Air Temperature Indicator in Aircraft – PART 6

Total Measurement of Air Temperature 

Air temperature happens to be quite a significant parameter on which various types of performance monitoring as well as different control variables tend to depend. During the flight, the air temperature (static) is constantly changing, & accurate measurements are quite hard to get. Below Mach 0.2, a simple resistance-type/bimetallic temperature gauge could possibly give relatively correct readings for air temperature measurements. At higher speeds however, friction, air compressibility & boundary layer behaviors tend to create difficulty with correct temperature measurements. Total-air-temperature (i.e. TAT) happens to be the static air temperature added to any temperature increase due to the rapid movements of the aircraft in the air. The rise in the temperatures is called ram rise. TAT sensors are specifically designed for capturing such values accurately & sending signals for pilot detection and usage in different engine systems as well as aircraft systems. 

Simpler TAT systems tend to consist of the sensors as well as the detectors with in-built resistance-balancing circuits. The airflow through the sensor has been designed in such a way that air (at the exact temperature) tends to hit the platinum alloy resistive element. Sensors are designed in such a way that they help in detecting any changes in the temperatures versus the variations in the element resistance. When the pointer is placed in the bridge circuit, it moves in response to the imbalance caused by the variable resistance. 

More advanced systems tend to utilize the technology of signal correction as well as amplified signals that are sent to the servo motor for adjusting the cockpit indicators. Such systems consist of precisely regulated power supply as well as fault monitoring. These usually utilize digital drum-type readouts; however, they can also be sent to the LCD controllers for illuminating the LCD screens. Various LCD displays tend to be multi-functional, and they are also able to display static air temperatures & actual air speed. In a totally digital system, the correction signals tend to feed to the ADC. They can be properly processed there for cockpit displays or systems that need temperature data. 

The designs of the TAT sensors/probes are indicated by the possibility of ice formation in icy cool conditions. Sensors that are left unheated might stop working properly. Adding a heating element comprises accurate data collection. The heating of the sensors should not affect the sensor element’s resistance. 

During the design phase, special attention tends to be paid to the air flow as well as material conductivity. Some of the TAT sensors direct the airflow through the devices for influencing the ambient airflow so that it directly flows into the platinum sensors without additional energy from the sensor heaters.