JPH06331679A - Switching circuit fault detecting device - Google Patents

Abstract

PURPOSE:To make it easy to detect the fault of a switching circuit which turns a load on and off. CONSTITUTION:A signal-transmitting transformer T1 is inserted in series with a first snubber circuit 6 connected in parallel to a relay contact 4a, so that a fault detection signal generated by a signal generator circuit 8 is transmitted to the first snubber circuit 6. A signal-receiving transformer T2 is inserted in series with a second snubber circuit 7 connected in parallel to an SSR (solid- state relay) 5, so that the fault detection signal transmitted to the first snubber circuit 6 is received by the signal-receiving transformer T2. Therefore, when the relay contact 4a or the SSR 5 is shortcircuited, no fault detection signal is transmitted to the signal-receiving transformer T2 and the output of the signal-receiving transformer T2 becomes a logical value of 0. When a load is off in a normal state, a fault detection signal is transmitted to the signal- receiving transformer T2 and the output becomes a logical value of 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switch circuit failure detection device for detecting a failure of a switch circuit for turning on / off a drive current of a load to be controlled.

[0002]

2. Description of the Related Art Conventionally, a switch circuit for turning on / off a drive current of a load to be controlled is constructed by connecting contacts of an electromagnetic relay and a semiconductor switch element, for example, a slit state relay (SSR) in series, There is a load drive circuit that controls power supply to a load by controlling ON / OFF of a relay contact and an SSR.

That is, in the switch circuit, when the drive input signal of the load is input, first, the electromagnetic relay contact is turned on.
Then, after the SSR is turned on, the drive current flows to the load for the first time, and when the load drive input signal is stopped, the SSR is reversed.
Is turned off first, power supply to the load is stopped, and then the electromagnetic relay contact is turned off. With this configuration, when the switch circuit is normal, the load drive current is turned on / off substantially by turning the SSR on / off.
OFF is controlled, and the electromagnetic relay contacts turn on the drive current.
Although not directly involved in OFF, when the SSR causes a short-circuit fault and the load drive current cannot be turned OFF, the load drive current can be forcibly turned OFF by turning OFF the electromagnetic relay contact.

By the way, as a conventional circuit for detecting the short circuit of the SSR, a secondary side of a transformer is inserted in series in a load feeding circuit in which a load and a switch circuit are inserted in series, and the primary side of this transformer is inserted. The AC short-circuit detection signal is supplied from the side to the load power supply circuit via the secondary side. In this case, a noise prevention circuit (a snubber circuit composed of a series circuit of a capacitor and a resistor) is usually connected in parallel to the electromagnetic relay and the SSR of the switch circuit, and when the SSR or the electromagnetic relay contact has a short-circuit failure. In addition, the impedance of the power feeding circuit seen from the primary side of the transformer decreases. Therefore, the short circuit of the switch circuit is detected by monitoring the output change based on the decrease in the impedance.

[0005]

However, as in the conventional short-circuit failure detection circuit, in the method of detecting the short-circuit failure of the switch circuit by monitoring the output change based on the impedance change of the feeding circuit, the output level is reduced. The change is detected, and the threshold setting is troublesome. Further, if a short circuit failure of the capacitor of the snubber circuit is to be taken into consideration, the threshold setting is further troublesome, and the accuracy of failure detection is not sufficient.

The present invention has been made in view of the above circumstances, and the presence or absence of a short circuit fault in a switch circuit can be represented by a binary output form of a logical value 1 (with output) and a logical value 0 (without output). An object is to provide a failure detection device for a switch circuit.

[0007]

Therefore, according to the present invention, a series circuit of an electromagnetic relay contact and a semiconductor switch element is provided, and when the load drive signal is input, the electromagnetic relay contact and the semiconductor switch element are turned on to apply a load. A resistor and a capacitor in a switch circuit failure detection device for detecting a failure in a switch circuit configured to stop power supply to a load by supplying power and stopping input of a load drive signal when the electromagnetic relay contact and a semiconductor switch element are turned off. A first noise prevention circuit formed of a series circuit of the above and connected in parallel to the electromagnetic relay contact, and a second noise circuit formed of a series circuit of a resistor and a capacitor, connected in parallel to the semiconductor switching element. The noise prevention circuit, the signal generation circuit that generates the switch circuit failure detection signal, and either of the noise prevention circuits are inserted in series. A signal transmission transformer for transmitting to the radio interference suppression circuit side the switch circuit failure detection signal Te,
A signal receiving transformer that is inserted in series with the other noise prevention circuit and receives and extracts the switch circuit failure detection signal, and receives a signal when at least one of the electromagnetic relay contact and the semiconductor switch element is short-circuited. The extracted output of the transformer has a logical value of 0.

