JPS5816128B2 - netsushikiriyuryokei - Google Patents

Description

[Detailed Description of the Invention] This invention measures the flow rate of the fluid by inserting a pair of self-heating thermometers into a fluid flow path and detecting the difference in the amount of heat transferred from the two-side heating body to the fluid. This relates to a type of thermal flow meter.

In a conventional thermal flow meter that has a pair of self-heating temperature sensors, a bridge is constructed with the temperature sensors on two sides, and the heating elements on both sides are caused by the difference in the amount of heat transferred from each temperature sensor to the fluid. An electrical output corresponding to the flow rate is extracted using the temperature difference (that is, the difference in resistance value).

With such a configuration, accurate measurements can be obtained when the fluid pressure is high, but as the pressure decreases, the natural convection of the fluid absorbs less heat, causing the temperature of the thermometer to rise. As a result, measurement errors become significant.

An object of the present invention is to make each of the two self-heating type thermometers one side of an independent bridge circuit, and by controlling the temperature of the self-heating type thermometer to a constant value, the pressure of the measured value is It is an object of the present invention to provide an improved thermal flow meter that eliminates dependence and allows flow measurements to be obtained with sufficient accuracy even when fluid pressure is low.

An embodiment of the invention will be described with reference to the drawings.

The pipe indicated by the reference numeral 1 in the figure is for forming a fluid flow path therein, and in order to measure the flow rate of the fluid flowing within this flow path, a resistance heating element having appropriate temperature-resistance characteristics is used. A pair of self-heating thermometers 2a and 2b are provided.

The first temperature measuring element 2a constitutes a bridge circuit 6a together with resistors 3a, 4a, and 5a, and generates heat with a current from a power source 7a.

Further, a differential amplifier 8a is provided to detect the potential difference between two opposing points of the bridge circuit 6a, and the output of the differential amplifier 8a is supplied to a current controller 9a. It has become.

This current controller 9a is composed of a variable resistance element whose resistance value changes depending on, for example, the output of the differential amplifier 8a.

That is, the current supplied from the power source 7a to the temperature measuring element 2a is controlled so that the voltage between its input terminals becomes zero (the bridge circuit is balanced).

As a result, the temperature measuring element 2a is operated to maintain a constant temperature at all times.

That is, when the resistance value of the temperature sensing element 2a changes due to a temperature change due to exchange of thermal energy with the fluid (1) For example, when the resistance value of the temperature sensing element 2a decreases, the bridge circuit 6a becomes unbalanced and faces each other. A potential difference occurs between the two points.

The resistance value of the current controller 9a is changed by the output of the differential amplifier 8a which detects this potential difference, and the current flowing through the temperature measuring element 2a is controlled to restore the temperature of the temperature measuring element to a constant temperature.

As a result. The resistance value of the temperature measuring element 2a returns to the used value, and the bridge circuit 6a becomes in an equilibrium state.

At this time, the potential obtained at one end of the temperature measuring element 2a corresponds to the current.

A similar circuit is also provided for the second temperature measuring body 2b.

This circuit element is the same as that provided for the first temperature measuring body 2a.

The symbol a attached to the reference numerals will be shown in place of b, and the explanation thereof will be omitted.

Then, a potential corresponding to the flow rate obtained at one end of the temperature measuring elements 2a and 2b in both bridge circuits 6a and 6b is taken out from the output terminals 10a and 10b. , 10b
The output between is used as a flow rate measurement of the fluid flowing through the channel.

As explained above, according to the present invention, a pair of self-heating temperature measuring elements are placed in a fluid flow path.

Because the temperature is controlled so that it is always constant.

Even when the pressure of the fluid is extremely low, there is no temperature increase due to the reduced heat transfer to the fluid, so accurate measurement values are always obtained, and the structure is extremely simple.

[Brief explanation of the drawing]

The drawing is an electrical circuit diagram of a thermal flowmeter according to an embodiment of the present invention. 1...Pipe, 2at2b...Temperature measuring element, 3a to 5a, 3b to 5b...Resistance, 6at6
b...Bridge circuit, 7at7b...
Power supply, 8at8b...Differential amplifier, 5at9b
...Current controller, 10a. 10b...Output terminal.

Claims (1)

[Claims] 1 A pair of self-heating thermometers placed in a fluid flow path, two bridge circuits each having each of the above self-heating thermometers as one side, and each of the above self-heating thermometers. a power supply provided separately for each of the self-heating type thermometers to generate heat by passing a current through them; and two differential amplifiers for detecting the potential difference between two opposing points of each of the bridge circuits. , corresponding to the self-alloying thermometer so as to control the current supplied to each of the self-heating thermometers in order to receive the output of each of the differential amplifiers and balance the bridge circuits. A thermal flowmeter comprising a current controller provided separately for each, and an output terminal for taking out the potential difference between the two bridge circuits as a measured value of the flow rate of the fluid flowing through the flow path.