JP2698670B2 - Flow compensator for flow meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate correcting device for a flow meter, and more particularly to a flow rate correcting device for a flow meter configured to correct a measurement error caused by a change in a pulse frequency accompanying an increase or a decrease in a flow rate. About.

2. Description of the Related Art A flowmeter for measuring a fluid to be measured (in this case, a gas to be measured is referred to as a gas hereinafter) is provided in a pipe for supplying a measured fluid such as city gas to each home. Has been established. As this type of flow meter, a turbine type flow meter which has a small load at the time of flow measurement and can measure a wide range from a minute flow to a large flow is used. However, in a turbine type flow meter, a turbine rotor as a rotating body rotates in proportion to the flow rate, and the number of rotations is detected to output a rotation detection pulse (hereinafter simply referred to as a pulse). Then, the rotation speed of the turbine rotor cannot follow the flow rate change due to inertia, and a pulse number different from the actual flow rate is output.

Therefore, in the conventional flow rate correction device, the main counter A for integrating the above-mentioned pulse, another counter B for integrating the pulse when the flow rate suddenly decreases, and whether or not the rotation speed of the turbine rotor has decreased due to the decrease in the flow rate. A monitoring means for monitoring at predetermined time intervals is provided. When the rotation speed of the turbine rotor decreases, the pulse for each rotation of the turbine rotor is integrated by the counter B, and the flow correction device subtracts a measurement value due to the inertia of the turbine rotor when the rotation of the turbine rotor becomes constant. Then, the value S (actual flow rate when the rotational speed decreases) is obtained, and the value S is added to the main counter A to correct overmetering when the flow rate decreases.

SUMMARY OF THE INVENTION However, the conventional flow rate correction device described above has a problem that when the time from when the rotation speed of the turbine rotor is reduced to a constant value is short due to a rapid decrease in the flow rate, or when the rotation speed of the turbine rotor is increased from a decrease. When the speed suddenly changes, the detection of the change in the number of revolutions is delayed, so that there is a problem that accurate flow rate correction cannot be performed. In addition, the conventional apparatus has a problem that when the flow rate suddenly increases, the measurement may be dropped due to a missing pulse due to a delay in rotation detection.

Accordingly, an object of the present invention is to provide a flow rate correction device for a flow meter that solves the above-mentioned problems.

Means for Solving the Problems The present invention relates to a flow rate correction device for a flow meter, wherein a storage means for storing a cycle or a frequency of a pulse corresponding to a flow rate of a fluid to be measured, and when a flow rate of the fluid to be measured becomes constant. Calculating means for obtaining a correction value according to the measurement error based on the change rate of the pulse cycle or frequency stored in the storage means, and adding or subtracting the correction value to or from the flow integrated value to correct the flow integrated value. It becomes.

In the present invention, the change in the cycle or frequency of the pulse due to the change in the flow rate is not directly detected, the cycle or the frequency of the pulse corresponding to the flow rate of the fluid to be measured is temporarily stored, and the cycle or the frequency stored when the flow rate is constant. Is read to detect the change rate.

Then, a correction value corresponding to the measurement error is calculated based on the change rate of the cycle or the frequency, and by correcting the flow rate integrated value, accurate correction can be performed without a pulse measurement drop even in a sudden increase or decrease of the flow rate. .

Embodiment FIG. 1 shows an embodiment of a flow rate correction device for a flow meter according to the present invention. In the figure, a flow meter body 2 of a turbine type flow meter 1 is shown.
Is arranged in the middle of a pipe for feeding a fluid to be measured such as gas, with its axis aligned in the vertical direction. The fluid is supplied as indicated by the arrow in the figure.

Reference numeral 3 denotes an upstream cone, which is inserted into the flow channel 2a of the flowmeter main body 2 from below, and is attached to and held by the column 3a. Also,
Reference numeral 4 denotes a downstream cone, which is inserted into the flow path 2a of the flowmeter main body 2 from above, and is attached to and held by the column 4a. Bearing holes 3b, 4b having a predetermined depth are formed in the axes of the opposing surfaces of the upstream and downstream cones 3, 4, and each bearing hole 3b, 4b has a superalloy, a jewel (artificial sapphire). Pivot bearings
5,6 are buried. In the center of each of the pivot bearings 5, 6, for example, a hemispherical bearing portion is formed.

Reference numeral 7 denotes a turbine rotor, in which a rotary shaft 9 is inserted and fitted and fixed in a central hole of a rotor hub 8, and a plurality of blades 10 are integrally formed on an outer periphery of the rotor hub 8. The rotating shaft 9 is made of, for example, cemented carbide or steel, and has an upstream end 9a and a downstream end 9b.
Are each formed in a hemispherical shape, and are slidably supported at low friction on bearing portions of pivot bearings 5 and 6 of the upstream and downstream cones 3 and 4, respectively.

Reference numeral 11 denotes two magnets provided inside the upper surface of the rotor hub 8. Reference numeral 12 denotes a rotation detecting pickup made up of a magnetoresistive element or the like, which is embedded in the downstream cone 4 so as to face the magnet 11. Therefore, the turbine rotor 7 rotates at a rotation speed proportional to the flow rate of the fluid to be measured flowing in the flow passage 2a, and the rotation speed is detected by the pickup 12 that detects passage of the magnet 11.

