CompactLogix/ RS Logix 5000

JkellyNPFD · Dec 18, 2007

I have a very easy question. I'm sure it exists, but I just can't find the exponential function (i.e. Exp(4)) Does anyone know the syntax for an exponential function in rs logix 5000?

LJBMatt · Dec 18, 2007

In ladder its the XPY (x to the power of y) instruction

JkellyNPFD · Dec 18, 2007

Thanks LJBMatt. I knew it was around somewhere.

TConnolly · Dec 18, 2007

You can also use a double asterisk in the CPT function.

CPT X Y**Z

JkellyNPFD · Dec 18, 2007

Thanks Alaric

Mike6158 · Dec 18, 2007

Alaric said:
You can also use a double asterisk in the CPT function.

CPT X Y**Z

I thought ** was "raise to the power of" and EXP was the exponential function- y = e raised to the power of x, and x is Eulers number (2.718281828)... actually... I know it is.

JkellyNPFD · Dec 18, 2007

Your right, but instead of explicitly looking for a function [e ^ 5] I can use 2.718281828 ** 5, which is the same.

JkellyNPFD · Dec 18, 2007

Mike6158 said:
I thought ** was "raise to the power of" and EXP was the exponential function- y = e raised to the power of x, and x is Eulers number (2.718281828)... actually... I know it is.

Also, I believe (and I could be wrong, since I am by no means a math major) e^1 is Euler's number, not x in e^x

Ken Roach · Dec 18, 2007

A small clarification: The Logix 5000 instruction set has an "X to the power of Y" function.

In relay ladder logic and function block languages, this instruction uses the "XPY" block.

In Structured Text and inside Compute instructions, the syntax is "x ** y".

RSLogix 5000 has no built-in operators for Euler's number or for Pi. There is no "EXP" function that returns euler's number-to-the-X-power in RSLogix 5000 like there is in many PC programming languages like C++.

There is a Natural Log (LN) instruction, as well as a Log Base 10 (LOG) instruction, which are often used in similar applications.

Mike6158 · Dec 18, 2007

JkellyNPFD said:
Your right, but instead of explicitly looking for a function [e ^ 5] I can use 2.718281828 ** 5, which is the same.

That's what I did. I never found the function that I needed and I only needed it in one place

JkellyNPFD said:
Also, I believe (and I could be wrong, since I am by no means a math major) e^1 is Euler's number, not x in e^x

Maybe so... I read it somewhere... but don't remember where.

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