JPH11295123A - Flow measurement device - Google Patents

Abstract

(57) [Problem] To provide a flow measurement device capable of measuring a flow value with a small amount of calculation and reducing power consumption. SOLUTION: The flow measuring device comprises an upstream thermopile 101 and a downstream thermopile 10 of a flow sensor 107.
3 are input to the differential amplifier 109, respectively. The peak of the data differentially and amplified by the differential amplifier 109 is detected by the peak hold circuit 111, and then the data is A / D converted by the A / D converter 113. The A / D converted peak data is stored in the microcomputer 1
The determination unit 115 determines whether to change the pulse width with reference to the look-up table 117 or to calculate the flow value by the flow calculation unit 119.

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 determining a flow rate of a fluid using a heater and a temperature sensor.

[0002]

2. Description of the Related Art Fluid meters are used to measure the flow rate of a fluid to be measured, such as gas, through a pipe of a specific size and shape over a certain period of time. However, for the measurement at the time of a low flow rate, a flow rate measuring device attached for complementing a fluidic meter is generally used. This flow measurement device includes a flow sensor having a micro heater and a thermopile (temperature sensor).

FIG. 9 is a block diagram showing a configuration example of a conventional flow rate measuring device. The flow rate measuring device includes an upstream thermopile 1001 which is a temperature measuring resistor provided on the upstream side in the flow direction of the measurement target fluid, a downstream thermopile 1003 which is the same temperature measurement resistance provided on the downstream side in the flow direction of the measurement target fluid, and Micro heater 10 provided at an intermediate position between upstream thermopile 1001 and downstream thermopile 1003
05, and the upstream thermopile 103 based on the peak voltage of the downstream thermopile 1003.
Differential amplifier 101 for subtracting and amplifying the peak voltage of the differential amplifier 101
1, a peak hold circuit 1013 for detecting the peak of the output of the differential amplifier 1011, and a peak hold circuit 1013.
A / D which A / D converts the peak value detected by
A microcomputer 1021 having a D converter 1015, a memory 1017 for storing A / D converted data, and a flow rate calculation unit 1019 for calculating a flow rate value by performing arithmetic processing on the A / D converted peak value. , A display 1023 for displaying a flow value, and the micro heater 100
5 and a lithium battery 1027.

Next, the operation of the conventional flow rate measuring device will be described. When the gas as the fluid to be measured flows and the flow measurement is started, the micro heater 1005 of the flow sensor 1009 is operated by the heater drive circuit 1025. The heat generated by the microheater 1005 is transmitted to the downstream thermopile 1003 using a gas flowing from the upstream thermopile 1001 side to the downstream thermopile 1003 side as a medium. The downstream thermopile 1003 is constituted by a temperature measuring resistor that senses heat as a voltage from the difference between the thermoelectromotive force and the difference in heat capacity between the cold junction and the hot junction, and detects the temperature of the gas as the fluid to be measured by the voltage value. . On the other hand, the upstream thermopile 1001 also detects the temperature of the gas by the voltage value in the same manner as the downstream thermopile 1003.

The downstream voltage value measured by the downstream thermopile 1003 and the upstream voltage value measured by the upstream thermopile 1001 are input to a non-inverting input terminal and an inverting input terminal of the differential amplifier 1011, respectively. The differential amplifier 1011 differentiates the upstream voltage value from the input downstream voltage value and amplifies the difference. The amplified differential voltage value is output from the differential amplifier 1011 and input to the peak hold circuit 1013. Peak hold circuit 10
At 13, a peak value of the amplified differential voltage value is obtained. The obtained peak value is converted by an A / D converter 1015 into A / D
The D-converted and digitized peak value is calculated by the microcomputer 10
21 is stored in the memory 1017.

The microcomputer 1021 inputs the digitized peak value to a variable corresponding to the peak value in the polynomial using a polynomial showing a curve as shown in FIG. Desired. The obtained flow rate value is displayed on a display 1023 or the like connected to the microcomputer 1021.

