Technical FAQs

# How to set Analog Output in I/O expansion board to use 4-20 mA instead of 0-20mA?

Issue
User is trying to use 4-20mA scale for Analog Output instead of the default 0-20mA

Product Line
I/O expansion board

Environment
Analog Output Module
ION modules

Resolution
You only need to calculate the Zero Scale and Full Scale values if your meter’s analog output port has a different range than the sensor connected to it; for example if your meter has a 0 - 20 mA range and the sensor reading the analog output port expects values in the 4 - 20 mA range. You can calculate the Full Scale and Zero Scale values by analyzing the system. The relationship between the Source input and the Normalized output is linear, so a graph can represent the six points used to produce the operation:

The mathematical relationship between the values is shown by the following equation:

Solving for Zero Scale:

Calculation Example
The meter is monitoring a 0 to 120 kW system. The receiving device can read a signal from 4 - 20 mA and your meter’s analog hardware output port has a 0 to 20 mA range. The Full Scale and Zero Scale registers need to be set up to scale the output accordingly. The variables for the module operation are:

 Full Scale = 120 kW
 X = 0 kW
 Af = 20 mA
 Ax = 0 mA
 Aa = 4 mA

Solve for Zero Scale:

The Analog Output module setup registers are programmed as follows:
 Full Scale = 120 kW
 Zero Scale = -30 kW
This will produce a 0 to 120 kW output represented by a 4 to 20 mA signal.

Those values can be programmed using ION Setup software. The software can be downloaded from here
Refer to ION Setup user guide for information on how to connect to your meter in ION Setup software.

After connecting to your meter in ION Setup, open setup assistant and navigate to Analog Out and choose which output you want to configure.
You can configure the Source, Zero Scale, Full Scale, and port to use for that Analog Output as below: