JPH11190654A - Integrating flowmeter and gas meter using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption to prevent generation of measurement error by providing a flow sensor driven intermittently in response to a measurement timming, and randomly changing the measurement tinning in a specified cycle. SOLUTION: A hot-wire flow sensor 20 is provided with a heater 4 and upstream and downstream temperature sensors 3, 5 and placed on a wall surface of a flow passage 1. The heater 4 is driven by a heater driving circuit 12 to heat a gas to have a constant temperature rise therein, and the temperature is detected by temperature sensors 3, 5. Outputs of temperature sensors 3, 5 are amplified through a bridge circuit 6 and input to a sampling circuit 8. The sampling circuit 8 samples an output of the amplifier 7 at a specified interval according to a measurement timing signal S3 form a timing circuit 13. An output S6 of the sampling circuit 8 is A/D converted 9 and input to a CPU for obtaining an integration value. The CPU 10 outputs a control signal S9 to the timing circuit 13 to control the driving timming of each part in an optimum manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated flow meter for measuring a flow rate per unit time with a flow sensor and integrating the measured values to obtain an integrated flow rate, and a gas meter using the same.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a configuration and a measurement waveform of a conventional integrating flow meter. FIG. 6A shows a circuit configuration when a hot wire type flow sensor 20 is used as a flow sensor. Since the hot-wire type flow sensor 20 measures the flow velocity of the fluid, the integrated flow rate is obtained from the flow velocity as follows.

The fluid flowing in the flow path 1 in the direction of arrow 2 is heated by a heater 4 driven by a heater drive circuit 12 so that the vicinity of the heater 4 has a predetermined temperature. The temperature of the fluid near the heater 4 is detected by the upstream temperature sensor 3 and the downstream temperature sensor 5. If there is no flow in the fluid, the upstream temperature sensor 3 and the downstream temperature sensor 5
Are equal. On the other hand, if the fluid has a flow,
The temperature detected by the upstream temperature sensor 3 is
Lower than the detected temperature.

The upstream and downstream temperature sensors 3 and 5 include:
Platinum thin film resistors whose resistance changes with temperature are used,
The change in the resistance value is detected by the bridge circuit 6. The output of the bridge circuit 6 indicates the flow rate of the fluid.
The flow rate of the fluid flowing through the flow path 1 is converted into the flow rate per unit time in consideration of the flow velocity distribution and the cross-sectional area of the flow path 1.

FIG. 6 (2) shows a flow rate per unit time (hereinafter, referred to as an instantaneous flow rate) Q [m converted as described above.
³ / s]. The horizontal axis is time t [s]. FIG.
(2) shows a state where a constant instantaneous flow rate Q1 has flowed from time t1.

The output of the bridge circuit 6 is input to an integrating circuit 50. The integrating circuit 50 is a circuit that integrates the instantaneous flow rate over time. FIG. 6C shows the integrated value V [m ³ ] which is the output of the integrating circuit. In FIG. 6C, the integrated value increases at a constant slope from time t1, and reaches integrated value V2 at time t2. This integrated value is displayed on the display circuit 51.

As described above, the integrated flow rate can be calculated by driving the flow rate sensor continuously over time and integrating the sensor output. Further, the integrated flow rate can be calculated by driving the flow rate sensor intermittently and sequentially adding a value obtained by multiplying the intermittent instantaneous flow rate by the measurement time interval.

[0008]

The flow sensor includes a hot wire type flow sensor, an ultrasonic type flow sensor, and the like. However, these sensors require electric power at the time of driving, and require another electric circuit when driven continuously. Power consumption tends to increase in conjunction with In particular, a problem arises in the case of a portable flow meter or an integrated flow meter that is used in a gas meter attached to each gas consumer and cannot be used for commercial power and is a battery-driven type.

When the flow sensor is intermittently driven, the problem of power consumption is reduced, but a measurement error may occur when the flow of the fluid to be measured contains a pulsation component due to disturbance. That is, this is a case where the measurement interval of the flow sensor is an integral multiple of the cycle of the pulsating component.

FIG. 7 is an explanatory diagram when a measurement error occurs due to a pulsation component due to disturbance. FIG. 7A shows a case where a fluid such as a gas is supplied from the common flow channel 60 to each of the consumers A, B, and C through the respective flow channels 61, 62, and 63. The integrated flow rate of each consumer is measured by the integrated flow meters 64, 65, 66 installed in the respective flow paths.