[0007]

However, the flow rate measuring device of the prior art described above must use a high-order polynomial in order to calculate the flow value. There is a problem that the processing time becomes longer and the operation processing time becomes longer. Also,
This also increases power consumption. This type of flow rate measuring device often uses a small battery such as a lithium battery as a power supply, and it is desired to reduce power consumption.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a flow rate measuring device capable of measuring a flow rate value with a small amount of calculation and reducing power consumption.

[0009]

According to a first aspect of the present invention, there is provided a heater, a downstream temperature sensor installed downstream of the heater, and an upstream temperature sensor installed upstream of the heater. A flow sensor having an upstream temperature sensor; a heater drive circuit for outputting a drive pulse for driving the heater; and a peak value for detecting a peak value of a difference between outputs of the downstream temperature sensor and the upstream temperature sensor. Detecting means, an A / D converter for A / D converting the peak value output from the peak value detecting means, and a relationship between the peak value and the flow rate value according to the A / D converted peak value. Parameter changing means for changing a parameter for changing the peak value so as to be a linear function, and flow rate calculating means for calculating a flow rate value from the A / D converted peak value by a predetermined linear function formula A processing means having a a flow rate measuring apparatus characterized by comprising a.

In the above-described configuration, the flow rate value with respect to the peak value can be represented by a linear function, whereby the scale of arithmetic processing in the microcomputer can be reduced and power consumption can be reduced.

The invention according to claim 2 further comprises pulse generating means for generating a pulse signal for generating the driving pulse, wherein the parameter changing means changes a pulse width of the driving pulse as the parameter. 2. The flow rate measuring device according to the above item 1, wherein an instruction is given to the pulse generating means.

In the above configuration, by changing the pulse width of the heater drive pulse, the flow rate value with respect to the peak value can be made to have a linear function relationship, thereby reducing the operation processing scale in the microcomputer and reducing power consumption. Can be reduced.

[0013] The invention according to claim 3 further comprises a gain changeable amplifying means for amplifying a difference between the outputs of the downstream temperature sensor and the upstream temperature sensor, and the parameter changing means includes the amplification as the parameter. 2. The flow measuring device according to claim 1, wherein the flow rate measuring device is instructed to change the gain of the means.

In the above configuration, the flow rate value with respect to the peak value can be made to have a linear function by changing the gain of the amplifying means, thereby reducing the scale of arithmetic processing in the microcomputer and reducing power consumption.

Further, in the invention according to a fourth aspect, the parameter changing means switches the parameter for each predetermined range of the peak value, and the flow rate calculating means corresponds to the peak value and the flow rate corresponding to each of the switched parameters. 2. The flow rate measuring device according to the item 1, wherein the flow rate value is calculated from the peak value by a linear function formula with a value.

In the above configuration, the flow rate value with respect to the peak value can be made to have a linear function relationship, thereby reducing the scale of arithmetic processing in the microcomputer and reducing power consumption.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a flow measurement device according to a first embodiment of the present invention. The flow rate measuring device includes an upstream thermopile 101 that is a temperature measuring resistor provided on the upstream side in the flow direction of the measurement target fluid, and a downstream thermopile 103 that is also a temperature measurement resistance provided on the downstream side in the flow direction of the measurement target fluid. Upstream thermopile 10
Flow sensor 107 including a micro heater 105 provided at an intermediate position between the thermopile 1 and the downstream thermopile 103.
And a differential amplifier 109 for subtracting the peak voltage of the upstream thermopile 101 from the peak voltage of the downstream thermopile 103, and a peak hold circuit 111 as a peak value detecting means for detecting the peak of the output of the differential amplifier 109.
And an A / D converter 113 for A / D converting the peak value detected by the peak hold circuit 111, and comparing the A / D converted peak value with the previously input peak value to change the pulse width. Judgment unit 1 that judges whether it is necessary to do
15. A flow rate calculation unit 119 as a flow rate calculation means for calculating a flow rate value by calculating a lookup table 117 and a peak value which are referred to when changing the pulse width.
A microcomputer 121 serving as a processing unit having: a display 123 for displaying a flow rate value;
5, a heater driving circuit 125 for driving the heater 5, a pulse generator 127 as a pulse generating means for generating a pulse signal to be supplied to the heater driving circuit 125, and a lithium battery 129 as a power supply.

