JPH0447225A - Thermal type flow velocity sensor and fluidic flowmeter using the same - 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 [Industrial Application Field] The present invention relates to a thermal flow rate sensor (hereinafter referred to as a "flow sensor") and a fluidic flowmeter using this flow sensor.

[Prior Art] As shown in FIG. 3, a flow sensor includes a heater 2, a temperature sensor 3.3a, and an ambient temperature sensor 4 for detecting gas temperature inserted into a flow path l of a gas to be measured. The temperature rises from the gas salt detected by the ambient temperature sensor 4 and the heater 2
In this method, the flow velocity is measured by increasing the temperature of the flow rate and detecting the temperature change of the temperature sensor 3.3a. 5 in the diagram
6 is a heater drive circuit, and 6 is a flow rate detection circuit.

[Problems with the Prior Art] Therefore, if the gas composition (gas type) differs, the amount of heat released by the heater also differs, so the so-called sensitivity changes, causing measurement errors. Figure 4 shows the conventional 70 for 13A gas and air.
- Indicates the sensitivity of the sensor.

Therefore, conventionally, the sensitivity of the flow sensor must be adjusted in advance according to the gas type, or this procedure is cumbersome.

In addition, in the case of city gas, several types of gas are mixed to adjust the calorie content, and if the mixture types are different, the sensitivity may be affected, so it is not necessary to adjust the sensitivity of the flow sensor each time. Practically impossible.

From this point of view, it is desired to propose a flow sensor that does not require sensitivity adjustment each time.

[Means for Solving the Problems] The present invention is proposed in view of the above points, and its configuration is as follows.

1. Thermal flow rate sensor configured to drive the heater with constant power.

2. A drive electronic circuit that drives a heater inserted between two temperature sensors with constant power; a detection electronic circuit that detects a change in temperature caused by the flow velocity detected by the temperature sensor as a resistance value; A fluidic flowmeter that combines a flow rate calculation circuit that calculates the flow rate from the resistance value detected by the detection electronic circuit, a thermal flow rate sensor consisting of the following, and a fluidic element.

In addition, in the above two gas flowmeters, if the flow rate above a certain flow rate is detected by a fluidic element, and the flow rate below is detected by using the flow sensor described in 1, the characteristics of each will be You can take advantage of it.

[Operation] A constant power is supplied to the heater to generate heat, and two temperature sensors detect the temperature change, or resistance value, on the upstream and downstream sides of the heater, and the flow rate is calculated based on the change in resistance value. . In this way, when the heater is driven with constant power, even if the amount of heat absorbed by the gas changes due to a change in the composition of the gas, the heater temperature rises and falls accordingly, and the amount of heat radiated from the temperature sensor does not change. As a result, the same sensitivity is exhibited even for gases of different compositions that flow at the same velocity. FIG. 2 shows the sensitivity of the flow sensor of the present invention to 13A gas and air, and it can be seen that the sensitivity is improved compared to the conventional flow sensor shown in FIG. 4 in which the heater temperature is kept constant.

[Example] FIG. 1 shows a flow sensor according to the present invention. 1 is a gas flow path, 2 is a heater, 3.3a is a temperature sensor, 7 is a heater drive circuit for driving the heater 2, and constant power is supplied from this circuit 7 to the heater 2. The temperature sensor 3.3a detects the flow velocity, and based on this, the flow rate detection circuit 6 calculates the flow rate.

[Effects of the present invention] According to the present invention, as described above, since the heater is driven with constant power instead of raising the heater to a constant temperature,
It is possible to obtain a 70-sensor with good sensitivity that is not affected by changes in gas composition, ie, heat dissipation characteristics of the fluid to be measured.

[Brief explanation of drawings]

Figure 1 is an example diagram of the flow sensor according to the present invention, Figure 2 is an explanatory diagram showing the output characteristics (sensitivity) of 13A gas and air when the flow sensor of the present invention is used, and Figure 3 is a conventional diagram. FIG. 4 is an explanatory diagram of the output characteristics of 13A gas and air when a conventional flow sensor is used. l...Gas passage 2...Heater 3.3a...Temperature sensor 6...Flow rate detection circuit 7...Heater drive circuit (sensitivity) Figure 1, Figure 2, Figure 3, Section II ! J4 diagram

Claims (1)

[Claims] 1. A thermal flow rate sensor configured to drive a heater with constant power. 2. A drive electronic circuit that drives a heater inserted between the two temperature sensors with constant power, and a detection electronic circuit that detects a change in temperature caused by the flow velocity detected by the temperature sensor as a resistance value; A fluidic flowmeter that combines a flow rate calculation circuit that calculates the flow rate from the resistance value detected by the detection electronic circuit, a thermal flow rate sensor consisting of the following, and a fluidic element. 3. The fluidic flow meter according to claim 2, wherein the flow rate above a certain flow rate is detected by a fluidic element, and the flow rate below is detected using the thermal flow rate sensor according to claim 1.