JPS5830203Y2 - Resistive burnout circuit - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a resistive burnout circuit.

Generally, in a temperature-measuring bridge circuit using a temperature-measuring resistor, breakage of the lead wire of the temperature-measuring resistor and short-circuiting of the temperature-measuring resistor occur.

Such a disconnection or short circuit of the resistance thermometer means that the temperature reaches infinity and vice versa, and the output of the receiving instrument normally swings to the high temperature side and low temperature side (burnout), generating an abnormality alarm, Controls the regulator to stop heating and cooling.

That is, this maintains the safety of the device and system against disconnection and short circuit of the resistance temperature sensor.

The purpose of this invention is to generate a voltage output corresponding to the resistance change of the resistance temperature sensor in a temperature bridge circuit using a 3-wire resistance temperature sensor, and also to ensure that any one of the 3 lead wires is disconnected. An object of the present invention is to provide a resistive burnout circuit that can detect disconnection even when the wire is disconnected.

Hereinafter, one embodiment of this invention will be described in detail based on the drawings.

The drawing shows an example in which this invention is applied to temperature control of an electric furnace.

Reference numeral 1 indicates an electric furnace, reference numeral 2 indicates a control thyristor for controlling the amount of heat generated in the electric furnace 1, and reference numeral 3 indicates an arithmetic circuit, for example, PID or ON/OFF operation output based on the amplified output of the operational amplifier 4. occurs.

This arithmetic circuit 3 and control thyristor 2 are included on the receiving instrument side.

On the other hand, the symbol Rt is a resistance temperature detector, and this resistance temperature detector Rt is attached to the electric furnace 1, and is connected to a resistance R1 via a lead wire a through an adjustment resistor r, and a resistance R3 via a lead wire S. each connected.

The connection point between the lead wire C and the resistor R3 is grounded via the lead wire C to serve as a common potential point.

Further, a resistor R2 is connected between the resistor R1 and the resistor R3, and a temperature-measuring bridge circuit is formed by the four-side resistances of the temperature-measuring resistor Rt and the resistors R1, R2, and R3.

The unbalanced output of the temperature measuring bridge is taken out from the connection point A between the resistor R1 and the adjustment resistor r, and the connection point B between the resistors R2 and R3, and this unbalanced output is calculated via the input resistors R4 and R5. The signals are supplied to the non-inverting side (→ and inverting side (-) input terminals of the amplifier C1, respectively).

The amplified output of operational amplifier IC1 is also output from operational amplifier ■C2.
is supplied to the inverting side input terminal (-) of

R, □, and Rf2 are feedback resistors, respectively.

Reference numeral 5 is a filter, and 4 is an operational amplifier for performing impedance conversion.

Reference numeral e denotes an increasing power supply terminal, to which a reference voltage of, for example, 9V is applied.

This reference power supply terminal is connected to the connection point C between the resistors R1 and R2 via a resistor R8.

The potential at this connection point C is supplied to the positive input terminal of the operational amplifier IC3.

The amplified output of the operational amplifier c3 is supplied to the base of the transistor Tr2.

Further, the inverted output of the operational amplifier 2C2 is supplied to the base of the transistor Tr.

Transistor Tr1. The emitter of Tr2 is grounded via a Zener diode Zd.

When either transistor Tr or Tr2 is turned on, a photocoupler (PH) consisting of a light emitting diode and a phototransistor connected to its collector side is activated.
The operational output (up or down) is supplied to the positive input terminal of the operational amplifier 4 via C).

Now, for example, the sum of the resistance temperature detector Rt and the adjustment resistor r is 300g with minimum human power, the value of the resistors R1, R2, and R3 is each 300g, the value of the resistor Re is 600Q, and the potential at point A is e.
Next, the operation of the above circuit will be described, assuming that the potentials at points A and B are eB, the potential at point C is ec, the reference voltage is -7.5V as mentioned above, and the Zener voltage of the Zener diode Zd is -7.5V.

