We have 2-wire loop powered (24VDC/4~20mA) inductive sensor installed on Steam Turbine Turning Gear Motor for engaging/ disengaging purpose. This sensor basically senses the movement of plate gap (mm) and transforms this gap (mm) information into mA.
The problem is when its target moves, sensor mA & biasing voltage also starts fluctuating simultaneously (Volts fluctuates from 24VDC to 6VDC & signal current fluctuates from 5mA to 19mA).
The sensor is loop powered from INFI90 Bailey DCS (Analog Input Slave Card having Termination Unit#NTAI05). Though the Slave Card Termination unit supply remains constant.
We did this checks on several new sensors but observing the same results.
Wire loop from DCS till sensor is OK. DCS card also checked, verified and found ok.
Please suggest what could be the possible reason for such fluctuation?
Sensor Model# PEPPERL+FUCHS NJ2-12GM-N