JPH0968451A - Flow rate meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow actual using environment to be reflected to the correction in the case where a detection value of a flow rate detected by means of a flow sensor such as a thermal flow sensor is corrected in accordance with a drift of the flow sensor. SOLUTION: In the case where it is judged that a flow rate is zero by a stop judgment means 15 in accordance with a pressure of the flow detected by a pressure sensor 7, a detection value of a flow sensor 8 is stored as a reference value in an NVRAM 18 or the like and the detection value of the flow sensor 8 is corrected, based on the stored reference value. The reference value for the flow correction is taken from the flow sensor 8 under the condition that the flow rate is actually zero so that actual correction environment is reflected to the correction of the flow rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device for correcting a detection value of a flow rate sensor.

[0002]

2. Description of the Related Art Conventionally, flow rate sensors for measuring the flow rate of fluids such as gas and liquid have been put into practical use. For example, in the heat-sensitive flow rate sensor, temperature sensors are arranged upstream and downstream of the heating element, and the flow rate of the fluid is detected by the difference between the detection values of these temperature sensors. Such a flow sensor is
Ideally, the detected values of the upstream and downstream temperature sensors are the same when the flow rate of the fluid is "0", but in reality an error occurs due to deterioration of the temperature sensor over time and changes in the fluid temperature. To do. Such an error occurs as a drift even when the flow rate of the fluid is not "0", so it is desirable to correct it.

Flow rate measuring devices for correcting such an error are disclosed in Japanese Utility Model Laid-Open No. 1-87209, Japanese Patent Laid-Open No. 3-53127, Japanese Patent Laid-Open No. 3-53128, and the like. Actual Kaihei 1-
In the flow rate measuring device disclosed in Japanese Patent No. 87209, the heating element of the heat-sensitive flow rate sensor is periodically stopped, and the detection value of the flow rate sensor in this state is recorded as a reference value. When the heating element of the flow rate sensor is driven to measure the flow rate of the fluid, the reference value is subtracted from the detected value to eliminate the drift.

In the flow rate measuring device disclosed in Japanese Patent Application Laid-Open No. 3-53127, in the final adjustment before the product is shipped,
The reference state in which the flow rate is "0" is generated to suspend the heating element of the flow rate sensor, and in this state, the detection values of the two temperature sensors are corrected to the same value by the correction circuit. Furthermore, the flow rate is "0"
The heating element of the flow rate sensor is driven in the reference state, and the difference between the detection values of the two temperature sensors is detected and recorded in this state.
In this way, the difference between the detected values of the flow sensor when the heating element is at rest and when it is driven is detected, and the measured value of the flow sensor is corrected based on this difference. In this way, not only the drift of the heating element at rest but also the error at the time of driving are corrected, so that the measurement error of the flow rate sensor due to the deterioration of the temperature sensor over time or the temperature change of the fluid is also corrected.

In the flow rate measuring device disclosed in Japanese Patent Application Laid-Open No. 3-53128, in the final adjustment before the shipment of the product,
The flow rate sensor when the flow rate is "0" is generated by driving the heating element of the flow rate sensor by generating the reference state of the flow rate "0" and correcting the detection values of the two temperature sensors to the same value by the correction circuit. Eliminate the drift of. In addition, with respect to changes over time after shipment of the product, the heating element of the flow rate sensor is stopped while the fluid is flowing, and in this state the detection values of the two temperature sensors are corrected to the same value by the correction circuit. ,
It also corrects measurement errors due to deterioration of the temperature sensor over time and changes in fluid temperature.

[0006]

[Problems to be Solved by the Invention] Actual Kaihei 1-8720 described above
The flow rate measuring device of the 9th publication corrects the drift based on the detected value of the state where the heating element of the flow rate sensor is stopped. However, this corrects the drift of the flow rate sensor when the flow rate is "0". It cannot be corrected.

Further, Japanese Patent Laid-Open Nos. 3-53127 and 3-53
In the flow rate measuring device of Publication No. 128, the drift of the flow rate sensor is corrected when the flow rate is "0". This is because the flow rate is "0" at the time of adjustment before shipment of the product. . However, in the actual product, the environment before and after the adjustment is different from the environment before and after the shipment, so the drift of the flow rate sensor when the flow rate is "0" cannot be accurately corrected. .