Further, a rectifier circuit for rectifying the extracted output of the signal receiving transformer, and the rectified output of the rectifier circuit are inputted, and when the rectified output level is within a predetermined range, it is judged that the switch circuit is normal and the logical value is 1 And a window comparator that generates the output of the. Further, the secondary side for generating the extraction output of the signal receiving transformer is provided with signal supply means for supplying a signal having a reverse phase to the extraction output.

[0009]

In such a structure, when both the electromagnetic relay contact of the switch circuit and the semiconductor switch element are normal and there is no short-circuit failure, the alternating current transmitted from the signal generation circuit to the one noise prevention circuit is transmitted through the signal transmission transformer. The switch circuit failure detection signal is received by the signal reception transformer inserted in the other noise prevention circuit. In this case, the extracted output from the signal receiving transformer has the logical value 1 (output is present).

On the other hand, when one of the electromagnetic relay contact and the semiconductor switch element is short-circuited, an AC switch circuit failure detection signal transmitted from the signal generation circuit to one noise prevention circuit via the signal transmission transformer. Is not received because it does not flow to the signal receiving transformer side due to the short circuit of the switch circuit. Therefore, the extraction output from the signal receiving transformer has a logical value of 0 (no output).

Further, when the capacitor of the noise prevention circuit is short-circuited, the current flowing in the primary side of the signal receiving transformer changes due to the impedance change of the noise prevention circuit,
The extraction output level of the signal receiving transformer changes. Then, by setting the extraction output level at the time of the short circuit to be outside the window range (setting level range) of the window comparator, it is possible to detect the short circuit failure of the capacitor of the noise prevention circuit.

When the capacitor of the noise prevention circuit is short-circuited by providing a signal supply means for supplying a signal having a reverse phase to the extracted output on the secondary side for generating the extracted output of the signal receiving transformer. The level change rate of the extraction output of the signal receiving transformer can be expanded, and the threshold setting in the level test becomes easy.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a load drive circuit to which a first embodiment of a failure detection device for a switch circuit according to the present invention is applied. The failure detection device shown in FIG. 1 is for the case where only a short circuit failure of the switch circuit is considered.

In FIG. 1, a switch circuit 3 is connected in series with the load 2 to a power feeding circuit for feeding an alternating current from a load driving power source 1 which is a commercial AC power source to the load 2. The switch circuit 3 comprises a series circuit of a relay contact 4a which is turned on when the electromagnetic relay 4 is excited and a semiconductor switch element, for example, an SSR 5. A first snubber circuit 6, which is a first noise prevention circuit including a series circuit of a resistor R ₁ and a capacitor C ₁ , is connected in parallel to the relay contact 4a in order to prevent noise when the contact is turned off. Also, SS
A second snubber circuit 7, which is a second noise prevention circuit and is also composed of a resistor R ₂ and a capacitor C ₂ , is connected in parallel to R5. Then, a signal transmission transformer T1 for transmitting to the first snubber circuit 6 an AC switch circuit failure detection signal generated in the signal generation circuit 8 to the first snubber circuit 6 side.
Secondary windings are inserted in series. A primary winding of a signal receiving transformer T2 that receives and extracts the switch circuit failure detection signal transmitted to the first snubber circuit 6 is inserted in series in the second snubber circuit 7. A rectifier circuit 9 that rectifies the extracted output is connected to the secondary winding of the signal receiving transformer T2. Here, the first and second snubber circuits 6 and 7, the signal transmitting transformer T1, the signal receiving transformer T2, the signal generating circuit 8 and the rectifying circuit 9 constitute the failure detecting device 10 of the present embodiment. Similarly, the load 8 is also provided with a noise preventing snubber circuit including a series circuit of a resistor R ₃ and a capacitor C ₃ .

