Thermocouple calibration shift.

Mk-1533 through 1535 discussions.

Thermocouple calibration shift.

Postby j79guy on Mon Jan 12, 2009 9:32 pm

This seems to be effecting many Avon users. Over time, their exhaust gas thermocouple calibrations are drifting, towards the conservative. Each user insists that their calibration is good, and that they duly drive a millivolt signal through the system, and read the appropriate temperature on the panel. This is not the way to calibrate thermocouples!
There is only ONE way to calibrate thermocouples, and that is to apply a verified heat source to all the T/C tips, and then observe the indicated reading on the panel. And, the readings must be accurate at the high end, where maximum power is developed. If you are not doing your calibrations using a verified heat source, try it, you may be surprised at what you find.
A good rule-of-thumb indicator, is when the operator complains that the engine seems to not be performing as well as it should, and all engine parameters are depressed, (With the exclusion of indicated EGT) such as CDP, Fuel flow, Power turbine RPM, ect. then likely the indicated EGT is out of synch. If one or more other performanc indicators are low as well, then likely there is a controls or engine mechanical problem.
One of my Avon customers' T/C calibration had "slipped" almost 50 degrees C. at the high end. Calibrating properly, dramatically transformed the units, and we "magically" gave them back over 2000 shaft horsepower per installation.

Robin.
j79guy
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