JP3170335B2 - Gas 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 gas flow meter.

[0002]

2. Description of the Related Art A gas flow meter using two sensors for expanding a measurement range, one of which measures a medium to large flow rate region and the other of which measures a small flow rate region, is disclosed in Japanese Unexamined Patent Publication No. Hei.
-96817 and JP-A-3-264821.

In both of these prior arts, a medium to large flow rate region is measured by a fluidic oscillation element, and a small flow rate region is measured by a thermal flow sensor, and a flow rate range in which both measurement ranges overlap is provided. When there is a target flow rate in the flow rate range,
Based on the measurement value of a highly stable fluid oscillation device (hereinafter referred to as FD), the measurement value of a thermal flow sensor (hereinafter referred to as FS), which is liable to cause errors due to dust and moisture adhesion and aging, is automatically calculated. It is configured to be used while calibrating.

[0004] Of the above prior art, Japanese Patent Application Laid-Open No. 3-9681
An outline of the flow meter described in Japanese Patent Publication No. 7 will be described below with reference to FIGS. 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 rate of a nozzle 3 of the FD. A thermal flow sensor (FS) 4 for detecting the flow rate and converting it into an electric signal; an electronic circuit 5 for calculating the integrated flow rate by calculating signals of the fluid vibration detecting sensor 2 and the flow velocity detecting FS 4; And an indicator 6 for displaying the integrated flow rate obtained in the step (a).

As the fluid vibration detecting sensor 2, a polymer piezoelectric film sensor is used, and as the flow velocity detecting FS4, Japanese Unexamined Patent Publication No.
FS as described in JP-A-182315 is used.
Then, the fluid vibration detection sensor 2 generates an electric signal of a frequency corresponding to the fluid vibration, and the FS 4 generates an analog electric signal corresponding to the flow velocity of the nozzle unit 3.

The FS4 has a fluid temperature detecting section disposed upstream and downstream of the heating section on the surface of the silicon chip where the flow is applied. The electric resistance of the fluid temperature detecting section on both sides of the heating section depends on the flow rate. Since the change occurs, the change is detected as an electric signal, amplified, A / D converted, and the flow rate is obtained by a microcomputer.

The electronic circuit 5 has a configuration shown in FIG. Reference numeral 4A denotes an A / D conversion circuit which converts an analog electric signal in a small flow rate range detected by the FS 4 into an electric pulse signal having a pulse number proportional to the flow rate.

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

Reference numeral 13 denotes an analog amplifier for amplifying the electric signal of the sensor 2, 14 denotes a waveform shaping circuit for shaping the output signal of the analog amplifier 13 into a rectangular wave, and 15 denotes a waveform shaping circuit 14.
(Signal A) is input, and when the frequency is equal to or higher than a predetermined value, the signal A is set as the signal J having the same frequency.
Is a signal determination circuit to be transmitted.

Reference numeral 16 denotes a clock control circuit which receives a command from the microcomputer 8 and converts the clock signal H into an A / D signal 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 predetermined value, the signal J is calculated by the microcomputer 8 and becomes a flow rate integrated value. In a small flow rate region where the frequency of the signal A is equal to or lower than a predetermined value, the signal B based on the FS4 is used.
Is calculated by the microcomputer 8, and the integrated flow amount of the total number of pulses of the signal J and the signal B is obtained and displayed on the display 6.

The analog voltage of the FS4 is synchronized with the clock signal to generate a 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).
The characteristics of the A / D conversion circuit 6 are determined so that [1 / h] is 300 pulses and the number of pulses is proportional to the flow rate.

Then, based on the measured value of FD, FS
When calibrating the measured value of FS4, the analog signal of FS4
The calibration has been performed by changing the pulse constant when the digital conversion into an electric pulse is performed by the / D conversion circuit 4A.

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

[0014]

In the above prior art,
In the flow area where the measurement areas overlap, FD and F
Both S use a region that maintains linearity between the flow rate and the sensor output.

