JPH0736445Y2 - Inspection device for level detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an inspection device for a level detection circuit.

(Prior Art) A level detection circuit which operates when a given input exceeds a predetermined level is generally widely used. In such a level detection circuit, it is necessary to always operate correctly, and therefore an inspection device is prepared.

As an inspection device, a level detection circuit is supplied with an inspection input equal to or higher than its operation level, and it is determined whether or not it operates.

On the other hand, in such an inspection device, when the inspection input is given and the level detection circuit operates, the inspection input is eliminated, and the level detection circuit is thereby automatically restored. There is.

Therefore, if a regular input higher than the operation level is input during the period when the inspection input is given, the level detection circuit remains in the operating state even after the inspection input is lost, and it becomes impossible to recover. I will end up.

Normally, when the inspection input is given, the output of the level detection circuit is locked, so if it becomes impossible to recover as described above, a regular input above the operation level comes in. However, since the output has been locked by then, the detection result cannot be taken out as the output.

FIG. 2 (see Japanese Patent Laid-Open No. 56-121327) was previously proposed by the present inventor to solve this problem.
The example shown in the figure shows a configuration used when, for example, when a voltage of a certain monitored line becomes an overvoltage, this is detected and the line is cut off.

According to the figure, the voltage of the line is applied to the input terminal I and dropped by the transformer T to a suitable voltage. .
Then, after being rectified by the full-wave rectifier RE, the resistance
It is smoothed by R ₁ , R ₂ and the capacitor C, and given to the level detection circuit D.

When the voltage applied to the input terminal I becomes excessive and the voltage applied to the level detection circuit D becomes equal to or higher than the operation level voltage, the level detection circuit D operates and the contact d ₁ closes. Then, the circuit L is turned on, which cuts off the line.

In order to inspect the level detection circuit D, a relay A for inspection start, a relay B for inspection output lock and a positive DC power source E
Is prepared.

a _{1 to} a ₃ are contacts of relay A, b _{1 to} b ₃ are contacts of relay B (however, b ₁ and b ₃ are normally open, b ₂ is normally closed contact), d _{1 to} d ₃ are level detection circuit D contact (provided that d _1, d ₃ but which opens and closes upon operation
Is a normally open contact and d ₂ is a normally closed contact).

The inspection is started by turning on the inspection start command contact ST for a short time. This activates relay A,
The contacts a _{1 to} a ₃ are closed. When the contact a ₁ is closed, the relay A is self-held via the contact d ₂ on condition that the level detection circuit D is not operating.

If the level detection circuit D is operating at this time, the relay A is not self-held, and before the contacts a ₂ and a ₃ are closed,
The check start command contact ST is turned off and relay B does not operate.

After the relay A is self-held, the contact B ₂ is closed to operate the relay B, the contacts b ₁ and b ₃ are closed, and the contact b ₂ is opened. The circuit L is opened by opening the contact b ₂ , and the output of the level detection circuit D is locked by this.

When the contacts a ₃ and b ₃ are both closed, the voltage of the DC power supply E is applied to the level detection circuit D as a check input. Since this voltage is set above the operation level of the level detection circuit D, if the level detection circuit D is normal, the contacts d ₁ and d ₃ are closed and the contact d ₂ is opened.

By opening the contact d ₂ , the self-holding of the relay A is released and the relay A returns. Even if the contact a ₂ is opened by this return, the relay B is still held by the contact d ₃ being closed, so that the relay B is still in the operating state, and therefore the circuit L is open and the output of the level detection circuit D is still. It is locked.

However, since the contact a ₃ is opened by the return of the relay A, the inspection input by the DC power source E is released, and the input of the level detection circuit D returns below the operating level. By this return, the contacts d ₁ and d ₃ are closed and the contact d ₂ is opened.

When the contact d ₃ is opened, the relay B is released from its self-holding and returns. This return causes the contacts b ₁ and b ₃ to open and the contact b ₂ to close. By closing the contact b ₂ , the level detection circuit D
The output lock of is released. By the above, all the states are returned to the initial state.

In this process, by knowing the open / closed state of the contact d ₁ (or the operating state of the relays A and B), it becomes possible to check whether or not the level detection circuit operates correctly.

In this configuration, when the contacts a ₃ and b ₃ are both closed as described above, and the voltage of the DC power source E is applied to the level detection circuit D as an inspection input, it is applied to the input terminal I. If the regular input becomes excessive, the input of the level detection circuit D becomes higher than the operation level.

Therefore, even if the contact a ₃ is opened by the return of the relay A and the inspection input to the level detection circuit D is lost, the level detection circuit D does not return and the contacts d ₁ and d still remain.
_{Since contact 3} remains closed and relay B does not return, contact b ₂ remains open.

