JPS6346829Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an inspection circuit for inspecting thermocouple abnormalities such as polarity of the thermocouple and disconnection status.

(Prior art) As a conventional thermocouple inspection method, the first
As shown in the waveform diagram in the figure, a method is usually used in which the thermocouple is heated by electricity (heating time T _H ), and then the thermocouple is connected to a measurement circuit to measure the thermoelectromotive force.

In this case, the temperature of the thermocouple drops until the relay or the like is switched and measurement of thermoelectromotive force is started (switching time T _R ), and sufficient thermoelectromotive force cannot be measured in many cases.

If the thermocouple is heated to a high temperature to prevent this, there is a risk of damaging the thermocouple due to annealing, fusing, etc.

Furthermore, this method has the problem that the thermoelectromotive force of the thermocouple is measured once and in a short period of time, making it susceptible to noise during this period.

(Problems to be solved by the invention) The present invention solves the above conventional problems and provides a thermocouple inspection circuit that can reliably inspect thermocouple abnormalities such as polarity and disconnection without damaging the thermocouple. With the goal.

(Means for Solving the Problems) The present invention has been developed to achieve the above objectives by: 1. A diode that passes voltage from an AC power supply every half wave and periodically heats a thermocouple by energizing it; an amplifier circuit that amplifies the thermoelectromotive force of the thermocouple; a voltage limiter circuit installed at the input terminal of the amplifier circuit or inside the amplifier circuit;
The present invention proposes a thermocouple inspection circuit comprising display means for displaying the output amplified by the amplifier circuit.

(Function) (1) The thermocouple inspection circuit of the present invention has the configuration described in the claims for utility model registration, and in particular, the thermocouple is periodically heated by energization by a diode and energized by an amplifier circuit and a voltage limiter circuit. Since the thermoelectromotive force during rest is detected periodically, thermocouple abnormalities such as thermocouple polarity and disconnection status can be reliably inspected without being disturbed by noise.

(2) The thermocouple inspection circuit of the present invention has the same configuration as above, in particular, the heating of the thermocouple is carried out by cutting off a half-wave of AC voltage with a diode, while most of the heating voltage is cut off with a voltage limiter circuit. Therefore, the thermoelectromotive force of the thermocouple can be accurately detected while the current is not flowing.

(Example) A thermocouple inspection circuit of the present invention will be described below according to an example shown in the drawings.

FIG. 2 shows a thermocouple testing circuit according to the present invention, which has a transformer circuit 1 that adjusts the voltage supplied from the AC power source to a predetermined value.

The transformer circuit 1 is connected to one end of a current adjustment circuit 3 via a diode 2 (forward direction).

The current regulating circuit 3 is connected at the other end to the thermocouple 5 and supplies a heating current to the thermocouple 5 within a set value (for example, a value that does not damage the thermocouple 5).

Next, the thermocouple 5 is connected together with the current adjustment circuit 3 to one end of an amplifier circuit 8 that amplifies the thermoelectromotive force.

A voltage limiter circuit is installed between the input terminal of the amplifier circuit 8 and the ground line, and the thermocouple 5
Heating power exceeding a set value that is set to be larger than the thermoelectromotive force can be cut off.

A display means 10 is connected to the other end of the amplifier circuit 8, and the display means 10 displays the amplified thermoelectromotive force so that it can be recognized.

The operation of the thermocouple inspection circuit of the present invention shown in the above embodiments will now be described.

That is, the alternating current voltage that has been set to a predetermined value by the transformer circuit 1 is supplied to the current adjustment circuit 3 after having its half wave cut off by the diode 2 .

The current adjustment circuit 3 adjusts the current within the set value to the thermocouple 5.
It is heated by passing electricity through it.

Since the current flowing through the thermocouple 5 is an alternating current with a half wave cut off, the thermocouple 5 is repeatedly energized and stopped.

Therefore, while the thermocouple 5 is heated while energized, it generates a thermoelectromotive force due to this heating when it is not in use.

