Control Voltage to plc tripped

bornwild · May 16, 2010

hello everyone
My control voltage (24v) to plc and sensors tripped. I tried to reset the C.B ,it tripped again. the 24 v is goin to 8 sensors and the plc. How do i check which sensor is giving me the problem and causing the breaker the trip. Is there any easy way to check which sensor wires are faulty without having to check each sensor

Mickey · May 16, 2010

How do you know its one or more of the senors?

Disconnect all the sensors and see if the breaker stays on.

Use a meter to check each sensor for shorts while they are disconnected.

There are only 8 of them, should be pretty easy to find it.

keithkyll · May 16, 2010

With power off, put meter in low Ohms mode. Connect across 24DC supply output. Disconnect power lead to each sensor one at a time at PLC. When resistance goes high (maybe 1000 Ohms or more), you found the short.

The problem may be a shorted cable. Rubbing against a moving part, for example. Do a good physical examination first.

bornwild · May 16, 2010

@keith.
So should i disconnect the wires which are input to plc and check the resistance ?

PS: needless to say i am fresh graduate.

keithkyll · May 16, 2010

No. 24DC supply to the sensors. Is the breaker on the input or output to the 24DC supply? The supply itself could be bad.

bornwild · May 16, 2010

breaker is input

inst_tech · May 16, 2010

Is the inputs connected to the input card via a removable terminal block? If so just remove the whole lot. If not then power down the system and remove the entire card. The PLC may go to fault but this wont matter for the purpose of the test.

If the power stays on, do what the others have suggested and test each sensor one by one.

If the power goes off the try removing the output card. Carry on like this until you find the problem.

bornwild · May 16, 2010

yes there are connected via remote terminal block .So i ll just test from the terminal block.Is that ok?

whippee2 · May 17, 2010

ye thats fine, give that a shot

bornwild · May 17, 2010

checked from terminal block. one sensor was shorted. Thanks a lot everyone

Mickey · May 17, 2010

bornwild said:
checked from terminal block. one sensor was shorted. Thanks a lot everyone

Good to hear you found your problem.
And thanks for getting back to us with your solution. Its always nice
to hear success stories.

Control Voltage to plc tripped

bornwild

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