That is, the output of the level detection circuit D is still locked, so that the line to be monitored cannot be cut off. This means that the line cannot be protected from overvoltage, and the function of the level detection circuit D cannot be fulfilled.

Therefore, in the configuration shown in FIG. 2, a negative power source E ′ is prepared and connected to the connection points of the contacts a ₃ and b ₃ via the resistor R ₃ .

According to this, as described above, when the contact a ₃ is opened due to the return of the relay A, the negative voltage from the power source E ′ causes the resistance R ₃ ,
It is given to the level detection circuit D via the contact b _3, and the level detection circuit D is restored by this.

Here, as the negative voltage of the power source E ′, the input to the level detection circuit D due to the excessive input applied to the input terminal I is canceled so that the input actually applied becomes equal to or lower than the return level. It has been selected in advance.

According to this, if the inspection input is given,
Even if an excessive input is given to the input terminal I, the level detection circuit D
Will be restored by opening the contact a ₃ .

When the level detection circuit D returns, the contacts d ₁ and d ₃ open, and the relay B returns. Therefore, by opening the contact b ₃ , application of a negative voltage is cut off, and by closing the contact b ₂ , level detection is performed. The output lock of the circuit D is released.

Therefore, if the input terminal I is over-inputted at this time, the level detection circuit D operates normally,
The contact d ₁ is closed, the circuit L is turned on, and the monitored line is cut off.

(Problem to be solved by the invention) However, according to such a configuration, since the power source E ′ is connected to the connection point between the contact point a ₃ and the contact point b ₃ via the resistor R ₃ , the contact point a ₃ is When closed, the power supply E becomes short-circuited by the resistor R ₃ . Therefore, the resistance value of the resistor R ₃ cannot be reduced infinitely.

Therefore, when there is an excessive input above a certain value,
The potential of the resistor R ₃ may exceed the reference level, and in such a case, it may not be possible to unlock the check output relay.

The purpose of this invention is to forcibly release the lock of the relay for the inspection output lock and restore the normal operation even when an excessive input enters during the inspection.

(Means for Solving Problems) This invention is a contact that is closed when a level detection circuit is activated by an inspection input and the relay for inspection startup is restored by the operation of this level detection circuit. It is characterized in that a short circuit composed of a short-circuit resistor connected in series is connected so as to short-circuit the input end of the level detection circuit.

(Operation) When the inspection start relay is restored, the power supply for supplying the inspection input is disconnected from the level detection circuit, and instead the short-circuit resistance short-circuits the input end of the level detection circuit. Therefore, no matter what input is applied, the check output lock relay can be unlocked.

(Embodiment) An embodiment of the present invention will be described with reference to FIG. The second
Portions with the same reference numerals as those in the figure indicate the same or corresponding portions. According to this invention, the contact a _{3 and} the contact b ₄ are prepared. Then, the resistor R ₃ is connected via the contact point a ₄ .

With the above configuration, Relay A
When is restored, the contact a ₃ is opened and the contact a ₄ is turned on. Therefore, the power supply E is disconnected from the level detection circuit D, and the input end of the level detection circuit D is connected to the short circuit resistor R ₃
Will be short circuited through.

Therefore, no matter what input is applied to the input terminal I at this time, the relay B returns in response to the return of the relay A.
Will also be reinstated and will never be locked.

When relay B returns, contact b ₃ opens,
The short circuit at the input end of the level detection circuit D due to the resistor R ₃ is released, and the initial state is restored.

(Effect of the Invention) As described in detail above, according to the present invention, when the level detection circuit is inspected, the power supply for inspection input may be short-circuited due to the return of the relay for inspection start unlike the conventional configuration. Even if any input is given, the fact that the check output locking relay is locked has the effect of reliably avoiding this.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. D: level detection circuit, A: inspection start relay, B
...... inspection output lock for the relay, to open and close when the contacts of a ₁ ~a ₄ ...... relays A, b ₁ ~b ₃ contacts ...... relay B, d ₁ to d ₃ ...... level detection circuit is activated Contact, E ... Power supply for inspection input,

Claims (1)

[Scope of utility model registration request] Claim: What is claimed is: 1. A first relay for inspection start, which is activated and operated during inspection, and a second relay for inspection output lock which operates by the operation of the first relay and locks an output of a level detection circuit. And a power supply for giving a check input at a level equal to or higher than the operating level to the level detection circuit via first and second contacts that are closed when the first and second relays operate, and The second relay includes a third contact that is closed when the first relay returns due to the operation of the level detection circuit, and a short-circuit resistor that is connected in series to the third contact. An inspection device for a level detection circuit, which comprises a short circuit that short-circuits the input terminal of the level detection circuit until the level is restored.