 10 seconds), and erases the storage after the predetermined time has elapsed. The averaging unit 19 calculates an average value of the time differences stored in the memory 18.

The switch circuit 22 includes a zero point correction switch 2
When the switch 5 is turned on, the output of the timer circuit 23 is inverted, and the timer circuit 23 holds the output for a certain period of time.

As shown in FIGS. 3A, 3B, and 3C, when the zero-point correction switch 25 is turned on, the output of the timer circuit 23 outputs the rising edge of the zero-point correction signal from the switch 25. To an L level in synchronism with, and returns to an H level after a certain time (for example, 10 seconds).

The judgment circuit 21 checks whether or not the time difference stored in the memory 18 falls within the range of the time difference when the flow rate is zero, and all the time differences stored in the memory 18 fall within the zero range (that is, the time difference is zero). When the flow rate falls within a predetermined time difference), it is determined that the flow rate is zero, and an L level signal is output. If the time difference stored in the memory 18 is out of the range of the zero flow rate, the determination circuit 21 determines that the flow rate does not correspond to the zero flow rate, and outputs an H level signal.

The latch section control circuit 24 comprises an exclusive NOR circuit 26, a flip-flop 27, and an AND circuit 28. This exclusive NOR circuit 2
6 and the flip-flop 27 are supplied with outputs from the determination circuit 21 and the timer circuit 23. The outputs from the exclusive NOR circuit 26 and the flip-flop 27 are supplied to the AND circuit 28. The output of the timer circuit 23 is changed from H level to L level.
Is set by the change to the level, and the output of the decision circuit 21 is set to H
Reset at the change from level to L level.

When the latch section 20 changes the clock terminal from L level to H level, the average value from the averaging section 19 is newly sampled and the new average value is stored as a zero point. The average value previously sampled is maintained even when the signal level reaches the L level.

Here, the operation at the time of zero point correction will be described.
As an operation at the time of zero point correction, first, a main valve (not shown) provided on the upstream side of the mass flow meter 1 is closed to reduce the flow rate to zero. The sensor tubes 2 and 3 are vibrated at a constant frequency as in the flow rate measurement.

Since the flow rate in the sensor tubes 2 and 3 is zero, Coriolis force is not originally generated in the sensor tubes 2 and 3 and output signals from the pickups 9 and 10 must be output with a time difference of zero. However, due to processing errors in the manifold 4 supporting the sensor tubes 2 and 3 and variations in dimensions of the sensor tubes 2 and 3 itself, temperature, pressure, and the like, a shift occurs between the inflow side and the outflow side of the sensor tubes 2 and 3. And the output signal of the pickup 9 on the inflow side and the pickup 1 on the outflow side even though the flow rate is zero.
A time difference from the output signal of 0 occurs.

The time difference when the flow rate is zero is stored in the memory 18.
When the zero-point correction switch 25 is turned on, the target range is a predetermined time before the switch 25 is turned on, up to 10 seconds before in the present embodiment, and the range is stored in the memory 18. Are read out, and the averaging unit 19 calculates an average value. Then, the calculated average value is stored in the latch unit 20 as a new zero point.

As shown in Case 1 in FIG. 3, when the zero-point correction switch 25 is turned on, the output of the switch circuit 22 becomes L level, so that the output of the timer circuit 23 is kept for a certain period of time (10 in this embodiment). (Assumed to be seconds). That is, the timer circuit 23 has the zero point correction switch 25.
Has the same function as being operated for 10 seconds.

As shown in (D), (E), and (F) of FIG. 3, when the output of the timer circuit 23 goes low, the output of the decision circuit 21 is low, that is, the memory 18
If the time difference (measured flow rate) stored in the memory is within the range of zero flow rate, the output of the exclusive NOR circuit 26 is switched from L level to H level at the time when the switch 25 is turned on, and the flip-flop circuit 27 When the output of the circuit 23 falls, the level is switched from L level to H level.

Therefore, the output of the AND circuit 28 switches from the L level to the H level, whereby the latch section 18 performs a latch operation. As described above, when the sample signal is supplied to the clock terminal of the latch unit 18, the new average value calculated from the time difference stored in the memory 18 for a certain period of time (10 seconds) by the averaging unit 19 becomes a new zero. Stored as a point.