In particular, since the drift of the flow rate measuring device fluctuates due to deterioration over time, even if the drift can be accurately corrected before shipping as described above, the drift will occur in the used state. In the flow rate measuring device disclosed in Japanese Patent Laid-Open No. 3-53128, the heating element of the flow rate sensor is stopped while the fluid is flowing, and the detection values of the two temperature sensors are the same with respect to the change over time after shipment of the product. However, the drift in the state where the flow rate is “0” cannot be corrected accurately.

Further, when the above flow rate measuring device is used for a gas meter or the like, for example, even when the gas is not used for a long period of time due to the absence of a user, it is necessary to keep the heating element of the flow rate sensor constantly generating heat. Therefore, power is consumed unnecessarily.

[0010]

According to the first aspect of the present invention,
A flow rate sensor for detecting the flow rate of the fluid, a pressure sensor for detecting the pressure of the fluid, a stop determining means for determining whether the flow rate is "0" or not based on the pressure of the fluid, and a flow rate is determined as "0". In this case, there is provided a reference storage means for storing the detected value of the flow rate sensor as a reference value and a flow rate correction means for correcting the detected value of the flow rate sensor based on the stored reference value. Therefore, the reference value is fetched from the flow rate sensor when it is determined from the detection value of the pressure sensor that the flow rate of the fluid is “0”, and the flow rate of the fluid detected by the flow rate sensor is based on this reference value. Will be corrected.

According to a second aspect of the present invention, in the first aspect of the present invention, the detection value of the flow rate sensor when the flow rate of the fluid is determined to be "0" by the stop determination means is stored in the reference storage means as a reference value. An automatic updating means is provided for causing the operation to be performed at predetermined intervals. Therefore, the processing operation of acquiring the reference value of the flow rate sensor is automatically repeated.

According to a third aspect of the present invention, in the second aspect of the present invention, a change detecting means for detecting a change in the reference value between the previous time and the present time is provided, and the automatic updating means next time responds to the detected change. An interval changing means for changing the interval is provided. Therefore, if the fluctuation of the reference value of the flow sensor is small,
When the interval of the operation of updating the reference value is extended and the fluctuation of the reference value of the flow rate sensor is large, the interval of the operation of updating the reference value is shortened.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the detection value of the flow rate sensor when the flow rate of the fluid is determined to be "0" by the stop determination means is stored in the reference storage means as a reference value. A manual updating means for performing the operation to be performed in response to the manual operation is provided. Therefore, the processing operation for acquiring the reference value of the flow rate sensor can be executed as desired.

According to a fifth aspect of the present invention, in the first aspect of the invention, the drive power of the flow rate sensor until the stop determination means determines that the fluid flow rate is not "0" after the reference value is stored by the reference storage means. A power control means for reducing the power consumption is provided. Therefore, the drive power of the flow rate sensor is reduced until the fluid flow is restarted.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. First, as illustrated in FIG. 1, the flow rate measuring device 1 illustrated here is provided in a pipe 5 that communicates from a gas cylinder 2 to a stop valve 4 of a gas appliance 3, and a pressure regulator 6 is provided in the pipe 5. , A pressure sensor 7, and a heat-sensitive flow sensor 8 which is a flow rate sensor are sequentially arranged.

The gas cylinder 2 is a fluid LPG (L
iquefied Petroleum Gas) is press-fitted and this LP
G is supplied to the pipe 5 at a pressure of "300 (mmH ₂ O)". The gas appliance 3 is, for example, a gas burner that burns LPG, and consumes the LPG supplied from the pipe 5.

The pressure regulator 6 is an existing device that mechanically regulates the pressure of flowing gas, and regulates the pressure of LPG supplied from the gas cylinder 2 to the gas appliance 3. More specifically, a pressure chamber 10 is provided in parallel with the gas flow passage 9, and a piston 11 is slidably arranged at a position where the pressure chamber 10 and the flow passage 9 communicate with each other. The piston 11 is elastically held by springs 12 and 13, and the downstream side of the flow passage 9 and the pressure chamber 10 are connected by a pilot passage 14.

