JP2002310763A - Flow-rate measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow-rate measuring device which performs a definite temperature compensation irrespective of an ambient temperature. SOLUTION: A sensor-coil-current detecting resistance 2 is connected in series with a sensor coil 1. A temperature sensor 3, a temperature-difference setting resistance 5 and a sensor-coil-current detecting resistance 4 are connected in series. A bridge circuit is composed of them. According to the temperature change of a resistor in the sensor coil 1 due to the ambient temperature of the sensor coil 1 or due to a fluid temperature, the difference between the electrical resistance value of the temperature sensor 3 and the electrical resistance value of the sensor coil 1 is controlled, and the influence of the ambient temperature of the sensor coil 1 with reference to a flow rate or the fluid temperature is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow measuring device.

[0002]

2. Description of the Related Art In general, a thermal type flow meter has a flow path of a fluid made of a high heat conductive material, and a pair of sensor coils are mounted on an outer periphery of the conduit along a flow path of the fluid, upstream and downstream. An electric current is applied to both sensor coils to thermally act on the fluid, and the mass flow rate is measured by utilizing the relationship between the exchange of heat quantity between them. In this type of thermal flow meter, when the ambient temperature or the temperature of the fluid pipe changes, the temperature difference between the sensor coil and the fluid and the resistance of the sensor coil also change, so that temperature compensation is required. As a fluid temperature compensation, a constant temperature difference method for maintaining a constant difference between the sensor coil temperature and the temperature of the temperature sensor has been conventionally proposed (Japanese Patent Laid-Open No. 1-150817). The constant temperature difference method utilizes that the amount of heat transmitted from the sensor coil to the fluid is proportional to the flow rate and the temperature difference between the sensor coil and the fluid.

[0003]

The conventional constant temperature described above
In the difference method, the sensor coil current: I_s, Sensor
Coil voltage: E_s, Sensor coil power: P_s= I_sE_s
= I_s ^Two× R_s, Sensor coil temperature: t_s, Sensor carp
Resistance: R_s= R_s0(1 + α_sΔt_s), Δt_s= (T
_s-T₀), Sensor coil current detection resistor: R_a,temperature
Sensor current: I_t, Temperature sensor temperature t_t, Reference temperature: t
₀, Δt_t= (T_s-T₀), Temperature sensor resistance: R_t=
R_t0(1 + α_tΔt_t), Temperature sensor current detection resistance: R
_bFrom the basic law of thermodynamics, the temperature t_aObject S
Temperature t_tConducted to the object T per unit time
Quantity P_sIs P, where H is the thermal resistance between the objects S and T._s= H
(T _s-T_t), The fluid and sensor
It is necessary to generate heat that is conducted to the surrounding structure of the coil.
Power P_sIs P_s= I_sE_s= I_s ^TwoR_sAnd the fluid flow
Quantity Q and temperature t_t(It is equal to the temperature sensor temperature
) Is approximated by the following equation (1).

[0004] _{P s = I s E s =} I s 2 R s = H 0 (t a -t t) + H q Q (t a -t t) ...... (1)

[0005]

(Equation 1)

[0006] (2) a sensor coil generated according to the temperature change of the sensor coil at a constant temperature difference formula to maintain a constant difference in temperature of the sensor coil temperature and the temperature sensor constant (t _a -t _t) from the equation Due to the temperature change of the resistance R _s = R _s0 (1 + α _s Δt _s ), the temperature influence of I _s cannot be sufficiently reduced.

For this reason, there is a problem that the relationship between the flow rate and the output of the flowmeter varies depending on the ambient temperature as shown in FIG.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a flow rate measuring device capable of performing constant temperature compensation regardless of the ambient temperature.

[0009]

According to the flow rate measuring apparatus of the present invention, a first temperature-dependent electric resistor is arranged in a flow path of a measurement object, and the first temperature-dependent electric resistor is fluidized by the first temperature-dependent electric resistor. A flow rate for measuring a flow rate of a fluid to be measured by measuring a current supplied to the first temperature-dependent electrical resistor for maintaining the temperature of the first temperature-dependent electrical resistor with respect to the amount of heat taken away A second temperature-dependent electrical resistor responsive to an ambient temperature or a temperature of a fluid, wherein the first temperature-dependent electrical resistance of the first temperature-dependent electrical resistor depends on an ambient temperature or a fluid temperature; Controlling a difference between an electric resistance value of the second temperature-dependent electric resistance and the first temperature-dependent electric resistance value in accordance with a temperature change of the body to thereby change the first temperature-dependent electric resistance with respect to a flow rate; Ambient or fluid temperature of resistor current Influence so as to reduce the.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a diagram showing a resistor constituting a bridge circuit of a thermal type flow measuring device according to an embodiment of the present invention. In FIG. 1, a sensor coil 1 is mounted on the outer periphery of a conduit 10 through which a fluid flows, and a fixed resistor 2 for detecting a sensor coil current is connected in series with the sensor coil 1 outside the conduit 10. A temperature sensor 3 for detecting an ambient temperature is disposed near the conduit 10. A fixed resistor 4 for temperature sensor current detection and a fixed resistor 5 for temperature difference are connected in series with the temperature sensor 3. Each of the sensor coil 1 and the temperature sensor 3 is a temperature-dependent electric resistor.

[0011] By connecting the two series circuits in parallel,
The electric bridge circuit shown in FIG. 2 is configured. The bridge circuit of FIG.
A connection point between the fixed resistor 2 and the sensor coil 1 and a connection point between the fixed resistor 4 and the fixed resistor 5 are connected to one end and the other end of the input of the operational amplifier 6, respectively. The output terminal of the operational amplifier 6 is connected to a connection point between the fixed resistor 2 and the fixed resistor 4.