5.1 shows the output waveform of the connection path P between the thermocouple 5 and the current adjustment circuit 3, and shows the heating voltage from the current adjustment circuit 3 whose half-wave is cut off and the heat generated by the thermocouple 5 when the current is not flowing. It can be seen that the power g ₁ or h ₁ is repeated alternately.

This thermoelectromotive force g ₁ or h ₁ corresponds to the polarity of the thermocouple (h ₁ for positive polarity, g ₁ for negative polarity).

Returning to FIG. 2, these outputs will be amplified by the amplifier circuit 8.

Here, since a voltage limiter circuit is installed between the input terminal of the amplifier circuit 8 and the ground line, the thermoelectromotive force g ₁ or h ₁ of the thermocouple 5 is amplified, but the heating exceeds the set value in the voltage limiter circuit. Most of the voltage will be cut off.

Details of the voltage limiter circuit will be described below with respect to the embodiment of FIG.

The output of the amplifier circuit 8 is displayed on the display means 10, and abnormalities of the thermocouple 5, such as polarity and disconnection, are checked.

Regarding the connection direction of the diode 2 shown in the above configuration, even if this is reversed, the same function will be achieved only by reversing the polarity of the half wave that interrupts the AC voltage.

Furthermore, the output of the amplifier circuit 8 is fed back to the current adjustment circuit 3 through a feedback path, so that when the temperature of the thermocouple 5 rises (thermoelectromotive force rises), the current flowing through the thermocouple 5 in the current adjustment circuit 3 is reduced. It may be configured such that automatic adjustment is possible.

Next, a timer may be connected to the current adjustment circuit 3 to stop heating and measurement after a predetermined period of time to prevent the temperature of the thermocouple 5 from rising excessively.

Furthermore, the current adjustment circuit 3 is used to adjust the heating currents for the various thermocouples 5 to correspond to each one.

Therefore, if the present invention is applied only to a certain type of thermocouple 5, the current adjustment circuit 3 can be omitted.

FIG. 3 shows another thermocouple testing circuit of the present invention, which has the following features.

First, a voltage limiter circuit common to the embodiment shown in FIG. 2 will be explained.

That is, as shown in Figures 5 and 2, the voltage limiter circuit maintains a constant voltage V _C at the output of the connection P.
This is to block the above.

In other words, the voltage V _C is the thermoelectromotive force h ₁ of the thermocouple 5 or
It is set to a value slightly larger than g ₁ , and the thermoelectromotive force h ₁ or
g ₁ is amplified and adjusted so that most of the heating voltage f (portion above voltage V _C ) is cut off.

Next, the amplifier circuit 8 inverts and amplifies the thermoelectromotive force h ₁ or g ₁ (positive to negative, negative to positive) as shown in Figures 5 and 3, and applies a bias voltage V _B to the thermocouple. 5
Positive output regardless of polarity (h ₂ or g ₂ )
It will be adjusted so that

Here, the bias voltage V _B used in the amplifier 8 is derived from a constant voltage generation circuit 7 that generates a DC constant voltage, as shown in FIG.

Next, as a feature of this test circuit that is different from that shown in FIG.
It is connected to the.

This display circuit 9 compares the constant voltage derived from the constant voltage setting circuit 7 with the output voltage from the amplifier circuit 8, classifies abnormalities of the thermocouple 5 such as polarity, disconnection status, etc., and displays the results on a display means 10. It is to be displayed.

Other than the above configuration, the configuration and operation of the inspection circuit in FIG. 3 are the same as those in FIG. 2, and their explanation will be omitted.

An example of a specific configuration of the test circuit whose block diagram is shown in FIG. 3 will be explained based on FIG. 4.

That is, the transformer circuit 1 and diode 2 are as shown in the figure, and their explanation will be omitted.

The current adjustment circuit 3 is composed of a variable resistor 13 and a transistor 14.

Next is the constant voltage setting circuit 7, which uses a voltage setting device 18 to generate a constant voltage from a voltage rectified and smoothed by a diode 16 and a capacitor 17.