The pressure sensor 7 is a PZT (Lead Zirco).
It is an existing device made of ceramics such as Titanate) and statically detects the pressure of fluid. The flow determination circuit 15 serving as stop determination means connected to the pressure sensor 7 has a microprocessor in which a predetermined program is set, and determines whether or not the flow rate is "0" based on the fluid pressure. To do. More specifically, as shown in FIG. 3, when the stop valve 4 of the gas appliance 3 is opened, the gas pressure detected by the pressure sensor 7 first decreases and then vibrates and stabilizes, When the stop valve 4 of the gas appliance 3 is closed, the pressure of the gas detected by the pressure sensor 7 first rises and then oscillates and stabilizes. Therefore, the flow determination circuit 15 operates as described above. The stop of gas is judged based on the vibration of pressure.

The flow sensor 8 has an LP on the surface of the substrate.
A cavity communicating with the flow direction of G is formed, and an elongated thin film-like bridge that is orthogonal to the flow direction of LPG is formed on the cavity. On the surface of this bridge, one heating element is arranged at the center of the flow direction of the LPG, and two temperature sensors are individually arranged upstream and downstream thereof.
Such a flow sensor 8 is an existing device and detects the flow rate of LPG flowing through the pipe 5.

A sensor drive circuit 16 is connected to the flow sensor 8, and the sensor drive circuit 16 outputs a power source for driving the heating element to a constant temperature and an output of the temperature detected by the two temperature sensors. It consists of a detection circuit that detects the difference. The flow determination circuit 15 is connected to the sensor drive circuit 16, and an output processing circuit 17 is connected to these circuits 15 and 16. This output processing circuit 17 also
It has a microprocessor in which a predetermined program is set and is a storage device NVRAM (NO Volatili
zation Random Access Memory) 18, display 1
9. The reset switch 20 is connected.

In the flow rate measuring device 1 described above, the circuits 15 to 17 execute predetermined processing operations based on the detection values of the sensors 7 and 8 and the like, whereby the reference storage means, the flow rate correction means, and the automatic updating means are provided. , Change detecting means, interval changing means, manual updating means, and power control means.

The reference storage means has the output processing circuit 17 and the NVRAM 18 as hardware, and the flow determination circuit 15 causes the flow rate of LPG to be "0".
The detection value of the flow sensor 8 when it is determined that the reference value is stored. More specifically, the flow determination circuit 1
When 5 determines that the flow rate is “0” from the pressure of the LPG detected by the pressure sensor 7, the output processing circuit 17 causes the output value of the flow sensor 8 driven by the sensor drive circuit 16 to be detected. The NVR
Store it in AM18.

The flow rate correction means is the output processing circuit 1
7 and corrects the detection value of the flow sensor 8 based on the reference value stored as described above. More specifically, the output processing circuit 17 reads the reference value stored in the NVRAM 18 while capturing the detection value of the flow sensor 8, and subtracts the reference value from the detection value as a normal detection value, The display is output to the display 19.

The automatic updating means is the output processing circuit 1
7 and NVRAM 18, and as described above, L
When it is determined that the flow rate of PG is “0”, the operation of storing the detection value of the flow sensor 8 in the NVRAM 18 is executed at predetermined intervals. More specifically, the NVRAM
The operation interval is variably set in 18 according to the time and the number of pulses, and the output processing circuit 17 fetches the determination result of the flow determination circuit 15 when the detection result of the built-in timer coincides with the set operation interval. LP based on this judgment result
When it is detected that the flow rate of G is “0”, the detection value of the flow sensor 8 is fetched and stored in the NVRAM 18. When it is detected by the determination result of the flow determination circuit 15 that the flow rate of LPG is not "0", for example, waiting until it becomes "0",
It is possible to stop the processing operation and postpone it until the next timing.

The change detecting means is the output processing circuit 1.
When the processing operation for storing the reference value in the NVRAM 18 is executed by the automatic updating means as described above, the change in the reference value between the previous time and the present time is detected.
The interval changing means has the output processing circuit 17, and changes the interval until the next time of the automatic updating means in accordance with the detected change. More specifically, the NVRAM
When a new reference value is stored in 18, the output processing circuit 17 reads the previous reference value from the NVRAM 18 and subtracts it from the present reference value, and the absolute value of this operation result is smaller than a predetermined lower limit value. In this case, the operation interval of the automatic updating means stored in the NVRAM 18 is extended by multiplication by a coefficient of "1" or more, and when the absolute value of the calculation result is larger than a predetermined upper limit value, the operation of the automatic updating means The interval is shortened by multiplying the coefficient by "1" or less.

