JP2769241B2 - Mass flow meter - Google Patents

Description

Description: 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 measures a mass flow rate of a fluid using Coriolis force.

The mass of the fluid depends on the type of fluid, its physical properties (density, viscosity, etc.),
It is desirable that the weight be represented by a mass that is not affected by the 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.

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.

2. Description of the Related Art Conventionally, as a mass flow meter that measures a mass flow rate by using the Coriolis force, a fluid flows through a pair of U-shaped sensor tubes, and the pair of sensor tubes approaches and separates from each other. 2. Description of the Related Art There is known a device which vibrates in a direction and detects a displacement of a sensor tube caused by generation of a Coriolis force proportional to a mass flow rate to measure a mass flow rate.

In the mass flow meter configured to vibrate the sensor tube in this way, 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 the signals detected by the inflow side pickup and the outflow side pickup that detects 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 calculated as the time difference when the flow rate is zero. Had to be corrected.

Problems to be Solved by the Invention However, in the related art, when the zero point correction is performed, when the zero point correction switch is operated in a state where the flow rate is zero, the inflow side pickup and the outflow side pickup for a fixed time (for example, 10 seconds) after the switch is operated. Detect the time difference between the output signal and
Since the zero point is obtained from the average value of the time difference, there is a problem that the user has to 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.

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

Means for Solving the Problems 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, and detecting displacement on the inflow side and outflow side of the sensor tube. A pair of pickups, a zero point correction switch that is operated when the flow rate flowing through the sensor tube is zero, a memory that stores a time difference between an output signal of the inflow-side pickup and an output signal of the outflow-side pickup, and Averaging means for averaging the stored time differences; latch means for holding the output of the averaging means when the zero point correction switch is operated; output signals of the inflow side pickup and the outflow side pickup; Calculating means for calculating a mass flow rate from a time difference between the output signal and an average value of the time difference supplied from the latch means.

Operation 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 pickup stored in the memory before the zero point correction. There is no waiting time until the correction is completed, and the flow measurement can be restarted immediately.

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

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, a pair of sensor tube
Manifold 4 to which sensors 2 and 3 are connected, and sensor tubes 2 and 3
And a box-shaped cover 1c that protects it.

The pair of sensor tubes 2 and 3 extend in the horizontal direction from the manifold 4 and are disposed so as to be symmetric in the horizontal direction via 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 inflow side connection port of the manifold 4. A second straight pipe portion 2b that is connected and fixed and extends in parallel with the first straight pipe portion 2a, and is bent so as to be folded back from the distal ends of the first and second straight pipe portions 2a and 2b toward the base end side. Curved parts 2c, 2d
And a U-shaped connecting portion 2e connecting the curved portions 2c and 2d.

Also, the other sensor tube 3 is the sensor tube 2
The straight tubes 3a and 3b are arranged symmetrically with the sensor tube 2 so that the straight tubes 3a and 3b are parallel to the outflow tube 6 and the straight tubes 2a and 2b. In addition, the connection part 2 of the sensor tubes 2 and 3
e and 3e are connected by a holding member 8 and held together.

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 arranged between the straight pipe sections 2a and 3a on the inflow side and between the straight pipe sections 2b and 3b on the outflow side.

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

The pickup 9 includes 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 straight pipe section 3a
Are relatively displaced in the direction of the arrow X between the magnets. Therefore, the straight pipe sections 2a, 3a
The pickup 9 detects the displacement of the straight pipe section 3a from the voltage of the coil section.

Reference numerals 23 and 24 denote vibrators between the ends of the straight pipe sections 2a and 2b and the straight pipe section 3
It is provided between the tips of a and 3b.

The vibrator 23 has substantially the same configuration as the electromagnetic solenoid,
It comprises a coil section attached to the inflow side straight pipe section 2a, and a magnet section attached to the outflow side straight pipe section 2b and fitted into the coil section. Accordingly, when the vibrator 23 is energized, the vibrator 23 vibrates the straight pipe portions 2a and 2b in the direction of the arrow X (up and down).

Since the vibrator 24 has the same configuration as the vibrator 23,
The description is omitted.