FIG. 7B shows the flow rate used by the customer A as an instantaneous flow rate Q [m ³ / s]. The customer A is at time t3
Up to this time, the constant flow rate Q3 was used, but a load in which the use flow rate fluctuates greatly from time t3 is used. These loads include a heat pump, an engine, a blower, and the like, which not only consumes a large amount of gas but also fluctuates greatly in, for example, a cycle t. These loads affect adjacent consumers as disturbances. However, these loads usually have a period of 2 Hz to 20 Hz.

FIG. 7 (3) shows an integrated flow meter 65 of the customer B.
Shows the instantaneous flow rate Q [m ³ / s] measured by the following equation. Consumer B
However, even if the constant flow rate Q4 is always used, the pulsating component of the cycle t is detected after the time t3 when the adjacent customer A starts using the load such as the heat pump.

Even if the integrating flow meter 65 of the consumer B detects the pulsating component of the period t, the pulsating component oscillates symmetrically with respect to the instantaneous flow rate Q4. The effect is gone. However, when the instantaneous flow rate is measured at a fixed measurement interval and the integrated flow rate is obtained by multiplying the instantaneous flow rate by the measurement interval, the influence of the pulsation component appears on the integrated flow rate value.

FIG. 8 is an explanatory diagram in a case where an erroneous integrated flow rate is measured by intermittently driving the flow rate sensor. FIG. 8 illustrates a case where the consumer A uses a load such as a heat pump, but the consumer B does not use gas. Fig. 8 (1)
Is an instantaneous flow rate detected by the integrating flow meter 65 of the consumer B, and includes a pulsating component of a cycle t due to the influence of disturbance from the consumer A. The flow sensor is intermittently driven at a constant period T, and the measured value at the drive timing is indicated by a circle. FIG. 8A shows a case where the cycle T of the drive timing is twice the cycle t of the pulsation component, that is, T = 2t. In this case, the instantaneous flow rate of the customer B, which should be zero, is detected as Q5.

FIG. 8B shows the integrated flow rate V [m ³ ] measured by the integrated flow meter 65 of the customer B in this case. After the time t5, the integrated flow rate of the consumer B is as follows: V5 = Q5 × T V51 = V5 + Q5 × T In this way, the demand B is integrated as if the instantaneous flow rate Q5 was continuously used, even though the gas was not used.

FIG. 8 (3) shows an integrated flow meter 65 of the customer B.
Is a case where the intermittent driving is performed at the timing of the negative peak of the pulsation component. In this case, the integrating flow meter 6 of the customer B
5 indicates an erroneous integrated value that is integrated on the negative side after time t6, as shown in FIG. 8 (4).

Accordingly, an object of the present invention is to provide an integrated flow meter that reduces power consumption and prevents the occurrence of measurement errors.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide an integrated flow meter for successively adding a product of a predetermined cycle and a flow rate per unit time within the predetermined cycle to obtain an integrated flow rate. This is attained by providing an integrating flow meter having a flow sensor that is driven intermittently in response and that randomly varies the measurement timing within the predetermined cycle.

According to the present invention, since the measurement timing fluctuates randomly within a predetermined period, the power consumption is reduced by intermittent driving, and the integrated flow rate that suppresses a measurement error caused by a pulsation component due to disturbance. Can provide a total.

Further, the above object is to provide an integrated flow meter for successively adding a product of a flow rate per unit time at a measurement timing and a time between the measurement timings to obtain an integrated flow rate. This is achieved by providing an integrated flow meter having a flow sensor that is driven in a controlled manner and randomly varying the time between the measurement timings.

According to the present invention, since the time between measurement timings fluctuates randomly, an integrated flow meter that reduces power consumption by intermittent driving and suppresses a measurement error caused by a pulsation component due to disturbance is provided. Can be provided.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, such embodiments do not limit the technical scope of the present invention.

FIG. 1 is a block diagram of the integrating flow meter according to the present embodiment. Fluid such as gas flows in the flow path 1 in the direction of arrow 2, and the flow velocity is measured by the hot-wire flow sensor 20. The hot wire type flow sensor 20 has a heater 4, an upstream temperature sensor 3, and a downstream temperature sensor 5, and is installed on a wall surface of the flow path 1. The heater 4 is driven by the heater drive circuit 12, and is heated so that the gas in the vicinity of the heater 4 exhibits a constant temperature rise. The temperature of the gas near the heater 4 is detected by the upstream temperature sensor 3 and the downstream temperature sensor 5. The upstream and downstream temperature sensors 3, 5 utilize the fact that the resistance value of the platinum thin film resistor changes with temperature.