That is, the pickup 12 outputs a pulse corresponding to the rotation speed of the turbine rotor 7, in other words, a pulse having a frequency proportional to the flow rate.

Numeral 13 denotes a flow rate compensating device which constitutes a main part of the present invention. A control device 14 having a period measuring unit 14A for measuring the period T of the pulse supplied from the pickup 12;
Monitoring the change of the cycle T from the measurement data read from the first and second storage devices 15 and 16 for storing the measurement data such as the measurement time t and the like; And an integration counter 18 that integrates a unit flow rate ΔQ corresponding to the cycle T for each pulse cycle T.

Normally, when the flow rate of the gas flowing through the flow path 2a is measured by the turbine type flow meter 1, the pulse from the pickup 12 is input to the control device 14, and the interval between the pulses is measured by the cycle measuring unit 14A of the control device 14. That is, the cycle T is measured. Then, the control device 14 initially stores the pulse period T and the time t in the first storage device 15, and when the storage capacity of the first storage device 15 becomes full, the control device 14 continues the period T and the time t after the second storage device 16. t is stored. When the storage capacity of the second storage device 16 becomes full, the measurement data is stored again in the first storage device 15, and this is repeated.

When the storage capacity of the first storage device 15 becomes full, an arithmetic unit
17 reads the measurement data stored in the first storage device 15 and monitors the rate of change of the cycle T. When the cycle T is constant and does not change, the integrating counter 18 integrates a unit flow rate corresponding to the cycle T. While the measurement data is being read from the first storage device 15 as described above, the second
Since the measurement data is stored in the storage device 16, no pulse drop occurs even if the flow rate changes during the above calculation.

However, when the flow rate increases or decreases and the cycle T changes, the arithmetic unit 17 obtains a correction value corresponding to the change rate of the cycle T as described below, and adds this correction value to the integrated value of the integration counter 18 or The flow rate integrated value is corrected by subtraction.

For example, when a plurality of gas appliances on the downstream side of the turbine type flow meter 1 are used at the same time, and then the use of one gas appliance is stopped, the flow rate Q changes as shown in FIG. In the figure, the flow rate Q is rapidly increased at time t ₀ is stabilized at a flow rate Q _1. At time t ₁ after a while the flow rate plummeted from Q ₁ to Q _2, it is stabilized at a flow rate Q _2. As described above, when the flow rate suddenly increases or decreases, the turbine rotor 7 cannot follow the flow rate change due to its own inertia, and the flow rate measured by the turbine type flow meter 1 changes as shown in FIG. (See Fig. 2)
On the other hand, when the _value increases rapidly, the undermetering is delayed by t ₀ −t _1, and when the value decreases rapidly, the over metering is delayed by t ₂ −t ₃ . As a result, the turbine flowmeter 1 can not measure a third hatching portion of the area S ₁ when the flow surge, also a part of the flow rate rapidly decreases during the area S ₂ results in extra measure.

Therefore, f ₁ the frequency of the arithmetic unit in the 17 rotation speed of the turbine rotor 7, as shown in FIG. 4 rises pulse f ₀
When the cycle T becomes shorter, the unit flow rate ΔQ corresponding to each cycle T is added to the integrating counter 18 and the decreasing rate of the cycle T is calculated at the time t ₁ when the cycle T becomes constant.
Check up to. And when rate of change ΔT in the period T is in a predetermined range DerutaTu, determines that the turbine rotor 7 can not follow the increase of the actual flow rate, adds the flow rate corresponding to the area an area S ₁ in integration counter 18.

Also, adding speed normal flow measurement and unit flow ΔQ commensurate with the same period T from the time t ₁ is the period T becomes constant is constant until t ₂ of the turbine rotor 7 (T) in integrating counter 18.

Further, the rotational speed of the turbine rotor 7 is reduced, the frequency of the pulses from f ₁ from the time t ₂ when the time interval of the period T decreases to f ₂ becomes long until time t ₃ when the period T is constant again, with unit flow ΔQ commensurate with the period T (T) is added by integrating counter 18, examine the rate of increase in the period T until time t _3. Then, the ratio ΔT is within a predetermined range ΔT _D (> ΔTu)
At this time, it is determined that the rotation of the turbine rotor 7 cannot follow the change in the actual flow rate and is rotating at a rotational speed higher than the actual flow rate due to inertia, and a correction value corresponding to the area S ₂ in FIG. 3 is calculated. Subtract from the accumulation counter 16.

Further, when the change rate of the rotation cycle T of the turbine rotor 7 is outside the above-mentioned predetermined range, the arithmetic unit 17 sets the change rate ΔT in another predetermined range ΔTui, ΔT _Dj (i
= 2,3... N, j = 2,3... N), and the correction value Si or Sj corresponding to the corresponding ΔTui, ΔT _Dj is added to or subtracted from the integrating counter 18 to determine the flow rate. Correct the integrated value.