In the look-up table 117 of the microcomputer 121, as shown in FIG. 2, the peak value and the pulse width of the pulse signal supplied to the heater drive circuit 125 corresponding to the peak value are set. Using the lookup table 117, the unit 115 determines which pulse width the input peak value corresponds to. Also, the determination unit 115 and the lookup table 11
7 constitutes parameter changing means. On the other hand, the flow rate calculation unit 119 has a function of calculating a flow rate value by substituting the input peak value into a variable of a predetermined linear function formula obtained in advance for each predetermined pulse width.

Next, the operation of the flow measuring device according to the first embodiment will be described below. Gas as the fluid to be measured flows,
When the flow measurement device of the present embodiment starts measurement, the heater heater circuit 125 activates the micro heater 105 of the flow sensor 107. The heat generated by the micro heater 105 is transmitted to the downstream thermopile 103 using gas as a medium. The downstream thermopile 103 detects the temperature of the gas as a voltage value by sensing heat as a voltage from the difference between the thermoelectromotive force and the difference in heat capacity between the cold junction and the hot junction. On the other hand, similarly to the downstream thermopile 103, the upstream thermopile 101 detects the gas temperature by a voltage value.

The downstream voltage value measured by the downstream thermopile 103 and the upstream voltage value measured by the upstream thermopile 101 are input to the non-inverting input terminal and the inverting input terminal of the differential amplifier 109, respectively. In the input downstream voltage value and upstream voltage value, the upstream voltage is differentiated from the downstream voltage and amplified. The amplified differential voltage value of several mV is output from the differential amplifier 109 and input to the peak hold circuit 111. In the peak hold circuit 111, a peak value of the amplified differential voltage value is obtained. The obtained peak value is converted by an A / D converter 113 into an A / D signal.
The converted and digitized peak value is input to the determination unit 115 of the microcomputer.

The determination unit 115 of the microcomputer 121 compares the peak value obtained this time with the peak value obtained last time using the lookup table 117, and
It is determined whether the pulse width of the pulse supplied to 5 needs to be changed. By referring to the look-up table 117, when the corresponding pulse width between the currently obtained peak value and the previously obtained peak value is different, the pulse width is changed. If the corresponding pulse widths of the peak value obtained this time and the peak value obtained last time are the same, the flow rate calculation unit 1
At 19, an operation for obtaining the flow value is performed.

Next, a detailed description will be given of changing the pulse width. After the pulse width change is determined, the microcomputer 12
The first determination unit 115 determines and determines the pulse width corresponding to the obtained peak value by referring to the look-up table 117. In the look-up table 117, as shown in FIG. 2, the correspondence between the peak value and the pulse width is set for each predetermined range of the peak value.
The pulse width supplied to the heater drive circuit 125 is determined by the determination unit 1
15 is determined by the pulse generator 12 so as to generate a pulse signal having the determined pulse width.
7, the pulse generator 127 supplies a pulse signal of the designated pulse width to the heater drive circuit 125.
As a result, a drive pulse having the determined pulse width is output from the heater drive circuit 125 and supplied to the micro heater 105.

The downstream voltage value in the state where the pulse width is changed is different from the downstream voltage value before the pulse width is changed. FIG. 3 shows that the peak value increases as the pulse width increases even at the same flow rate value. Therefore, when the pulse width is reduced by the determination unit 115 of the microcomputer 121, the peak value measured by this pulse width becomes smaller than the peak value obtained last time, and when the pulse width is increased, the peak value obtained last time is obtained. The peak value is larger than the peak value. However, there is no change in the flow value before and after the pulse width change.

