JP2001004418A - Gas meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas meter which can obtain a proper precision and precisely detect gas leakage by restraining the change of a measured value especially in fine flow rate level (gas leakage detecting level), in a gas meter using a principle of measuring instantaneous flow rate. SOLUTION: When a measured instantaneous flow rate is at least the minimum flow rate wherein precision can be ensured (step S3, YES), result processed by a low-pass filter having a small time constant is outputted as a measured result (step S4). In the other case, i.e., when a measured instantaneous flow rate is at the minimum flow rate level, processing by a low-pass filter having a large time constant is performed (step S5). Basically, when the result is equal to or greater than a leakage detecting flow rate (step S8, YES), the result processed by the low-pass filter having a large time constant is outputted as a measured result (step S10). When it is decided that a rapid change in the flow rate is generated in practical use (step S6, YES), the result processed by the low-pass filter having a small time constant is outputted as a measured result (step S7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas meter, and more particularly to a gas meter based on the principle of measuring an instantaneous flow rate.

[0002]

2. Description of the Related Art Conventionally, a gas meter for measuring and displaying gas consumption has been installed in each household, for example, a gas consumer. Conventionally, the mainstream of this gas meter is a so-called “volume type”. In general, a predetermined space (“room” or “bag”) is prepared in the middle of a gas flow path, and the volume of the space is mechanically measured and displayed as a minimum resolution. However, in this method, a "room" occupying the predetermined space is required, so that it is difficult to reduce the size of the gas meter, and the mechanical measuring mechanism is complicated. In addition, in the integrated value (integrated flow rate), when an abnormality such as a gas leak occurs, a detailed history of the gas usage status up to the occurrence of the abnormality cannot be known, and it is difficult to determine the cause of the accident. There was a problem.

In order to solve such a problem, a gas meter of a type that measures an instantaneous flow rate of a gas flowing in a gas flow path and integrates an instantaneous flow rate that changes every moment has been proposed in recent years. As a method of measuring such an instantaneous flow rate,
For example, one that uses ultrasonic waves (ultrasonic flow meter), one that uses Karman vortex (what is called fluidic)
Is mentioned.

[0004] The ultrasonic flowmeter is described in, for example, Japanese Patent Application Laid-Open No. 10-142019.

[0005]

As described above, the gas meter of the type which measures the instantaneous flow rate has various advantages as compared with the conventional positive displacement type gas meter, and is expected to be put to practical use.

However, there is a problem regarding, for example, an error (accuracy) of a measured value. That is, normally, the accuracy shown in FIG. 4 is required for the gas meter. However, when measuring the instantaneous flow rate, a sudden change in the measured value due to noise or the like occurs or a change in the measured value occurs. The value error increases. At present, at least the applicant of the present invention is able to satisfy the required accuracy as long as the gas flow rate is at least a certain level (hereinafter, referred to as a flow rate that can guarantee the accuracy). However, when the gas flow is small (small flow rate), the leakage detection flow rate (FIG. 4)
In the vicinity of 3 liters / h), it is necessary to identify a flow rate of 0 to detect a gas leak. Therefore, it is difficult to identify a flow rate of 0 unless the change of the measured value is particularly small, and the integration error Causes the size to increase. At present, it cannot sufficiently cope with the accuracy shown in FIG. 4, and some countermeasures are required.

[0007] In addition to the above, normally, a gas meter is required to have a responsiveness that can cope with "abrupt change in actual use", for example, when a flow suddenly changes from a zero flow state.

FIG. 4 is a diagram showing the flow rate measurement accuracy (accuracy as an integrated value) required of the gas meter. In the figure, an integrated flow rate per hour of 3 (liter / h) is the leak detection flow rate, and the leak detection flow rate (3 liter / h)
The following accuracy is specified in the range of “several ten percent to zero output”. That is, when the flow rate is equal to or less than the leak detection flow rate, the measurement result is set to zero (hereinafter, referred to as zero cut output).
Is allowed.

If an attempt is made to apply a gas meter of the type that measures the instantaneous flow rate to such specifications, it is considered that the change in the measured value is large at the above-mentioned minute flow rate, especially near the leak detection flow rate (3 liter / h). However, there is a problem that the zero cut output is performed in spite of the fact that the flow rate is equal to or higher than the leak detection flow rate, and the leak detection flow rate is also a reference for gas leak detection as also referred to as a gas leak detection level. Therefore, if the change in the measured value is large, there is a problem that accurate gas leak detection cannot be performed.

