Original, complete WW II German Aircraft Temp-Anzeiger - TEMPERATURE GAUGE Fl.20349 – 60 / + 20 °C.
Designation: electr. Outdoor air temperature indicator
Requirement Character: Fl.20349
Unit #: 127-1078 B-1
Measuring range: – 60 / + 20 °C
Manufacturer: Hartmann & Braun, Frankfurt/Main
Year of construction: approx. 1942
Information about the outside air temperature was extremely important for the pilot to take appropriate measures in good time (pitot tube heating, weapon heating, de-icing systems, etc.).
The electric "remote thermometer" shows the temperature of the outside air. It consists of the actual thermometer (electrical temperature sensor, Fl.20341), a temperature-sensitive resistance wire, the display device and the power source for the measuring current (board battery). The thermometer consists of a winding surrounded by a metal protective cover. The electrical resistance of this winding changes with temperature and is determined using a meter calibrated in degrees of temperature, which can be placed at any distance from the transmitter (temperature sensor). The display device itself is a so-called cross-coil measuring instrument. The display instrument shows the incoming voltage, with the dial being calibrated in °C. The measuring method is based on the ohmic principle, which means that the resistance of a metal increases with increasing temperature.
The advantage of such electrical Temperature indicator is the high measuring accuracy and the easy separability of the measuring line. The temperature sensor (Fl.20341) associated with the measuring system was installed on the outer skin of the aircraft (underside of the fuselage or wings, away from the exhaust jet).