JPS62280617A - Thermal type flow meter - Google Patents

Abstract

PURPOSE:To eliminate influence caused by variation in fluid temperature and to take an accurate measurement speedily by dividing an energy difference given between temperature sensing bodies provided in a fluid and a stationary area by energy given to the temperature sensing body in the stationary area and thus taking a measurement. CONSTITUTION:Temperature sensing resistance bodies 7S and 8S and heaters 7H and 8H are formed by thin film resistance body patterns on the bases and wafers of the heat sensing bodies 7 and 8 provided in the fluid flow area and stationary areas. Potentials VA1 and VA2 at connection points 33 and 34 and potentials VB1 and VB2 at connection points 35 and 36 of bridge circuits 17 and 18 including the resistance bodies 7S and 8S are inputted to control circuits 25 and 26 to put switching elements 27 and 28 with difference signals S1 and S2. Outputs P1 and P2 generated so as to hold the temperature sensing bodies 7 and 8 at the same constant temperature at any time are processed by the subtraction of a circuit 39 and outputs P1-P2 and P2 proportional to a flow rate are inputted to a dividing circuit 40. The circuit 40 performs arithmetic (P1-P2)/P2 to compensate the temperature influence of fluid and multiplying a value proportional to the flow rate by a constant to measure the accurate flow rate.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Industrial Application Field] The present invention relates to a thermal 11ft meter, and particularly relates to a fluid flow area in a flow path through which a fluid flows and a fluid flow area in the fluid flow area. The present invention relates to a thermal flowmeter in which a temperature sensing element is provided in each communicating fluid stationary region.

(Prior Art) As the flowmeter, for example, U.S. Pat. No. 2,859,617 is known. FIGS. One sensor 52 is provided in a fluid flow region 51 in which F flows, and the other sensor 55 is provided in a fluid stationary region 44 that communicates with this fluid flow region 51 and is shielded by a buff full 53 so that fluid F does not act directly. , both these sensors 52
．． 55 through leads 56 and 57 to resistor 58
．． 59 constitutes a prefuji circuit-3, and the voltage E is applied to the bridge circuit H via conductive wires 60 and 61. Note that 62 is a resistor for zero balance adjustment.

The flowmeter configured in this manner has the advantage of being able to compensate for temperature changes in the fluid and effectively correcting the zero point.

[Problem that the invention seeks to solve]

However, in the above-mentioned prior art, the two sensors 52 and 55 are incorporated into one bridge circuit 5 and are not configured to be individually temperature controlled, resulting in poor responsiveness, especially for gases. The drawback is that the responsiveness is not good. Another disadvantage is that the sensitivity changes depending on the temperature of the fluid to be measured, and therefore it is necessary to perform calibration with respect to the fluid temperature.

The present invention has been made with the above-mentioned considerations in mind, and its purpose is to provide excellent responsiveness and to perform accurate measurements without changing sensitivity depending on the temperature of the fluid to be measured. Our goal is to provide a thermal flowmeter that can

[Means for solving problems]

In order to achieve the above-mentioned object, the thermal flowmeter according to the present invention senses each of the temperature sensing elements provided in the fluid flow region in the flow path through which the fluid flows and the fluid stationary region communicating with the fluid flow region. Two constant-temperature control circuits each comprising a temperature-sensitive resistor and a heater are provided independently, and the constant-temperature control circuit always keeps the temperatures of both temperature-sensitive bodies equal and constant. The mass flow rate of the fluid in the flow path is determined based on the value obtained by dividing the difference in energy given to both temperature sensitive bodies by the energy given to the temperature sensitive body provided in the fluid stationary region. It is unique in that it measures .

[Effect]

In the above configuration, the constant temperature control circuits each including the two temperature sensitive resistors are each composed of a bridge circuit and an arithmetic circuit, and each constant temperature control circuit keeps the temperatures of the two temperature sensitive bodies equal and constant. It is controlled to remain constant. The output of each constant temperature control circuit indicates the energy required to maintain each rfA hot body at a constant temperature, and by dividing the difference by the energy given to the temperature sensitive body provided in the fluid static area, An output proportional to the fluid mass flow rate is obtained, with temperature effects compensated for.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 schematically show the structure of a thermal flowmeter according to the present invention. In both figures, ▪ is a block made of metal such as stainless steel or plastic, and a conduit 2.
2 are connected, and these block body l and conduit 2.2
A flow path 3 is formed through which a fluid F such as gas or liquid to be measured flows.