As described above, it is necessary to further suppress the change in the measured value especially near the leak detection flow rate. Furthermore, the above responsiveness requirement must be satisfied. An object of the present invention is to provide a gas meter that measures instantaneous flow rate, and in particular, can suppress fluctuations in measured values at a minute flow rate level (gas leak detection level) to have appropriate accuracy, and thus can accurately detect gas leak. To provide.

[0011]

SUMMARY OF THE INVENTION A gas meter according to the present invention is a gas meter for measuring a gas consumption by integrating an instantaneous flow rate sampled at a predetermined time interval. An instantaneous flow rate calculating means for calculating an instantaneous flow rate from a time, a first low-pass filter for performing a low-pass filter process with a predetermined time constant on the instantaneous flow rate, and a time constant of the first low-pass filter for the instantaneous flow rate. A second low-pass filter that performs a low-pass filter process with a large time constant; and a unit that switches between the first and second low-pass filters based on the magnitude of the measured instantaneous flow rate. Flow rate correction processing means for outputting any of the processing results of the second low-pass filter as an instantaneous flow rate, and the flow rate correction processing means And an output means for outputting a measurement result by totalizing the output.

It is desirable that the switching of the low-pass filters having different time constants be performed on the condition that the magnitude of the instantaneous flow rate is equal to or larger than the minimum flow rate value that can guarantee the accuracy inherent to the meter.

In the above gas meter, the flow rate correction processing means calculates a difference between a processing result by the first low-pass filter and a processing result by the second low-pass filter,
There may be provided a comparing and judging means for judging whether or not the difference exceeds a predetermined value set in advance, and when the difference exceeds the predetermined value, a result of processing by the first low-pass filter may be output. .

Further, when the measured value is less than the leak detection flow rate, if zero cut output is permitted,
The flow rate correction processing means is provided with a zero cut output means for outputting an output 0, and the instantaneous flow rate is set to 0 on condition that the processing result by the second low-pass filter is equal to or less than the minus instrumental difference of the leak detection flow rate. You may make it output.

In the gas meter, it is desirable to add a noise removing means for removing spike noise from the instantaneous flow rate measured before performing the processing by the first or second low-pass filter. A filter shall be used.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In the embodiments described below, a gas meter using an ultrasonic flow meter will be described as an example, but the present invention is not limited to this.
The present invention can be applied to all gas meters using the principle of measuring the instantaneous flow rate, such as the fluidic described above.

FIG. 1 is a diagram schematically showing the configuration of the entire gas meter using the ultrasonic flow meter according to the present embodiment.
In the figure, a pair of ultrasonic vibrators 1a and 1b are attached to a gas pipe (gas flow path) having a sectional area S. The distance between the ultrasonic transducers 1a and 1b is "L".

In such a configuration, the ultrasonic pulse propagation time tdown when transmitting from the ultrasonic transducer 1a on the upstream side to the ultrasonic transducer 1b on the downstream side, and the upstream side from the ultrasonic transducer 1b on the downstream side In general, the flow velocity and flow rate are measured by utilizing the fact that the propagation time difference due to the gas flow occurs between the ultrasonic pulse propagation time tup when transmitted to the ultrasonic transducer 1a.

That is, first, the timing generation circuit 2
Generates a start pulse and starts the transmission circuit 3. When transmitting from the ultrasonic transducer 1a on the upstream side to the ultrasonic transducer 1b on the downstream side, the two changeover switches Sw are switched to the side as shown in FIG. Transmission circuit 3 activated by
Applies a voltage to the ultrasonic transducer 1a on the upstream side to transmit ultrasonic waves.

When the ultrasonic wave is received by the ultrasonic transducer 1b on the downstream side, the received signal is amplified by the amplifier circuit 4 and input to the received wave detection circuit 6 via the tuning filter 5.

The time difference measuring circuit 7 is a circuit for measuring a time required from when the timing generating circuit 2 generates a start pulse to when a received signal is detected by the received wave detecting circuit 6, and is composed of, for example, a counter. Circuit. In this case, the ultrasonic wave propagation time tdown from the upstream side to the downstream side is detected by the time difference measurement circuit 7.

