JPH09320377A - Contact welding detection circuit - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a contact welding detection circuit that can quickly detect welding of contacts of a switch, reduce running costs, and have a long life, small size, and low cost. SOLUTION: An AND gate 7 and an OR gate 6 have 2N. The signals supplied from the contacts X and Y of the O contact switch 1 are input, and the D latch 8 performs a latch operation based on the output signal of the AND gate 7 and a clear operation based on the output signal of the OR gate 6. Further, the output signals of the AND gate 7 and the D latch 8 are input to the AND gate 13, and the D latch 11 outputs a welding detection signal by performing a latch operation based on the output signal of the AND gate 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact welding detection circuit for detecting welding of contacts of a switch, and more particularly to a contact welding detection circuit suitable for detecting contact welding of a switch having a plurality of contacts.

[0002]

2. Description of the Related Art Conventionally, in industrial equipment, in order to enhance the safety of workers, a switch such as a switch is provided with a two-contact switch capable of opening and closing two contacts at substantially the same time by operating one operator. Things are known. Also, for industrial equipment that is highly dangerous to workers, a contact welding detection circuit that detects the welding of the contacts of the two-contact switch is installed,
There are also known ones with a higher degree of safety. As this conventional contact welding detection circuit, a relay circuit using a safety relay is used. This safety relay includes a plurality of N.S. O
(Normally Open) contacts and a plurality of N. C (N
normally close) contacts, If the O contact is welded, the N.O.
The C contact is not closed, and the N.C. If the C contact is welded,
Even if power is supplied to the relay coil, The O contact has a function of not closing.

[0003]

However, the relay circuit using the safety relay is expensive and cannot be downsized.
Since the relay generates heat, power consumption increases, running cost increases, operation speed is slow, and mechanical operation is involved, resulting in short service life. The present invention has been made under such a background, and an object thereof is to quickly detect welding of contacts of a switch, reduce running cost, and have a long life, small size, and inexpensive contact welding detection circuit. To provide.

[0004]

According to the present invention, in a contact welding detection circuit for detecting contact welding of a switch having a plurality of contacts, the contact welding detection circuit is composed of a logic circuit including semiconductor elements. Further, the present invention is, in a contact welding detection circuit for detecting contact welding of a switch having a plurality of contacts, a first AND gate and an OR gate to which a signal supplied from the plurality of contacts is input, A first D-latch that performs a latch operation based on the output signal of the AND gate and a clear operation based on the output signal of the OR gate; and an output signal of the first AND gate and the first D-latch. The contact welding detection by a logic circuit having a second AND gate to which is input and a second D latch that outputs a welding detection signal by performing a latch operation based on the output signal of the second AND gate. It constitutes the circuit.

According to the present invention, the contact welding detection circuit for detecting the contact welding of the switch having a plurality of contacts is constituted by the logic circuit by the semiconductor element, not by the conventional relay circuit. The contact welding detection can be performed quickly, the running cost can be reduced, and the contact welding detection circuit has a long life, is small, and is inexpensive.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a contact welding detection circuit according to an embodiment of the present invention will be described. As shown in FIG. 1, the present contact welding detection circuit is composed of a logic circuit including semiconductor elements, and has a normally open contact X, Y 2N. O contact switch 1, ie 1
This is a circuit for detecting the welding of one of the contacts of a two-contact switch that can open and close two contacts almost simultaneously by operating one operator. To the normally open contacts X and Y of the O-contact switch 1, in order to transmit the switch ON / OFF signal to the logic circuit as a digital signal,
Low pass filters 2 and 3 for normally open contacts X and Y and Schmitt triggers 4 and 5 are connected.
Then, the logic circuit latches a signal indicating the closed state of the OR gate 6 and the AND gate 7 and the normally open contacts X and Y to which the digital signals from the normally open contacts X and Y are respectively input.
AND gates 9 and 2N. It has an AND gate 10 for outputting a switch-on signal indicating the opening / closing operation of the O-contact switch 1, and a D latch 11 for performing welding detection output.

The output signal of the AND gate 7 is input to the clock input terminal C of the D latch 8 via the inverter 12, and the AND gate 10 receives the AND gate 7 and D.
The output signal of the latch 8 is input, the output signals of the AND gate 7 and the D latch 8 are input to the AND gate 13, and the output signal of the AND gate 13 is the D latch 11
Of the clock input terminal C. 2N. The normally open contacts X and Y of the O-contact switch 1 have pull-up resistors 14 and 15 respectively.
The D terminals of the D latches 8 and 11 are always connected to H
A level signal is being input. The Schmitt triggers 4 and 5, the clear terminal CLR of the D latch 8 and the input terminal of the AND gate 10 on the D latch 8 side are negative input terminals.

Next, the circuit operation will be described with reference to the time chart of FIG. 2 showing the signal levels at points a to f shown in FIG. 2N. When the O contact switch 1 is turned on,
Normally open contacts X and Y close with a time difference. Then, the L level signal is input to the low pass filters 2 and 3 by the action of the pull-up resistors 14 and 15, and the H level signal is output from the negative input type Schmitt triggers 4 and 5. In addition, 2N. When O switch 1 is turned off, normally open contacts X, Y
If welding is not generated on the contacts, the contacts X and Y are opened with a time difference, and the H level signal is input to the low pass filters 2 and 3 by the action of the pull-up resistors 14 and 15.
From the negative input type Schmitt triggers 4 and 5, L
A level signal is output. At this time, 2N. The chattering component of the contact is removed by the low pass filters 2 and 3, and the operation signal of the O contact switch 1 is waveform-shaped by the Schmitt triggers 4 and 5 and output.