The manual updating means is the output processing circuit 1.
7 and the reset switch 20, the operation of storing the detection value of the flow sensor 8 in the NVRAM 18 when the flow rate of the LPG is determined to be “0” as described above corresponds to the manual operation. Let it run. More specifically,
When the reset switch 20 is manually operated, the output processing circuit 17 takes in the determination result of the flow determination circuit 15 and confirms that the flow rate of LPG is “0”.
After this confirmation, the detection value of the flow sensor 8 is fetched and stored in the NVRAM 18. When it is detected by the determination result of the flow determination circuit 15 that the flow rate of LPG is not "0", for example, waiting until the flow rate becomes "0" or "stop gas on the display 19" is displayed. It is possible to display guidance such as "please".

The power control means is the output processing circuit 1.
7 and the sensor drive circuit 16
After storing the reference value by the AM 18, the flow judgment circuit 1
The drive power of the flow sensor 8 is reduced until it is determined by 5 that the flow rate of LPG is not "0". More specifically, as described above, the flow rate of LPG is determined to be "0" based on the detection value of the pressure sensor 7, the flow sensor 8 is driven by the sensor drive circuit 16, and the detection value is used as a reference value. When stored in the NVRAM 18, the output processing circuit 17 causes the sensor driving circuit 16 to stop driving the flow sensor 8. In this state, the output processing circuit 17 monitors the detection value of the pressure sensor 7 by the flow determination circuit 15, and the LPG is detected by this detection value.
When it is determined that the flow starts, the sensor drive circuit 16 starts driving the flow sensor 8.

In such a structure, the above-described flow rate measuring device 1 measures the flow rate of LPG supplied from the gas cylinder 2 to the gas appliance 3. At this time, the flow rate of the LPG is detected by the flow sensor 8 and displayed on the display 19, but since the drift of the flow sensor 8 is corrected by the output processing circuit 17 based on the reference value stored in the NVRAM 18, the LPG The flow rate is accurately detected. The reference value thus stored in the NVRAM 18 is fetched from the flow sensor 8 when the flow rate of LPG is “0”,
Since the fact that the flow rate of LPG is "0" is judged from the detection value of the pressure sensor 7, an appropriate reference value is obtained in the environment where the LPG is actually used.

Various processing operations of the flow rate measuring device 1 will be sequentially described below. First, the processing operation of periodically storing the reference value, which is the zero point error of the flow sensor 8, in the NVRAM 18 will be described. The output processing circuit 17 is
The detection result of the built-in timer is constantly compared with the operation interval stored in the NVRAM 18, and if they match, the determination result of the flow determination circuit 15 is fetched. Based on this judgment result, LPG
When it is detected that the flow rate is 0, the detected value of the flow sensor 8 is fetched and stored in the NVRAM 18 as a reference value.

The reference value thus stored in the NVRAM 18 is the flow sensor 8 when the flow rate of LPG is "0".
Since the detected value is, this reflects the actual usage environment of the flow rate measuring device 1. That is, the flow rate of the LPG detected by the flow sensor 8 is corrected by the error of the flow sensor 8 when the flow rate of the LPG is actually “0”, so the flow rate measuring device 1 corresponds to the actual usage environment. Therefore, the flow rate of LPG can be accurately measured.

When the reference value is stored in the NVRAM 18 as described above, the output processing circuit 17 stops the driving of the flow sensor 8 by the sensor drive circuit 16 and the flow determination circuit 1
5, the detection value of the pressure sensor 7 is monitored, and if the start of the flow of the LPG is judged from this detection value, the sensor drive circuit 1
The driving of the flow sensor 8 by 6 is started.

That is, as described above, the storage of the reference value of the flow sensor 8 is executed when the flow rate of LPG is "0", so immediately after this there is no point in measuring the flow rate of LPG at "0". Therefore, by suspending the flow sensor 8 until the flow of LPG is restarted, useless power consumption by the heating element is prevented. In addition, when the flow sensor 8 is stopped in this way, “0” is continuously displayed on the display 19.

When the flow of the LPG is judged from the detection value of the pressure sensor 7 as described above and the driving of the flow sensor 8 is restarted by the sensor drive circuit 16, the output processing circuit 17 detects the detection of the flow sensor 8. Take in the value and N
The reference value stored in the VRAM 18 is read, and this reference value is subtracted from the detected value. Since the calculation result is displayed and output on the display 19 as a normal detection value, the display 19 displays the flow rate of LPG in which the drift of the pressure sensor 7 is accurately corrected.