Now, the resistance of the sensor coil 1 is set to R_s, Sensor
The resistance of the coil current detection resistor 2 is R_a, Temperature sensor 3
Of the current detection resistor 4 of R_b, Temperature sensor 3 resistance
To R _t, Temperature difference setting resistor between flow sensor coil and fluid
R of 5_cThen, in the circuit of FIG.
After taking the balance condition of the bridge circuit,
It is represented by

R _s = (R _a / R _b ) (R _t + R _c ) Power consumption of the flow rate sensor coil P _s = I _s E _s = I _s ² R _s
A fluid flow rate Q, the relationship between the flow rate sensor coil and the temperature difference between the fluid temperature sensor (t _s -t _t) is a general formula (11)
Wherein the flow sensor coil current I _s in (12), in particular is approximated by equation (13).

[0014] _{P s = I s E s =} I s 2 R s = F q {Q (t s -t t)} + F 0 {q (t s -t t)} ...... (11)

[0015]

(Equation 2)

I_sIs t_tNot be affected by
Is (t_s-T_t) = H (1 + α)_s0t _Three).

[0017] From the equilibrium condition of the bridge _{circuit, R s = (R a /} R b) (R c + R t) R t = R t0 (1 + α t0 t t) R s0 (1 + α s0 t s) = (R a _{/ R b) {R c +} R t0 (1 + α t0 t t)} t t = {t s (α s0 R s0) + R s0 - (R a / R b) (R c + R t0)} / {(R a _{/ R b) (α t0 R} t0)} {R s0 R b / R a - (R c + R t0)} _{[1 + t s (α t0 R} t0 -α s0 R s0 R b / R a) / {R R _{b / R a - (R c} + R t0)} ] = in _{(α t0 R t0) hR s0} (1 + α s0 t s) ...... (14) (14) expression holds regardless of t _s is, R _s0 R _b / R _a − (R _c + R _t0 ) = (α _t0 R _t0 ) hR _s0 (15) (α _t0 R _t0 −α _s0 R _{s0 Rb} / R _a ) / ｛R _s0 R _b / R _a − (R _c + R _t0 )｝ (16) From equations (15) and (16), R _b / R _a = ｛(α _{t 0} R _t0 ) / (α _s0 R _s0 )｝ (1−hα _s0 R _s0 ) (17) (R _c + R _t0 ) / R _t0 = (α _t0 / α _s0 ) ｛1-2hα _s0 R _s0 ｝ (18) From the equations (15) and (16), the resistances R _a and R
_b, and R _c (17) equation (18) by selecting so as to satisfy the equation, the effect of the temperature sensor the temperature of the sensor coil current can be almost eliminated. Note that the constant h
Determines the temperature difference between the sensor coil and the temperature sensor.

According to this embodiment, the relationship between the flow rate and the flow rate measurement output is not affected by the ambient temperature, as shown in FIG.

The same can be said for the electric bridge circuit shown in FIG.

[0020]

According to the present invention, a second temperature-dependent electric resistor which is sensitive to the ambient temperature or the temperature of the fluid is provided, and the second temperature-dependent electric resistor is controlled by the ambient temperature or the fluid temperature of the first temperature-dependent electric resistor. Controlling a difference between an electric resistance value of the second temperature-dependent electric resistor and the first temperature-dependent electric resistance value in accordance with a temperature change of the first temperature-dependent electric resistor;
Since the influence of the ambient temperature or the fluid temperature of the current of the first temperature-dependent electric resistor on the flow rate is reduced, a predetermined measurement output according to the flow rate can be obtained regardless of the ambient temperature. .

[Brief description of the drawings]

FIG. 1 is a diagram showing resistors constituting a bridge circuit of a thermal type flow measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a circuit connection of an electric bridge circuit of the thermal flow meter of the embodiment.

FIG. 3 is a diagram illustrating another electric bridge circuit.

FIG. 4 is a characteristic diagram showing flow rate (%) / flow meter output (%) using the ambient temperature of the thermal mass flow meter of the embodiment as a parameter.

FIG. 5 is a characteristic diagram showing a flow rate (%) / flow meter output (%) using the ambient temperature of a conventional thermal mass flow meter as a parameter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor coil 2 Sensor coil current detection resistor 3 Temperature sensor 4 Temperature sensor current detection resistor 5 Temperature difference setting resistor 6 Operational amplifier

 ──────────────────────────────────────────────────続 き Continued on front page F-term (reference) 2F035 EA09

Claims (1)

[Claims] 1. A first temperature-dependent electric resistor is disposed in a flow path of an object to be measured, and the first temperature-dependent electric resistance is reduced by the amount of heat taken by the fluid from the first temperature-dependent electric resistor. A flow rate measuring device that measures a current supplied to a first temperature-dependent electrical resistor for maintaining a temperature of a conductive electrical resistor and measures a flow rate of a fluid to be measured, the device being responsive to an ambient temperature or a temperature of a fluid. A second temperature-dependent electrical resistor to be provided, and the second temperature-dependent electrical resistor is changed according to a temperature change of the first temperature-dependent electrical resistor due to an ambient temperature or a fluid temperature of the first temperature-dependent electrical resistor. Controlling the difference between the electrical resistance value of the temperature-dependent electrical resistor and the first temperature-dependent electrical resistance value to influence the ambient temperature or the fluid temperature of the current of the first temperature-dependent electrical resistor on the flow rate; Characterized by reducing Flow measurement device.