# 4-20ma output question

Discussion in 'General Electronics Chat' started by Aj_foor, Nov 11, 2018.

1. ### Aj_foor Thread Starter New Member

Nov 11, 2018
2
0
I’ll start by saying I’m new to this type of thing so I’m a bit clueless and any and all help will be great... We have a raytek pyro paired with an Endress-Hauser RIA16 digital readout. The problem is I can’t get the readout to match what the actual pyrometer is displaying.. I think maybe it has to do with scaling but I’m not sure how to go about getting the correct scale.

If anyone needs more information to help me figure this out I’ll try to get it! Thanks again!

2. ### MrChips Moderator

Oct 2, 2009
19,132
6,148
Welcome to AAC!

The first thing you need to do is provide links to the operating manuals of both units. Don't expect people to have to go searching for these in order to help you.

Next, read each manual and find out what are the interface requirements for each unit.
Then come back and ask questions if you do not understand what the manuals say.

For someone here to help you, that person has to do exactly that - read the manual.

Nov 11, 2018
2
0
4. ### Picbuster Well-Known Member

Dec 2, 2013
978
126
The 4-20mA system is build as follows:
0-4mA is not used for measurement but intended to detect cable fail or supply aux voltage (3-5V)
that implies that your actual measurement = 0 to 16mA on the line +4mA resulting in 4-20mA.
In m&r (measure and control) we use % so that 0-16mA provide 0-100%.
You as an user will link this 100% to the full scale of voltage,speed, ph, temperature,watt and so on.

e.q. voltage goes from -8V to +8V the LINE will produce @ 0V 4+8 =12mA and @-8V to 4mA.
The system should create an offset related to 12mA-4mA and decide if a span of 8 is seen as 100% or
as a span of 50% or -8 =0% and +8 =100%.

Your first step is to define the span input from minimum to maximum =100% =0-16mA.
The received current value from sensor -4mA = the actual measured value.
Make a link (formulae) between the 0-100% and the wanted value at receiver.
Use that formulae to display the value measured.

It looks difficult but it isn't.

Picbuster