4-20ma

JWUNSCH

Member
Join Date
Jan 2012
Location
CT
Posts
5
I'm new to this so it maybe a dumb question but i'm using a slc500 a.b. 0-20ma output to a 4-20ma input on a rectifier how do i scale the plc output to match the rectifier input?
4 = 0, 20 = 20
 
The PLC has a 0-20mA Output, and the input of the other device is 4-20mA?

In that case you should scale your output between 0-16mA and then add 4mA.

Let's assume that it's a 12bit analog output module. Then

0mA = 0
20mA = 4095 ---> 16mA = 3276 AND 4mA = 819

To make the calculations for the output, work with the range 0 - 3276, and the add 819 before setting the analog output. (You cannot work with 819 - 4095 directly, because thats not a linear function) That way, when you need a 0, you are setting a 819 that is 4mA and your rectifier will understand it as a "0", and the same for the upper limit.

I hope you understand what I'm trying to explain. Good luck!
 
Last edited:
What is the part number on the card? some cards you can select the output and you maybe able to change the output to 4-20 then its a easier

Just a thought...
 
It's an allen bradley analog output #1746-no4i module 0-20ma i didn't see anywhere to change it on the module.
 

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