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November 1946 Radio-Craft
 [Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
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The Eye of Sauron
... a different kind of eye that never closes ... at least until Frodo tosses
his ring into the abyss.
Here is something you
probably didn't know. I certainly didn't, but I'm not surprised. As with many
advances in electronics and communications, Bell Telephone Laboratories invented
the thermistor. According to this infomercial from a 1946 issue of Radio-Craft
magazine, the thermistor was developed to adjust the amplification needed in its
relay circuits to provide proper signal strength. It monitored the temperature
of the output stage to determine the level. Bell claims the device was sensitive
to within one millionth of a degree and could "see" the warmth of a man's body a
quarter of a mile away on the battlefield (during World War II). As with
most things, improvements have been continually in the thermistor in terms of
temperature range, stability, accuracy, ruggedness, etc., all while lowering the
price as mass production helps amortize production costs across huge volumes.
Bell Telephone Laboratories - The Eye That Never Closes
 You are looking at a thermistor - a speck
of metallic oxide imbedded in a glass bead hardly larger than a pin-head and mounted
in a vacuum. The thermistor was developed by Bell Telephone Laboratories to keep
an eye on the amplification in long-distance telephone circuits.
When a thermistor is heated, its resistance to electric current changes rapidly.
That is its secret. Connected in the output of repeater amplifiers, it heats up
as power increases, cools as power decreases. This change in temperature alters
the resistance, in turn alters the amplification, and so maintains the desired power
level. Current through the wire at the left provides a little heat to compensate
for local temperature changes.
Wartime need brought a new use for this device which can detect temperature changes
of one-millionth of a degree. Bell Laboratories scientists produced a thermistor
which could "see" the warmth of a man's body a quarter of a mile away.
Thermistors are made by Western Electric Company, manufacturing branch of the
Bell System. Fundamental work on this tiny device still continues as part of the
Laboratories program to keep giving America the finest telephone service in the
world.
Bell Telephone Laboratories
Exploring and Inventing, Devising and Perfecting for Continued Improvements and
Economies in Telephone Service
Posted March 25, 2022
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Laboratories Infomercials |
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