The signal transmitting transformer T1 may be provided on the second snubber circuit 7 side and the signal receiving transformer T2 may be provided on the first snubber circuit 6 side. On the other hand, the signal input unit for inputting the load drive signal to the switch circuit 3 is the self-holding circuit 11
And a fail-safe OFF delay circuit 12, a fail-safe ON delay circuit 13, and the electromagnetic relay 4.

The self-holding circuit 11 is provided in the failure detecting device 1
The output of 0 (output of the rectifier circuit 9) is used as a trigger input, the load drive signal IN is used as a reset input, and the trigger input is held by itself. The fail-safe OFF-delay circuit 12 rises at the same time when the output of the self-holding circuit 11 is input, and when the output of the self-holding circuit 11 stops, the output falls after a predetermined time delay to excite / demagnetize the electromagnetic relay 4. ON / OFF the relay contact 4a
Control. The ON delay circuit 13 includes the self-holding circuit 11
When the output of (1) is input, the output rises with a delay of a predetermined time, and when the output of the self-holding circuit 11 stops, the output falls at the same time to control ON / OFF of the SSR 5.

The self-holding circuit 11 has a fail-safe structure in which the output becomes a logical value of 0 when a failure occurs, and O
The FF delay circuit 12 and the ON delay circuit 13 also have a fail-safe configuration in which only the failure on the delay time side is allowed. Next, the operations of the load drive circuit and the failure detection device will be described. First, the case where the switch circuit 3 is normal will be described.

Before the load drive signal IN is generated, the short circuit fault detection signal from the signal generation circuit 8 is transmitted from the primary side to the secondary side of the signal transmission transformer T1 and is transmitted to the first snubber circuit 6. . At this time, since the relay contact 4a of the switch circuit 3 and the SSR 5 are in the OFF state, this short-circuit fault detection signal is extracted on the secondary side via the primary side of the signal receiving transformer T2 and the logical value of the high energy state is obtained. The output of 1 (with output) is input to the rectifier circuit 9. The rectified output of the rectifier circuit 9 is input to the self-holding circuit 11 as a trigger input signal. In this state, when the load drive signal IN is input as the reset input signal of the self-holding circuit 11, an output is generated from the self-holding circuit 11 and is input to the OFF delay circuit 12 and the ON delay circuit 13. In the OFF delay circuit 12, an output rises and the electromagnetic relay 4 is excited at the same time when the signal from the self-holding circuit 11 is input. As a result, as shown in FIG. 2, the relay contact 4a is turned on after a delay time t ₂ which is determined by the relay characteristic from the rising of the self-holding circuit 11. Also, the ON delay circuit 1
As shown in FIG. 2, the output of the signal No. 3 rises after a predetermined delay time t ₁ (t ₁ > t ₂ ) from the input of the signal from the self-holding circuit 11, and the SSR 5 is turned on. In this way, the SSR 5 turns on after the relay contact 4a turns on.
Then, a drive current flows through the load 2 and the load 2 is driven. From the time when the relay contact 4a is turned on, the signal from the signal generating circuit 8 is not transmitted to the signal receiving transformer T2 side, the output level of the rectifying circuit 8 becomes a logical value 0, and the trigger input signal of the self-holding circuit 11 is obtained. However, the trigger input is self-held by the output of the self-holding circuit 11, and the self-holding circuit 11 continues to generate an output.

After that, when the load drive signal IN is stopped,
The output of the self-holding circuit 11 falls at the same time, the output of the ON delay circuit 13 also falls at the same time, and SSR5 is immediately turned off, so that the drive current is not supplied to the load 2 and the driving of the load 2 is stopped. Then, as shown in FIG.
SSR5 relay contacts 4a to output drops electromagnetic relay 4 Standing degaussing the OFF to OFF delay circuit 12 after a predetermined time t ₃ from the turned OFF.