4 is an opening 5 formed in a part of the peripheral surface of the block body l,
This is a ceramic base body that is detachably installed via a rubber O-ring 6.

7.8 is 2 of the chip-shaped body held by the base body 4
These temperature sensing elements 7.8 each have the same configuration, for example, a silicon single crystal wafer is used as the base, and the temperature sensing resistor and heater are formed on this wafer by a thin film resistor pattern. . One planetary body 7 is provided in the fluid flow area 9 of the channel 3 through which the fluid F flows, and the other temperature sensing element 8 is connected to the fluid flow area 9 by a partition 10 to prevent the fluid F from directly acting on it. Shielded fluid stationary area 11
It is set in.

12, 12 are lead frames for supporting the temperature sensing elements 7, 8, 13... are lead wires made of gold wire, 14...
is an external connection line.

FIG. 3 is a circuit diagram showing the electrical connection relationship of the thermal flowmeter, in which 15 and 16 are the temperature sensing elements 7 and 16, respectively.
8 temperature sensitive resistor? 3.8S as each component of the bridge circuits 17 and 18, the defined temperature control circuits 15 and 16 are constructed of the same parts so as to have the same characteristics, and the temperature sensing elements 7. 8 heater 7
11.8H, respectively, so that the temperatures of the temperature sensing elements 7 and 8 are always equal and constant.

That is, one constant temperature control circuit 15 is a bridge circuit 1 composed of a temperature-sensitive resistor 7S and resistors 19, 21, and 23.
7, a control circuit 25 such as an operational amplifier, a switching element 27 such as a transistor, and a DC type a29.31. The other constant temperature control circuit 16
A bridge circuit 18 composed of a resistor 8S and resistors 20, 22, and 24, a control circuit 26 such as an operational amplifier, a switching element 28 such as a transistor, and a DC power supply 30.
．． It is composed of 32. Also, are resistors 19 to 24 temperature-sensitive resistors? A material having a sufficiently smaller temperature coefficient than 5.8S is used.

33 and 34 are temperature sensitive resistor 7S, 85 and resistor 1, respectively.
At the connection point with 9°20, the potential VAl+"AX is inputted as one input signal of the control circuit 25.26, respectively. 35.36 is connected to the resistor 21 and 23.2, respectively.
At the connection point between 2 and 24, the potential ■□+VIg is inputted as the other human input signal to the control circuits 25 and 26, respectively. The control circuits 25 and 26 respectively compare the input signals Va+ and Vll, and also compare the input signals Vat and Vat, and output control signals S+ and Si when there is a difference, respectively.

The switching elements 27 and 28 receive the control signals S+, St
By this switching operation, the temperature sensitive resistor 7S,
The power supply to 8S will be controlled on and off. The outputs P+ and Pg appearing at the respective connection points 37.38 between the switching element 27.28 and the heater 711.811 represent the energy supplied to the heaters 7H and 8H, respectively.

39 is input with the outputs P, , Pt, and (P+ Pg
) is a subtracter that performs the operation. The output (P+-Pg) of this subtraction circuit 39 is the temperature sensor 7 located in the fluid flow area 9.
In order to keep the temperature and the temperature sensing element 8 located in the fluid flow area 10 at the same and constant temperature, each type a29. It is proportional to the fluid flow rate of the fluid F flowing through the flow path 3 at the same time.

40 receives the output (P, -P,) and the output P□, and (P + -P x)/P! This is a divider that performs the following operation. The output of this arithmetic unit 40 (P + −P z
)/P z indicates the exact mass flow rate of fluid F with temperature effects of fluid F removed.

Next, the operation of the thermal flow meter having the above configuration will be explained.