Moreover, since the reference value for correcting the drift of the flow sensor 8 is periodically and repeatedly updated as described above when the flow rate measuring device 1 is actually used, environmental fluctuation and deterioration with time occur. Also, a proper reference value is always set, and the flow rate measuring device 1 can always detect the flow rate of LPG satisfactorily.

Further, the flow rate measuring device 1 detects the reference value of the flow sensor 8 as described above, and the NVRAM 18
The processing operation to be stored in is repeated at a predetermined interval, and this operation interval is corrected in accordance with the change in the reference value. That is, as described above, the reference value of the flow sensor 8 is detected and the NVR
When stored in the AM 18, the output processing circuit 17 reads the previous reference value from the NVRAM 18 and subtracts it from the current reference value. If the absolute value of the calculation result is smaller than the predetermined lower limit value, the operation interval stored in the NVRAM 18 is extended by multiplication of a coefficient of "1" or more, and if the absolute value of the calculation result is larger than the predetermined upper limit value, , The operation interval is "1"
It is shortened by multiplying the following coefficients.

Therefore, when the fluctuation of the reference value of the flow sensor 8 is minute, the operation interval for updating the reference value is extended, so that the flow measuring device 1 consumes less power and the fluctuation of the reference value is reduced. In a large number of cases, the operation interval for updating this is shortened, so that the flow rate measuring device 1 can obtain an appropriate reference value.

As described above, the flow rate measuring device 1 automatically and repeatedly updates the reference value of the flow sensor 8 and the update interval is also properly adjusted according to the change in the reference value, but the user still desires. There are cases where it is desired to update the reference value of the flow sensor 8. In such a case, when the reset switch 20 is manually operated, the output processing circuit 17 captures the determination result of the flow determination circuit 15 and confirms that the flow rate of LPG is “0”, and after this confirmation, the flow sensor. The detected values of 8 are fetched and stored in the NVRAM 18.

For this reason, the reference value can be updated according to the user's desire, separately from the automatic update of the reference value of the flow sensor 8 as described above. The latest reference value of the flow sensor 8 can be obtained when the gas cylinder 2 is replaced.

The present invention is not limited to the flow rate measuring device 1 described above, and allows various modifications. For example, the above-described flow rate measuring device 1 uses the flow sensor 8 when the pressure sensor 7 detects that the flow rate is “0”.
This operation is automatically repeated at a predetermined interval in the case of obtaining the reference value of, and this interval is automatically adjusted according to the change of the reference value, and after the reference value is obtained, until the flow is restarted. It has been illustrated that the flow sensor 8 is stopped and the reference value can be obtained by manual operation. However, it is not necessary to realize all the functions as described above in one device, and this can be selected according to the specifications of the device.

Although LPG is used as an example of the fluid here, any fluid can be used as long as the fluid can be detected by pressure. Specifically, high-pressure gas is most suitable, and air, oxygen, nitrogen, or the like is preferable, but liquid nitrogen or liquid air may be used when the gas is stored in the gas cylinder 2. Further, the flow rate measuring device 1 detects the flow rate of the high-pressure LPG stored in the gas cylinder 2, but the flow rate measuring device 1 can measure the air volume of the air conditioner.

Further, although the pressure sensor 7 is arranged upstream of the flow sensor 8, this arrangement may be reversed and the pressure sensor 7 and the flow sensor 8 may be arranged at the same position in one flow path, or A pressure sensor 7 is provided in each of the two branched flow paths.
It is also possible to arrange the flow sensor 8 and the flow sensor 8.

Although the pressure sensor 7 is made of ceramic such as PZT, various devices capable of detecting the fluid flow by pressure can be used.
For example, a diaphragm type pressure sensor using an organic piezoelectric film such as PVDF (Polyvinylidene Fluoride), a minute pressure sensor made of silicon, a pressure sensor for vibration detection of a fluidic flow meter, a microphone for voice input,
Etc. are available.

In the flow sensor 8, two temperature sensors are arranged upstream and downstream of one heating element and the flow rate is detected from the temperature difference between them, but the temperature sensor is not provided. A flow sensor that detects the flow rate with only one heating element, a flow sensor that detects the flow rate with multiple heating elements without having a temperature sensor, a flow sensor that detects the flow rate with one heating element and one temperature sensor, etc. Can also be used, and a semiconductor type flow sensor can also be used.

