JPS5828538B2 - temperature measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature measuring device that measures temperature by providing a resistance temperature detector in a bridge circuit, and particularly relates to a temperature measuring device that measures temperature by providing a resistance temperature detector in a bridge circuit, and is particularly applicable to upper or lower limit burnout in the event of a failure in which the resistance temperature detector cannot function. The present invention relates to a temperature measuring device that accurately detects temperature and issues alarms, etc.

Conventionally, when performing temperature measurements, a constant current is extracted from the secondary winding of an isolation transformer and added to a bridge circuit that has a resistance temperature detector on one side, and the change in resistance due to temperature of this resistance temperature detector is converted into a millivolt voltage signal. This signal is supplied from the bridge circuit to the subsequent chopper type isolation amplifier.

This isolated amplifier converts a millivolt voltage signal into a DC voltage signal, and then uses a constant current circuit of a transistor with a DC current on the emitter side to convert it into a constant DC current that corresponds to temperature changes. is measured, and the DC constant current is applied to an oscillator to generate pulses, which are fed back to the bridge circuit via the isolation transformer.

In the above device, if one side of the bridge circuit into which the resistance temperature detector is inserted is disconnected (for example, the resistance bulb itself is disconnected or the lead wire of the resistor is disconnected) and a failure occurs, the bridge circuit Since most of the power supply voltage is supplied to the chopper type isolation amplifier via the resistor on the other side, the constant DC current flowing out from the constant current circuit increases and the measured temperature swings toward the upper limit. .

In addition, if the side where the resistance temperature detector is inserted and the other side connected to it are disconnected, the power supply voltage of the bridge circuit will not enter the positive input section of the chopper type isolation amplifier, and conversely, the resistance of the resistance temperature detector or other Voltage enters the negative power section of the chopper type isolation amplifier through the voltage, and the measured temperature swings to the lower limit side.

Further, if the lead wire on one polarity side of the power supply voltage of the bridge circuit that is loosely connected to the temperature measuring resistor is disconnected, the output current of the constant current circuit becomes unstable.

Conventionally, among the above-mentioned disconnection failures, a warning device was installed on the collector side of the amplification transistor to generate an alarm in the event of upper limit burnout, especially for disconnection of the resistance temperature sensor and its lead wire. was.

However, in actual usage, it is necessary to issue an alarm not only for upper limit burnout but also for lower limit burnout as necessary.

The present invention has been made in response to the above-mentioned demands, and is designed to prevent not only disconnection on one side of the bridge circuit into which the resistance temperature sensor is inserted, but also to prevent the resistance temperature sensor from fulfilling its original function. The present invention provides a temperature measuring device that can generate an alarm or the like even in the event of a disconnection of a power supply voltage connection lead wire or the like on another side or in a bridge circuit, which would otherwise be impossible.

An embodiment of the present invention will be described below with reference to the drawings.

This device basically uses a bridge circuit configured as shown in FIG.

That is, in this bridge circuit, the span adjustment resistor R
Connect a resistance temperature detector RTD to one end of the resistor RT
The other end of D is connected to the positive polarity of the DC power supply Eb of the bridge circuit, and the other end of the span adjustment resistor R8 is connected to the negative polarity of the power supply Eb via the resistor R1.
form the edges.

Also, connect one end of the zero point adjustment resistor RZ to the positive polarity of the power source Eb,
The other end of the resistor RZ is connected to the negative polarity of the power source Eb via the resistor R2 to form the other two sides.

Furthermore, diodes DI and D are connected from the positive polarity of the power supply Eb to one end of the span adjustment resistor R8 and the zero point adjustment resistor RZ, respectively.
2 is connected.

Under normal conditions, the measurement voltage of the resistance temperature detector RTE is applied to the diode D1, and the lead wire 10 is applied to the diode D2.
Only a voltage drop of
It flows through the routes of ■ and ◎ without flowing through I and D2.

For a failure that does not allow the resistance temperature detector RTD to function, current flows as follows.

1 First, disconnection at point A or disconnection in resistance temperature detector RTD: In this case, diode D1 turns on and the positive polarity of power supply Eb -
A current flows through a closed circuit consisting of the diode D1, the span adjustment resistor R8, the resistor R1, and the negative polarity of the power source Eb.

