Why does this work?

Prgram was not working, a 5/05 that should turn on a pump through a latching output when level gets to 60% or more (GEQ). Used a SCP for the sensor, and another used for output to the motor. The unlatch would happen at 20% or less (LEQ).

Problem was the motor would latch on at 20% and turn back off at 20%. I found the SCP for the motor was set as 0.0 for scaled minimum, and 100 for scaled maximum.

When I changed it to the same values the 4-20ma sensor was set at, the program started working normally.

So my question is... Why did changing the SCP for the motor, allow the program to turn on at 60% and not 20?

As far as I can tell, the SCP should have no effect on the motor turning on or off, but it does, so why?

Thanks!

1. Can you post the program - you'll have to zip it (forum rules).

2. I don't like the idea you have "latching outputs", there are safety issues involved.

Ooops, just realised I don't have RSLogix5, but there's loads of people here who do.....

Ooops, just realised I don't have RSLogix5, but there's loads of people here who do.....

Click to expand...

If you have RSLogix500 you should be able to help. (SLC5/05) A PLC5 does not have a "SCP" instruction.

To the OP,

If and when you post your program, post the version that was giving you trouble. Also the corrected one.

And point us to the rungs in question.