Sinking transistor outputs

Lc1

Member
L
Join Date
Jan 2014
Location
Uk
Posts
59
Hi,
I have a cpm1a that has sinking transistor outputs. I have recently used this to power a relay coil. The relay coil is energised as soon as I wire it in and switch on the plc. The output status indication light remains off. Has anyone came across this before?

Thanks
 
Its possible for solid state leakage to do this. It depends on the relay. Is it a solid state relay?
Relay "coil" grounded?
 
It’s a 24vdc relay coil,not grounded. I’ve tried it on the first two outputs and it does the same thing, not sure what is happening as I can’t force the output on/ off from the plc program either.
 
Can you install a interposing relay with dry contacts between the PLC and your 24v relay?

Just to test the leakage theory.
 
I will try it. Need to get another relay first. Just bought one relay to mess around with.

Thanks
 
I'm guessing it's mis-wired.

Omron CMP1A transistor sink output sinks current from the perspective of the load, not from the perspective of the channel's transistor. The relay's A1 or (+) terminal should connect to the output channel, and the relay's A2 or (-) terminal should connect to the module's COM terminals.

$
 
Hi,
Yes that’s the way it’s wired. Just went and double checked. I’m now not getting anything from the digital output and the relay is not energising. I’m maybe thinking it’s an addressing issue. I am assuming that first output is 1.00 and second is 1.01 third is 1.02 and so on. Really not sure what the problem is.
 
Hi.
I have the power supply v+ connected to terminal A1 of the relay. Terminal A2 is connected. to the channel. The power supply V- is connected to the com.

Thanks
 
Not much left, other than the stuff we're certain you checked.
PLC bad. Not in Run. 24VDC low. PLC is Sourcing, not Sinking. Does this PLC have a diagnostic mode where all outputs are off?
Inputs working, and you can see them on the PC?
 
That is an old PLC. 1.00 is an input not an output. Check the manual but I think outputs start at 10.00 - have not seen one of them for many years. Make sure the relay has a flywheel diode in it.
 

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