Air Temperature Indicator in Aircraft – PART 2

Air Temperature Indication for Aircrafts

Utilizing electricity to measure different temperatures is quite prevalent in the aviation industry. Different ranges of temperature tend to be measured in a more suitable way by one or the other sort of the system. Below mentioned are some measuring systems as well as indication systems that are largely seen in various sorts of aircraft. 

Electrical-Resistance Thermometers

The main parts of electrical-resistance thermometers happen to be the indicator instrument, the element (or the bulb) that is temperature-sensitive & the connecting wires along with the plug connectors. Such type of a thermometer is largely used in various types of aircraft for measuring carburetor air, oil, free-air temperature etc. These are utilized for measuring low & medium temperatures between -70 degree Celsius and 150 degree Celsius. 

The electrical resistance of most metals alters when the temperatures of those metals tend to change. A resistance thermometer works on this principle. Normally, the electrical resistance of metals tends to augment with increasing temperatures. Different metal alloys tend to have high temperature-tolerance coefficient, which means that their resistance differs significantly with temperatures. This property makes them highly suitable to be used in devices used for sensing temperatures. The metal resistors are in contact with the liquid or the area where the temperatures are to be measured. This is wired to a device in the cockpit detector. Optionally, the instrument dial tends to be calibrated in degrees Celsius or degrees Fahrenheit instead of ohms. As the measured temperature tends to change, the metal resistance also changes, and the indicator shows the exact extent to which the change is happening.

A common electrical-resistance thermometer appears to be like any other such thermometer. For use in multi-engine aircraft, these detectors are available in 2 different forms. Most such indicators themselves compensate for cabin temperatures. A thermally-sensitive resistor is designed to have its own resistance for every temperature value within its operating range. The temp-sensitive resistive element happens to be the length or coil made of nickel or manganese wire or any other such suitable insulating material alloy. The resistor tends to be protected by a sealed metal tube that is connected to a hexagonal head. The 2 ends of the coil are soldered or welded to a socket designed to accept the plugs of the plug connector. 

Such indicators include the resistance measuring devices. They sometimes use a modified form of the Wheatstone Bridge circuit that works on the principle of balancing 1 unknown resistance with other such known resistances. 3 resistance values ​​of the same are connected in a bridge circuit that is diamond-shaped. One resistor, whose value is unknown, also happens to be one part of the circuit. The unknown resistance shows the temperature bulb’s resistance of the electric-resistance thermometer system. A galvanometer is fixed at 2 points in the circuit. 

If the temperature makes the resistance of the bulb the same as the other resistances, there’s no potential difference between the 2 points in the circuit. So, no current will flow in the galvanometer’s leg of the circuit. As the temperature of the bulb changes, so does its resistance, and the bridge tends to become imbalanced, leading to the current to flow through the galvanometer in 1 direction or the other. The pointer of a galvanometer is basically the pointer of a gauge. The time of it moving against that dial-face that is calibrated in degrees, the temperature is shown. Many such pointers are equipped with a zero adjustment screw on the front of the instrument. This adjusts the tension of the pointer reset spring when the bridge is at the balancing point (this happens to be that position where the bridge circuit tends to balance & no current flows through that meter).