4-20mA input (SCP)

[Alfa20ad 0]

Sorry, Totally new to PLC programming. My question is that i have a 4-20mA input into a 1769-IF4 card, i have connected my 4-20mA input into V/I in 0- and I in 0+ When i write the SCP command for this input and go online the instruction can see the input change as i vary the 4-20mA signal but i cannot see the output side change as i do this on the function block What am i doing wrong? Also how would i achieve when the mA signal reaches a certain setpoint, this then triggers an output?

[TimWilborne 108]

Post your program so we can have a look

[Alfa20ad 0]

As file attached C17941newprogamme.ACD

[Michael Lloyd 85]

The program must be a higher version than 19. I can't open it. It sounds like you aren't calling the routine

[Alfa20ad 0]

What do you mean by not calling the routine. Can this image help? Edited 28 Apr 2014 by Alfa20ad

[TimWilborne 108]

Were you attaching something? Post a PDF

[TimWilborne 108]

Never mind. Is your health check program calling your compressor program with a JSR instruction?

[Alfa20ad 0]

This is the first page.

[TimWilborne 108]

You need a jsr in your first program to jump to your second program. Just insert a new rung with a jsr instruction

[Alfa20ad 0]

Will give it a try. Thanks.

[Alfa20ad 0]

One other thing. Does the Allen-Bradley have a function similar to the P_On function like the Omron version?

[Alfa20ad 0]

Done that, but still i can see the input increasing and decreasing but the output value stays at 0.0.

[TimWilborne 108]

Put and unconditional rung with an OTE going to an unused tag before your SCP and see if it turns on so we know if your rung is executing.

[TimWilborne 108]

One other dummy check. Is your processor in run mode?

[Alfa20ad 0]

I can see it change now. Thanks. Just one other thing what instruction would i use to say if this input reaches say 5mA then energise an output.

[TimWilborne 108]

I would do GRT source a COMP1_33_SCALED source b the scaled value odd 5ma then an OTE instruction.

[TimWilborne 108]

P_ON... is that a pulse on? Have a look at the ONS.

[Alfa20ad 0]

Looking for an instruction to say that the PLC is healthy. That is all.

[Nelliyan 1]

DDT instruction can be used for reading diagnostics Regards, Nelliyan.G Edited 2 May 2014 by Nelliyan