Behaviour of Micrologix 1400 Outputs during startup

[rmb550]

I will test it later today thanks for all the input.
rmb550

 

[Ron Beaufort]

and PLEASE come back and let us know how this finally turns out ...

 

[TConnolly]

One additional test you can perform is to switch to program mode and then back to run mode without cycling power. If it is a first scan program bug then the output will pulse, since the processor performs the same actions when switching to run mode from program mode as it does on power up. If it is a hardware problem related to powering up you won't see the pulse since everything is already powered up. These checks should help you determine whether to be looking at hardware or software.

 

[rmb550]

I will do both tests and let you know.
rmb550

 

[rmb550]

I disconnected my custom board from the PLC module ran some tests and found that the output does pulse when going from Program to Remote Run Mode. I also programmed a rung that sends S:1/2 (Run Mode) to an unused output point on the same module and found that the 2 ouputs turn on at the same time.
rmb550

 

[TConnolly]

That definitely sounds like some kind of software issue. Can you zip and post your .RSS file? Sometimes an extra set of eyes (or several as in the case of the board) can spot things.

 

[rmb550]

It did end up being a software issue that relied on latching relays to define the system state. I used the S:1/15 First Scan bit to ensure the offending relays were unlatched on start up and the problem is resolved.
Thanks to ALL who chimed in and offered there thoughts & ideas.
This really is a great resource.
rmb550

 

[TConnolly]

I'm happy to hear you were able to solve the problem.

 

[tracer]

I dunno if this helps but I have one machine, which when ever the SLC receives a fault, It opens a relay which provides power to the outputs. Loss of power is considered a fault. and must be reset manaully by operator.
another solution might be to have your output fire a relay, if the relay is large enought (amp draw not physical size) the pulse will be gone before there is enough current flow to engage the relay.