How to program PLC5 to calculate difference in percent

[mlash1]

Hi everyone,
I need to program a PLC 5 to calculate the difference in percent between the highest and lowest of either 2 or 4 floating point values so it can be displayed. For example, the 4 values might be: 225.1, 225.5, 225.8, 225.3. The math looks like this: 225.8 (highest value) minus 225.1(lowest value)= 0.7, then 0.7 divided by 225.1 (lowest value) = 0.0031097, times 100 = 0.31097 %. I am sure there is a way to do this but I haven't been able to figure it out. Thanks very much!

 

[Mickey]

Look up the "sort File" (SRT) instruction to sort the values. Then use a Compute (CPT) or
the math instructions to compute the percentage.

See instruction set manual below if you don't have it.

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1785-rm001_-en-p.pdf

 

[TConnolly]

Welcome to the forum.

Which PLC/5 are you using?

If you are using an enhanced PLC/5 (models ending in 0 rather than 5, such as 5/20 or 5/40) then use the SRT command. Move the four values into four consecutive registers and then sort those registers. The lowest value will be in first register and the highest value will be in the last register. From there you can use the CPT instruction or conventional math instructions.

If you are using a non-enhanced PLC/5 then you'll have do do a series of brute force compares to find the min and max, still pretty easy to do with just four numbers.

edit: See attached. First six rungs are for an enhanced PLC/5. The rest are for a non-enhanced PLC/5.

 

[mlash1]

Thanks! I will have to check which type of processor but pretty sure it is a 5/40.

 

[mlash1]

Thanks very much.