JPS594263Y2 - Temperature difference measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring the difference in temperature between two locations using a resistance temperature detector.

In conventional temperature difference measuring devices using resistance temperature detectors, the resistance of the conductor from the detection end at the measurement site to the converter that processes the signal is added to the resistance temperature detector, and the temperature difference is detected by the resistance of the resistance thermometer. Due to the difference in distance to the two measurement sites, the resistance of the conductor wires differs between the two resistance temperature sensors, which has the disadvantage of causing errors.

The present invention provides a device that can effectively eliminate the influence of the conductor resistance as described above and accurately measure the temperature difference between two locations with a simple configuration.

FIG. 1 is a connection diagram showing one embodiment of the device of the present invention.

In the figure, Rtl is a three-wire resistance temperature detector placed at the first measurement location, Rt2 is a three-wire resistance temperature detector located at the second measurement location, 11□, l 12. l 13
are the conductors of Rt1, and 120, 12□, 123 are the conductors of Rt1, respectively.
The conductors of t2, al, bl, and CI are the Rt1 (7) conductor terminals, a2. b2. C2 are respective conductor terminals of Rt2.

The conductor terminal a1 is connected to the current source ■, C1 is connected to a2, and C2 is connected to the reference point.
→１１□→R1,→１１３→c１→a2→１２□→R1
It is configured to flow along the path 2→l 23→C2.

OPl and O20 are each operational amplifiers.

The conductor terminal a1 is connected to the inverting input terminal (←) of OPl via the arithmetic resistor R1, and the output terminal of O20 is connected via the arithmetic resistor R2, and the non-inverting input terminal (T)
A conductor terminal b1 is connected to the terminal b1.

Further, a calculation resistor R3 is connected between the input and output terminals of O20.

O20 has a non-inverting input terminal (1) connected to a conductor terminal b2, and an inverting input terminal (-) connected to a voltage dividing point of operational resistors R4 and R5 that divide the output of O20.

In the device of the present invention constructed in this way, the current i from the current source ① is Rtl whose signal source is the calculation resistor R1.

Rt, 2. l□1. l□3. l 21. The resistor R1 is selected to be sufficiently large compared to the resistor R123.
There is almost no shunt to the side, and since the input impedances of OPl and O20 are sufficiently large, there is almost no shunt of current to the non-inverting input terminal (1) side of OPl and O20.

Also, the conductor 11 of Rtl. The resistances of 112 and l 13 are almost equal, and this is rl, and the conductor 120 of Rt2 is
．． l 22. The resistances of terminals a1 and 23 of the conductive wire are also almost equal, and if this is designated as r2, The voltages El, R2, and R3 generated at bl and cl, respectively, are given by the following equations.

Ell(2rl + 2r2 + RJ + R
t2) (R2= 1(rl + 2rz + RthI+ Rt
2) (2) R3= t (r2+
Rt2) (3)
Then, the output voltage Eo#i of the operational amplifier *OPt is given by, and the output E4 of the operational amplifier oP2 is also given by f, so (

(No.

(5).

(4).

From equation (5), the output voltage Eotj is obtained, where: 2R1, R2, R3(η 3R4, R5 RJ-Rt2)i
(The influence of the conductor resistances r1 and r2 can be effectively removed, and an output voltage Eo corresponding only to the difference in resistance value between the resistance temperature sensors R11 and R42 can be obtained.

Therefore, the measuring resistor Rt1. If Rt2 is a copper resistance temperature sensor, the resistance value is linear with respect to temperature, so
If the current i is constant, the output voltage Eo is, If the output voltage Eo#i, Eo = K (T I -72)
(2) However, K is a constant, and the temperature difference between two places can be accurately measured without being affected by the resistance of the conductor.

FIG. 2 is a connection diagram showing another embodiment of the device according to the present invention, in which platinum resistance temperature detectors are used as Rtl and Rt2.

As is well known, platinum resistance thermometers have a nonlinear relationship between resistance value and temperature, and usually T″:k (Rt+αRt2)
(1:0 However, klα is approximated by a constant, and depending on the temperature, the
The difference in the resistance values of the two thermometers is different.

In this embodiment, such nonlinearity is corrected so that temperature differences can be measured accurately.

