RSLogix500 CPT Instruction Help

julianf400 · Jul 15, 2012

Hi all,

I am having a few difficulties with the CPT instruction and getting the dreaded "invalid expression ! Two operands in sequence! ", my formula is as follows:

Pw = EXP (C8/Tg+C9+C10*Tg+C11*Tg^2+C12*Tg^3+C13*Ln(Tg))

and my CPT function logic is this

( 2.7182818284 * ( F8:0 | F8:6 + F8:1 + F8:2 * F8:6 + F8:3 * ( XPY ( F8:6 , 2 ) ) + F8:4 * ( XPY ( F8:6 , 3 ) ) + F8:5 * ( LN ( F8:6 ) ) )

all of my "Cxx" and "Tg" values are either constants or derived from previous compute functions which are compiling fine.

kolyur · Jul 15, 2012

I don't see any glaring errors but usually when I have to do an exponent in CPT I use **, as in F8:6**2.0.

DamianInRochester · Jul 15, 2012

Which processor are you using?

julianf400 · Jul 15, 2012

System is a Micrologix 1400 Cat: 1766-L32BXBA - not sure which revision the hardware will be but development file is setup for Ser B

julianf400 · Jul 15, 2012

I believe the problem to be with the orientation of the XPY command, if i replace them with the "**" it will compile, however it then re-arranges my equation to look like this automatically?

2.718282 * ( ( ( ( ( ( F8:0 | F8:6 ) + F8:1 ) + ( F8:2 * F8:6 ) ) + ( F8:3 * ( F8:6 ** 2.0 ) ) ) + ( F8:4 * ( F8:6 ** 3.0 ) ) ) + ( F8:5 * ( LN F8:6 ) ) )

DamianInRochester · Jul 15, 2012

Unless I mis-counted, you don't appear to have an equal number of "(" and ")"
One the first expression.

DamianInRochester · Jul 15, 2012

( 2.7182818284 * ( F8:0 | F8:6 + F8:1 + F8:2 * F8:6 + F8:3 * ( XPY ( F8:6 , 2 ) ) + F8:4 * ( XPY ( F8:6 , 3 ) ) + F8:5 * ( LN ( F8:6 ) ) )
8 red ones
7 green ones

kolyur · Jul 15, 2012

I confirmed that XPY is not a valid operator for the CPT instruction; you have to use **. Once I made this change to your original expression, and corrected the number of parentheses, it compiled OK on my system.

julianf400 · Jul 16, 2012

Thanks for the help everyone, i will run manual calcs before commissioning just to confirm that more parentheses isnt going to upset anything.

lokeshdhayal7940 · Jun 28, 2018

rslogix500 comput instruction

plz tell me that how to use compute in rslogix500

Ken Roach · Jun 28, 2018

Welcome to the PLCTalk forum community, lokeshdhayal7940.

In general, it's best to create a new thread with a new question. This thread is six years old and is specifically about the Exponent operator.

For general questions, always start with a user manual or reference manual.

The SLC-500 instruction set reference is detailed in the RSLogix 500 Instruction Set Reference Manual, available in PDF format from Rockwell:

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1747-rm001_-en-p.pdf

There may be minor differences when you're dealing with a modern MicroLogix controller, but your general question of "how does the CPT instruction work" should be well answered by that manual.

lokeshdhayal7940 · Jul 2, 2018

what is the differnce between plc and slc
what can i do for globle certificate

RSLogix500 CPT Instruction Help

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