Using a 4-20mA sensor with the MPM

Issue

Connecting a 4-20mA sensor to an analog input on the MPM

Product Line

SmartStruxure Lite

Environment

Multi Purpose Manager (MPM)

Cause

"Input Type" for an Analog Input can only be set to either "Volts" or Ohms"

Resolution

A shunt resistor is required to be installed across the input and ground terminals on the MPM in order to be able to measure the voltage drop over the resistor (see image below). An AIC object is then used to convert the voltage readings to mA reading.

Set up AI and AIC as shown in the images below

 

Note: The shunt resistor needs to be a precision resistor of 0.05 % and needs to be mounted as close as possible to the data acquisition system. Preferably directly screwed into the differential inputs, otherwise, you will measure the voltage over the resistor minus the voltage drop of the additional cable which aects the accuracy of your measurement.