JP2003121227A - Thermal flow meter - Google Patents

Abstract

(57) [Abstract] [Problem] Without adversely affecting the accuracy of flow measurement,
Provided is a thermal flow meter capable of significantly reducing power consumption by a heater element Rh and saving power. SOLUTION: A flow sensor including a heater element and first and second temperature sensors provided in a flow direction of a fluid with the heater element interposed therebetween, and energizing the heater element at predetermined time intervals. Heat (sampling means 21)
At the same time, the flow rate detecting means 22 for obtaining the flow rate of the fluid flowing through the flow rate sensor from the difference between the temperatures detected by the first and second temperature sensors when the heater element is energized and heated.
In particular, according to the frequency of flow of the fluid flowing through the flow rate sensor within a predetermined unit time (the number-of-times
3) Time interval setting means 2 for variably setting the energization time interval of the heater element when fluid is not flowing through the flow sensor.
4 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow meter capable of suppressing power consumption when a fluid is not flowing.

[0002]

2. Related Background Art A micro flow sensor constituting a thermal type flow meter has a silicon base B as shown in FIG.
It has an element structure in which a pair of temperature sensors Ru and Rd formed of temperature measuring resistors are provided in the fluid flow direction F with a heater element Rh formed of a heating resistor provided therebetween. The thermal flow meter utilizes the fact that the diffusion degree (temperature distribution) of the heat emitted from the heater element Rh changes due to the flow of the fluid, and based on the resistance change due to the heat of the temperature sensors Ru and Rd, It is configured to detect the flow rate Q of the fluid.

Specifically, the heat generated from the heater element Rh is added to the temperature sensor Rd on the downstream side according to the flow rate Q of the fluid, so that the resistance value change due to the heat of the temperature sensor Rd causes the temperature on the upstream side to change. The flow rate Q is measured by utilizing the fact that it is larger than the sensor Ru. Rr in the figure
Is a temperature sensor including a resistance temperature detector provided at a position distant from the heater element Rh, and is used for measuring the ambient temperature.

FIG. 5 shows a schematic structure of a thermal type flow meter using the above-mentioned micro flow sensor. That is, the drive circuit of the heater element Rh includes the heater element Rh, a temperature sensor Rr for measuring the ambient temperature, and a pair of fixed resistors R1, R.
2 is used to form a bridge circuit 1, a voltage Vcc supplied from a predetermined power source is applied to the bridge circuit 1 via a transistor Q, and the bridge output voltage of the bridge circuit 1 is applied to a differential amplifier 2. Then, the transistor Q is feedback-controlled so that the bridge output voltage becomes zero (0), and the heater driving voltage applied to the bridge circuit 1 is adjusted. The heater driving circuit configured as described above controls the heat generation temperature of the heater element Rh to be always higher than the ambient temperature by a constant temperature difference.

On the other hand, the flow rate detection circuit for detecting the flow rate Q of the fluid flowing along the microflow sensor from the change in resistance value of the pair of temperature sensors Ru and Rd due to heat is
The pair of temperature sensors Ru, Rd and the pair of fixed resistors Rx,
The Ry is used to form the bridge circuit 3 for flow rate measurement, and the bridge output voltage according to the change in the resistance value of the temperature sensors Ru and Rd is detected via the differential amplifier 4. Then, under the condition that the amount of heat generated by the heater element Rh is made constant by the heater drive circuit, the flow rate Q of the fluid flowing along the microflow sensor is obtained from the bridge output voltage detected via the differential amplifier 4. It has become a thing.

The flow rate Q is calculated, for example, by incorporating the bridge output voltage (sensor output) into the arithmetic processing unit (CPU).

[0007]

By the way, when this type of thermal flow meter is used as a household gas meter, it is an important problem to save power. Therefore, it is considered that the heater element Rh is energized at predetermined time intervals and the flow rate Q at that time is sampled and detected to reduce the power required for energizing the heater element Rh.

Further, Japanese Patent Laid-Open No. 10-82670 discloses that
When the flow rate change is large, the measurement cycle (sampling cycle) of the flow rate Q is shortened, and when the flow rate change is small, the flow rate Q is small.
It has been proposed that the number of energizations of the heater element Rh be reduced by prolonging the measurement cycle of 1 to reduce the power consumption. However, in this way the heater element R
Even if the energization time interval of h (flow rate measurement cycle) is varied, there is a limit in reducing the power consumption of the heater element Rh.