[When welding does not occur] First in FIG.
As shown in the ON / OFF operation for the second time, when welding does not occur, H-level signals are output from the Schmitt triggers 4 and 5 during the closing period of the normally open contacts X and Y (Fig. (See signals a and b in 2). In conjunction with this, the output signals of the OR gate 6 and the AND gate 7 change as shown in c and d of FIG. in this case,
In the D latch 8, when the output signal of the AND gate 7 falls (see the signal at point d in FIG. 2) and the output signal of the inverter 12 rises, that is, an H level signal is input to the clock input terminal. At this point, the H level signal at the D input terminal is latched, and the output signal (latch signal) of the OR gate 6 falls (see the signal at point c in FIG. 2) and the output signal of the AND gate 9 becomes It is cleared when it falls (see the signal at point e in FIG. 2). Further, the switch-on signal output from the AND gate 10 becomes exactly the same as the output signal of the D latch 8, and the welding detection signal output from the D latch 11 does not change while the output signal of the AND gate 13 remains at L level. Therefore, the L level is maintained.

[When welding occurs] As shown in the second ON / OFF operation of FIG. 2, for example, when welding occurs at the normally open contact Y, even if the OFF operation is performed, the normally open operation is performed. Since the contact Y remains closed, the output signal of the Schmitt trigger 5 does not change to L level but remains H level. Therefore, the output signal of the AND gate 9 also keeps rising, and the clear to the D latch 8 does not work, and the D latch 8 remains in the latched state (the second turn-on at the point e in FIG. 2). / Refer to the signal when turning off). In this case, the switch-on signal output from the AND gate 10 is normally output as shown in the signal at the second on / off operation at point f in FIG.

As described above, when welding occurs at the contacts, the D-latch 8 remains in the latched state even if the OFF operation is performed. Therefore, in the ON / OFF operation after welding, the third time in FIG. The switch-on signal from the AND gate 10 is not output as shown in the ON / OFF operation of. Further, in the ON operation after welding, the output signal of the AND gate 13 rises in conjunction with the rise of the output signal of the AND gate 7, and the rise of the output signal of the AND gate 13 triggers the D latch 11 to enter the D input terminal. H level signal is latched, and the H level latch signal is output as a welding detection signal (the third ON / OFF at the point g in FIG. 2).
Refer to the signal when turning off). On the industrial control device side, interlocking based on this welding detection signal makes it possible to avoid a dangerous operation.

As described above, since the contact welding detection circuit is composed of the semiconductor element logic circuit, the contact welding can be detected more quickly and the running cost can be reduced as compared with the conventional contact welding detection circuit using the relay circuit. It becomes possible to make a contact welding detection circuit that has a long life, is small, and is inexpensive. It should be noted that the present invention is not limited to the above-described embodiment, and for example, the contact welding detection circuit by the logic circuit as described above is multiplexed and redundancy is provided to further improve safety. Is also possible.
Also, by simply replacing the Schmitt trigger circuit of the active input type with the normally closed type 2N. It can also be applied to a C contact switch (switch). further,
It is also possible to apply to a multi-contact type switch (switch) having three or more contacts.

[0013]

As described above, according to the present invention,
Since the contact welding detection circuit for detecting the contact welding of the switch having a plurality of contacts is configured by the logic circuit by the semiconductor element, not by the conventional relay circuit, the contact welding can be detected quickly, and The running cost can be reduced, and the contact welding detection circuit has a long life, is small, and is inexpensive.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a contact welding detection circuit according to an embodiment of the present invention.

FIG. 2 is a time chart showing the operation of the circuit of FIG.

[Explanation of symbols]

1 ... 2N. O contact switch, 2, 3 ... Low pass filter, 4, 5 ... Schmitt trigger circuit, 6 ... OR gate, 7, 13 ... AND gate, 8, 11 ... D latch, X, Y ... Normally open contact.

Claims (4)

[Claims] 1. A contact welding detection circuit for detecting contact welding of a switch having a plurality of contacts, wherein the contact welding detection circuit is composed of a logic circuit including a semiconductor element. 2. A contact welding detection circuit for detecting contact welding of a switch having a plurality of contacts, wherein a first AND gate and an OR gate to which a signal supplied from the plurality of contacts is input, and the first A first D-latch that performs a latch operation based on the output signal of the AND gate and a clear operation based on the output signal of the OR gate; and the output signals of the first AND gate and the first D latch. The contact welding detection circuit is formed by a logic circuit having a second AND gate input and a second D latch that outputs a welding detection signal by performing a latch operation based on an output signal of the second AND gate. A contact welding detection circuit characterized by comprising: 3. The contact welding detection circuit according to claim 1, wherein the switch has two contacts. 4. The signals supplied from the plurality of contacts are
4. The contact welding detection circuit according to claim 1, wherein the contact welding detection circuit is configured to be input to the first AND gate and the OR gate via a low pass filter and a Schmitt trigger circuit.