My ID Fan is in Stop Condition but Rpm is Showing around 700 in DCS.

1. I Have Checked the Sensor Healthiness and Sensor found Good.

2. Checked Sensor o/p Which Goes to DCS.It is Showing 4ma.

3. I thought May be Channel in DCS May be Fault. But the Channel is Healthy.

Please Tell Me How to Rectify this Problem.

 

Possibilties:

1) Field signal has a ground loop which adds some current that the DCS analog input (AI) sees.

This problem can be masked when a check of the AI is done with a battery powered, floating signal source and it shows everything is fine because a battery powered simulator creates no ground loop.

Solution:
a) Check junction boxes and field device for water in the electronics. Water can cause a ground loop current.

If water in a junction box creates a ground loop, checking the output at the field device might show only 4.0mA, whereas the ground loop adds XmA at a more distant point in the loop.

b) Check output of field device with a calibrator that can detect ground loop current in loop powered loops, like a PIE 334Plus.

c) Use a loop isolator to isolate the field device from the AI.

2. Someone re-configured the AI range from 0 to X rpm = 4-20mA to 700 to Y rpm = 4-20mA. The channel can be 'healthy', but misconfigured so as to misinterpret the range of the input signal.

Solution: check the AI configuration yourself and confirm what it is.

 

Thank for Suggesting me. My Problem is Rectified.