The present invention has been made in consideration of such circumstances, and an object thereof is to significantly reduce the power consumption in the heater element Rh without adversely affecting the accuracy of flow rate measurement, and to save the power consumption. It is to provide a thermal type flow meter capable of achieving electric power conversion.

[0010]

In order to achieve the above-mentioned object, the thermal type flow meter according to the present invention has a considerable period in which the fluid does not flow through the flow rate sensor when it is used as a household gas meter, for example. When measuring the flow rate by energizing the heater element at predetermined time intervals, set the energization time interval of the heater element to be long when the fluid is not flowing, thereby saving power. It was done like this.

That is, the thermal type flow meter according to the present invention is provided with a heater element and a flow sensor having a first temperature sensor and a second temperature sensor provided in the fluid flow direction with the heater element interposed therebetween. And a fluid flowing through the flow rate sensor from the difference in temperature detected by the first and second temperature sensors while electrically heating the heater element at predetermined time intervals. Flow rate detection means for determining the flow rate of the heater element, and in particular, energization of the heater element when the fluid is not flowing through the flow rate sensor according to the flow frequency of the fluid flowing through the flow rate sensor within a predetermined unit time. It is characterized in that it comprises a time interval setting means for variably setting the time interval.

[0012] Preferably, the time interval setting means sets an energization time interval of the heater element when a fluid is flowing through the flow rate sensor (when gas is not used) when a fluid is flowing through the flow rate sensor. The heater element is configured to be variably set in a time width range longer than the energization time interval (basic sampling period) of the heater element (when gas is used).

In a preferred aspect of the present invention, the time interval setting means sets the number of times when the flow rate detected by the flow rate detecting means is not zero in each predetermined sampling period within the predetermined unit time as the distribution frequency. The counting means to be obtained and the energization time interval of the heater element is set short when the number of times of measurement obtained by the counting means is larger than a preset number of times, and the heater element is set when the number of times of measurement is less than the preset number of times. It is realized as a time interval changing means for setting a longer energization time interval.

At this time, in the flow rate detecting means, it is desirable that the timing of temperature detection by the first and second temperature sensors be varied in association with the control of the energization time interval of the heater element. When the predetermined unit time is set by dividing one day into a plurality of time zones, the temperature detection timings of the first and second temperature sensors are changed according to the time zones. Is also good.

Further, the time interval setting means stores the number of times when the flow rate detected by the flow rate detecting means is not zero as a learning value for each of a plurality of time zones, and the flow rate detected by the flow rate detecting means is stored. When it is zero, the energization time interval of the heater element is set according to the number of times when the past flow rate is not zero in the same time zone as the current time zone.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A thermal type flow meter according to the present invention will be described below with reference to the drawings, taking a case where it is used as a household gas meter as an example. FIG. 1 is a schematic configuration diagram of a main part of a thermal type flow meter according to this embodiment. Reference numeral 10 denotes a pair of temperature sensors Ru and Rd in a fluid flow direction F with a heater element Rh interposed therebetween as shown in FIG. It is a micro flow meter having an element structure provided with. Reference numeral 11 in the drawing uses the heater element Rh, the temperature sensor Rr for measuring the ambient temperature, and the pair of fixed resistors R1 and R2 as shown in FIG.
To drive the heater element Rh so that the heat generation temperature of the heater element Rh is always higher than the ambient temperature by a constant temperature difference. Further, as shown in FIG. 5, 12 is a pair of temperature sensors Ru and Rd and a pair of fixed resistors R as shown in FIG.
The bridge circuit 3 for flow rate measurement is formed by using x and Ry, and the bridge output voltage corresponding to the change in the resistance value of the temperature sensors Ru and Rd is used as the difference between the temperatures detected by the temperature sensors Ru and Rd. It is a detection circuit for detecting the corresponding sensor output Vout.

CPU for inputting such sensor output
The (arithmetic processing circuit) 20 is basically a sampling means 21 which drives the heater driving circuit 11 at predetermined time intervals to drive the heater element Rh to generate heat, and the heater which is driven by the sampling means 21. Element Rh
A flow rate calculating means 22 is provided which takes in the sensor output Vout from the detection circuit 12 in synchronism with the heat generation driving of 1 and obtains the flow rate Q of the fluid corresponding to the sensor output Vout. On this occasion,
It is of course possible to control the driving power applied to the microflow sensor 10 by the sampling means 21 to control the power supply to the microflow sensor 10 itself.

