best way to scale 1794-ie8 in controllogix

I usually use function blocks to do the scaling, but I no longer have that software. I dont believe I can scale on the card either with the flex.

is it acceptable to use a compute function with this expression?

(RAW DATA FROM ANALOG CHANNEL - LOW SIGNAL) * (HIGH ENG - LOW ENG) / (HIGH ENG - LOW ENG) + LOW ENG

or would it be better to use the different math functions instead of putting it all in the compute?

any other suggestions?

The CPT instruction will be just fine, in fact its the best way to do more than one math operation because it does not require storage of intermediate results in memory.

If you have RSLogix V16 or higher you can download an SCP AOI and use it, works like SCP in RSL500.

thanks for the help. I have ver 15 so I wont be able to use the scp. when you read the instruction help for cpt, it kind of states that it is memory intensive so i wasnt sure if there was a better way.

diat150 said:

.... when you read the instruction help for cpt, it kind of states that it is memory intensive so i wasnt sure if there was a better way.

Click to expand...

I think it probably means that CPT instructions take longer to execute, rather than being "memory intensive". In fact using CPT can save on memory usage, because you don't need intermediate result storage, and there are less ladder instructions, branches and rungs to consider.

As you can't use AOI, I would suggest using a subroutine containing the pseudo-SCP CPT with the equation you quoted. All you would have to do is pass the unscaled value, and relevent min. & max. EU values as parameters, returning the scaled EU value. Since you are using only the one CPT instruction in your subroutine for all your analog input scaling, you have a "fit and forget" solution.