Subsequently, the two changeover switches Sw
Is switched to the side as shown in the figure, and, similarly to the case of the measurement of the ultrasonic propagation time tdown from the upstream to the downstream, this time, the ultrasonic propagation time tup from the downstream to the upstream is
Is measured.

The measured ultrasonic propagation times tup and tdo
wn is input to the arithmetic unit 8 and is expressed by the following equation (1).
An instantaneous flow rate Q is determined. Then, the arithmetic unit 8 integrates the flow values after the flow correction processing described below to calculate an integrated flow value, and outputs the integrated flow value to the display device 9 for display.

[0024]

(Equation 1)

The calculation up to the above-described instantaneous flow rate Q has been conventionally performed. The feature of the gas meter of the present invention lies in the second processing shown in the arithmetic unit 8, that is, the flow rate correction processing. This will be described later in detail with reference to FIGS.

FIG. 2 is a flowchart (part 1) for explaining the flow rate correction processing executed by the arithmetic unit 8. In the figure, when the instantaneous flow rate Q is obtained as described above, first, spike noise removal processing is performed (step S1).

In the present embodiment, this spike noise processing is performed using a median filter. The median filter is a filtering technique used for noise removal in the field of image processing, for example, and is used for spike noise removal in the present embodiment. The “median” is the median value of the statistics. The median value of the instantaneous flow rates Q obtained up to the current time of the instantaneous flow rate Q obtained as described above at a predetermined time interval is calculated as the median value of the current time. This is a technique that is regarded as the value of the instantaneous flow rate Q. The "plurality" is, for example, three values obtained this time (current time), the previous time, the previous time, and the previous time. For example, if the value of the instantaneous flow rate Q is extremely high due to the influence of spike noise, Since this is very unlikely to be the middle value among the three values, this noise can be removed by the median filter.

Next, in order to reduce a change in the measured instantaneous flow rate, a low-pass filter process with a small time constant is performed (step S2). An example of the low-pass filter processing is “moving average processing”. The time constant is determined so as to maintain a responsiveness that can cope with a sudden change in the flow rate in actual use. Therefore, the reduction of the change in the flow rate value is sacrificed to some extent. Therefore, the required accuracy cannot be guaranteed at the minute flow rate level (gas leak detection level).

Next, it is determined whether or not the flow value after the low-pass filter processing is equal to or more than the minimum flow value that can guarantee the accuracy (step S3). In the example shown in FIG. 4, it is determined whether or not the flow rate per hour is equal to or more than X (liter / h) according to the standard shown in FIG. 4 (X;
Minimum flow rate (per hour) that can guarantee accuracy.

Although the value of X (liter / h) is not clearly determined, for example, it is empirically determined to be 10 (liter / h).
The degree is a guide. From this, when the flow rate is equal to or more than the minimum flow rate value at which the accuracy can be guaranteed (step S3, YES), the value subjected to the “low-pass filter processing with small time constant” of step S2 is output as it is as the measured value at the current time. (Step S4).

On the other hand, if it is less than the minimum flow rate value at which the accuracy can be guaranteed (step S3, NO), the above-mentioned step S2
A low-pass filter process in which the time constant is made larger (the cutoff frequency is made smaller) than in the case of is performed (step S
5). The time constant is set so that the width of the change in the measured value is equal to or less than Y (liter / h). The value of Y is set, for example, by “leakage detection flow rate × instrument error”. The leak detection flow rate is 3 (liter / h) as shown in FIG.
If the instrumental error is, for example, −20%, the value of Y is 3 ×
0.2 = 0.6 (liter / h). As is well known, the instrumental error indicates how much each instrument has an error with respect to a reference instrument (gas meter). For example, in a gas meter having an instrument difference of -10%, the value of Y is 3 × 0.1 = 0.3 (liter / h).

In the process of step S5, as described above, it is necessary to make the change in the flow value smaller than usual at the minute flow rate level. At the sacrifice, processing for suppressing a change in the flow value is performed.

As described above, at the minute flow rate level, basically, the result of the low-pass filter processing with a large time constant in step S5 is used.
For example, it may not be possible to cope with a sudden change in the flow rate in actual use such as when gas is suddenly used from a zero flow state,
An integration error may occur.