That is, the CPU 20 basically energizes the heater element Rh every predetermined period T to drive heat generation as shown in FIG. 2, and the sensor output Vout is synchronized with the heat generation drive of the heater element Rh. Input by sampling. Then, the sensor output V sampled by the flow rate calculating means 22
The flow rate Q corresponding to out is obtained, and the flow rate value is held until the next sampling timing, whereby the flow rate of the fluid (gas) flowing through the microflow sensor 10 is continuously measured. The sampling period T is set to, for example, about 1 second as a basic time interval at which a measurement error due to sampling can be substantially ignored.

In this way, the microflow sensor 10
In a CPU 20 having a function of performing sampling and driving at a predetermined cycle to measure a flow rate, a feature of this embodiment is that a microflow sensor is provided according to the flow rate Q measured as described above as shown in FIG. A use frequency integrating means (counting means) 23 as a means for measuring the flow frequency of the fluid flowing through it in a predetermined unit time, and a flow rate sensor according to the flow frequency obtained by the use frequency integrating means 23. And a sampling interval setting means (time interval setting means) 24 for variably setting the energization time interval of the heater element when the fluid is not flowing (when gas is not used). Further, the number-of-uses accumulating means 23 and the sampling interval setting means 24 are provided with a 24-hour timer 25.
Under the control of, the operation is controlled for each time zone that defines a predetermined unit time as described later.

The CPU 20 has a memory 30 composed of, for example, an EEPROM. The memory 30 stores a flow rate conversion table (not shown) showing the relationship between the flow rate Q of the fluid (gas) and the sensor output Vout for use in the calculation of the flow rate Q in the flow rate calculation means 22 and the use thereof. The number-of-uses table 31 for storing the information on the flow frequency of the fluid for each predetermined time period obtained by the number-of-times accumulating means 23 is stored.

The use number accumulating means 23 will now be described. The use number accumulating means 23 keeps the flow rate Q at zero each time the flow rate calculating means 22 executes the flow rate measurement within the above-mentioned predetermined unit time. It is determined whether or not there is. If the flow rate Q is not zero, it is determined that the fluid (gas) is flowing through the microflow sensor 10, that is, the gas is in use, and this state is accumulated as the number of times of use detection of gas. ing. Then, the number of times of use state detection with respect to the total number of times of sampling within the predetermined unit time is obtained as the fluid flow frequency. More simply, the number of times of use state detection itself is regarded as the number of times of use of the gas within the predetermined unit time, and the state of use is monitored. The number of times obtained in this way (the number of times of use state detection) is stored in the number-of-uses table 31 in the memory 30 for each measurement time period, and thereafter the sampling interval setting means 24 controls the variable setting of the sampling interval. Used.

On the other hand, the sampling interval setting means 24
Is the flow rate Q of the fluid calculated by the flow rate calculating means 22.
Is zero, that is, when no gas is flowing in the microflow sensor 10, when the fluid flows through the microflow sensor 10 for the energization time interval (sampling interval) of the heater element Rh by the sampling means 21 ( The heater element Rh is set longer than the energization time interval (basic sampling period) T of the heater element Rh (when gas is used), and the heater element is set according to the number of times of use of gas (use state detection number) obtained by the number-of-uses integrating means 23. R
It plays the role of variably setting the energization time interval (sampling interval) of h.

That is, the sampling interval setting means 24 is
Sampling drive cycle of the microflow sensor 10 when gas is not used (energization drive interval of the heater element Rh)
Is set to be long, and the interval is changed according to the frequency of use (number of times) of gas. In particular, when the gas usage frequency (number of times) becomes greater than the predetermined number (set number), the energization drive interval of the heater element Rh is shortened, and conversely, the gas usage frequency (number of times) is set to the predetermined number (set number). When it is less than the set number of times, the energization drive interval (sampling interval) of the heater element Rh is changed by lengthening the energization drive interval.

The variable setting of the energization drive interval (sampling interval) is executed for each time zone described above under the control of the 24-hour timer 25. More specifically, the heater element Rh is energized in accordance with the gas usage frequency (number of times) obtained for each time zone and stored in the usage frequency table 31 according to the past gas usage frequency (number of times) in the corresponding time zone. The drive interval (sampling interval) is set. The variable setting of the energization drive interval (sampling interval) of the heater element Rh is performed by selecting one of a plurality of kinds of energization time intervals which are preset as 1 second, 2 seconds, 5 seconds, 10 seconds, and the like. Made by choosing one.

FIG. 3 shows the CP for variably setting the energization drive interval (sampling interval) of the heater element Rh described above.
It shows an example of a schematic processing procedure in U20.
The processing procedure will be described. First, as the microflow sensor 10 is driven, the microflow sensor 10 is driven.
The flow rate Q at that time is measured according to the sensor output Vout detected from [step S1]. Then, it is determined whether the gas is being used by checking whether the measured flow rate Q is zero (0) [step S2].