The calculation unit 15 calculates the flow rate from the time difference from the time difference detection circuit 14 and the zero point (the average value of the time difference) stored in the latch unit 20. The zero point stored in the latch unit 20 when the zero point correction switch 25 is turned on as described above is an average value in the past 10 seconds before the switch 25 is operated. Therefore, the zero point can be corrected at the same time when the switch 25 is operated.
It is not necessary to wait until a new average value is output after the operation of 5 is operated. Therefore, the time for interrupting the flow measurement for the zero point correction can be shortened, and the influence on the production line and the like can be minimized.

Next, case 2 shown in FIG. 3 will be described.

In case 2, the zero point correction switch 25 is turned on within a predetermined time (10 seconds) in which the memory 18 stores the time difference after the main valve is closed.

In such a case, even if the main valve is closed, the memory 18 partially stores the time difference when the fluid in the sensor tubes 2 and 3 is flowing.
The output of 1 is at the H level when the zero point correction switch 25 is turned on, and eventually changes to the L level when all the time differences stored in the memory 18 fall within the range of zero flow.

Therefore, since the output of the decision circuit 21 is at the H level when the zero point correction switch is turned on, the output of the exclusive NOR circuit 26 is at the L level and the output of the AND circuit 28 is The output remains at the L level, and the latch operation is not performed in the latch unit 20. When the output of the determination circuit 21 changes to L level while the output of the timer circuit 23 holds L level, the output of the exclusive NOR circuit 26 changes from L level to H level.
Then, the output of the AND circuit 28 rises to the H level, and the latch unit 20 performs a latch operation to store a new zero point.

As described above, even when the time difference stored in the memory 18 is not within the range of zero flow rate when the zero point correction switch 25 is turned on, the timer circuit 23 holds the H level. If the flow rate becomes within the range of zero within a certain time, a new zero point is stored in the latch unit 20 at that time. Therefore, the calculation unit 15 calculates the flow rate from the time difference from the time difference detection circuit 14 and the new zero point (the average value of the time difference) stored in the latch unit 20.

Next, case 3 shown in FIG. 3 will be described.

In this case 3, the zero point correction switch 2
5 is turned on and the output of the determination circuit 21 is H
The case where the flow rate is not determined to be zero at the level is shown.

In this case, the output of the determination circuit 21 remains at the H level and the output from the AND circuit 28 is at the L level despite the fact that the timer circuit 23 holds the L level. Is not done.

However, if the output of the determination circuit 21 remains at the H level (the flow rate is not zero) after a certain period of time has elapsed since the switch 25 was turned on, the output of the timer circuit 23 turns the switch 25 on. It has been 1 since
Since the level returns from the L level to the H level after 0 seconds, the output of the AND circuit 28 is automatically switched to the H level when a predetermined time elapses after the switch 25 is turned on. Therefore, in the latch unit 20, the latch operation is performed simultaneously with the rise of the output of the timer circuit 23, and a new zero point is stored.

As described above, while the timer circuit 23 maintains the ON state of the switch 25 for a certain period of time, the determination circuit 21
Does not judge that the flow rate is zero, when the ON state of the switch 25 by the timer circuit 23 is cut off, the output of the AND circuit 28 changes to the H level and the latch operation is performed.

Therefore, as in the above cases 1 to 3, the zero point correction switch 25 is turned on and the zero point stored in the latch unit 20 is determined by the average value or the past average value 10 seconds before the switch 25 is operated. This is the average value for 10 seconds from the time when the flow rate is determined to be zero or the average value for 10 seconds after the switch 25 is operated. Therefore, when the switch 25 is operated, the average value of the time difference of 10 seconds before and after the switch 25 is reliably stored in the latch unit 20 as a new zero point.

Therefore, the time during which the flow meter is interrupted for the zero point correction can be limited to 10 seconds after the operation of the switch 25, so that the influence on the fluid supply line is minimized. That is, since the judgment circuit 21 does not judge the flow rate to be zero even though the switch 25 is operated, the troublesome operation of repeating the zero point correction many times is eliminated, and the zero point can be surely corrected by one switch operation. It is also convenient, especially when the zero point must be corrected within a certain time so as not to disturb the fluid supply in the line.

The above-mentioned zero point correction can be similarly performed by using a microcomputer. FIG. 4 shows processing by the microcomputer.

Since the configuration of the microcomputer is the same as that of a one-chip microcomputer including a CPU, a memory, a timer counter, etc., the configuration of the microcomputer is omitted. In FIG. 4, when the power is turned on, the CPU executes step S1.
(Steps will be omitted hereinafter) to initialize the memory and clear the timer counter for measuring the time difference between the outputs of the pickups 9 and 10 and the time.