Therefore, if the flow rate suddenly changes in actual use, the result of the "low-pass filter processing with small time constant" in step S2 is used. This is because, for example, the result of the low-pass filter processing with a small time constant in step S2 is compared with the result of the low-pass filter processing with a large time constant in step S5, and if the difference is larger than a certain value (step S6, YES). Assuming that the flow rate in actual use has suddenly changed, the result of the low-pass filter processing with a small time constant in step S2 is output as a measured value at the current time (step S7). It should be noted that the “difference in difference is not less than a certain value” is not limited to a clear value, and a value that can determine whether or not a sudden change in the flow rate in actual use may be appropriately determined.

On the other hand, if not (step S
6, NO), the result of the “low-pass filter processing with a large time constant” in step S5 is output as a measured value at the current time. However, due to the specifications of the gas meter, if the measured value is less than the leak detection flow rate, , Zero cut output is also permitted. From this, it is determined in step S8 whether the leak detection flow rate is equal to or greater than the leak detection flow rate. If the leak detection flow rate is less than the zero detection output, the zero cut output is performed (step S9). If there is, the result of the "low-pass filter processing with a large time constant" is output (step S10).

In the figure, the judgment in step S8 is “leakage detection flow rate × 0.8 or more?” Because the instrumental error in the description of the processing in step S5 is 20% (in this case, minus). Side is set to 20%). In the same manner as described above, for example, in a gas meter having an instrument difference of 10% (10% on the minus side), step S
The judgment of 8 is “leakage detection flow rate × 0.9 or more?”.

According to the flow rate correction processing according to the above-described embodiment, even if the measurement accuracy of the instantaneous flow rate cannot meet the requirements of the gas meter specifications especially near the determination of the leak detection flow rate (small flow rate level), By suppressing the change of the measured value by `` low-pass filter processing with a large time constant '', the leak detection flow rate judgment can be performed accurately,
The probability of erroneously performing zero cut output is extremely low, so that accurate gas leak detection can be performed. In some cases, "low-pass filter processing with small time constant"
By using the result of the above, it is possible to cope with a sudden change in the flow rate in actual use.

An example in which the above-described low-pass filter processing is performed by obtaining a “moving average” will be described below with reference to FIG.
This will be described with reference to FIG. FIG. 3 is a flowchart (part 2) for explaining the flow rate correction processing executed by the arithmetic unit 8.

In the figure, the spike noise removal processing (step S11) is the processing of step S1 in FIG. 2, and the description is omitted. Next, the moving average (N
1) is obtained (step S12). For example, assuming that the measurement of the instantaneous flow rate is performed at fixed time intervals and the instantaneous flow rate at the time tn is measured, the moving average (N1) with the small time constant is, for example, tn,
The average of three measured values of tn-1 and tn-2 (measured values after the above spike noise removal processing) is obtained. In the next measurement, tn +
For 1, the average of three measured values of tn + 1, tn and tn-1 is obtained.

The next step S13 is a step S13.
3, and the description is omitted. If the flow rate is equal to or more than the minimum flow rate (X liter / h) for which the accuracy can be guaranteed (step S13, YES), the moving average processing (N
The result of 1) is output as a measured value at the current time (step S14).

Minimum flow rate (X liter /
h) (Step S13, NO), a moving average (N2) with a large time constant set so that the variation width of the measured value is equal to or less than Y (liter / h) is obtained (Step S15). Incidentally, Y is, for example, 0.6 (liter / liter).
h).

The moving average processing (N1) with a small time constant is
Although the average of the three measured values is taken, in the moving average processing (N2) with a large time constant, the number of target measured values (parameter of the moving average) is increased. The number may be appropriately determined so that the width of the change in the measured value is equal to or less than Y (liter / h). Here, the “moving average process with small time constant (N1)” in step S12 is used. In order to clearly show the difference from the above, for example, an average of 1000 measurement values is taken. That is, 1000 from time tn to time tn-999
Take the average of the measurements.

By doing so, for example, at the next time tn + 1
Even if there is some variation in the measured value of, the average value (time tn +
It is clear that the average value from 1 to the time tn-998) is hardly different from the current average value, and the range of change of the measured value is very small.