When the gas is being used, the number of times of use of the gas in the present time zone is incremented by the number-of-uses accumulating means 23 [step S3], and the sampling interval is substantially reduced by the above-mentioned sampling measurement error. Is set as 1 second, which is a basic time interval that can be ignored (step S4). Then, the timing for driving the microflow sensor 10 next is managed according to the set sampling interval, and if the microflow sensor 10 is driven after a predetermined time, the processing procedure from step S1 is repeatedly executed.

At this time, when the gas is continuously used, it is determined that the gas is being used even at the next measurement timing, so that the number of times of use is accumulated. On the other hand, when the flow rate Q is zero at the next measurement timing, it is determined that the gas is unused (step S2). In this case, it is determined whether or not a fixed time has passed since the gas was stopped [Step S5], and if the fixed time has not passed, the sampling interval is set again to 1 second [Step S6]. ].
This process is a process for not changing the driving conditions of the microflow sensor 10 immediately after the use of the gas is stopped, and the above-mentioned fixed time is set to, for example, about 1 minute. This process prevents a detection delay when the gas is used immediately after the gas is stopped.

On the other hand, when a certain period of time has passed since the gas was stopped to be used [step S5], the number of times of past use in the present time zone is obtained by referring to the number of times of use table 31. The time zone is set, for example, by dividing one day into two hours. Whether the number of times of use in the same past time zone obtained from the number of times of use table 31 exceeds, for example, [5] [step S8],
[4] or [5], [step S9], or [1]
To [3], [step S10] is determined.

If the number of times of use in the same time zone in the past exceeds [5] [step S8], the sampling interval (energization drive interval of the heater element Rh) is set to 1 second, which is the same as when gas is used. [Step S11]. If the number of times of use is [4] or [5], [Step S
9], the sampling interval (the energization drive interval of the heater element Rh) is set to 2 seconds [step S12]. Further, when the number of times of use is [4] or [5], [Step S
9], the sampling interval is set to 2 seconds [step S12]. When the number of times of use is [1] to [3] [step S10], the sampling interval is set to 5 seconds [step S13], and when neither of them is met, that is, when the number of times of use is [0] In step S14, the sampling interval is set to 10 seconds.

That is, if it is detected that the flow rate Q is zero, the actual result data (number of times of use) in the same time zone in the past
Accordingly, the energization time interval (sampling interval) of the heater element Rh is variably set. In this way, the heater element R
If the energization time interval (sampling interval) of h is variably set, even if the unused state of the gas is detected at the beginning of the time zone that defines the unit time for measuring the number of times of use of the gas, the gas at that time is detected. Regardless of the cumulative value of the number of times of use of the heater element Rh, the energization time interval of the heater element Rh when the gas is not used can be set long according to the usage state of the gas in the same past time period. That is, it is possible to drive the heater element Rh at appropriate time intervals while learning the gas usage status for each time period.

Thus, according to the thermal type flow meter in which the sampling interval is variably set and the energization driving interval of the heater element Rh is changed by this, when the unused state of the gas is detected, the heater Since the time interval for energizing the element Rh can be set long, the electric power required for energizing the heater element Rh can be greatly reduced. Further, when the energization drive interval of the heater element Rh, which is set to be long when the gas is not used, is variably set according to the past usage situation, and when the use of the gas is expected to start,
Since the energization time interval is set to be relatively short, it is possible to sufficiently reduce the start delay of the flow rate measurement. Therefore, there is an effect that there is almost no possibility of impairing the measurement accuracy.

By the way, according to the control of the sampling interval described above, for example, the time zone in which the gas is most frequently used, the time zone in which the gas is most frequently used, the time zone in which the gas is rarely used, and other time zones. It is possible to separately set the energization time interval (sampling interval) of the heater element Rh when the gas is not used. Therefore, as illustrated in the following table, for example, the sampling interval is set according to the usage status of gas in each time zone, and the number of energization driving of the heater element Rh at the middle of the night is reduced to save power of the microflow sensor 10. Is possible.

