JPH05231902A - Gas flowmeter - Google Patents

Abstract

PURPOSE:To prevent the increase of measuring errors with time in the region of the small flow rate by performing calibration when the measured value of a thermal flow sensor is not larger than a value of the saturating region in the case where a measurement object is present in the range of the flow rate. CONSTITUTION:An area of the intermediate-large flow rate is measured by a fluidic oscillating device 1, while an area of the small flow rate is measured by a thermal flow sensor 4. Moreover, there is arranged an overlapping range where the measuring areas are overlapped. When a measurement object is present in this range of the flow rate, it is detected whether the measured value of the thermal flow sensor 4 is in the saturating area or not larger than a value of the saturating area. When the measured value is not larger than a value of the saturating area, the measured value of the thermal flow sensor is calibrated on the basis of the measured value of the fluidic oscillating device 1 as a reference.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to gas flow meters.

[0002]

2. Description of the Related Art For the purpose of expanding a measurement range, a gas flow meter which uses two sensors, one of which measures a medium to large flow rate range and the other of which measures a small flow rate range, is disclosed in Japanese Patent Laid-Open No. Hei 3 (1999) -311.
-96817 and JP-A-3-264821.

In both of these prior arts, a fluidic oscillation element is used to measure a medium to large flow rate range and a thermal type flow sensor is used to measure a small flow rate range, and a flow rate range in which both measurement ranges overlap is provided. When the flow rate to be measured is in the flow rate range,
Based on the measurement value of a highly stable fluid oscillation element (hereinafter referred to as FD), the measurement value of a thermal type flow sensor (hereinafter referred to as FS) that easily causes an error due to dust and water adhesion and secular change is automatically It is configured to be used while calibrating.

Among the above-mentioned conventional techniques, Japanese Patent Laid-Open No. 9681/1993
An outline of the flow meter described in Japanese Patent No. 7 will be described below with reference to FIGS. 3 and 4. As shown in FIG. 3, this gas flow meter includes a fluidic oscillation element (FD) 1, a sensor 2 that detects fluid vibration of the FD 1 and converts it into an electric signal, and a flow velocity of a nozzle portion 3 of the FD. A thermal type flow sensor (FS) 4 for detecting the flow rate and converting it into an electric signal, an electronic circuit 5 for calculating signals of the fluid vibration detecting sensor 2 and the flow velocity detecting FS 4 to obtain an integrated flow rate, and the electronic circuit 5 And an indicator 6 for displaying the integrated flow rate obtained in step 1.

A polymer piezoelectric film sensor is used as the fluid vibration detection sensor 2, and a flow velocity detection FS4 is disclosed in Japanese Patent Laid-Open No. 59-59.
The FS as described in Japanese Patent Laid-Open No. 182315 is used.
Then, the fluid vibration detecting sensor 2 generates an electric signal having a frequency corresponding to the fluid vibration, and the FS 4 generates an analog electric signal corresponding to the flow velocity of the nozzle portion 3.

The FS4 has a fluid temperature detecting portion arranged on the upstream side and the downstream side of the heat generating portion on the surface of the silicon chip on which the flow hits. The electric resistance of the fluid temperature detecting portions on both sides of the heat generating portion depends on the flow rate. Since it changes, the change is detected as an electric signal, amplified and A / D converted, and the flow rate is obtained by a microcomputer.

The electronic circuit 5 has the structure shown in FIG. 4A is an A / D conversion circuit, which digitally converts an analog electric signal in the small flow rate region detected by the FS4 into an electric pulse signal having a pulse number proportional to the flow rate.

Reference numeral 7 is a counter for temporarily stocking the high-speed electric pulse (signal B) output from the A / D conversion circuit 4A to the microcomputer 8, 9 is a power source, and 10 is a piezoelectric film circuit section 11. It is a voltage control circuit that controls a drive voltage supplied to the thermal flow sensor circuit unit 12.

Reference numeral 13 is an analog amplifier for amplifying the electric signal of the sensor 2, 14 is a waveform shaping circuit for shaping the output signal of the analog amplifier 13 into a rectangular wave, and 15 is a waveform shaping circuit 14.
Output (signal A) is input, and when the frequency is equal to or higher than a certain value, the signal A is regarded as the signal J having the same frequency and the microcomputer 8
It is a signal determination circuit for transmitting to.

Reference numeral 16 is a clock control circuit which receives a command from the microcomputer 8 and A / D converts the clock signal H for A / D conversion.
It is sent to the D conversion circuit 4A. When the signal frequency of the sensor 2, that is, the frequency of the signal A is equal to or higher than a certain value, the signal J is calculated by the microcomputer 8 and becomes a flow rate integrated value. Further, in the small flow rate region where the frequency of the signal A is below a certain value, the signal B based on FS4
Is calculated by the microcomputer 8 and the total flow rate integrated value of the pulse numbers of the signal J and the signal B is obtained and displayed on the display 6.

The analog voltage of FS4 is synchronized with the clock signal, and A / A is applied to the flow rate signal B having a pulse number proportional to the flow rate.
It is converted by the D conversion circuit 4A. This signal B is output at every interval (cycle) T ₀ (for example, T ₀ = 5 seconds), and the number of pulses at each time is 0 pulse at a flow rate of 0 [l / h] and a flow rate of 50.
The characteristic of the A / D conversion circuit 6 is determined so that the number of pulses becomes 300 / l / h and the number of pulses is proportional to the flow rate.

