Flex I/O 1794-IF4I Data Read to RSLogix 5000

Hey all. I was curious as to how I could read and manipulate the data from a 4-20 mA input on a 1794-IF4I module in RSLogix 5000. My count range would be from 6240 to 8737 for 0-5 Amps. However, what ways could I convert these counts to a more user-friendly amperage feedback?

Thanks!

The easiest way is to use the Scale (SCL) instruction in the function block language. Otherwise you're going to put together a simple linear equation in ladder logic.

1794 FLEX has this crude data handling because it dates back to being an I/O platform that could be used with Classic PLC-5's and RIO. Modern Logix I/O virtually all has scaling onboard.

and by "put together a simple linear equation in ladder logic", I mean "open your old algebra textbook to remind yourself", which is what I did. Do I have to surrender my geek credentials now ?

Since you have the minimum and maximum values of the raw data, and the minimum and maximum values of the amperage they represent, you have a "two point" description of your linear equation. Call these points h,k (6240, 0) and p,q (8737,5).

The two-point format for a simple linear equation is:

y - k = ((q-k) / (p-h)) * (x-h)


Here's an example of doing the math before you enter the Compute statement (the slope-intercept format) or doing the math inside the Compute statement (the two-point format).

If you have Logix V16, just make the scaling equations Ken posted up there into an AOI, and have your very own Value_Scale AOI that can be used in LAD.

(one of the first I wrote for 16)

This is excellent! Thanks everyone! Makes much more sense now.