In the next step S2, it is checked whether the vibration of the sensor tubes 2 and 3 has lasted one cycle. When the sensor tubes 2 and 3 vibrate, the time difference between the inflow side and the outflow side of the sensor tubes 2 and 3 generated by the Coriolis force is measured and stored in a memory, and the time difference between the inflow side and the outflow side is measured. The mass flow rate is calculated by multiplying the time difference calculated from the average value of the time difference set as the zero point by a constant (calculation means), and the flow rate display is rewritten (S3). still,
The time difference is stored in the memory in time series.

In the next step S4, it is checked whether the zero point correction switch 25 has been turned on.
When 5 is turned on, the process proceeds to the next S5. In S5, the timer operates to count the elapsed time (timer means).

Subsequently, it is checked whether or not at least the current time difference stored in the memory at S6 is zero (determination means). If the flow rate is zero in the past fixed time in S6, the process proceeds to S7, where the pickups 9 and 1 in the past fixed time are set.
Averaging the value of the time difference of the output signal of 0 (averaging means),
The average value is stored in the memory as the value of the zero point (latch means), the timer is stopped, and the process returns to S2.

The average value obtained in S6 is used as a zero point when measuring the mass flow rate.
A more accurate time difference between the time difference between the ten outputs and the average value is obtained. To determine whether or not the flow rate is zero in S6, it can be determined that the flow rate is zero if the current outputs of the pickups 9 and 10 are within the range of zero flow rate.

However, in the above S4, the switch 2
If 5 is not on, the process proceeds to S8 to determine whether or not the timer is stopped. If the timer is operating, it is determined in S9 whether or not the elapsed time is 10 seconds or more.

In S9, if the timer operation is 1 to 10 seconds, the process proceeds to S6 described above. If the timer operation is 10 seconds or more, the process proceeds to S7, the average of the time difference is stored in the memory, the timer is stopped, and S2 is performed. Return to

Next, a case is considered where the flow rate is not zero at the time when the zero point correction switch 25 is turned on. In this case, after the processes of S1 to S5 are performed, the process returns from S6 to S2. Then, in S4, since the switch 25 has already been operated, the process proceeds to S8, and in S5, since the timer is operating, the process proceeds to S9.

This is because the switch 25 is turned on and the
When the flow rate is determined to be zero in 0 second (case 2 described above)
) Is equivalent to performing zero point correction. Therefore, if the flow rate is determined to be zero in S6 during the elapsed time of 10 seconds, the process proceeds to S7, a new zero point is stored in the memory, and the timer is stopped.

However, when the flow rate does not become zero during the elapsed time of 10 seconds (case 3 described above), the process proceeds from S9 to S6, and the processes of S2 to S4, S8, S9, and S6 are repeated. If the elapsed time becomes 10 seconds or more in S9 without the flow rate becoming zero in S6, S
Then, the process proceeds to step S7, where the average value of the time difference at that time is stored in the memory, and the timer is stopped.

Therefore, by operating the switch 25 only once, the zero point is corrected when the flow rate becomes zero during the timer operation, so that the flow rate is not zero when the switch 25 is turned on. When the flow rate does not become zero during the operation of the timer, the zero point correction is performed when the timer is stopped, and it is convenient when there is no time to repeat the zero point correction.

FIG. 5 shows a modification of the present invention.

In this figure, the description of the same parts as in FIG. 4 is omitted.

In S6, it is checked whether or not all the time differences stored in the memory are within the range of zero flow rate.
That is, it is checked whether or not the flow rate is zero at all times going back 10 seconds after the switch 25 is turned on. Therefore, a time difference other than the flow rate of zero is excluded, and the zero point correction becomes more accurate.

In S9, if the elapsed time of the timer exceeds 10 seconds without determining that the flow rate is zero in 10 seconds of the timer, the process proceeds to S10, where the timer is stopped, and the zero point correction is not performed.

In this case, for example, despite the fact that the main valve is closed, the main valve cannot completely close the fluid, or the time difference stored in the memory due to the variation in the processing accuracy of the sensor tubes 2 and 3 or the like. It is conceivable that the flow rate does not fall within the range of zero.

In the above-described embodiment, when the flow rate does not become zero during the operation of the timer, the average value at the time when the timer stops is latched. However, even if the flow rate does not become zero, the average value of the time difference is latched. Error may be large if the zero point is corrected based on In this case, when the elapsed time becomes 10 seconds or more in S9, the timer is stopped and zero point correction is not performed.

Therefore, in the flow rate calculation, the flow rate correction is performed based on the zero point of the average value at the time of the previous zero point correction.