First, when the fluid F is not flowing through the flow path 3, power is applied to the temperature sensitive resistors 7S and 8S from the power sources 31 and 32 via the bridge circuits 17 and 18, respectively, and both the temperature sensitive resistors 7S , 8S are held at a temperature determined by resistors 19 and 20, respectively. And the resistors 19, 2
Since the temperature characteristics of 0 are equal to each other, the temperature sensitive resistor 7S,
The temperatures of 8S will be equal, and therefore the outputs PI+P2 will be equal. As a result, the output of the arithmetic unit 40 becomes zero,
It can be seen that fluid F is not flowing.

Next, when the fluid F is flowing in the flow path 3, the temperature sensing element 7 located in the fluid flow area 9 is deprived of heat by the fluid F, but the temperature sensing element 8 located in the fluid stationary area lO is absorbed by the fluid F. Almost no heat is taken away by F. Therefore, the switching element 2
Energy is supplied from the power sources 29 and 30 via the temperature sensor 7.28, but as mentioned above, the amount of heat removed from the temperature sensor 7 is larger than that from the temperature sensor, so the constant temperature control circuit 15 and 16 Outputs P,,P! appear at connection points 37 and 38 as outputs, respectively. , PI > pg. The output P1. The difference in Pt (PI F is the fluid F
is proportional to the size of

The output (P+Pg) of the subtraction circuit 39 is input as one input signal of the division circuit 40, and the output P2
is manually inputted as the other input signal of the division circuit 40, and the calculation (P, -Pt)/Pt is performed in the division circuit 40. The output of the division circuit 40 (PDP/Pg is the fluid F
Since it is proportional to the fluid flow rate of fluid F that compensates for the temperature influence of
A fluid flow rate of

Note that the shape of the partition wall body 10 shown in FIG.
The amount of <'a is several tens of 17 si.
n or more), the rise may be made smaller.

FIG. 4 shows another embodiment of the present invention, which differs from the one shown in FIG. The point 34 is connected to one input terminal of the control circuit 26, and the connection point 35 of the resistors 21 and 23 of the constant temperature control circuit 15 is connected to the other input terminal of the control circuit 26. The operation in the case of this configuration is the same as that in the above embodiment, so a description thereof will be omitted.

〔Effect of the invention〕

As explained above, in the thermal flowmeter according to the present invention, each of the temperature sensing elements provided in the fluid flow area in the flow path through which the fluid flows and the fluid stationary area communicating with the fluid flow area is connected to the temperature sensing resistor. two constant temperature control circuits each comprising a body and a heater and each including the temperature sensitive resistor;
The constant temperature control circuit controls the temperatures of both temperature sensing elements so that they are always equal and constant, and the difference in energy given to both temperature sensing elements is applied to the temperature sensing element provided in the fluid stationary region. Since the mass flow rate of the fluid in the flow path is measured based on the value divided by the given energy, not only is the zero point corrected skillfully, but the response is also improved, especially when the fluid is a gas. It is possible to significantly improve responsiveness in these cases. Further, with respect to temperature changes in the fluid to be measured, calibration is required to a minimum, and therefore, it is possible to eliminate the adverse effects caused by changes in fluid temperature, so that accurate and rapid measurements can be performed.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, FIG. 1 is a sectional view of the main part, and FIG. 2 is taken along line mn of FIG. 1. iI sectional view, FIG. 3 is a circuit diagram, FIG. 4 is a circuit diagram according to another embodiment, and FIG.
6 and 6 show a conventional example, FIG. 5 is a sectional view, and FIG. 6 is a circuit diagram. 3... Channel, 7, 8... Temperature sensing element, 7S, 8S...
- Temperature sensitive resistor, 7H, 8H... Heater, 9... Fluid flow area, 11... Fluid stationary area, 15.16... Constant temperature control circuit.

Claims (1)

[Claims] In a thermal flowmeter in which a temperature sensing element is provided in a fluid flow area in a flow path through which fluid flows and a fluid stationary area communicating with the fluid flow area, each of the temperature sensing elements is replaced with a temperature sensing resistor and a heater. 2, each containing the temperature-sensitive resistor.
Two constant temperature control circuits are provided independently, and the constant temperature control circuit controls the temperature of both temperature sensing elements so that they are always equal and constant, and the difference in the energy given to each of the temperature sensing elements is reduced. . A thermal flow meter, characterized in that the mass flow rate of the fluid in the flow path is measured based on the value divided by the energy given to the temperature sensing element provided in the fluid stationary region.