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

During flow measurement, the pair of sensor tubes 2 and 3 are
Vibration is caused by the operation of 3, 24 while the fluid is flowing inside. The fluid to be measured flowing into the manifold 4 from the inflow pipe 5 is divided and flows into the straight pipe sections 2a and 3a below the sensor tubes 2 and 3, and the curved sections 2c and 3c, the connection sections 2e and 3e, and the curved section 2d. , 3d to the upper straight pipe sections 2b, 3b, merge at the outflow path (not shown) of the manifold 4, and flow out of the outflow pipe 6. Also, since the sensor tubes 2 and 3 are vibrated by the vibrators 23 and 24, the sensor tubes 2 and 3 and the spring constant and the sensor tubes 2 and 3 are vibrated.
It vibrates in the direction of the arrow X (vertical direction) at a natural frequency determined by the flow rate flowing through the inside.

Coriolis force acts in the vibration direction of the sensor tubes 2 and 3,
In addition, since they act in opposite directions on the inflow side and the outflow side, the straight tubes 2a, 2b, 3a, 3b of the sensor tubes 2, 3 are twisted, and the twist angle is proportional to the mass flow rate. The pickups 9, 10 measure the relative displacement due to the torsion of the sensor tubes 2, 3 as a time difference between the output signals to measure the mass flow rate.

FIG. 2 is a block diagram of the flow measuring unit 11 of the mass flow meter 1. In FIG. 2, reference numeral 12 denotes a time difference detection circuit, which outputs an output signal from the pickup 9 on the inflow side and a pickup on the outflow side.
The time difference (phase difference) from the output signal from 10 is detected. The sign from the time difference detection circuit 12 is input to the calculation unit 13, which calculates the flow rate from the time difference and displays the flow rate on the display unit 14.

Reference numeral 15 denotes a zero point correction unit, which includes a memory 16, an averaging unit 17, a latch unit 18, and a switch circuit 19. The memory 16 stores the time difference obtained within a predetermined time (for example, about 10 seconds), and erases the storage after the predetermined time. The averaging unit 17 calculates an average value of the time differences stored in the memory 16.

When the zero point correction switch 20 is turned on, the switch circuit 19 supplies the average value of the averaging unit 17 to the latch unit 18.

When the L level is applied to the clock terminal, the latch section 18 samples the average value from the averaging section 17 and holds the new average value even when the average level becomes H level, and stores the new average value as a zero point.

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 the output signals from the pickups 9 and 10 must be output with a time difference of zero. However, a processing error of the manifold 4 that supports the sensor tubes 2 and 3 and a deviation between the inflow side and the outflow side of the sensor tubes 2 and 3 occur due to variations in dimensions of the sensor tubes 2 and 3 itself, temperature, pressure, and the like. This causes a time difference between the output signal of the pickup 9 on the inflow side and the output signal of the pickup 10 on the outflow side despite the fact that the flow rate is zero.

The time difference at the time when the flow rate is zero is stored in the memory 16, and when the zero point correction switch 20 is turned on, a certain time before the switch 20 is turned on, 10 seconds before in this embodiment. Is a symmetric range, the time difference within the range is read from the memory 16, and the averaging unit 17 calculates the average value. Then, the calculated average value is stored in the latch unit 18 as a new zero point.

Switch circuit when zero point correction switch 20 is turned on
Since the output of 19 becomes L level, a sample signal is given to the clock terminal of the latch unit 18 and the new average value from the averaging unit 17 is held.

The operation unit 13 is configured to detect the time difference from the time difference detection circuit 12 and the latch unit.
The mass flow rate is calculated from the zero point (average time difference) stored in 18. As described above, the zero point stored in the latch unit 18 when the zero point correction switch 20 is turned on is the output signal of the past pickup 9 and the output signal of the pickup 10 until 10 seconds before the switch 20 is operated. Is the average value of the time difference between Therefore, the zero point can be corrected at the same time when the switch 20 is operated, and it is not necessary to wait until a new average value is output after the switch 20 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.

FIG. 3 shows a modification of the present invention. In FIG. 3, the same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 3, reference numeral 21 denotes a judgment circuit for judging whether or not the flow rate is zero. The allowable range of the time difference is set in consideration of the variation of the time difference when the flow rate is actually zero.
The determination is made based on whether or not the time difference stored in 16 is within the allowable range. Reference numeral 22 denotes a latch unit that holds a signal from the determination circuit 21. When the flow rate in the sensor tubes 2 and 3 is zero within the range stored in the memory 16, the determination circuit 21
Is at L level. Where the zero point correction switch
When the switch 20 is turned on, the output of the switch circuit 19 becomes L, so that the output of the latch section 22 becomes L.

