Logix 500 CPT

old97ss · Jun 19, 2019

so I have to find the standard deviation for amperage readings at my plant. when I input the formula into the CPT instruction it is automatically adding parenthesis in places I don't want. any help?? pictures attached of what I want and what it is doing. there is nothing in front of the sqr. it adds a set of parenthesis. and open in front of f43:14 and a closed at the end.

JaxGTO · Jun 19, 2019

It will add them automatically to enforce the order of operation. If you want a different order of operation then you have to add the parenthesis where you want to force it.

A lot of time for the SLC 500 it may be easier to break it down into single operations. Then you can control it the way you want.

old97ss · Jun 20, 2019

all right. thanks for that. but oof if i have to break these up.

kamenges · Jun 20, 2019

"Good" and "bad" in this case are subjective evaluations. The two cases are functionally equivalent. While the processor order of operation doesn't require the set of parentheses that surround what is added to F40:19, their presence doesn't change the result.

Keith

old97ss · Jun 20, 2019

hmmm. from the way I'm seeing it "bad" would subtract f40:17 from f43:14 then square the number. then divide by 13. then add f40:19 then take the sqroot of that answer. NOT what I want. should subtract first. then square add f40:19 next, divide that. then take sqroot. they are not the same unless I'm not understanding Logix 500 order of operations. (2+4)/6 = 1....2+(4/6) = 16/6.

old97ss · Jun 20, 2019

nevermind. both are bad. i ended up breaking it down and doing it in steps so all is good.

kamenges · Jun 20, 2019

The way good is shown will not do what you want given normal order of operation.

Good is shown as:

SQR(F40:19+((F43:14-F40:17)**2)/13)

That will perform the subtraction, square that result, divide by 13, add F40:19 and take the square root of that result.

What you want is:

SQR((F40:19+((F43:14-F40:17)**2))/13)

Keith

old97ss · Jun 21, 2019

yep. I noticed good wasn't good after I posted. thanks for the info.

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