JPH0862056A - Resistor type temperature measuring circuit - Google Patents

Abstract

PURPOSE: To realize highly accurate temperature measurement by eliminating the influence of wiring resistance and the like. CONSTITUTION: A temperature measuring resistor 1 is connected, at one end thereof, with a first lead wire 21 and, at the other end thereof, with second and third lead wires 22, 23 wherein the second lead wire 22 is connected with reference resistors 31, 32. A current is fed from a current source 5 to the first lead wire 21 or the reference resistors 31, 32 and the measurement data is passed through an amplifier 6, an A/D converter 7 and a processing means 8 and stored in a memory 9. The processing means 8 performs predetermined operation, e.g. subtraction, to remove the wiring resistance thus measuring the temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance type temperature measuring circuit which measures temperature using a temperature measuring resistor such as platinum.

[0002]

2. Description of the Related Art When measuring a temperature using a resistance temperature detector, industrially, so-called three conductors are connected to the resistance temperature detector to pass an electric current, and the voltage drop across the resistance temperature detector is reduced. The temperature is measured by measuring the voltage and changing the resistance value.

[0003]

However, since the resistance of the lead wire connected to the resistance temperature detector causes a measurement error,
It is necessary to remove the influence of this wiring resistance.

In view of the above points, the present invention is to provide a resistance type temperature measuring circuit capable of highly accurate measurement by removing wiring resistance.

[0005]

According to the present invention, there is provided a first conductor wire connected to one end of a resistance temperature detector, and a second conductor wire and a third conductor wire connected to the other end of the resistance temperature detector. At least one reference resistance connected to the second conducting wire and a changeover switch for switching and supplying a current from the current source to the first conducting wire or the reference resistance are provided, and the third conducting wire and the changeover switch are provided. It is a resistance type temperature measuring circuit that takes out the output from the space.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural explanatory view showing an embodiment of the present invention. In the figure, a first conducting wire 21 having a resistance value r1 is connected to one end of a resistance temperature detector 1 such as platinum, a second conducting wire 22 having a resistance value r2 and a third conducting wire 21 having a resistance value r3 are connected to the other end. The conductor wire 23 is connected. The third conducting wire 23 is grounded, and the second conducting wire 22 is provided with a first reference resistor 31 having a resistance value Ro of 0 ° C. and a resistance Rs corresponding to, for example, a span, if necessary. The second reference resistor 32 is included. Then, switches (which may be contacts) S1, S2, and S3 for switching and supplying the current i from the current source 5 are included in the first conducting wire 21, the first reference resistor 31, and the second reference resistor 32. A changeover switch 4 is provided.

Then, the output voltage taken out between the connection point between the changeover switch 4 and the current source 5 and between the third conducting wire 23 is amplified by the amplifier 6 and converted into a digital signal by the AD converter 7. , ΜCPU, and the like, each measurement data is stored in the memory 9 through the processing means 8, and the processing means 8 performs predetermined arithmetic processing.

In the case of measurement, by controlling the drive by the processing means 8 and the like, when only the switch S1 of the changeover switch 4 is closed, the current i1 from the current source 5 is transferred to the first conducting wire 21,
The resistance due to the contact of the switch S1 etc. is ro (the switches S2 and S3 are ro)
Then, the output voltage e1 corresponding to the voltage drop is given by the following equation.

E1 = i1. (Ro + r1 + Rt + r3) (1) This output e1 is stored in the memory 9 via the amplifier 6, the AD converter 7, and the processing means 8. The same processing is performed thereafter.

Next, when only the switch S2 of the changeover switch 4 is closed, the current i2 of the current source 5 becomes the first reference resistance 3
It flows through the first, second conductor wire 22, and the third conductor wire 23, and the output voltage e2 of the following equation is obtained.

E2 = i2 (ro + Ro + r2 + r3) (2) Similarly, when only the switch S3 of the changeover switch 4 is closed, the current i3 becomes the second reference resistor 32, the second conductor r2,
The third conducting wire r3 and the flow output voltage e3 of the following equation is obtained.

E3 = i3 (ro + Rt + r2 + r3) (3) Here, the resistance values of the conductors 21, 22 and 23 are equal and r =
r1 = r2 = r3, and the currents are also equal i = i1 = i2
= I3, (1), (2), (3), the equations are as follows.

E1 = i (Rt + 2r + ro) (4) e2 = i (Ro + 2r + ro) (5) e3 = i (Rs + 2r + ro) (6) Here, these measurement data are read from the memory 9 by the processing means 8. By performing the subtraction process of the expression (5) from the expression (4), the value e4 of the following expression is obtained.

E4 = i · (Rt−Ro) (7) According to this, influences of wiring resistance including connection resistance of the conductive wires 21, 22, 23 and contact resistance of the connector and the contact resistance of the switch are eliminated, A correct output from 0 ° C is obtained, and this can be converted into temperature for temperature measurement.

Next, the processing means 8 reads out from the memory 9 to perform an operation for obtaining the difference ratio of the following equations from the equations (4), (5) and (6) to obtain the output e5. Good.

E4 = K. (E1-e2) / (e3-e2) = K. (Rt-Ro) / (Rs-Ro) (8) According to the equation (8), the current i is erased, Even if the current source 5 fluctuates due to consumption of a power source such as a battery, it is less affected and temperature can be measured. Note that K is a constant.

[0017]

As described above, according to the present invention, since the changeover switch is switched to supply the current to the resistance temperature detector and the reference resistance, the influence of the wiring resistance of the conducting wire and the contact resistance of the switch is not affected. It can be removed and highly accurate temperature measurement becomes possible. Further, the influence of the fluctuation of the current source is small, and it is suitable for measurement using a power source such as a battery.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resistance temperature detector 21, 22, 23 Conductor wire 31, 32 Reference resistance 4 Changeover switch 5 Current source 6 Amplifier 7 A-D converter 8 Processing means 9 Memory

Claims (1)

[Claims] 1. A first conductive wire connected to one end of a resistance temperature detector, a second conductive wire and a third conductive wire connected to the other end of the resistance temperature detector, and a small amount connected to the second conductive wire. Both are equipped with one reference resistance and a changeover switch for switching and supplying a current from a current source to the first conductor or the reference resistance, and an output is taken out between the third conductor and the changeover switch. A resistance type temperature measuring circuit.