Then, with the measured value of FD as a reference, FS
When calibrating the measured value of, the analog signal of FS4
It was calibrated by changing the pulse constant when digitally converting into an electric pulse in the / D conversion circuit 4A.

The details of such a calibration operation are well known from the above-mentioned Japanese Patent Laid-Open No. 3-96817.

[0014]

SUMMARY OF THE INVENTION In the above conventional technique,
In the flow rate range where the measurement range overlaps, FD and F
Both S use a region that maintains linearity between the flow rate and the sensor output.

To widen this region, it is necessary to expand the lower limit of FD measurement and the upper limit of FS measurement, which is technically difficult. Therefore, the calibration range, which is the overlapping measurement range, is narrow, and when this type of flow meter is used as a gas meter as a measuring instrument for measuring the gas usage amount, it is difficult for the gas usage flow rate in the field to fall within the calibration range. However, there is a problem that the chance of calibration is reduced, and in some cases, calibration cannot be performed.

Therefore, it is an object of the present invention to solve the problems of the present invention and to provide a gas flowmeter suitable for a gas meter which can increase the chances of calibration.

[0017]

In order to achieve the above object, the gas flowmeter of the present invention is a fluidic oscillation element (1) in the medium to large flow rate range and a thermal type flow sensor in the small flow rate range. In addition to the measurement in (4), a flow rate range in which both measurement areas overlap is provided, and when there is a measurement target flow rate in this flow rate range, the thermal flow sensor is based on the measurement value of the fluidic oscillation element (1) as a reference. In the flow meter for calibrating the measurement value of (4), when there is a measurement target in the flow rate range, it is discriminated whether the measurement value of the thermal type flow sensor (4) is in a saturation region or below the saturation region, and below the saturation region. The calibration operation is performed at the time.

[0018]

When the FS changes with time and the sensitivity decreases, the sensor output with respect to the flow rate is
It becomes like the curve B in FIG. Therefore, measurement is performed in the flow rate range of FIG. 9B overlapping with the FD, and the measurement is performed below the saturation region of the output characteristic (sensitivity curve) of the FS, and calibration is performed based on the curve C that is the output of the FD. By doing this,
Compared with the calibration range A of the prior art, the calibration range can be greatly expanded.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1 and 2. The hardware structure of the flow meter is the same as that of the prior art described with reference to FIGS. 3 and 4, and only the software is different. There is.

In FIG. 2, curves a and b show the relationship between the flow rate of the FS and the output (the number of pulses of the signal B), a is the initial data, and b is around 60% of the initial value due to changes over time. The FS essentially has a state in which the output is saturated at about 2000 pulses in any curve, which is data when the sensitivity is lowered.

C shows the FD characteristic and shows relatively good linearity, but at a flow rate less than Q ₁ , the oscillation is unstable or impossible and cannot be measured. Q ₂ is the upper limit flow rate that can be practically measured by the FS, and the flow rate range indicated by the symbol A between Q ₁ and Q ₂ overlaps with the conventional technique and FD and FS
Both are measured and used as the calibration range.

The calibration flow in this prior art is the same as steps 33 to 46 in FIG. In the present invention, the calibration range (overlapping measurement range) is significantly widened as shown in FIG.
Saturation data around 2000 pulses is removed from the S measurement data (step 40), and the FS measurement value excluding the saturation region is changed with the FS pulse constant based on the FD measurement data to complete the calibration operation (Fig. Steps 34 to 4 of 1
1) When the flow rate is in the range of A, the calibration is performed by the same flow as in the conventional steps 42 to 46.

The calibration range B of the gas meter using this calibration method is shown in Table 1 in comparison with the calibration range A of the prior art. Although slightly different depending on the number of meters, the calibration range of all meters has been expanded and improved by about 2.5 times.

[0024]

[Table 1]

[0025]

Since the gas flow meter of the present invention is configured as described above, the calibration range of the thermal type flow sensor can be expanded to a little more than double that of the conventional type, and therefore the characteristic of the thermal type flow sensor has changed. In this case, the chances of calibration increase, and it is possible to prevent the measurement error in the small flow rate range from increasing with time.

[Brief description of drawings]

FIG. 1 is a flowchart of an embodiment of the present invention.

FIG. 2 is a diagram of flow rate and sensor output.

FIG. 3 is a conventional system diagram.

FIG. 4 is a block diagram of a prior art electronic circuit.

[Explanation of symbols]

 1 Fluidic oscillator 4 Thermal flow sensor

Claims (2)

[Claims] 1. A medium to large flow rate range is measured by a fluidic oscillation element (1), a small flow rate range is measured by a thermal flow sensor (4), and a flow rate range in which both measurement ranges overlap is provided. Every other time, when there is a flow rate to be measured in this flow rate range, in the flow meter for calibrating the measurement value of the thermal type flow sensor (4) with the measurement value of the fluidic oscillation element (1) as a reference, there is a measurement target in the flow rate range. A gas flow meter, characterized in that the measured value of the thermal type flow sensor (4) is sometimes discriminated whether it is in a saturated region or below a saturated region, and the calibration operation is performed when the measured value is below the saturated region. 2. The gas flow meter according to claim 1, which is a gas meter as a meter for measuring the amount of gas used.