2. Disconnection at point B: Diodes DI and D2 are turned on, each forming a closed circuit, and current flows.

3 Disconnection at point C: Diode D2 turns on and power supply Eb
A current flows through a closed circuit consisting of the positive polarity of - the zero point adjustment resistor RZ - the resistor B2 - the negative polarity of the power source Eb.

Therefore, the diode DI. By detecting the current flowing through D2, it can be seen that the m resistance temperature detectors are not substantially functioning.

FIG. 2 shows a temperature measuring device according to an embodiment of the present invention, which is realized by applying a bridge circuit adopting the operating principle shown in FIG.

This bridge circuit 11 commonly connects the anode sides of diodes DI and D2 to the base side of a PNR type transistor Q1, and connects the emitter side of this transistor Q1 to the positive polarity of a power source Eb.

Further, the collector side of the transistor Q1 is connected to the negative polarity of the power source Eb via the photocoupler light emitting element PCD.

Then, at the time of disconnection between points A and C, the transistor Q1 is turned on to cause the light emitting element PCD to emit light.

Reference numeral 12 inputs the output signals outputted from the respective movable terminals of the zero point adjustment resistor RZ and the span adjustment resistor R8 of the bridge circuit 11, and chops the signals with the chopper CH1 to convert them into alternating current. This is a chopper type isolation amplifier that demodulates the signal with chopper CH2, amplifies this signal with DC amplifier A2, and outputs the signal.

12a is a chopper signal generator.

The output section of the isolation amplifier A2 is connected to the transistor Q2. Constant current circuit 1 with two-stage direct connection configuration of Q3
Connected to 3.

The PCT is a photocoupler light receiving element, and its emitter side is grounded, and its collector side is connected to the up terminal 14 or the down terminal 15 through a switch or a setting pin on a pin board.

The up terminal 14 is connected to the inverting input part of the DC amplifier A2, and the down terminal 15 is connected to the common part of the resistors R3 and R4.

Ec indicates a DC power supply, the positive polarity side of which is connected to the emitter side of the latter-stage transistor Q3 of the constant current circuit 13 that outputs a constant current, and the power supply of the DC amplifier A2, as well as a series circuit of resistors R5 and R6 whose other end is grounded. is connected to.

A common portion of the resistors R5 and R6 is connected to a non-inverting input portion of the DC amplifier A2.

RL is a temperature measuring resistor that causes a voltage change in response to temperature, and one end of this resistor is connected to the negative polarity side of the DC power source Ec.

The other end of this temperature measuring resistor RL and the collector side of the transistor Q3 are connected to the input part of an oscillator 16 that generates pulses with a constant current, and the pulses generated here are transmitted to the insulating transformer T.
2, a constant current is taken out from the secondary winding of this transformer T2 and supplied to both ends of the spurn adjustment resistor R8.

17 is an alarm device connected to the collector side of the transistor Q3.

Next, the operation of the temperature measuring device configured as above will be explained.

When there is no disconnection between points A and C and the resistance temperature detector RTD is functioning normally, the diode D is connected from the bridge circuit 11.
Since the configuration is such that I, D2, etc. are removed, there is almost no difference in operation from the conventional one.

That is, the resistance temperature detector RTD captures temperature changes and replaces them with changes in resistance value.

As a result, an unbalanced state appears in the bridge circuit 11, and a voltage signal corresponding to the unbalanced state appears in the chopper type isolation amplifier 1.
2, where it is chopped by a chopper CH1 to become an alternating current, insulated by an insulating transformer T1, taken out to the secondary winding, and demodulated by a subsequent chopper a (2) to become a direct current voltage signal.

This DC voltage signal is converted into a DC constant current corresponding to the temperature in the subsequent constant current circuit 13, and this is output to the temperature measuring resistor RL.
Measure the temperature.

Further, this constant DC current is input to an oscillator 16 to generate a pulse, which is applied to the primary winding of the isolation transformer T2.

Then, a constant current is taken out to the secondary winding of the isolation transformer T2 and fed back to the bridge circuit 11.

Next, the disconnection at point A of the bridge circuit 11 will be described.

A current flows into the emitter of the transistor Q1 due to the positive potential of the power source Eb, turning on the transistor Q1.

