JP2008191131A - Thermometric resistor measuring circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermometric resistor measuring circuit capable of detecting individually disconnection of each conductor in a thermometric resistor. <P>SOLUTION: This thermometric resistor measuring circuit is provided with the thermometric resistor with one end side connected to the two conductors b, B and with the other end side connected to the one conductor A, the first constant current source connected to the conductor b, the second constant current source connected to the conductor B, a reference resistance for connecting the conductor A to a common potential point, and a voltage measuring means for measuring a voltage in a connection point between the conductor A and the reference resistance, an output current value from the first constant current source is set to be different from that from the second constant current source, and the disconnected conductor is specified based on a change of a voltage measured value measured by the voltage measuring means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resistance temperature detector measurement circuit, and more specifically, it is possible to accurately identify which conductor of a resistance temperature detector is broken.

  A resistance temperature detector is for electrically measuring the temperature of a measurement object based on a change in resistance value due to a temperature change of the resistor, and is widely used as a temperature sensor in various plant plants and research fields.

  FIG. 2 is a circuit diagram showing an example of use of a conventional three-wire resistance thermometer. In FIG. 2, a resistance wire RT having a resistance value rA is connected to one end of a resistance temperature detector 1 having a resistance value RT, and a conductor wire B having a resistance value rB and a conductor wire b having a resistance value rb are connected to the other end. Has been. The conducting wire A is connected to a constant current source 2 that outputs a constant current i, and the conducting wire b is connected to a common potential point via a reference resistor 3 having a resistance value RS. In addition, the ends of the conducting wires A, B, b of the resistance temperature detector 1 are connected to the arithmetic circuit 4. In addition, the resistance value of the conducting wire A and the conducting wire b is selected so that rA = rb.

In such a configuration, the output current i of the constant current source 2 flows to the common potential point through the path of rA → RT → rb → RS. The arithmetic circuit 4 has a sufficiently high input impedance, and measures the end voltages VA, VB, Vb of the conductors A, B, b of the resistance temperature detector 1 to obtain the resistance value RT of the resistance temperature detector 1. To find out, the following calculation is performed.
RT = (VA−2VB + Vb) * RS / Vb (1)

JP-A-8-247857

  By the way, as described in paragraph 0014 of Patent Document 1, the resistance temperature detector 1 is exposed to a high temperature atmosphere to be measured and a large temperature cycle environment from room temperature to high temperature. b or the body of the resistance temperature detector 1 may be disconnected, and the temperature measurement result may remain abnormal, and the temperature measurement may be disabled.

  Occurrence of a temperature measurement impossible state impedes stable operation in a system that performs temperature control of a continuous process based on the temperature measurement result of the resistance temperature detector 1, and quickly detects and grasps the cause of the abnormal state Therefore, it is necessary to take measures.

  According to the circuit configuration of FIG. 2, when the conducting wire A is disconnected, the end voltage VA can be completely shifted to the potential on the constant current source 2 side, so that the disconnection of the conducting wire A can be detected, and when the conducting wire b is disconnected, the end voltage Vb is detected. Can be detected in the potential of the common potential point side, so that the disconnection of the conductor b can be detected.

  However, if the conducting wire B is disconnected, the input voltage of the arithmetic circuit 4 is sufficiently high, so that the end voltage VB becomes indefinite, and it is impossible to detect the disconnection of the conducting wire B. In order to detect disconnection of the conducting wire B, an additional circuit and arithmetic processing are required in addition to the circuit of FIG.

  The present invention pays attention to such a conventional problem, and an object thereof is to provide a resistance temperature detector measurement circuit capable of individually detecting disconnection of each conductor of the resistance temperature detector.

In order to achieve such a problem, the invention of claim 1
A resistance temperature detector having two conductors b and B connected to one end and a conductor A connected to the other end, a first constant current source connected to the conductor b, and a conductor B A second constant current source, a reference resistor for connecting the conductor A to the common potential point, and a voltage measuring means for measuring the voltage at the connection point of the conductor A and the reference resistor,
The output currents of the first constant current source and the second constant current source are set to different values, and the disconnected conductor is specified based on the change in the voltage measurement value of the voltage measurement means.

The invention of claim 2 is the resistance temperature detector measuring circuit according to claim 1,
It has an alarm means which is selectively driven according to a change in the voltage measurement value of the voltage measuring means, and visualizes and displays the disconnected conductor.