Next is the amplifier circuit 8, which has an amplifier 20 whose output from the connection path P is led to its negative input terminal.

The output of this connection path P is grounded by a diode 22 (forward direction) that functions as a voltage limiter, and the conduction start voltage (positive minute voltage) of the diode 22 is used as the voltage V _C shown in Figures 5 and 2. This means that

As a result, at a voltage equal to or higher than the conduction start voltage of the diode 22, the diode 22 becomes conductive, and the input voltage from the connection path P to the amplifier 20 is cut off at a portion equal to or higher than the voltage V _C .

Next, a resistor 29 is connected to the positive input terminal of the amplifier 20,
30, a voltage obtained by dividing the constant voltage from the constant voltage setting circuit 7 is input, and the bias voltage V _B shown in FIGS. 5 and 3 is generated.

As a result of the above, the outputs shown in FIGS. 5 and 3 are obtained by the amplifier 20.

As is clear from FIGS. 5 and 3, the amplifier 20 is a single power supply operational amplifier and does not output a negative output.

In this way, the single power supply operational amplifier itself functions as a voltage limiter circuit.

Therefore, if a single power supply operational amplifier is used, the separately installed voltage limiter circuit using the diode 22 described above can be omitted.

However, the diode 22 described above also has the function of blocking unexpected excessive input to the amplifier 20, and in this sense it is preferable to add it.

Next is the display circuit 9, which is equipped with three comparators 25, 39, and 40, each of which indicates (in order) the disconnection status of the thermocouple 5, and whether or not the polarity of the thermocouple 5 is negative. and determines whether the polarity of the thermocouple 5 is positive or not, and these will be explained below.

First, the comparator 25 has a negative input terminal to which the earth terminal of the thermocouple 5 is connected via a smoothing circuit including a diode 23 and a capacitor 24 .

In other words, if the thermocouple 5 is not disconnected, an alternating current voltage is generated at the earth terminal of the thermocouple 5 while the thermocouple 5 is heated by electricity, and this is smoothed and becomes a direct current voltage at the negative input terminal of the comparator 25. will be input.

On the other hand, a voltage obtained by dividing the constant voltage from the constant voltage setting circuit 7 by resistors 31 and 32 is input to the positive input terminal of the comparator 25, and this voltage is compared with the voltage input to the negative input terminal.

As a result, if the thermocouple 5 is not disconnected, the voltage at the negative input terminal of the comparator 25 is higher than the certain voltage at the positive input terminal, so the output terminal of the comparator 25 has a low resistance.

Therefore, current flows through the light emitting diode 41 of the display means 10, causing it to emit light.

That is, the disconnection status of the thermocouple 5 is displayed by the light emitting diode 41.

Next is the comparator 39, to which the output of the amplifier circuit 8 is smoothed via a smoothing circuit including a diode 27 and a capacitor 28 and input as a DC voltage to its negative input terminal.

On the other hand, the constant voltage from the constant voltage setting circuit 7 is connected to the positive input terminal of the comparator 39 through the resistors 33, 34,
The voltage divided by 37 is input.

This voltage is compared with the DC voltage obtained by smoothing the output of the amplifier circuit 8, and if the latter is larger than the former, the output terminal of the comparator 39 has a low resistance, the light emitting diode 42 of the display means 10 emits light, and the buzzer 4 is activated. I'll be crying.

Here, the voltage value input to the positive input terminal of the comparator 39 is derived when the voltage introduced to the negative input terminal of the comparator 39 when the thermocouple 5 has negative polarity and the thermoelectromotive force are zero. The voltage is set to an intermediate value.

Therefore, the light emission from the light emitting diode 42 indicates that the thermocouple 5 has negative polarity.

Here, a transistor 36 is connected between the resistors 34 and 37, and its base is connected to the output terminal of the comparator 25.

In other words, transistor 36 is comparator 2
When the output terminal of 5 has a low resistance (the thermocouple 5 is not disconnected), it is used as a switch to establish continuity between the emitter and the collector.