Changes in the resistance values of the upstream and downstream temperature sensors 3 and 5 are converted into voltage changes in the bridge circuit 6. The voltage signal S4 of the bridge circuit 6 is amplified by the amplifier 7 to become S5 and input to the sampling circuit 8. The sampling circuit 8 samples the output S5 of the amplifier 7 at predetermined intervals, which will be described in detail later, based on the measurement timing signal S3 from the timing circuit 13.

The output S6 of the sampling circuit 8 is A / D
The digital signal S7 is converted by the converter 9 into a digital signal S7.
The value is input to 10 and the integrated value of the flow rate is obtained. Also, C
The PU 10 outputs a control signal S9 to the timing circuit 13 to control the drive timing of each unit. Furthermore, CPU
10 outputs a signal S8 and displays the integrated value of the flow rate on a display circuit (not shown).

The timing circuit 13 outputs a heater drive signal S1 to the heater drive circuit 12 based on a control signal S9 from the CPU 10, and outputs a measurement timing signal S3 to a measurement system such as the sampling circuit 8. In the integrating flow meter of the present embodiment, the power supply Vcc is supplied to each unit by the battery 11, but by controlling the drive timing of each unit optimally as described later in detail, low power consumption and measurement accuracy can be achieved. It is both secure and secure.

FIG. 2 shows the structure and signal waveforms of the hot-wire flow sensor 20 used in the present embodiment. Fig. 2 (1)
As shown in the figure, the hot wire type flow sensor 20 has a cavity 21 in a silicon chip, and a heater 4, an upstream temperature sensor 3 and a downstream temperature sensor 5 are integrated on a dielectric thin film on the cavity 21. Is done. The heaters 4 and the like are connected to the electrode terminals, respectively, and are connected to the bridge circuit 6 described above.
The silicon chip has a length and width of, for example, about 1.7 mm and a thickness of about 0.4 mm.

FIG. 2B shows the drive timing of the hot wire type flow sensor 20. FIG. 2B shows the heater drive signal S1 output from the timing circuit 13 shown in FIG. 1 to the heater drive circuit 12. The heater drive circuit 12
A drive current is supplied to the heater 4 in synchronization with the heater drive signal S1. FIG. 2B shows the temperature S <b> 2 near the heater 4. The temperature S2 in the vicinity of the heater 4 does not change at the same time as the heater drive signal S1 because of the thermal time constant.
A time delay of several tens of ms occurs between r and the fall time tf.

FIG. 2B shows the measurement timing signal S3 output from the timing circuit 13 to the sampling circuit 8 and the like. The measurement timing signal S3 is output during a period from time t21 to time t24 in which the temperature near the heater 4 is stable. Then, the period t22 of the measurement timing signal S3
The gas flow rate is measured between t23.

FIG. 3 is a measurement flowchart according to the present embodiment. In this embodiment, each circuit block is intermittently driven for low power consumption, and measurement is performed at the following timing to cancel a measurement error caused by the intermittent drive.

In step P1, the CPU 10 activates the timing circuit 13 to start a series of measurement sequences. In step P2, the timing circuit 13 outputs the heater drive signal S1 to the heater drive circuit 12,
Start heating. In order to stabilize the temperature in the vicinity of the heater 4 after the heating of the heater 4 is started, as described above, several tens m
It takes s time.

In step P3, the bridge circuit 6, the amplifier 7, the sampling circuit 8, and the A / D converter 9 constituting the measuring system are activated. Until the temperature in the vicinity of the heater 4 is stabilized, each circuit of the measurement system is also stabilized, and measurement data is obtained in Step P4. When the measurement data is obtained, the heating of the heater 4 is immediately stopped in Step P5. This is because the heater 4 consumes the most power.

Next, in step P6, the measurement data S7 converted into a digital signal by the A / D converter 9 is sent to the CPU 10. As a result, one measurement sequence is completed, and each circuit of the measurement system is stopped in Step P7, and the timing circuit 13 is stopped in Step P8.

In step P9, a random time is generated in the CPU 10, and the process waits until the next measurement timing. That is, in the present embodiment, the measurement timing is randomly changed in order to cancel the measurement error caused by the intermittent driving.

FIG. 4 shows a waveform in which the measurement error is suppressed by randomly varying the measurement timing in the present embodiment. FIG. 4A shows a situation similar to that of FIG.
Is a case where gas is not used and the adjacent customer A uses a load such as a heat pump.

