Shaft torque measurement

A method of determining the power output of a gas turbine engine having a compressor coupled therewith, the engine including a power shaft, at least one multiple blade turbine disk coupled to the shaft, a speed sensor, and a pyrometer, the method comprising the steps of:

• rotating the shaft under relatively low load conditions and obtaining a first set of signals from the speed sensor corresponding to the angular rotation of the shaft and a second set of signals from the pyrometer representing the temperature of each blade turbine disk as each blade passes a predetermined point adjacent the pyrometer;
• conditioning the first and second sets of signals to develop corresponding first and second sets of pulse signals in which each pulse signal in the first set of pulse signals has a determinable first phase relationship to each pulse signal in the second set of pulse signals;
• operating the engine under at least another relatively higher load condition and obtaining another first set of signals from the speed sensor and another second set of signals from the pyrometer;
• conditioning the another first and second sets of signals to develop another corresponding set of pulse signals;
• determining another phase relationship between at least one pulse developed from the another first set of signals and at least one pulse developed from the another second set of signals;
• comparing the first phase relationship to the another phase relationship and obtaining a difference therebetween;
• determining the degree of twist in the engine shaft corresponding to the obtained phase relationship difference;
• and
• converting engine shaft twist to a corresponding torque value which will induce such twist for determining the power output of the engine from predetermined relationships between torque and power.