First, when the resistance temperature detector Rt is in a normal state without being disconnected or shorted, the potential at point C is e.

is -3V, and a predetermined potential difference is extracted from eA and eB, and this potential difference is applied to the operational amplifier ■c1. The signal is applied to the receiving instrument via IC2, etc., and normal control operations are performed.

At this time, both transistors Tr1 and Tr2 do not operate, and burnout does not occur.

However, if lead wire a is now broken, the potential ec at point C will be Re=600,! Q and R2+R, = 600
．． ! The voltage is divided by Q and becomes -4.5V.

This -4.5V is supplied to the operational amplifier IC3, and the resistor R
If 6 and R7 are made equal, non-inverting amplification is performed with double the amplification degree.

Since this doubled amplifier output -9■ is lower than the Zener voltage -7,5■ of the Zener diode Zd, the transistor Tr2 is turned on and the photocoupler (PH
C) to the operational amplifier 4 with an output containing up (or down).

The operational amplifier 4 amplifies the signal output of the photocoupler (PHC) and supplies a command signal output to the operational circuit 3 in order to regulate the receiving instrument output to the positive (or negative) limit value.

The arithmetic circuit 3 operates to burn out the controller to the high temperature side (or low temperature side) and control the thyristor (SCR) to stop heating.

Further, even when the lead wire is disconnected, burnout and heating stop are performed in the same manner as in the case described above.

In the case of a break in lead wire C, the operation is exactly the same except that ec is 19■.

Next, a case where the resistance temperature detector is short-circuited will be explained.

When the resistance temperature detector Rt is in a normal state with no disconnection or short circuit, -eA≧-eB.

However, if the resistance temperature detector Rt is short-circuited, “A< e
B, and this unbalanced output is supplied to the operational amplifier Icm.

Operational amplifier 1c1 inverts and amplifies this to generate a positive output, and then operational amplifier IC2 inverts and amplifies this positive output to generate a negative output.

As a result, the transistor Tr1 is turned ON, and the operational amplifier 4 is connected to u via the photocoupler (PHC).
An output containing p (or down) is provided.

The subsequent operation is the same as in the case of wire breakage.

As explained above, according to this invention, by detecting the unbalanced output of the temperature-measuring bridge circuit, it is possible to extract the voltage output corresponding to the resistance change of the temperature-measuring resistor and use it for temperature control. By inputting the potential at the connection point with the reference power supply of the temperature measuring bridge to the operational amplifier circuit, it is possible to prevent disconnection of any one of the lead wires of the 3-wire resistance temperature detector with a simple configuration of one operational amplifier circuit. Each can be reliably detected and burnout or other actions can be taken.

Moreover, since the temperature measuring bridge is grounded and is not a floating power supply, the temperature measuring bridge power supply and the circuit power supply can be shared.

Note that the above embodiment is applied to the control of the calorific value of an electric furnace, but it is not limited to the case of heating, etc.
It goes without saying that the present invention can be similarly applied to cases such as cooling.

Further, if only a disconnection of the lead wire of the resistance temperature detector is to be detected, the operational amplifier C2 is not necessary.

[Brief explanation of drawings]

The drawing is an electrical circuit diagram showing an embodiment of this invention. 1... Electric furnace, 2... Control thyristor, 3... Arithmetic circuit, 4... Operational amplifier, Rt... Temperature measurement. Resistor, R1-R3...
・・Side resistance, IC1~■c3・・・・Operation amplifier.

Claims (1)

[Scope of utility model registration request] One side is the resistance temperature detector to which the first, second, and third lead wires are connected and is grounded via the third lead wire, and the other three sides are the resistance temperature detectors connected to the first, second, and third lead wires. a first operational amplifier that amplifies the unbalanced output of the temperature-measuring bridge and outputs an output corresponding to the resistance change of the temperature-measuring resistor, and is connected to the temperature-measuring bridge and a reference power supply. 4th to do
The first, second,
a second operational amplifier that detects disconnection of the third lead wire;
A resistive burnout circuit comprising a receiving instrument that receives the output of the first operational amplifier and the output of the second operational amplifier to perform temperature control and burnout.