The flow rate correction calculation by the calculation device 17 is performed by the control device 14.
The measurement is performed on the measurement data stored in the first storage device 15 in response to a command from the device. When the processing of all the measurement data in the first storage device 15 is completed, the measurement data is stored in the second storage device 16 during that time. Therefore, the flow correction calculation similar to the above is performed after the data storage in the second storage device 16 is completed.

In addition, the controller 14 instructs the arithmetic unit 17 to stop the arithmetic operation when the flow rate becomes zero and the above-described arithmetic processing is completed. Thereafter, when the gas flows again and the flow rate measurement is restarted and one of the first and second storage devices 15 and 16 is filled with the measurement data, the control device 14 instructs the calculation device 17 to restart the calculation.

When the processing of the measurement data in the first storage device 15 is completed in the arithmetic device 17 and the operation is switched from the first storage device 15 to the second storage device 16, or when the second storage device 16 is switched to the first storage device. When switching to the device 15, the previous storage devices 15, 16
After the last data is switched, it may be necessary for performing arithmetic processing. Therefore, the control device 14 operates the arithmetic unit 17 and the first and second storage devices 1 so that the data stored in the last predetermined range can be read even when new data is being written.
Control 5,16.

Further, the correction values Si, Sj and ΔTui, ΔT _Dj may be obtained by equations and parameters, or an arithmetic unit.
17 may be appropriately read from a data table stored in a memory in the memory 17 or a flow rate change rate ΔT
May be obtained by combining and using these two methods according to the value of.

Further, the unit flow rate ΔQ corresponding to the above-described period T is stored in a data table in a memory in the arithmetic unit 17,
The data may be read out each time, or may be calculated from an equation.

Further, in the above embodiment, the measurement of the number of revolutions of the turbine rotor 7 is replaced by the pulse cycle, but the measurement is not limited to the pulse cycle alone, but may be a frequency. Further, when the magnitude of the rotation speed, particularly when the pulse cycle at the time of measuring a large flow rate becomes considerably short, or the like, the method may be switched to a method of calculating using the frequency.

Further, it is a matter of course that the above-described flow rate correction arithmetic processing may be performed using a microcomputer instead of the flow rate correction device 13. Further, a display may be provided in the flow rate correcting device 13 so that the integrated value of the integrating counter 18 is displayed so that the corrected flow rate can be known on the spot.

Further, in the above embodiment, the description has been made using the turbine type flow meter. However, in addition to the turbine rotor, a flow meter of a type having a structure in which a rotating body that rotates according to the flow rate is supported at a low load is used. It can also be applied to a meter.

Further, in the above embodiment, the rotation of the turbine rotor is detected. However, the present invention is not limited to this. For example, a hot wire type flow sensor or a flow meter using a flow rate detecting means for detecting a change amount of heat or light according to the flow rate may be used. The present invention can also be applied to a flow meter that converts an output signal of the flow measurement into a pulse (frequency) by voltage-frequency conversion. In this case, when the output signal from the flow rate detecting means is converted into a pulse, a pulse conversion delay occurs with respect to the flow rate change in the process until the conversion.

Therefore, by applying the present invention to a flow meter other than the turbine type flow meter, a measurement error due to a delay in pulse conversion can be accurately corrected.

Effect of the Invention As described above, the flow rate correction device for a flow meter according to the present invention is:
Since the cycle or frequency of the pulse corresponding to the flow rate of the fluid to be measured is stored in the temporary storage means, and the data stored when the flow rate of the fluid to be measured becomes constant can be read to correct the measurement error when the flow rate changes, Under metering that occurs when the flow rate sharply increases and overmetering that occurs when the flow rate sharply decreases can be corrected, and a correction value can be obtained without missing pulses generated according to the flow rate. Changes can be examined in detail and corrected accurately. In particular, even when the flow rate increases or decreases in a short time and changes in complexity, the stored data can be read out and the correction operation can be performed after the rotation speed becomes constant. There is such a feature that a correction value (correction algorithm) for correcting the flow rate can be selected to correct the flow rate integrated value with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a flow rate correction device for a flow meter according to the present invention, FIG. 2 is a diagram showing a change in an actual flow rate, and FIG. Figure 4
The figure shows a change in the frequency and cycle of the pulse output according to the change in the flow rate. DESCRIPTION OF SYMBOLS 1 ... Turbine type flow meter, 2 ... Flow meter main body, 7 ... Turbine rotor, 11 ... Magnet, 12 ... Pickup, 13 ... Flow correction device, 14 ... Control device, 15 ... 1st
Storage device, 16 ... second storage device, 17 ... arithmetic device,
18 …… Counter.

Claims (1)

(57) [Claims] 1. A flow rate correcting device for a flow meter for measuring a flow rate by integrating pulses generated according to a flow rate of a fluid to be measured and correcting a measurement error caused by a change in the flow rate. Storage means for storing a pulse cycle or frequency corresponding to the measurement error, and when the flow rate of the fluid to be measured becomes constant, the measurement error is determined based on a change rate of the pulse cycle or frequency stored in the storage means. A flow rate correction device for a flow meter, comprising: a calculating means for obtaining a correction value and adding or subtracting the correction value to or from the flow rate integrated value to correct the flow rate integrated value.