Therefore, the peak value of the differential voltage value measured by the flow sensor 107 at the changed pulse width is
The determination is made again by the determination unit 115 of the microcomputer 121. If the pulse width corresponding to the peak value at this time is different from the pulse width corresponding to the previously obtained peak value, the pulse width is changed again.

When the pulse width of the driving pulse is in a steady state as a result of the above-mentioned pulse width change, a calculation process for obtaining the following flow rate value is performed.

When performing the calculation process, the flow rate calculation unit 119 of the microcomputer 121 inputs the obtained peak value to the variable of the linear function expression corresponding to the current pulse width,
The flow rate calculation unit 119 calculates the flow rate value. However, although the linear function formula for calculating the flow rate value differs for each pulse width, the linear function Y = aX + b (where Y
Is a flow rate value, X is a peak value, and a and b are constants. For setting the constants a and b, reference is made to the peak value-flow rate value characteristic for each pulse width in FIG. Then, a linear function expression having constants a and b corresponding to the pulse width is obtained for each peak value in FIG.
Is determined in advance as shown by a linear function of the following formula, and stored in the flow rate calculation unit 119.

The flow rate value thus obtained is displayed on a display 123 or the like connected to the microcomputer 121.

According to the first embodiment, by changing the pulse width so that the flow rate value and the peak value become a linear function, the calculation processing in the flow rate calculator 119 of the microcomputer 121 is simplified, and the power consumption is reduced. Can be reduced.

Next, a second embodiment of the present invention will be described. FIG. 6 is a block diagram showing the flow rate measuring device of the present embodiment. The flow rate measuring device includes an upstream thermopile 101 that is a temperature measuring resistor provided on the upstream side in the flow direction of the measurement target fluid, and a downstream thermopile 103 that is also a temperature measurement resistance provided on the downstream side in the flow direction of the measurement target fluid. A flow rate sensor 107 having a micro heater 105 provided at an intermediate position between the upstream thermopile 101 and the downstream thermopile 103, and a gain changeable by subtracting the peak voltage of the upstream thermopile 101 from the peak voltage of the downstream thermopile 103 And a peak hold circuit 1 for detecting a peak of an output of the programmable gain amplifier 601.
11, an A / D converter 113 for A / D converting the peak value detected by the peak hold circuit 111,
A determination unit 603 that compares the D-converted peak value with the previously input peak value to determine whether the gain of the programmable gain amplifier 601 needs to be changed, and a lookup table 605 that is referred to when changing the gain. A microcomputer 609 having a flow rate calculation unit 607 as a flow rate calculation means for calculating a flow rate value by calculating a peak value and a display 123 for displaying a flow rate value;
Heater drive circuit 12 for driving micro heater 105
5 and a lithium battery 127 as a power supply.

In the look-up table 605 of the microcomputer 609, a peak value and a gain of the programmable gain amplifier 601 corresponding to the peak value are set.
Using the lookup table 605, the determination unit 603 determines which gain the input peak value corresponds to. The determining unit 603 and the lookup table 605 constitute a parameter changing unit. On the other hand, the flow rate calculation unit 607 has a function of calculating a flow rate value by substituting a peak value into a predetermined linear function expression obtained in advance for each gain.

Next, the operation of the flow measuring device will be described below. When the gas as the fluid to be measured flows and the flow measurement device of the present invention starts measurement, the heater heater circuit 125 operates the micro heater 105 of the flow sensor 107. The heat generated by the micro heater 105 is transmitted to the downstream thermopile 103 using gas as a medium. The downstream thermopile 103 detects the temperature of the gas as the fluid to be measured as a voltage value by sensing heat as a voltage from the difference between the cold junction and the hot junction and the difference in heat capacity. On the other hand, the upstream thermopile 101 is also the downstream thermopile 1
Similarly to 03, the temperature of the gas as the fluid to be measured is detected by the voltage value.

