Air Temperature Indicator in Aircraft – PART 5

Indicating Systems for Turbine Gas Temperature 

EGT happens to be a critical variable in the operations of turbine engines. Such EGT indicator systems tend to show the visual temperatures inside the cockpits of turbine’s exhaust gasses once they tend to leave that particular turbine unit. In some types of these turbine engines, the exhaust gas temperatures are measured at the inlet of the turbine unit. Such values are called the Turbine-Inlet-Temperature (i.e., TIT) detection systems. 

Certain types of thermocouples happen to be utilized for measuring this EGT/TIT. Such thermocouples tend to be placed at intervals circling round the circumference of that engine’s turbine case or the exhaust pipe. The small thermocouple voltages are usually increased & are utilized to drive the servo motor that moves the indicator pointer. Moving the digital drum pointer out of the cursor movement is quite a common phenomenon. The EGT indicator happens to be in a hermetically sealed device. The instrument scale tends to range from 0 degrees Celsius to 1200 degree Celsius, with a vernier scale in the upper right corner of the dial and a power failure warning flag in the lower part of the dial. 

The TIT display system visually displays the temperature of the gasses entering the turbine on the instrument panel. Multiple thermocouples could possibly be utilized with an intermediate TIT voltage. Inside the sensor are 2 thermocouples that contain 2 junctions, which happen to be electrically independent. One of these 2 thermocouples happens to be in parallel to send signals to the cockpit detector. Another set of parallel thermocouples provides signals for temperature to the engine monitoring system as well as the control system. Every such circuit happens to be electrically independent, thus ensuring the reliability of the two systems. 

The circuits for the other 3 engines happen to be quite identical to that system. The detector includes a bridge circuit, a switch, a 2-phased motor for the purpose of driving the indicator, and a feedback potentiometer. Also included is a voltage reference circuit, amplifier, shutdown indicator, power supply, & overheat warning light. The output of the amplifier activates the adjustable field of the 2-phase motor, which positions the detector master pointer & the digital detector. The motor even utilizes a feedback potentiometer for providing a buzzer signal in order to stop the drive motor at the time when the correct pointer position (relative to that of the temperature signal) is reached. The voltage-reference-circuit gives a precisely regulated reference voltage inside the bridge circuit for avoiding errors generated from fluctuations in the input voltage of the indicator’s supply of power. 

The warning light telling about over temperature tends to illuminate when TIT happens to reach the predetermined limit. An test switch (external) is ideally installed for the engines overheating warning lights to be tested simultaneously. While making use of such a test-switch, an over-temperature signal tends to get simulated inside every bridge circuit for detector temperature control. 

Digital cockpit instruments do not require the use of resistance-type indicators or the regulated servo-driven thermocouples for communicating temperature information to the pilot. The sensor’s resistance & the voltage values tend to be entered inside a suitable computer wherein they are adjusted, processed, monitored & printed on the cockpit panels. They are even sent to other computers that need temperature data to control & monitor various integrated systems.