Therefore, in this modified example, when the switch 25 is turned on and when the flow rate is not determined to be zero during the timer operation, the zero point is not corrected, so that the zero point largely deviates and the measurement error is enlarged. Such erroneous operation is prevented, and the zero point can be updated only when the flow rate becomes zero.

After stopping the timer in S10, the program proceeds to S11
A warning is issued to inform the operator that zero point correction cannot be performed. Accordingly, the operator performs the inspection and repair so that the zero point correction is performed by re-operating the switch 25 or examining the reason why the flow rate does not become zero.

In the above-described embodiment, the fixed time of the timer circuit 23 is set to 10 seconds. However, the present invention is not limited to this, and a time of 10 seconds or less, that is, an arbitrary time which does not hinder the flow rate measurement is set. Is also good.

In the above embodiment, the sensor tubes 2, 3
Is described as bent as shown in FIG. 1. However, it is needless to say that the present invention can be applied to a mass flow rate in which the sensor tube is formed in a U-shape or a straight tube.

[0079]

As described above, in the mass flow meter according to the present invention, when the zero point correction switch is operated, the flow rate is determined to be zero by the determination means, and when the flow rate is determined to be zero. Since the zero point correction can be performed at the time of operation of the switch and the signal of the zero point correction switch is held for a certain period of time by the timer means, the flow rate is not determined to be zero when the zero point correction switch is operated. Even when the determination means determines that the flow rate is zero while the signal when the switch is turned on is output from the timer means, the zero point can be corrected. Therefore, even if the zero-point correction switch is operated, the zero-point correction is not performed, and the trouble of redoing the operation is reduced, or it is not necessary to keep pressing the switch until the flow rate becomes zero, so that one switch operation is effective. Can be corrected for zero point.

Further, when the zero-point correction switch is operated, the zero-point correction can be performed based on the time difference between the output signal of the inflow-side pickup and the output signal of the outflow-side previously stored in the memory. If the flow rate is zero, the waiting time from when the zero point correction switch is operated to when the zero point correction is completed is short, and a new zero point is set almost simultaneously with the operation of the zero point correction switch, and flow measurement is resumed immediately. be able to. Therefore, when installed in a production line such as a factory, the downtime of the line can be further reduced, and even when the environment such as temperature and pressure frequently changes, zero can be easily achieved according to changes in the environment. It has features such as point correction and accurate flow measurement at all times.

[Brief description of the drawings]

FIG. 1 is a perspective view of one embodiment of a mass flow meter according to the present invention.

FIG. 2 is a block diagram illustrating a circuit configuration of a flow measurement unit.

FIG. 3 is a timing chart showing an output state of each circuit at the time of zero point correction.

FIG. 4 is a flowchart illustrating a process executed by a microcomputer.

FIG. 5 is a flowchart illustrating a process performed by a microcomputer according to a modification.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mass flow meter 2, 3 Sensor tube 9, 10 Pickup 11, 12 Exciter 13 Flow rate measurement part 14 Time difference detection circuit 15 Calculation part (calculation means) 16 Display part 17 Zero point correction part 18 Memory 19 Averaging part (Average) 20 Latch (Latch) 21 Judgment Circuit (Judgment) 22 Switch Circuit 24 Latch Control Circuit 25 Zero-Point Correction Switch

Claims (1)

(57) [Claims] 1. A sensor tube through which a fluid to be measured flows, a vibrator for vibrating the sensor tube at a predetermined frequency, a pair of pickups for detecting an inflow side and an outflow side displacement of the sensor tube, A zero-point correction switch that outputs a zero-point correction signal, and a memory that stores a time difference between the output signal of the inflow-side pickup and the output signal of the outflow-side pickup that has been output from a predetermined time before to the present time. Determining means for determining whether or not the flow rate from a predetermined time to the present or the current flow rate is within a zero range based on the time difference stored in the memory, averaging the time difference stored in the memory, and outputting the signal Averaging means, latch means for holding the output of the averaging means, and a signal for a fixed time when a zero point correction signal is output from the zero point correction switch. The timer means to be continued, and the output from the averaging means is output to the latch means when the determination means determines that the flow rate is zero while the zero point correction switch is operated and the signal is output from the timer means. Control means for controlling the latch means so as to be held; calculation for calculating a mass flow rate from a time difference between an output signal of the inflow side pickup and an output signal of the outflow side pickup and an average value of a time difference supplied from the latch means; Means, and a mass flow meter.