JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. 11 October 19, 1921 No. 17 



PHYSICS.— i4 furnace temperature regulator.''- Howard S. Roberts, 



Geophysical Laboratory, Carnegie Institution of Washington, 

 (Communicated by Arthur L. Day.) 



In 1919 White and Adams described a temperature regulator for di- 

 rect current resistance furnaces- in which the heating coil of the furnace 

 was placed in one arm of a Wheatstone bridge and the heating current 

 was varied by a motor-driven switch controlled by the galvanometer 

 of the bridge. The switch opened or closed the circuit through a 

 shunt around a fixed resistance in series wdth the furnace but 

 outside the bridge. This arrangement causes the temperature of 

 the source of heat (the platinum wire) to oscillate within rather nar- 

 row limits at such a rate that the oscillations in the temperature of 

 a body within the furnace are imperceptible. 



Regulators of the Wheatstone bridge type are particularly adapted 

 to long narrow furnaces where the heating element covers nearly 

 all of the surface of the cavity; their use obviates the need for plac- 

 ing any part of the regulator within the furnace, and there is no ther- 

 mal lag whatever between heater and regulator as there is where the 

 regulator employs a thermocouple placed inside the furnace. 



The apparatus set up by White and Adams included a specially 

 constructed galvanometer-relay, and it was with the primary idea 

 of replacing the latter with stock apparatus that the present reg- 

 ulator was devised. Incidentally, the choice of a different type of gal- 

 vanometer has overcome one rather serious defect in their apparatus. 



DESCRIPTION OF THE REGUI^ATOR 



Figure 1 is a schematic diagram of the present regulator. It is 

 intended for use with furnaces whose resistance when hot lies between 

 2.5 and 10 ohms, requiring not more than 15 amperes at 110 volts 

 direct current. For heavier currents a different form of main relay 

 is necessary. 



1 Received September 2.3, 1921. 



2 Phys Rev. 14: 1 !-l8. 1919. 



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