JPH0443918A - Flowmeter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a flow meter that measures the flow rate of gas using a flow sensor, and in particular measures the thermal conductivity of gas and uses the thermal conductivity to determine the gas composition. This invention relates to a flow meter that performs correction.

[Conventional technology]

Conventionally, in a gas meter using a flow sensor, a so-called micro flow sensor, in order to correct gas composition fluctuations, for example, the method shown in Japanese Patent Application No. 1-160587 is used to correct gas composition fluctuations using a dedicated micro flow sensor for gas composition correction. The thermal conductivity and ratio were measured, and corrections were made using a correction formula.

[Problem to be solved by the invention]

However, in addition to the sensor that measures the flow rate, this method requires a separate gas composition correction sensor installed in a static atmosphere, and also requires complex signal processing for correction.

The present invention has been made in view of the above points, and its purpose is to provide a flowmeter with improved measurement accuracy by easily correcting gas composition fluctuations using one sensor. .

[Means to accomplish the task]

In order to achieve the above object, the present invention provides the upstream of the flow path,
Using a flow sensor that has a temperature measuring resistor provided downstream and a heating resistor provided between the temperature measuring resistors, this flow sensor detects the temperature difference between the temperature measuring resistors and determines the gas flow rate based on the output. In the flow meter to be measured, means for measuring a voltage corresponding to the temperature of each of the temperature-measuring resistance sections, and means for calculating a value corresponding to a base temperature rise of the temperature-measuring resistance section from each of the voltages; The device is equipped with means for calculating a correction coefficient based on this base temperature rise, and means for multiplying the flow rate signal determined in advance by the correction coefficient, thereby calculating the corrected flow rate. [Function] The present invention In this method, the thermal conductivity of the gas can be measured using a single sensor placed in the flow of the flow path, and the gas composition can be corrected using the thermal conductivity.

[Example] Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of a flowmeter according to the present invention. In the same figure, 1 is a flow sensor that detects the flow rate of gas, and this flow sensor 1 is, for example, as shown in FIG.
It consists of temperature sensors 11 and 12 as temperature measuring resistors provided on the upper upstream side and downstream side, respectively, and a heater 13 as a heat generating resistor provided between these sensors 11 and 12. Openings 14, 15' and 16 for etching are provided on the surface of the substrate 10, and the lower sides of the temperature sensors 11, 12 and the heater 13 are connected to the openings 14 to 14 provided on the surface of the substrate. By etching through the silicon substrate 16, a gap 17 is formed which communicates both the openings 14 and 15, and a temperature sensor 11 is placed above the gap 17 while being spatially isolated from the silicon substrate 10. ,12
A bridge portion 18 is formed in which the heater 13 is thermally insulated.

In the flow sensor l having such a structure, when the gas to be measured flows from the direction of the arrow 21 shown in the figure while the heater 13 is heated to a certain high temperature, the upstream temperature sensor 11
is cooled and its temperature decreases, whereas the temperature sensor 1 on the downstream side
2, heat conduction from the heater 13 is promoted using the gas flow as a medium, and the temperature rises, resulting in a temperature difference. For this reason, when these temperature sensors 11 and 12 are installed on each side of the bridging circuit 2, the bridging circuit 2 converts the temperature difference into a voltage, and can detect the flow rate, that is, the flow rate of the gas based on the voltage. In FIG. 2, reference numeral 19 denotes an ambient temperature-measuring resistance element, and 20 denotes a protection made of a material such as silicon nitride with low thermal conductivity in order to protect elements such as temperature sensors 11 and 12 formed on the silicon substrate 10. It is a membrane.

Further, 2 is a bridge circuit composed of upstream and downstream temperature sensors 11 and 12 of the flow sensor 1 and a resistor 3.4, and 5 corresponds to the temperature obtained from each sensor 11 and 12 of this bridge circuit 2. 6 is a multiplexer that receives the output of this amplifier 5 and the voltage of each of the temperature sensors 11 and 12 as input; 7 is an A/D converter; and 8 is an arithmetic operation unit. It is a device.

This calculation device 8 includes each temperature sensor 11 of the bridge circuit 2.
, 12 is input to the amplifier 5, and the output corresponding to the temperature difference between the temperature sensors 11 and 12 is taken out.The output is inputted to the multiplexer 6 and the A/D converter 7, and the flow rate is adjusted based on the output. Measure. Then, each voltage obtained from the temperature sensor 11.12 is inputted via the multiplexer 6 and the A/D converter 7, and from each voltage, the output voltage of the temperature sensor 11.12 is adjusted according to the temperature rise. At the same time, a correction coefficient is calculated from the base temperature increase, and the calculated flow rate is multiplied by this correction coefficient to calculate the corrected flow rate.

Next, the operation of the configuration of the above embodiment will be explained with reference to FIGS. 3 to 6.