Further, the output of the averaging unit 17 is the average of the time difference in the past 10 seconds when the flow rate is zero, so that an accurate zero point can be obtained.

If the original valve is not completely closed when the zero-point correction switch 20 is turned on, and the time difference within the range stored in the memory 16 at least once exceeds the allowable range, , The output of the determination circuit 21 becomes H level,
Is at H level. In this case, an alarm is issued to inform that the zero correction is not accurate. Therefore, the operator confirms that the flow rate is zero, turns on the switch 20 again, and performs the zero point correction again.

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

The configuration of the microcomputer is the same as that of a one-chip microcomputer including a CPU, a memory, a timer counter, and the like. Therefore, the configuration diagram of the microcomputer is omitted. In FIG. 4, when the power is turned on, the CPU initializes the memory in step S1 (hereinafter, the steps are omitted) and clears the timer counter for measuring the time difference between the outputs of the pickups 9 and 10 and the time.

In the next S2, it is checked whether the vibration of the sensor tubes 2 and 3 has lasted for one cycle. When the sensor tubes 2, 3 vibrate, the time difference between the inflow side and the outflow side of the sensor tubes 2, 3 generated by Coriolis force is measured and stored in a memory (S3).

In S4, the mass flow rate is calculated by multiplying the time difference obtained from the time difference between the inflow side and the outflow side and the average of the time difference set as the zero point by a constant (calculation means), and the flow rate display is rewritten. The time difference is stored in the memory in time series.

In the next S5, it is checked whether the zero-point correction switch 20 is turned on. If the zero-point correction switch 20 is not turned on, the process returns to S2 and S2 to S5 are repeated to measure the flow rate.

However, in step S5, when the zero point correction switch 20 is turned on, the time difference stored in the memory is changed for a predetermined time (for example, 10 seconds) from when the zero point correction switch 20 is turned on.
It is checked whether the flow rate was zero retroactively (S6). If the flow rate is zero for the past fixed time in S6, S7
Then, the value of the time difference between the output signals of the pickups 9 and 10 in the past fixed time is averaged (averaging means), and this average value is stored in the memory as the value of the zero point (storage means).

This average value is used as a zero point at the time of mass flow measurement, and a more accurate time difference between the output time difference of the pickups 9 and 10 and the average value is obtained in S3. To determine whether the flow rate is zero in S6, the flow rate can be determined to be zero if the time difference between the output signals of the pickups 9 and 10 is within a predetermined time difference range, that is, equal to or less than the predetermined flow rate.

As described above, when the zero point correction switch is operated, the mass flow meter according to the present invention has a time lag between the output signal of the inflow-side pickup and the output signal of the outflow-side pickup stored in the memory before that. Since the zero point correction can be performed based on the following, there is no waiting time from when the zero point correction switch is operated to when the zero point correction is completed. Flow measurement can be resumed. Therefore, when installed on a production line such as a factory, the downtime of the line can be further reduced, and even in a place where the environment such as temperature and pressure frequently changes, zero can be easily achieved in accordance with the environmental change. 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 flow meter according to the present invention, FIG.
FIG. 3 is a block diagram of a flow rate measurement unit of the present invention, FIG. 3 is a block diagram of a modification of the present invention, and FIG. 4 is a flowchart for explaining processing executed by the microcomputer. 1 ... Mass flow meter, 2,3 ... Sensor tube, 9,10 ...
Pickup, 11: Flow rate measurement unit, 12: Time difference detection circuit, 13: Operation unit, 14: Display unit, 15: Zero point correction unit, 16: Memory, 17: Averaging unit, 18 ... … Latch,
19: Switch circuit, 20: Zero point correction circuit, 21: Judgment circuit.

Claims (1)

(57) [Claims] 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 displacement of an inflow side and an outflow side of the sensor tube; A zero-point correction switch that is operated when the flow rate flowing through the sensor tube is zero, a memory that stores a time difference between an output signal of the inflow-side pickup and an output signal of the outflow-side pickup, and averages the time difference stored in the memory. Averaging means, and a latch means for holding an output of the averaging means when the zero point correction switch is operated; and a time difference between an output signal of the inflow side pickup and an output signal of the outflow side pickup. Calculating means for calculating a mass flow rate from an average value of a time difference supplied from the latch means; and .