Dear All,

I need your guidance related to RTDs.

Process: 9E Gas Turbine Generator TEWAC

Instrument: 3 wire RTD PT 100

Problem: Resistance of two RTDs at same location 136 ohm. Value at HMI 40 deg C difference.

Control System: Mark VIe.

Can anyone suggest where the problem exists?

 

Hammad Ali Zaman,

When did this problem start? After a maintenance outage? Was a Mark VIe RTD input TB was changed? What changed before the problem started?

Have you verified the wiring? GE typically uses a "unique" RTD wiring scheme which must be done exactly correctly? (Many installations ground one of the two common leads of three-wire generator RTDs, and use two-wire, twisted, shielded pairs for generator RTD interconnecting wiring, using one or two conductors (cores) of a single pair for the "common" leg feedback, which requires jumpering the commons at the Mark VIe TB properly for it to work correctly.) Most all generator RTD issues (other than open RTDs) are the result of improper wiring.

Are there any Diagnostic Alarms on the RTD I/O Pack(s)?

Are there any IS barriers used on the inputs? Are they working correctly?

What happens when you exchange the two RTD inputs at the Mark VIe TB? Does the problem stay with the input or move with the wiring?

Has someone changed configuration parameters for one of the RTDs?

 

> Can anyone suggest where the problem exists?

dear sir

plz check the line resistance at the system side, and the range setting at the system.

 

try to check the value in the software. check the wiring and both MTL Barrier.

try to simulate by resistance box from the panel. check if there is offset or the type of RTD been changed by some one in the software.