On the other hand, in this case, it is impossible to cope with the sudden change in the flow rate in actual use. Therefore, it is determined whether or not a sudden change in the flow rate in actual use has occurred, and one of the moving average values in steps S12 and S15 is adopted according to the determination result (step S16). That is, when the difference between the result of the moving average processing with a small time constant (N1) and the result of the moving average processing with a large time constant (N2) is so large that it is not considered to be due to the fluctuation of the measured value (step S16, YE).
S), by using the result of the moving average processing (N1) with a small time constant (step S17), it is possible to cope with the flow rate sudden change in the actual use. On the other hand, if not (step S16,
NO), it is determined whether or not the result of the moving average process (N2) with a large time constant is equal to or greater than the leak detection flow rate (step S1).
8) If it is smaller than this, zero cut output is performed (step S19); otherwise, the result of the moving average processing (N2) with a large time constant is output (step S20). It should be noted that, as in the case of FIG. 2, the processing in step S18 corresponds to the example in which the instrumental difference is -20%, "leakage detection flow rate x 0.8
that's all? However, as described above, the processing changes according to the instrumental difference of each gas meter.

Normally, in a gas meter, a deviation (drift) of a measured value due to a long-term environmental change (temperature change, etc.) occurs in addition to the above-mentioned measured value change. Can be distinguished.

The arithmetic unit 8 is composed of, for example, a CPU and a memory. The CPU reads and executes a program stored in the memory and the like to execute the instantaneous flow rate calculation, the flow rate correction processing, the integration calculation, and the like. Done. Therefore,
The memory itself in which such a program is stored, or any recording medium (such as a program that allows the arithmetic unit 8 to perform the arithmetic / processing by downloading such a program to the memory). The recorded recording medium) itself is also included in the present invention.

[0047]

As described in detail above, according to the gas meter of the present invention, in a gas meter using the principle of measuring an instantaneous flow rate, a change in a measured value particularly at a minute flow rate level (gas leak detection level) is measured. The accuracy of determination of flow rate 0 near the leak detection flow rate can be increased and the responsiveness can be secured, the integration error can be reduced, and the accuracy specification required for the gas meter can be satisfied. It can be detected.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a configuration of an entire gas meter using an ultrasonic flowmeter according to the present embodiment.

FIG. 2 is a flowchart (part 1) for explaining a flow rate correction process executed by the arithmetic unit;

FIG. 3 is a flowchart (part 2) for explaining a flow rate correction process executed by the arithmetic unit;

FIG. 4 is a diagram showing an example of accuracy required for a gas meter.

[Explanation of symbols]

 1a, 1b Ultrasonic transducer 2 Timing generation circuit 3 Transmission circuit 4 Amplification circuit 5 Tuning filter 6 Received wave detection circuit 7 Time difference measurement circuit 8 Computing device 9 Display device

Claims (5)

[Claims] 1. A gas meter for measuring a gas usage amount by integrating an instantaneous flow rate sampled at a predetermined time interval, comprising: an instantaneous flow rate calculating means for calculating an instantaneous flow rate from a propagation time of an ultrasonic wave propagating in a gas; A first low-pass filter for performing a low-pass filter process on the instantaneous flow rate with a predetermined time constant, and a second low-pass filter process for performing a low-pass filter process on the instantaneous flow rate with a time constant larger than the time constant of the first low-pass filter. Based on the magnitude of the measured instantaneous flow rate,
Means for switching a second low-pass filter, a flow correction processing means for outputting any of the processing results of the first and second low-pass filters having different time constants as an instantaneous flow rate, and an output of the flow rate correction processing means An output means for performing an integration operation and outputting the result as a measurement result. 2. The gas meter according to claim 1, wherein
The gas meter according to claim 1, wherein the flow rate correction processing means compares the magnitude of the measured instantaneous flow rate with a minimum flow rate value that can guarantee the accuracy unique to the meter, and switches the first and second low-pass filters. 3. The gas meter according to claim 1, wherein
The flow rate correction processing means calculates a difference between a processing result by the first low-pass filter and a processing result by the second low-pass filter, and determines whether or not the difference exceeds a predetermined value. A gas meter, comprising: a determination unit, and outputs a processing result of the first low-pass filter when a predetermined value is exceeded. 4. The gas meter according to claim 1, wherein
The flow rate correction processing means has a zero cut output means for outputting an output 0, and when the processing result by the second low-pass filter becomes equal to or less than the minus instrumental difference of the leak detection flow rate, the instantaneous flow rate is reduced to 0. A gas meter characterized by outputting as 5. The gas meter according to claim 1, wherein
A gas meter, wherein the flow rate correction processing means has a noise removing means for removing spike noise from the measured instantaneous flow rate, and uses a median filter as the noise removing means.