First, in FIG. 3, the flow rate measurement by the flow sensor 1 is performed by transmitting the heat generated when the temperature is raised by Th degree Celsius above the ambient temperature by the heater 13 to each temperature sensor 11 and 12.
The temperature of each sensor 11, 12 is increased by Ts°C. Then, due to the gas flow, that is, the flow rate F, the temperature of the upstream temperature sensor 11 is cooled by ΔRuf°C, and the temperature of the downstream temperature sensor 12 is increased by ΔR□°C. This results in
From the prefuji circuit 2, the temperature difference Δ between the temperature sensors 11 and 12 is detected.
An output corresponding to R□-ΔRa'f is extracted.

At this time, the outputs V, , Vu of each temperature sensor 11, 12 change as shown in FIG. 4, and this change can be approximated by a straight line as shown in FIG. Therefore, these sensors 1
Changes from the reference temperatures of 1 and 12 can be expressed by rates of change α and β.

On the other hand, the thermal conductivity of hydrocarbon gases measured by micro flow sensors varies depending on the gas type.

Physical property constants such as specific heat are different. The above patent application Hei 1-16058
In No. 7, the thermal conductivity and specific heat are measured and corrected using a gas composition correction sensor placed in another stationary gas. The difference in thermal conductivity changes the temperature rise when the sensor's heater is on and the flow rate is zero, that is, the base temperature rise, and the difference in the output signal is proportional to the temperature rise. However, the present invention attempts to simply measure and correct only this thermal conductivity.

That is, in FIG. 6, (al represents the operation of a certain gas A at a flow rate F. Here, the base temperature rise of the flow sensor 1 is T, and the flow rate signal is fl.
bl represents the behavior of gas B at flow rate F. Similarly, the base temperature rise is T5. Let the flow rate signal be fh. At this time, f
-/T-#fb/Tb. Therefore, if gas B in FIG. 6(b) is a standard gas, the true flow rate f to be determined is fb = (f-/Tm)Tb... (1
). However, T can be determined using the temperatures 'ru, Ta and coefficients α and β of each temperature sensor 11.12. At this time, the temperatures T, , T of each temperature sensor 11, 12 are determined according to FIGS. 5 and 6.

is expressed by the following formula.

T, =T, -βF...(2) Ta
=T −+αF (3) Transforming these equations (2) and (3), αT, −αT, = −α
βF ・ ・ ・ ・(4) βTd −βT, = α
βF ・ ・ ・ ・(5) As a result, T can be found using the following equation.

αTu+βT4−(α+β)T.

A temperature difference of 1.12 is detected by the bridge circuit 2, and its output is input to the arithmetic unit 8 to determine the flow rate f1 in advance. The temperatures T, , T of these temperature sensors 11 and 12 are
, the voltages V, ,V corresponding to ,.

The base temperature rise T of the temperature sensors 11 and 12 is calculated from each voltage V, , V, and the correction coefficient k (=Tb/T,;
After calculating the flow rate (Tb is known), by multiplying the predetermined flow rate f by this correction coefficient, the corrected flow rate f can be taken out from the calculation device 8 as a correction output. [Effects of the Invention] As explained above. As described above, according to the present invention, the thermal conductivity of the gas is measured using one flow sensor placed in the flow of the flow path, and the gas composition is corrected using the thermal conductivity. This has the effect of effectively correcting measurement errors due to the gas composition of the flow rate and improving accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an embodiment of a flow meter according to the present invention, FIGS. 2 fa) and (b) are a perspective view showing the structure of the flow sensor in FIG. 1, and its r-vi sectional view;
Fig. 3 is a diagram showing the operating principle of the flow sensor in Fig. 2, Fig. 4 is a diagram showing the characteristics of the sensor output with respect to the flow rate of the flow sensor in Fig. 2, and Fig. 5 is an approximate characteristic diagram of Fig. 4. FIG. 6 is a diagram showing the temperature distribution of each element of the flow sensor for explaining the operation of the above embodiment. 1...Flow sensor, 2...Bridge circuit, 5...
・Amplifier, 6... Multiplexer, 7... A/D converter, 8... Arithmetic unit, 11, 12... Temperature sensor (
temperature measuring resistance), 13... heater (heating resistance). Third! ! 1 Figure 4 Figure 5 Figure 2 (G) (b)

Claims (1)

[Claims] A flow sensor is used that has a temperature-measuring resistor provided upstream and downstream of a flow path, and a heat-generating resistor provided between the temperature-measuring resistors, and the flow sensor measures the temperature difference between the temperature-measuring resistors. A flow meter that detects and measures the flow rate of gas based on the output thereof includes means for measuring a voltage corresponding to the temperature of each of the temperature-measuring resistors, and a rise in the base temperature of the temperature-measuring resistor from each voltage. , a means for calculating a correction coefficient based on this base temperature increase, and a means for calculating a corrected flow rate by multiplying a flow rate signal obtained in advance by the correction coefficient. Flow meter.