[0033]

[Table 1]

In particular, when the number of energization driving of the heater element Rh is controlled as described above, the energization of the temperature sensors Ru and Rd is also controlled in conjunction with this, that is, the driving of the microflow sensor 10 itself is controlled. By doing so, it is possible to further reduce power consumption. When controlling the number of times of energization driving of the microflow sensor 10 by checking the usage status of gas for each time zone as described above, the frequency (sampling interval) of energization driving of the microflow sensor 10 is determined according to the time zone. It may be variable. Specifically, not only the number of times the gas is used in a specific time period, but also the number of sampling times may be variably set according to the time of use. If such control is also used, it is possible to set the sampling interval at midnight as long as one minute, so that power saving can be further achieved.

The present invention is not limited to the above embodiment. For example, when determining the flow frequency of a fluid, if the gas is continuously used for 1 minute or more, it may be detected (counted) as one use, or the number of times the gas has been used is detected (counted). ). However, in this case, it may not be possible to distinguish between the case where the gas is continuously used for 1 hour and the case where the gas is used only once for 1 minute. However, since such a situation rarely continues every day, if the number of times of use is learned for each time period and the average number of times of use is obtained, the sampling interval can be controlled according to the frequency of use. It becomes possible to do effectively. It is also possible to divide the time zone into hour units.

Furthermore, it is of course possible to variably set the sampling interval when the gas is not used, over a wider width. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

[0037]

As described above, according to the present invention, the energization time interval of the heater element when the flow rate is zero can be set to be sufficiently long. Can be reduced and the power can be saved. Moreover, since the heat generation drive interval of the heater element is variably set according to the flow frequency of the fluid, the heat generation drive delay of the heater when the flow of the fluid is started can be sufficiently shortened, and the measurement accuracy thereof is almost the same. There are practically great effects such as no damage.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a main part of a thermal type flow meter according to an embodiment of the present invention.

FIG. 2 is a timing diagram showing a basic operation of the thermal type flow meter shown in FIG.

FIG. 3 is a diagram showing an example of a schematic processing operation in the thermal type flow meter shown in FIG.

FIG. 4 is a schematic configuration diagram of a microflow sensor.

FIG. 5 is a diagram showing a configuration example of a conventional general heater drive circuit and a flow rate detection circuit.

[Explanation of symbols]

Rh heater element Ru temperature sensor (upstream side) Rd temperature sensor (downstream side) Rr temperature sensor (for ambient temperature measurement) 1 bridge circuit (for driving the heater) 2 differential amplifier 3 bridge circuit (for flow rate measurement) 4 differential amplifier 10 Micro flow sensor 11 Heater drive circuit 12 Detection circuit 20 CPU 21 Sampling means 22 Flow rate detection means 23 Usage count integration means 24 Sampling interval setting means 25 24 hour timer 30 memory 31 Usage count table

Claims (7)

[Claims] 1. A heater element and first and second heater elements provided in the fluid flow direction with the heater element interposed therebetween.
And a temperature sensor for electrically heating the heater element at predetermined time intervals, and a difference in temperature detected by each of the first and second temperature sensors when electrically heating the heater element. Flow rate detection means for determining the flow rate of the fluid flowing through the flow rate sensor, and when the fluid does not flow through the flow rate sensor according to the flow frequency of the fluid flowing through the flow rate sensor within a predetermined unit time And a time interval setting means for variably setting an energization time interval of the heater element. 2. The time interval setting means sets an energization time interval of the heater element when a fluid is not flowing through the flow rate sensor, and an energization of the heater element when a fluid is flowing through the flow rate sensor. The thermal flow meter according to claim 1, wherein the thermal flow meter is variably set within a range of a time width longer than the time interval. 3. The time interval setting means is a counting means for calculating, as the distribution frequency, the number of times when the flow rate detected by the flow rate detecting means is not zero within the predetermined unit time, and the counting means. When the number of measurements is greater than a preset number of times, the energization time interval of the heater element is set short, and when the number of measurements is less than the set number of times, the energization time interval of the heater element is set long. The thermal flow meter according to claim 2, further comprising: 4. The flow rate detection means varies the timing of temperature detection by the first and second temperature sensors in association with control of the energization time interval of the heater element. Thermal flow meter. 5. The thermal type flow meter according to claim 1, wherein the predetermined unit time is set by dividing one day into a plurality of time zones. 6. The thermal type flow meter according to claim 5, wherein the flow rate detecting means varies the timing of temperature detection by the first and second temperature sensors in accordance with a time zone set by division. . 7. The time interval setting means stores the number of times when the flow rate detected by the flow rate detection means is not zero for each of a plurality of time zones, and the flow rate detected by the flow rate detection means is zero. At this time, the thermal type flow meter according to claim 1, wherein the energization time interval of the heater element is set according to the number of past measurements in the same time zone as the current time zone.