In our Gas Turbine (GE Frame 9 ) for GT cooling water there are 8 nos fans and fans are operated by a step controller. Step Controller has two inputs -one is 4 ~ 20 mA( from temperature sensor) and another is 0 ~ 1500 ohm which is coupled with motor.Motor is operated from the output of the Step Controller & Controller has one Set Point.When motor move then this 2nd input ohmic value also change as it is coupled with motor.I cannot understand why this 0 ~ 1500 ohm input is provided in the controller? Could anyone explain me?

 

maybe it's a ptc/ntc input for motor temperature protection.