This means that when the thermocouple 5 is disconnected, the circuit of the resistors 33, 34, and 37 is cut off by the transistor 36, and a large voltage is input to the positive input terminal of the comparator 39, so that the comparison result is always The output terminal of the comparator 39 has a high resistance, and the light emitting diode 42 does not emit light.

Next is the comparator 40, which is similar to the comparator 39 and causes the light emitting diode 43 to emit light when the thermocouple 5 has positive polarity.

FIG. 6 shows another thermocouple testing circuit of the present invention, which has the following features compared to the testing circuit of FIG. 3.

That is, a pair of thermocouples 5a and 5b can be tested simultaneously, and the constant voltage setting circuit 7 and the transformer circuit 1 are shared.

Diode 2 in Figure 3 is diode 2
Diode group 2' consisting of a, 2b, 2c, 2d
has been replaced by

This uses the positive value of the AC voltage supplied from the conversion circuit 1 to test one thermocouple (for example, 5a),
This is because the negative value is used to test the other thermocouple (for example, 5b).

That is, it is the same as that shown in FIG. 3 except that the pair of thermocouples 5a and 5b can be tested at the same time.

(Effects of the invention) The thermocouple inspection circuit of the invention has the following effects in the above configuration and operation.

(1) The thermocouple inspection circuit of the present invention has the configuration described in the claims of the utility model registration, and in particular, the thermocouple is periodically heated by energization by a diode, and is heated by an amplifier circuit and a voltage limiter circuit when the energization is stopped. Since thermoelectromotive force is detected periodically, thermocouple abnormalities such as thermocouple polarity and disconnection status can be reliably inspected without being disturbed by noise.

(2) The thermocouple inspection circuit of the present invention has the same configuration as above, and in particular, the heating of the thermocouple is carried out by blocking a half-wave of AC voltage using a diode, while most of the heating voltage is blocked by a voltage limiter circuit. Therefore, the thermoelectromotive force of the thermocouple can be accurately detected while the current is not flowing.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram showing a conventional testing method, Figure 2 is a block diagram of the testing circuit of the present invention, Figure 3 is a block diagram of another testing circuit similar to the above, and Figure 4 is a diagram of the testing circuit of Figure 3. Circuit diagram showing an example of a specific configuration, fifth,
Figure 1 is an output waveform diagram of the connection path P in Figure 3, Figures 5 and 2 are waveform diagrams for explaining the operation of the same amplifier circuit,
Figures 5 and 3 are output waveform diagrams of connection path Q in Figure 3, and Figure 6
The figure is a block diagram of another test circuit according to the present invention. 1...Transformer circuit (TR), 2...Diode,
2a, 2b, 2c, 2d...diode, 2'...
...Diode group, 3, 3a, 3b... Current adjustment circuit (IC), 5, 5a, 5b... Thermocouple, 7... Constant voltage setting circuit (AVC), 8, 8a, 8b... Amplification circuit (AMP ), 9, 9a, 9b... Display circuit (IND), 10, 10a, 10b... Display means (I), 13... Variable resistor, 14... Transistor, 16, 16a, 16b... Diode, 17
...Capacitor, 18...Voltage setting device, 20...
...Amplifier, 22...Diode, 23...Diode, 24...Capacitor, 25...Comparator, 27...Diode, 28...Capacitor, 29...... to, 34...Resistor, 36...Transistor, 37 ...Resistance, 39...Comparator, 40...Comparator, 41,42,
43...Light emitting diode, 44...Buzzer, f,
g ₁ , g ₂ , h ₁ , h ₂ ... Output waveform, P, Q ... Connection path.

Claims (1)

[Scope of utility model registration request] A diode that periodically heats a thermocouple by passing voltage from an AC power supply every half wave, an amplifier circuit that amplifies the thermoelectromotive force of the thermocouple generated by the electrical heating, and an input terminal of the amplifier circuit or A thermocouple inspection circuit comprising a voltage limiter circuit installed in an amplifier circuit and a display means for displaying the output amplified by the amplifier circuit.