The integrating flow meter 65 of the consumer B detects the pulsating component of the cycle t. In the present embodiment, the measuring timing is varied at random as follows, and the pulsating component is changed to the integrated flow value. So as not to affect That is,
In FIG. 4, a fixed integration time τ0 is set in advance, and measurement data is obtained at random timing from the start time (ta, tb, tc, etc.) of each integration time. Note that the integration time τ0
Is increased, the period in which the heater 4 and the like are intermittently driven becomes longer and the power consumption is reduced, but the measurement accuracy is reduced.

The start time of the integration time (ta, tb, tc)
Τn = rnd (n) × τ0, where τn is the time from the above to the measurement timing. Here, n is an integer of 1 or more, and rnd (n) is 0
This is the n-th random number less than or equal to one. Therefore, the instantaneous flow rate at the measurement timing t7 is Q7, and the instantaneous flow rate at the measurement timing t8 is Q8.

FIG. 4 (2) shows the integrated flow rate of the consumer B. In the period from ta to tb, V7 = Q7 × τ0, and in the period from tb to tc, V8 = V7 + Q8 × τ0. V8 becomes negative because the instantaneous flow rate Q8 is negative. Therefore, even if there is a periodic pulsation component, the sampling value is randomly sampled, and the integrated value converges to near zero as shown in FIG.

FIG. 5 shows another method for making the measurement timing random. In this case, the integrating flow meter 6 of the customer B
When 5 includes a pulsating component having a period t as in FIG. 4, the measurement timing interval τn is randomly varied.

In this case, assuming that the minimum interval of the measurement timing is tmin and the maximum interval is tmax, the interval τn of the measurement timing is τn = tmin + (tmax−tmin) × rnd
(N). Note that tmin is determined by the limitation of the power consumption and the response time of the flow rate sensor.
One second. Further, tmax is determined by the required measurement accuracy, and is about 1 to 3 seconds in the present embodiment.

FIG. 5B shows the integrated flow rate of the customer B. In this case, the integrated flow rate is the product of the instantaneous flow rate and the measurement interval, and V9 = Q9 × τ1 V10 = V9 + Q10 × τ2 V11 = V10 + Q11 × τ3 and the like. The reason why the integrated value decreases at V11 is that Q11 is a negative value. Therefore, also in the present embodiment, the integrated flow rate converges to zero.

By using the above-mentioned integrating flow meter for a gas meter which is attached to each gas consumer and is driven by a battery, in a gas meter which is guaranteed for about ten years, the consumption of the battery can be effectively suppressed. In addition, pulsation errors due to disturbance can be eliminated.

[0043]

As described above, since the measurement timing fluctuates at random, it is possible to provide an integrated flow meter which reduces power consumption by intermittent driving and suppresses a measurement error caused by a pulsation component due to disturbance. .

[Brief description of the drawings]

FIG. 1 is a block diagram of an integrating flow meter according to an embodiment of the present invention.

FIG. 2 is a hot wire type flow sensor according to an embodiment of the present invention.

FIG. 3 is a measurement flowchart according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a random measurement timing according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of another random measurement timing according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram of a conventional integrating flow meter.

FIG. 7 is an explanatory diagram in which a measurement error occurs due to a pulsating component.

FIG. 8 is an explanatory diagram of a conventional intermittent drive.

[Explanation of symbols]

 Reference Signs List 6 bridge circuit 8 sampling circuit 10 CPU 11 battery 12 heater drive circuit 13 timing circuit 20 hot-wire flow sensor

Claims (5)

[Claims] 1. An integrating flow meter for integrating a flow rate per unit time detected by a flow rate sensor, wherein the flow rate sensor is intermittently driven in response to a measurement timing to randomly vary the measurement timing. An integrating flow meter characterized by the following. 2. An integrated flow meter for successively adding a product of a predetermined cycle and a flow rate per unit time within the predetermined cycle to obtain an integrated flow rate, wherein the integrated flow meter is driven intermittently in response to a measurement timing. An integrated flow meter having a flow sensor, wherein the measurement timing is randomly varied within the predetermined cycle. 3. An integrating flow meter for successively adding a product of a flow rate per unit time at a measuring timing and a time between the measuring timings to obtain an integrated flow rate, wherein the integrating flow meter is driven intermittently in response to the measuring timing. An integrating flow meter having a flow sensor, wherein a time between the measurement timings is randomly varied. 4. A gas meter comprising the integrating flow meter according to claim 1, wherein the flow sensor is driven by a battery. 5. The gas meter according to claim 1, wherein the flow sensor is a hot wire flow sensor or an ultrasonic flow sensor.