In order to widen this area, it is necessary to increase the lower limit of the FD measurement and the upper limit of the 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 gas usage, the flow rate of gas used in the field is hard to enter the calibration range. However, there is a problem that the number of calibrations is reduced, and in some cases, the calibration cannot be performed.

An object of the present invention is to provide a gas flow meter suitable for a gas meter which can solve the problems of the present invention and can increase the chance of calibration.

[0017]

In order to achieve the above object, a gas flow meter according to the present invention comprises a fluid flow oscillating element (1) for a medium to large flow area and a thermal flow sensor for a small flow area. In addition to the measurement in (4), a flow rate range where both measurement areas overlap is provided, and when the flow rate to be measured is in this flow rate range, a thermal flow sensor is used based on the measured value of the fluid oscillation element (1). In the flow meter for calibrating the measured value of (4), it is determined whether the measured value of the thermal flow sensor (4) is in the saturation region or less than the saturation region when there is an object to be measured in the flow rate range. The calibration operation is performed at the time of.

[0018]

When the FS changes with time and the sensitivity decreases, the sensor output with respect to the flow rate becomes smaller than the initial normal sensitivity curve a.
It becomes like the curve B in FIG. Therefore, the measurement is performed so as to overlap with the FD in the flow rate range of FIG. B, and calibration is performed on the basis of the curve C which is the output of the FD, using the measured value of the output characteristic (sensitivity curve) of the FS which is equal to or less than the saturation region. By doing this,
The calibration range can be greatly expanded as compared with the calibration range A of the prior art.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1 and 2. The configuration of the hardware of the flow meter is the same as that of the prior art described with reference to FIGS. I have.

In FIG. 2, curves A and B show the relationship between the flow rate of FS and the output (the number of pulses of the signal B). Regarding the data when the sensitivity is lowered, the FS essentially has a state in which the output is saturated at about 2000 pulses in any of the curves.

[0021] c is a characteristic of the FD, while indicating relatively good linearity, it is less than the flow rate Q ₁ is impossible oscillation or unstable oscillation, can not be measured. Q ₂ is the upper limit flow rate that can be practically measured by FS, and the flow rate range indicated by reference symbol A between Q ₁ and Q ₂ is overlapped with FD and FS in the prior art.
Are measured in both cases, and set as the calibration range.

The flow of calibration 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 increased as shown in FIG.
The saturation data around 2000 pulses are removed from the S measurement data (Step 40), and the calibration operation is completed by changing the FS measurement value excluding the saturation region and the FS pulse constant based on the FD measurement data (FIG. Step 34 of 1
1) When the flow rate is in the range of A, the calibration is performed according to the same flow as the conventional one in 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 the meters, the calibration range of each of the meters is improved by approximately 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 twice as large as that of the conventional type, so that the characteristics of the thermal type flow sensor have changed. In such a case, the number of opportunities for calibration increases, and it is possible to prevent the measurement error in the small flow rate region from increasing over time.

[Brief description of the drawings]

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

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

FIG. 3 is a system diagram of the related art.

FIG. 4 is a block diagram of a conventional electronic circuit.

[Explanation of symbols]

 1 Fluidic oscillator 4 Thermal flow sensor

Claims (2)

(57) [Claims] 1. A medium to large flow rate region is measured by a fluidic oscillation element (1), a small flow rate region is measured by a thermal flow sensor (4), and a flow rate range in which both measurement ranges overlap is provided. When there is a flow rate to be measured in this flow rate range, in a flow meter for calibrating the measurement value of the thermal type flow sensor (4) based on the measurement value of the fluid oscillation element (1), the flow rate range has the measurement target. A gas flow meter characterized in that it sometimes discriminates whether a measured value of the thermal flow sensor (4) is in a saturation region or less than a saturation region, and performs the calibration operation when the measurement value is less than the saturation region. 2. The gas flow meter according to claim 1, wherein the gas flow meter is a gas meter as a measuring device for measuring the amount of gas used.