Word: thermistor
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...heart of the instrument is a tiny square "thermistor," one-tenth of a millimeter on a side, small than a pin head, and attached to two hairlike platinum wires. The electrical resistance of the thermistor changes in response to tiny fluctuations in temperature. Special filters allow only a very narrow band of the infrared, between eight and 14 microns, to fall on the thermistor. The filter rejects the shorter infrared waves omitted by the sun and reflected by the moon. The earth's atmosphere, where water vapor, ozone and carbon dioxide absorb other portions of the infrared, also acts...
Attached to the pyrometer is a 35-millimeter camera accurately aligned to take pictures of the exact area of the moon's surface from which the thermistor is recording. As the pyrometer scans, the camera and the thermistor record alternately...
Under favorable conditions, the thermistor can detect a change in temperature on the moon of less than one degree Fahrenheit. The Infrared Laboratory has invented and built another detector, called a ferroelectric bolometer, which promises to be even more sensitive. It should be able, for example, to detect the heat given off by a human hand flashing across it from across the room...
GETTING information from a satellite is tricky business. "If you want to measure the temperature up there," says Van Allen, "you can't put a mercury thermometer in your bird. You have to read temperature as an electrical signal." This is done with a tiny "thermistor," whose resistance to current put out by the satellite's batteries varies with temperature. The change affects the frequency of the electronic signal sent out by the satellite's transmitter, thus reporting the temperature to the ground...
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