SLC 500 SCP instruction

When I try to enter a new value into the SCP to see if a 4-20ma operated valve will stroke, the value for the input setting goes back to the original value that is there already. I will not take my changes. Why is this happening?

Sorry, I highlighted the wrong part I meant to circle where the setpoint of 900 is...I'm still asking the same thing.

Is it the Scaled Max that your are trying to change? If so, then if you are online, you would have to run throught the 3-step process to put your change into action. If you are editing the SCP Output, then when the PLC scans the instruction again, the Output will be recalculated and put back just like it was!

Okay, the Input is being calculated or dervived somewhere else, so it overrides your change on each scan of the PLC. You would have to find where "Input" comes from (looks like N10:111), and "force" that value.

If N10:111 is not being set by some program instruction, but is simply a constant, then go to Data Table N10, select word 111, (Radix - "Decimal"), and type in your new value. Make a note of what N10:111 was before, so you can put it back when you are done testing.

Lancie1 said:

Is it the Scaled Max that your are trying to change?

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No and Yes I'm trying to change where the set point 900 is. I'm trying to put in 450. When I hit enter it goes back to 900. Now I'm trying to change the 31208 to half, which is 15604 and it still goes back to 31208.

I'm trying to put in 450. When I hit enter it goes back to 900.

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Look in your Data Table (or Data Files) for N10:111, and change it there. Type in "450" at Word 111, press Enter.

If it still goes back to 900, then do a "Search, Find, Find What? = N10:111, Find All" for N10:111, and find the rung where it is being set by the program (probably set with a MOV command). Now go to that rung (that is setting the value of N10:111) and temporarily change the value, but be careful that you know how to get N10:111 back to its original setting.