When a short circuit fault occurs in the SSR5, the short circuit fault detection signal transmitted from the signal generation circuit 8 to the first snubber circuit 6 via the signal transmission transformer T1 is SSR5.
Due to the short circuit, the current does not flow into the second snubber circuit 7 and is not transmitted to the signal receiving transformer T2 side. Therefore, the extraction output level of the signal receiving transformer T2 becomes a logical value 0 (no output), and there is no trigger input signal of the self-holding circuit 11. Therefore, even if the load drive signal IN is input to the self-holding circuit 11, the self-holding circuit 11 does not generate an output, and the relay contact 4a is in the OFF state, so that the drive current is not supplied to the load 2. .

Therefore, after the SSR 5 is short-circuited,
Even if the load drive current IN is generated, the drive current is cut off by the relay contact 4a and the load 2 does not operate. Normally, the power supply to the load 2 is substantially controlled by the SSR 5 and the relay contact 4a does not turn ON / OFF the drive current of the load 2, so there is no fear of welding failure and the reliability is high.

In this way, the failure detection device 10 of this embodiment
Generates a logical 1 output when there is no short-circuit fault and
In the case of a fault, the output of logical value 0 is generated.
Since it is a binary output form whether force is generated or not,
Due to a short circuit compared to the conventional type that monitors level changes
The obstacle can be easily detected, and the detection accuracy is improved. Next, the figure
3 shows a second embodiment of the failure detecting device of the present invention. This fruit
In the example, not only the short circuit failure of the switch circuit 3 but also the first and
Capacitor C of the second snubber circuits 6 and 7 ₁, C₂Because of the short circuit
Obstacles are taken into consideration. The same as the first embodiment of FIG.
The same reference numerals are given to the parts and the description thereof will be omitted.

In FIG. 3, the failure detection device 2 of this embodiment is shown.
At 0, in addition to the configuration of the first embodiment, a fail-safe conventionally known window comparator WC whose output becomes a logical value 0 at the time of failure is connected to the subsequent stage of the rectifier circuit 9.
In such a configuration, the capacitor C of the snubber circuits 6 and 7
The impedances of the snubber circuits 6 and 7 change between when the C ₁ and C ₂ are normal and when there is a short circuit failure, and the current flowing through the snubber circuits 6 and 7 changes. As a result, the signal voltage extracted by the signal receiving transformer T2 changes.

Therefore, when setting the window range of the window comparator WC, the extraction output level of the signal receiving transformer T2 when the capacitors C ₁ and C ₂ are normal is within the window range.
Extracting the output level of the signal received transformer T2 when the capacitor C _1, C ₂ are short-circuited is set to be out of the range of the window. Accordingly, when the capacitors C ₁ and C ₂ are normal, the output of the logic value 1 is input from the window comparator WC to the self-holding circuit 11 as a trigger input signal, and when the capacitors C ₁ and C ₂ are short-circuited, the window comparator WC is output. Output becomes a logical value 0, and the trigger input to the self-holding circuit 11 disappears. Therefore, the capacitors C ₁ , C ₂
If there is a short-circuit failure, the self-holding circuit 11 does not generate an output even if the load drive signal IN is input, and the load 2 is not driven.
When the switch circuit 3 is short-circuited, the signal receiving transformer T
Since the output level of 2 has a logical value of 0 and is outside the window range of the window comparator WC, it goes without saying that a short circuit failure of the switch circuit 3 can also be detected.

By the way, in the configuration of the second embodiment, the change rate of the extraction output of the signal receiving transformer T2 is small when the capacitors C ₁ and C ₂ are normal and when the short-circuit failure occurs, and the window range of the window comparator WC is narrowed. It is necessary to set, and the setting is strict. Even if the capacitance of the capacitor is selected in order to increase the change rate between the normal state and the short circuit, the change rate is slightly less than twice. Moreover, in order to perform the function of the snubber circuit, the selection range of the capacitances of the capacitors C ₁ and C ₂ is narrow and the degree of freedom of selection is limited.

