Radio instruments and measurements. Issued March 23, 1918 by United States. National Bureau of Standards

Author:United States. National Bureau of Standards
Language: eng
Format: epub
Tags: Telegraph, Wireless
Publisher: Washington, U. S. Govt. print. off.
Published: 1918-03-25T05:00:00+00:00

Bi VSb

Hot wire

FlG. 113.— Duddell thermogahanometer

two metals is directly over, but not in contact with, the heater which is either a hot wire or thin gold leaf or film of platinum on glass. Currents as low as 10 microamperes may be measured when a heater of several thousand ohms resistance is used, but this great sensitivity is not available for radio measurements, which generally require heaters of less than 50 ohms resistance. The thermogalvanometer differs from the thermoelements described above in that the thermocouple is not in metallic contact with the heater, and thus the capacity of the galvanometer is less likely to cause leakage of high-frequency current from the main circuit.

Bolometer. — An instrument in which heat is measured by the change of resistance which it produces in a conductor is called a bolometer. Precise measurements of radiant heat, for instance,

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