Coaxial Electric Heaters
- Thursday, 27 March 2008
These devices can be used safely where magnetic fields are not tolerated.
Coaxial electric heaters have been conceived for use in highly sensitive instruments in which there are requirements for compact heaters but stray magnetic fields associated with heater electric currents would adversely affect operation. Such instruments include atomic clocks and magnetometers that utilize heated atomic-sample cells, wherein stray magnetic fields at picotesla levels could introduce systematic errors into instrument readings.
The resistance of the graphite film can be tailored via its thickness. Alternatively, the film can be made from an electrically conductive paint, other than a colloidal graphite emulsion, chosen to impart the desired resistance. Yet another alternative is to tailor the resistance of a graphite film by exploiting the fact that its resistance can be changed permanently within about 10 percent by heating it to a temperature above 300 °C. Figure 2 depicts a coaxial heater, with electrical leads attached, that has been bent into an almost full circle for edge heating of a circular window. (In the specific application, there is a requirement for a heated cell window, through which an optical beam enters the cell.)
This work was done by Dmitry Strekalov, Andrey Matsko, Anatoliy Savchenkov, and Lute Maleki of Caltech for NASA’s Jet Propulsion Laboratory.
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