GE gas turbines with Speedtronic Mark I controls utilized reference ovens for temperature control and overtemperature protection.  The thermocouples were averaged (for instance, the 12 control thermocouples) and the signal was then referenced to a 240 degrees Fahrenheit oven circuit.  If this millivolt signal exceeded 240 °F, the millivolt output to the thermocouple amplifier would “go positive.”  This signal was then sent to a circuit board called AIAC in the Speedtronic systems for amplification.   It was then amplified (300°F to 1000°F was calibrated on the AIAC card to give 1.0 to 4.5 DC volts).  See Fig. 1 and Fig. 2 below for two rear views of the averaging cabinet.  Fig.2 shows it with the cover removed.

Fig. 1: Rear view of temperature-averaging cabinet.  Top cover must be removed to view.

Fig. 2: Thermocouple 240 ?F ovens exposed once black cover is removed

The photo in Fig. 3 shows a close up of the reference ovens still in operating condition.

Fig. 3: Close-up of used 240 ?F oven circuits on control panel

Fig. 4 below shows a “burned out” reference oven needing replacement.  A client recently discovered the oven associated with the Temperature Control (TX) system was faulty.  It cost him over $5,000 to replace the three ovens!

 Fig. 4: Burned-out Temperature Oven shown removed from panel

PAL Engineering can replace the existing averaging cabinet, reference ovens and AIAC card with an OCS-210 Programmable Logic Controller (PLC) manufactured by Horner Electric (owned by GE) that can eliminate the above-described problems.  Also, it will have automatic thermocouple rejection for faulty (open, shorted or grounded) thermocouples.  See Fig. 5 for a photo of a typical system replacement for a gas turbine Speedtronic™ Mark I machine.

Fig. 5: PAL Engineering replacement for temperature measurement system.

For further information about the PAL temperature measurement system (TMS), contact Dave Lucier of Pond and Lucier, LLC by calling: 518-371\-1971 or 518-330-4801.