ARTICLE REF – ART235
This is the older version backup overspeed monitor which is still in service but no longer being used in new production. It has been replaced by the TACHPAK 30 which is a two channel overspeed monitor. The TACHPAK 3 has a single channel and monitors either ST008A or ST008B. In a Swiftpak it does not matter which speed sensor is connected, as both Power Turbine A and B rotate at the same speed. Ther danger is if you have the coupling out of side B due to maintenance for example and the monitor is connected to ST008B!
On the left you see the wiring for the sensors. At position 51 you have wire U14-720, which means the wire can be found on Unit Control Electrical Schematics Page 14, Line 72. The other two wires belonging to that sensor are in position 52 and 53. The signals comes in from the left and leaves on the right of the terminal stip.
The speed sensor from the turbine comes in at 54, 55 and 56, but they are not connected to wires leaving on the right. It is here that you must move the output wires from the output 51, 52 and 53 to 54, 55 and 56 if that is the side in service.
To be sure inject a signal close to the speed sensor on the side that is in service and ensure your overspeed trips, so you know the wiring is correct.