4-20 ma math

John Morris · Oct 1, 2015

Good morning to all

It's on to phase 100 of the learning process.

Using FTV 8.1, Rs Logix Micro developer and 1400 micro processors.

We are installing a conductivity meter that out puts 4-20. I need to learn how to write out the math equation to convert the 4-20 and display on the HMI, data log it, and turn on an alarm after the high set point is reached.

Can any one point me to a link of some sample programming?

Thank you all for your valuable time and attention.

Bob O · Oct 1, 2015

Look up the SCP instruction.
HTH

John Morris · Oct 1, 2015

That's great Bob. Thank you

I appreciate the direction.

ndzied1 · Oct 1, 2015

Just be careful to check the full range of the analog input you are using.

For instance, the 1762-IF4 set up for curent has a FULL range of 0-21mA resulting in counts from 0 to 32767. The following Counts/mA relationships are what you will see with that card:

Code:

32767   21 mA
31206   20 mA
6241    4 mA
0       0 mA

So for the SCP instruction you parameters would be
In Min: 6241
In Max: 31206
Scaled Min: Conductivity @ 4 mA
Scaled Max: Conductivity @ 20 mA

Paullys50 · Oct 1, 2015

y=mx+b

John Morris · Oct 1, 2015

Thank you all

Mickey · Oct 1, 2015

Scaling math if you need to show it.

John Morris · Oct 1, 2015

Thank you Mickey

Now I understands Paully's formula

Thank you Paully.

4-20 ma math

John Morris

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Bob O

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