5/01 4-20mA

i will start off saying this is such a great site, with a treasure trove of knowledge. i have been a member for quite some time, although i had to get a new user name since my crackberry crapped out on me and i couldnt remember my pass word. i was a reader and had never posted until this week, and this will be my second post. enough said now to my subject...


i am working with a slc 5/01, it is a very simple program i am running 6 pumps. what i need is to trend the user input on a chart. i need to know what instruction type to use to scale my user input into a 4-20mA signal. thank you in advance.

I should also mention that the SCL instruction isnt available in my instruction pallette.

And now i know why. Its not a available instruction on the 5/01.

A little more info would help someone help you.

How is this user input getting into your SLC? HMI?, analog input? or? Range of values?

Tell us the complete catalog numbers (class #) of any input, or output cards (modules) you have installed.

Valid point. I am at home working on this. So the machine isnt physically in front of me so i will pick back up on this monday when i get to work.

The SLC-5/01 doesn't support floating-point math, either, so this becomes a good exercise in the capabilities and limitations of 16-point signed integer math.

Scaling from one range of numbers to another is a straightforward linear equation. These are usually expressed as "ax + by = c", or in the more common format "y = m x +b".

Because these equations form a straight line on a graph, the m term is called the "slope", and it's calculated as m = (y2 - y1) / (x2 - x1).

That should look familiar: when you use the SCP equation, you enter the Minimum and Maximum values for both the input values and the output (x) values.

I'm not as good a teacher as our friend Ron Beaufort, so I'll just link to his excellent example of how the SCP instruction works and how to implement it in controllers like the 5/01.

http://www.ronbeaufort.com/y=mx+b_part1.pdf

http://www.ronbeaufort.com/y=mx+b_part2.pdf