From the above, the signal receiving transformer T
FIG. 4 shows an example of a failure detection device for increasing the rate of change of the extraction output of No. 2 as a third embodiment. The same parts as those in the second embodiment of FIG. 3 are designated by the same reference numerals. In FIG. 4, the failure detection device 30 according to the present exemplary embodiment includes, on the secondary side of the signal receiving transformer T2, a secondary winding C and a reverse winding C of the transformer T2.
_A is provided, and the winding C _A is connected in series with the primary winding of the signal transmission transformer T1 to the signal generation circuit 8 to supply a voltage of opposite phase to the extraction output to the secondary side of the signal reception transformer T2. . Here, the winding C _A and the signal generation circuit 8 constitute a signal supply means.

In such a configuration, the extraction output level of the signal receiving transformer T2 of this embodiment is smaller than that of the second embodiment of FIG. 3 by the amount of the reverse phase supplied by the winding C _A. On the other hand, changes in the extraction output level of the transformer T2 when the capacitors C ₁ and C ₂ are normal and when they are short-circuited are the same as in the second embodiment. Therefore, the rate of change between the extraction output of the signal receiving transformer T2 at the time of normal operation and at the time of failure, that is, the rate of change, is expanded by the amount of decrease in the extraction output level. Therefore, the output change of the signal receiving transformer T2 can be increased between the normal time and the failure time, the window range of the window comparator WC can be set easily, and the reliability of the failure detection can be improved.

[0028]

As described above, according to the present invention, it is possible to determine whether or not a switch circuit is short-circuited by a binary value, that is, a logical value of 1.
Can be represented by 0, and there is no need for level verification, which facilitates detection of short-circuit faults. Further, if a window comparator is provided at the final stage of the failure detection device, it is possible to detect a capacitor short circuit failure of the noise prevention circuit, and it is possible to enhance the fail-safety of load switch control.
It is extremely effective for interlock control of industrial machines.

[Brief description of drawings]

FIG. 1 is a first circuit diagram of a switch circuit failure detection device according to the present invention.
The figure which shows the example of the load drive circuit which applied the Example.

FIG. 2 is a time chart showing states of a relay contact, an SSR, and a load drive current according to the first embodiment.

FIG. 3 is a circuit diagram showing a second embodiment of the switch failure detection device according to the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the switch failure detection device according to the present invention.

[Explanation of symbols]

 1 load drive power supply 2 load 3 switch circuit 4 electromagnetic relay 4a relay contact 5 SSR (semiconductor switch element) 6 first snubber circuit 7 second snubber circuit 8 signal generating circuit 9 rectifier circuit 10, 20, 30 failure detection device T1 signal transmission Transformer T2 signal receiving transformer WC window comparator

Claims (3)

[Claims] 1. A series circuit comprising an electromagnetic relay contact and a semiconductor switch element, wherein when the load drive signal is input, the electromagnetic relay contact and the semiconductor switch element are turned on to supply power to the load, and the input of the load drive signal is stopped. In the switch circuit failure detection device for detecting a failure of the switch circuit configured to stop the power supply to the load by turning off the electromagnetic relay contact and the semiconductor switch element, the electromagnetic relay contact is composed of a series circuit of a resistor and a capacitor. A first noise prevention circuit connected in parallel to the switching circuit, a second noise prevention circuit which is also composed of a series circuit of a resistor and a capacitor and is connected in parallel to the semiconductor switching element, and a switch circuit failure detection signal. Which is inserted in series with either the noise generating circuit or the signal generating circuit for generating the switch circuit failure detection signal. A signal transmitting transformer for transmitting to the noise prevention circuit side, and a signal receiving transformer that is inserted in the other noise prevention circuit in series and receives and extracts the switch circuit failure detection signal, and an electromagnetic relay contact And a switch circuit failure detection device, wherein the extracted output of the signal receiving transformer becomes a logical value 0 when at least one of the semiconductor switching elements is short-circuited. 2. A rectifier circuit for rectifying the extracted output of the signal receiving transformer, and the rectified output of the rectifier circuit is input to determine that the switch circuit is normal when the rectified output level is within a predetermined range and a logical value of 1 is obtained. 2. The switch circuit failure detection device according to claim 1, further comprising a window comparator that generates the output of the switch circuit. 3. The switch circuit failure detection according to claim 2, wherein the secondary side for generating the extraction output of the signal receiving transformer is provided with signal supply means for supplying a signal of a reverse phase to the extraction output. apparatus.