As a result, a current flows through the diode D1 and the light emitting element PCD, and the light emitting element R emits light.

At this time, the light from the light-emitting element PCD enters the light-receiving element PCT and turns on, so the negative input section (inverting input) of the DC amplifier A2 is grounded via the up terminal 14 and the light-receiving element PCT.

As a result, the positive input section (non-inverting input) of the DC amplifier A2 has a DC power supply Bcl/
2 voltages are applied, and a high DC voltage signal is output from the chopper type isolation amplifier 12 and is supplied to the constant current circuit 13.

As a result, a constant current of 100φ or more flows from the circuit 13, and an alarm is generated from the alarm device 17 connected to the collector side of the transistor Q3.

Next, even if there is a disconnection at point C of the bridge circuit 11, the resistance temperature detector RTD cannot function normally, but in this case as well, current flows through the diode D2 by turning on the transistor Q1, which causes the light emitting element to Current also flows through the PCD, where it emits light.

The light emission signal of this light emitting element PCD is received by the light receiving element PCT, and the resistance of the same element PCT is minimized.

At this time, the collector side of the light receiving element PCT is connected to the down terminal 1.
5, the output section of the chopper type isolated amplifier 12 is grounded, so that the subsequent constant current circuit 1
Transistor Q4 constituting No. 3 is cut off, and the output current becomes 0% or less.

This is detected by the alarm device 17 and an alarm is generated.

Even if the bridge circuit 11 is disconnected at point B, the light emitting element PCD emits light by turning on the transistor Q1.
The alarm device 17 can warn that the resistance temperature detector RTD is not functioning normally.

In the above embodiment, one light emitting element PCD was used in the common part of the diodes DI and D2 via the transistor Q1, but for example, the bridge circuit 11 may be configured as shown in FIG. 1 to connect the respective diodes DI.

A transistor for detecting an on state may be provided in D2, and a light emitting element may be individually provided in the collector of these transistors.

In this case, light receiving elements corresponding to these light emitting elements are individually provided at the input/output section of the chopper type isolated amplifier.

As detailed above, according to the present invention, the light emitting element is made to emit light when the resistance temperature detector provided in the bridge circuit is disconnected and cannot function normally, so the overall configuration of a chopper type isolation amplifier is used. The signal at the time of the disconnection can be extracted using a part of the circuit without any trouble.

This means that even in cases where the output voltage becomes abnormally high due to a failure of the chopper-type isolated amplifier itself and an alarm is generated, the failure state can be easily distinguished by looking at the light reception state of the light receiving element and determine the failure state.

In addition, by providing the light receiving element that receives the light emitted signal of the light emitting element in the input/output section of the chopper type isolated amplifier, either in common or individually, it is possible to prevent the output current from the constant current circuit from being 100% or more or 0% or less. It is possible to issue an alarm, and it is possible to provide a system with sufficiently high reliability to suit the user.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the basic principle of a bridge circuit applied to the device of the present invention, and FIG. 2 is a configuration diagram of a temperature measuring device illustrating an embodiment of the present invention. 11...Bridge circuit, RTD...Resistance temperature sensor, D
i, D2...diode, PCD...light emitting element, P
CT... Light receiving element, 12... Chopper type isolation amplifier, 13... Constant current circuit, 16... Oscillator, 17...
・Alarm device, T2...Isolation transformer.

Claims (1)

[Claims] 1. The output signal of the bridge circuit, in which the DC power supply has a resistance temperature detector on one side, and the series circuits on the other two sides are connected in parallel, is connected to the subsequent constant current through an isolated amplifier. In a temperature measuring device that converts the direct current into a constant current corresponding to the temperature in a circuit and supplies it to a resistor of the temperature measuring section, a directional element connected in parallel to the other adjacent side of the semiconductor switching element via a switching signal input section, a light emitting element connected to the DC power supply via the semiconductor switching element, and the isolation amplifier. A light-receiving element is provided in the input/output section of the subsequent stage circuit for common switching and receives the light emission signal of the light-emitting element, and a light-receiving element is provided in the output part of the constant current circuit to detect upper limit burnout and lower limit barout when the light-receiving element is conductive. 1. A temperature measuring device comprising: a device for alerting the state;