Further, in the case of reducing the drive power of the flow sensor 8 until the flow is restarted, the power supplied from the sensor drive circuit 16 to the heating element is stopped. It is also possible to stop the electric power supplied from (not shown), and it is also possible to stop the electric power supply of the main body power supply within a range in which necessary functions can be maintained.

[0045]

According to the first aspect of the invention, the flow rate sensor for detecting the flow rate of the fluid, the pressure sensor for detecting the pressure of the fluid, and the determination of whether the flow rate is "0" or not are determined from the pressure of the fluid. Stop determination means, reference storage means for storing the detected value of the flow rate sensor when the flow rate is judged to be "0" as a reference value, and flow rate correction for correcting the detected value of the flow rate sensor based on the stored reference value. By including the means, the reference value for correcting the detection value of the flow rate sensor is taken in from the flow rate sensor when the flow rate of the fluid is actually “0”. Since it is determined from the detection value of the sensor, the flow rate of the fluid can be accurately detected by reflecting the actual usage environment.

According to the second aspect of the invention, the operation of storing the detection value of the flow rate sensor when the flow rate of the fluid is determined to be "0" by the stop determination means in the reference storage means as a reference value is executed at predetermined intervals. Since the processing operation for obtaining the reference value of the flow rate sensor is automatically repeated by providing the automatic updating means, it is possible to obtain the appropriate reference value even if environmental changes or deterioration with time occur.

According to the third aspect of the invention, the change detecting means for detecting the change in the reference value between the previous time and the current time is provided, and the interval changing means for changing the interval until the next time of the automatic updating means according to the detected change. By providing the means, when the fluctuation of the reference value of the flow sensor is small, the operation interval for updating the reference value is extended, so that the power consumption can be reduced and the fluctuation of the reference value of the flow sensor is large. Then, the interval of the operation of updating the reference value is shortened, so that the reference value can be appropriately maintained.

According to the fourth aspect of the invention, the operation of storing the detected value of the flow rate sensor as the reference value in the reference storing means when the flow rate of the fluid is judged to be "0" by the stop judging means corresponds to the manual operation. By providing the manual updating means for executing the processing, the processing operation for acquiring the reference value of the flow rate sensor can be executed as desired.

According to the fifth aspect of the present invention, after the reference value is stored in the reference storage means, power control means for reducing the drive power of the flow rate sensor is provided until the stop determination means determines that the flow rate of the fluid is not "0". As a result, the drive power of the flow rate sensor is reduced until the flow of the fluid is resumed, so that unnecessary consumption of power can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a flow rate measuring device of the present invention.

FIG. 2 is a vertical cross-sectional side view showing the internal structure of a pressure regulator.

FIG. 3 is a time chart showing pressure fluctuations.

[Explanation of symbols]

 1 Flow rate measuring device 7 Pressure sensor 8 Flow rate sensor 15 Stop judgment means

Claims (5)

[Claims] 1. A flow rate sensor for detecting the flow rate of a fluid, a pressure sensor for detecting the pressure of the fluid, a stop determination means for determining whether the flow rate is "0" or not based on the pressure of the fluid, and a flow rate of " Reference value storage means for storing the detection value of the flow rate sensor when it is determined to be "0" as a reference value, and flow rate correction means for correcting the detection value of the flow rate sensor based on the stored reference value. A flow measuring device characterized by. 2. The flow rate of the fluid is "0" by the stop judging means.
2. The flow rate measuring device according to claim 1, further comprising an automatic updating unit that performs an operation of storing the value detected by the flow rate sensor when the determination is made as a reference value in the reference storage unit at predetermined intervals. 3. A change detecting means for detecting a change in the reference value between the previous time and this time is provided, and an interval changing means for changing the interval until the next time of the automatic updating means is provided corresponding to the detected change. The flow rate measuring device according to claim 2, which is characterized in that 4. The flow rate of the fluid is "0" by the stop determination means.
2. The flow rate measuring device according to claim 1, further comprising a manual updating means for executing an operation of storing the detected value of the flow rate sensor as a reference value in the reference storage means when it is determined to correspond to the manual operation. . 5. A power control means for reducing the drive power of the flow rate sensor until the stop determination means determines that the flow rate of the fluid is not “0” after the reference value is stored by the reference storage means. The flow rate measuring device according to claim 1.