  Thus, the disconnected conductor of the resistance temperature detector can be identified from the change in the voltage measurement value.

  Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a specific example of an embodiment according to the present invention, and the same reference numerals are given to portions common to FIG. The difference between FIG. 1 and FIG. 2 is that the resistance temperature detector RT is connected upside down to the arithmetic circuit 4, the constant current source 2 that outputs a constant current 4 i is connected to the conductor b, and the conductor B is connected to the conductor B. Is that a constant current source 5 that outputs a constant current i is connected, and the conductor A is connected to a common potential point via a reference resistor 3 having a resistance value RS.

  In FIG. 1, the output current 4i of the constant current source 2 flows to a common potential point through a route of rb → RT → rA → RS, and the output current i of the constant current source 5 is a common potential through a route of rB → RT → rA → RS. Since the current flows to the point, a current of 4i + i = 5i flows in the path of RT → rA → RS. The resistance values of the conductor A, the conductor B, and the conductor b are selected so that rA = rB = rb.

The arithmetic circuit 4 having a sufficiently high input impedance measures the end voltages VA, VB, Vb of the conductors A, B, b of the resistance temperature detector 1 to obtain the resistance value RT of the resistance temperature detector 1. The following calculation is performed.
RT = − (VA−3VB + 2Vb) * RS / VA (2)

Here, attention is paid to the end voltage VA of the conducting wire A. In a normal state where each conductor A, B, b is not disconnected, it is represented by VA = 5i * RS. However, when each conductor A, B, b is disconnected individually, according to each disconnection,
1) When conductor A is disconnected: VA = 0
2) Conductor B is disconnected: VA = 4i * RS
3) Conductor b is disconnected: VA = i * RS
It changes as follows.

  As is clear from these, by measuring the end voltage VA of the conductor A, any one of the three conductors A, B, and b was disconnected based on the change in the magnitude of the voltage measurement value. Can be accurately identified.

  The arithmetic circuit 4 may be composed of an operational amplifier, or the end voltages VA, VB, Vb of the conductors A, B, b of the resistance temperature detector 1 are converted into digital signals by an A / D converter. After that, the CPU may perform arithmetic processing.

  In order to visualize which conductor has been disconnected, for example, three alarm lamps corresponding to the three conductors are provided, and each conductor is subjected to three stages of changes in the end voltage VA of the conductor A. The corresponding alarm lamp may be selectively turned on.

  In the above-described embodiment, the example in which the ratio of the output currents of the constant current source 2 and the constant current source 5 is set to 4: 1 is shown. However, the ratio of the output current is not limited to this. As long as it is possible to identify which of the three conductors A, B, and b is broken based on the change in the end voltage VA, the output currents of the constant current source 2 and the constant current source 5 may not be equal.

  Furthermore, it is only necessary to detect whether or not any one of the conductors is disconnected, and when it is not necessary to specify the disconnected conductor, the end voltage VA of the conductor A is VA <5i * RS. It is only necessary to provide a simple comparator having a predetermined threshold for simply comparing and determining whether or not.

  As described above, according to the present invention, a resistance temperature detector measurement circuit capable of individually detecting disconnection of each lead wire of the resistance temperature detector can be realized, which is suitable for temperature measurement in various fields.

It is a circuit diagram which shows the specific example of embodiment based on this invention. It is a circuit diagram which shows the usage example of the conventional 3-wire type resistance temperature detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resistance temperature detector 2 1st constant current source 3 Reference resistor 4 Arithmetic circuit 5 2nd constant current source

Claims (2)

A resistance temperature detector having two conductors b and B connected to one end and one conductor A connected to the other end, a first constant current source connected to the conductor b, and a conductor B A second constant current source, a reference resistor for connecting the conductor A to the common potential point, and a voltage measuring means for measuring the voltage at the connection point of the conductor A and the reference resistor,
The temperature measurement is characterized in that the output currents of the first constant current source and the second constant current source are set to different values, and a broken wire is specified based on a change in a voltage measurement value of the voltage measuring means. Resistor measurement circuit.   2. The resistance temperature detector measuring circuit according to claim 1, further comprising alarm means which is selectively driven in accordance with a change in a voltage measurement value of the voltage measuring means and visualizes and displays the disconnected conductor.

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