The embodiment shown in FIG. 2 differs from the embodiment shown in FIG. The main feature is that OP4 is used as the main component, and the output current i is changed according to the values of Rtl and Rt2.

That is, the reference voltage Es is applied to the inverting input terminal (-) of O20 via a calculation resistor R6, and the output E4 of O20 is applied via a calculation resistor R7.
The voltage E5 of the conductor terminal C1 is applied to the non-inverting input terminal (1).

Further, the output E6 of O20 is fed back to the inverting input terminal (-) via the operational resistor R8.

Therefore, the output E6 of O20 is given by the following equation.

Note that the voltage E5 of the conductor terminal C2 is given by the following equation.

R5= <zrz + atz) i
('1 Also, O12 is its inverting input terminal (
The output E6 of O20 is applied to Y via the operational resistor R9, and the voltage E2 of the conductor terminal b2 is applied to the non-inverting input terminal (→).

Also, since the output E7 of O12 is fed back to the inverting input terminal (-) via the operational resistor R1o, the output E7 becomes.

This output E7 is converted into a current i by a resistor Rf as shown in the following equation, and is supplied to the temperature measuring resistors R41 and Rt2.

Therefore, from each equation, the output current i of current source (2) is given by the following equation.

If the values of the operational resistors R6 to R1o are selected so as to satisfy ゛, R6=R7=2RB R9・Rlov), the output current i becomes R11
It changes according to the value of °R42.

Therefore, the output voltage Eo of O40 is becomes.

And in the case of a platinum resistance thermometer, holds true, so (
Equation 19) can be expanded as shown in Equation (21).

From equations (11) and (21), the output voltage Eo is as follows, the nonlinearity of the platinum resistance temperature sensor is corrected, and an output voltage that is accurately proportional to the temperature difference is obtained.

As explained above, according to the present invention, a temperature difference measuring device that can accurately measure the temperature difference between two locations without being affected by the resistance of the conductor wire can be obtained with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing one embodiment of the device of the present invention, and FIG. 2 is a connection diagram showing another embodiment of the device of the present invention. Rtl, R42...Resistance temperature sensor, OP1~OP
4...Operation amplifier, R1~RIO...
Arithmetic resistance, Rf...Resistance, ■...Current source, ■...Voltage source.

Claims (4)

[Scope of utility model registration request] (1) A 3-wire resistance temperature detector placed at the first measurement location, a 3-wire resistance temperature detector placed at the second measurement location, both resistance bulbs, and each temperature measurement means for connecting the conductors at both ends of the resistor in series to a current source, the remaining conductors of the first resistance temperature detector being connected to the non-inverting input terminal, and a current source for the first resistance temperature detector; A first operational amplifier whose side conductor is connected to the inverting input terminal via the operational resistor, and a second operational amplifier whose remaining conductor of the second resistance temperature detector is connected to the non-inverting input terminal.
an operational amplifier, an operational resistor for voltage-dividing the output of the second operational amplifier and returning it to its inverting input terminal, and an operational resistor for applying the output of the second operational amplifier to the inverting input terminal of the first operational amplifier. and an operational resistor for feeding back the output of the first operational amplifier to its inverting input terminal. A temperature difference measuring device characterized in that it is not affected by resistance. (2) The temperature difference measuring device according to claim 1, characterized in that a constant current source is used as the current source. (3) The temperature difference measuring device according to claim 1, which is a registered utility model, characterized in that it uses a current source whose output current changes depending on the resistance values of the first and second resistance temperature sensors. (4) A calculation resistor is provided between the input and output terminals, the reference voltage is applied to the inverting input terminal via the calculation resistance, and the output of the second operational amplifier is applied via the calculation resistance, and the A third operational amplifier having an inverting input terminal supplied with the potential at the connection point of the first and second resistance temperature detectors, and a third operational amplifier having an operational resistor between the input and output terminals, a fourth operational amplifier to which the output of the operational amplifier is applied via the operational resistor and the potential of one end of the first resistance temperature detector is applied to the non-inverting input terminal; and the output voltage of the fourth operational amplifier. Temperature difference measurement according to claim 1 of the utility model registration claim, characterized in that a current source configured with a resistor for converting into current and supplying the current to the first and second resistance temperature sensors is used. Device.