The downstream voltage value measured by the downstream thermopile 103 and the upstream voltage value measured by the upstream thermopile 101 are input to the non-inverting input terminal and the inverting input terminal of the programmable gain amplifier 601 respectively. The input downstream voltage value and upstream voltage value are
The upstream voltage is differentiated from the downstream voltage and amplified. The amplified differential voltage value of several mV is output from the programmable gain amplifier 601, and the peak hold circuit 111
Is input to In the peak hold circuit 111, a peak value of the amplified differential voltage value is obtained. The obtained peak value is A / D converted by the A / D converter 113, and the digitized peak value is input to the determination unit 603 of the microcomputer 609.

Using the look-up table 605, the determination unit 603 of the microcomputer 609 compares the currently obtained peak value with the previously obtained peak value to determine whether the gain needs to be changed. If the corresponding gain between the currently obtained peak value and the previously obtained peak value is different by referring to the lookup table 605, the gain is changed. If the correspondence between the peak value obtained this time and the peak value obtained last time is the same, the flow rate calculation unit 607
Perform the calculation to obtain the flow value.

Next, the programmable gain amplifier 601
A detailed description will be given of the case where the gain is changed. After determining to change the gain, the determination unit 603 of the microcomputer 609 determines and determines the gain corresponding to the obtained peak value by referring to the look-up table 605. The lookup table 605 stores the correspondence between the peak value and the gain for each predetermined range of the peak value. When the gain to be set in the programmable gain amplifier 601 is determined, the microcomputer 609 sends an instruction to the programmable gain amplifier 601 to set the determined gain. Programmable gain amplifier 6
In step 01, the designated gain is set by changing the state of the gain change switch in the program gain amplifier 601 or by changing the resistance value of the negative feedback loop of the programmable gain amplifier 601.

The downstream voltage value with the gain changed is different from the downstream voltage value before the gain is changed.
FIG. 7 shows that the peak value increases as the gain increases even at the same flow rate value. Therefore, when the gain is reduced by the gain change, the peak value measured by the changed gain is smaller than the peak value obtained before the gain change, and when the gain is increased, the peak value obtained before the gain change is obtained. The peak value is larger than the peak value.

Accordingly, the peak value due to the changed gain is determined again by the determining unit 603 of the microcomputer 609, and the gain corresponding to the peak value due to the currently changed gain corresponds to the peak value obtained last time. If the gain differs from the current gain, the gain is changed again. However, it is assumed that there is no change in the flow rate value before and after the gain change.

When the gain of the programmable gain amplifier 601 is in a steady state as a result of the above-mentioned gain change, a calculation process for obtaining a flow value as shown below is performed.

When performing the arithmetic processing, the flow rate calculating section 607 of the microcomputer 609 calculates the flow rate value by inputting the obtained peak value to the variable of the equation corresponding to the current gain. However, the formula for calculating the flow rate value differs for each gain, but a simple function such as a linear function Y = cX + d (where Y is a flow rate value, X is a peak value, and c and d are constants) regardless of the gain. Is set. In addition, the constants c and d are determined in advance by referring to the peak value-flow rate value characteristic of each gain of FIG. It is stored in the flow rate calculation unit 607.

A specific example will be described below with reference to FIG. When the peak value changes from (a) to (c), the flow rate calculation unit 607 changes the gain from 100 times to 50 times, then measures the peak value again, and the obtained peak value corresponds to the gain of 50 times. If so, the obtained flow rate value is calculated by substituting the obtained peak value into the variable X of the linear function expression with a gain of 50.

The flow rate value thus obtained is displayed on the display 123 or the like connected to the microcomputer 609.

However, in the present embodiment, as shown in FIG. 8, the hysteresis ABC in the peak value-flow rate characteristic is obtained.
D is provided. From the peak value-flow rate characteristic having the hysteresis ABCD, a gain setting with a width and a flow value calculation are performed for a peak value in a specific range.

Incidentally, an intermediate gain (for example, 75 times) may be provided to more finely set the peak value-flow rate value characteristics.

According to the second embodiment, the arithmetic processing in the microcomputer 609 is simplified by changing the gain of the programmable gain amplifier 601 so that the flow rate value and the peak value are linear functions, and the power consumption is reduced. Can be reduced.

