Scaling in AB CLX (relay ladder)

[PaulKraemer]

Hi,

I have a job where I am using an AB ControlLogix PLC. I have a REAL tag that can have values between 0.00 and 8,022.40 (always with two decimal places). I have to scale this value to an integer between 0 and 16,777,214.

I see that RSLogix 5000 has a SCL (Scale) function, but the online help says that this command is only available in the Structured Text editor. Unfortunately, I only own the Relay Ladder editor.

I am sure that I can use basic math functions to (1) multiply the real value by the necessary multiplier and then (2) convert the result to an integer. I think this would take me at least two rungs and three different tags (the original real tag, another real tag for the scaled value, and finally an integer tag for the scaled value after I truncate the decimal places).

I have to do this kind of scaling for quite a few tags. Before I start trying to work through this, I was just wondering if anyone might be able to suggest an easier approach that I might be missing.

Thanks in advance,
Paul

 

[widelto]

Your solution is out, It is located in the add on examples of version 16 CD.

 

[SNK]

Why don't you just use the scaling function in the card properties?
Am I missing something? Is it because you are using your REAL integer, rather than the DISCRETE I/O? Why not scale from the start?

 

[widelto]

here you are:

 

[rdrast]

Uhhh... that one's easy. Just multiply by 2091.2961. (16,777,214 / 8022.4)

 

[TConnolly]

Use the CPT instruction for any math that involves more than one operation. ADD SUB MUL DIV are faster for single operations only, but if you have to store intermediate values for additional computations, those instructions actually take longer. The CPT has the advantage in that there is no need to store intermediate values in a tag.