When the conventional technique is used, since the flow rate value and the peak output value have a higher-order function relationship, the calculation processing by the flow rate calculation unit of the microcomputer is relatively large, the calculation time is long, and the power consumption is low. Was big. However, according to the first embodiment and the second embodiment, since the calculation of the flow rate value is a linear function, the amount of calculation in the flow rate calculation unit can be reduced. Therefore, the power consumption of the flow rate measuring device including the microcomputer can be reduced, so that the present invention is particularly suitable when a small battery such as a lithium battery is used as a power supply.

[0045]

As described above, according to the flow rate measuring device of the present invention, the flow rate sensor, the peak value detecting means, the A / D converter, and the peak value in accordance with the A / D converted peak value. A parameter changing means for changing a parameter for changing a peak value so that a relationship with a flow rate value becomes a linear function;
Processing means comprising a flow rate calculating means for calculating a flow rate value from the converted peak value by a predetermined linear function formula, and changing the pulse width of the heater drive pulse or the gain of the amplifying means to obtain the peak value. Can be a linear function relationship. As a result, there is an effect that the operation processing scale in the microcomputer is reduced and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow rate measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a look-up table according to the first embodiment.

FIG. 3 is a graph showing a relationship between a peak value and a pulse width according to the first embodiment.

FIG. 4 is a graph showing a relationship between a peak value and a flow value for each pulse width according to the first embodiment.

FIG. 5 is a graph showing a linear function for each peak value used in the flow rate calculation unit according to the first embodiment.

FIG. 6 is a view showing a flow rate measuring device according to a second embodiment of the present invention.

FIG. 7 is a graph showing a relationship between a peak value and a flow value for each gain according to the second embodiment.

FIG. 8 is a graph showing a linear function for each gain used in a flow rate calculation unit according to the second embodiment.

FIG. 9 is a block diagram showing a conventional flow measurement device.

FIG. 10 is a characteristic diagram showing a relationship between a peak value and a flow value.

[Explanation of symbols]

 Reference Signs List 101 upstream thermopile 103 downstream thermopile 105 micro heater 107 flow sensor 109 differential amplifier 111 peak hold circuit 113 A / D converter 115, 603 determination unit 117, 605 lookup table 119, 607 flow calculation unit 121, 609 microcomputer 123 Display 125 Heater drive circuit 127 Pulse generator 129 Lithium battery 601 Programmable gain amplifier

Claims (4)

[Claims] 1. A flow rate sensor comprising a heater, a downstream temperature sensor installed downstream of the heater, and an upstream temperature sensor installed upstream of the heater, and driving the heater. A heater drive circuit that outputs a drive pulse; a peak value detection unit that detects a peak value of a difference between outputs of the downstream temperature sensor and the upstream temperature sensor; and a peak value output from the peak value detection unit. A
An A / D converter for performing A / D conversion; and a parameter change for changing a parameter for changing the peak value so that the relationship between the peak value and the flow rate value becomes a linear function in accordance with the A / D converted peak value. And a processing means for calculating a flow rate value from the A / D-converted peak value by a predetermined linear function expression. 2. A pulse generating means for generating a pulse signal for generating the driving pulse, wherein the parameter changing means instructs the pulse generating means to change a pulse width of the driving pulse as the parameter. The flow rate measuring device according to claim 1, wherein: 3. An amplifying means capable of changing a gain for amplifying a difference between outputs of the downstream temperature sensor and the upstream temperature sensor, wherein the parameter changing means changes the gain of the amplifying means as the parameter. The flow rate measuring device according to claim 1, wherein an instruction is given to an amplification unit. 4. The parameter changing unit switches the parameter for each predetermined range of the peak value, and the flow rate calculating unit calculates the peak value and the flow value corresponding to each of the switched parameters by a linear function expression. 2. A flow rate value is calculated from a peak value.
3. The flow measurement device according to 1.