RESISTANCE DEVICES 



153 



Carbon Compression Rheostats. Carbon compression rheo- 

 stats are exceedingly useful as laboratory appliances where 

 low-voltage currents are to be controlled as, for example, in 

 calibration work. 



The essential feature is a series of specially moulded carbon 

 plates, which can be forced into more or less intimate contact by 

 a screw. 



A convenient form of carbon compression rheostat is shown in 

 Fig. 80. It contains 90 plates each 1% m - by 1% in. by % in. 



A 4-volt current can be controlled between the limits 1 and 28 

 amp., the resistance of the circuit outside the rheostat being 0.1 

 ohm. 



FIG. 80. Carbon compression rheostat. 



References 



1. "Resistance Coils and Comparisons," (shows various forms of construc- 

 tion), C. V. DRYSDALE, The Eectrician, vol. 59, 1907, pp. 955, 989, 1035. 



2. "Alloys for Resistance Coils," ST. LINDECK, The Electrician, vol. 30, 

 1893, p. 119. "tlber die Haltbarkeit von Kleinen Widerstande am 

 Manganene Bleck im Praktischen Gebrauch," ST. LINDECK, Zeit. fur 

 Insirumentenkunde, vol. 23, 1903, p. 1. 



3. "The Variation of Resistances with Atmospheric Humidity," E. B. 

 ROSA and H. D. BABCOCK, Bulletin of the Bureau of Standards, vol. 4, 

 1907-08, p. 121. "A New Form of Standard Resistance," EDWARD B. ROSA, 

 Bulletin of the Bureau of Standards, vol. 5, 1908-09, 413. 



4. "Non-inductive Water-cooled Standard Resistances for Precision 

 Alternating-current Measurements," CLIFFORD C. PATTERSON and E. H. 

 RAYNER, Journal Institution of Electrical Engineers, vol. 42, 1908-09, p. 455. 

 "On Compensation for Self -inductance in Shunt Resistances," ALBERT 

 CAMPBELL, The Electrician, vol. 61, 1908, p. 1000. 



5. "t)ber Starkstromwiderstande mit Kleine Selbsinduktion," E. ORLICH, 

 Zeit. fur Instrumentenkunde, vol. 29, 1909, p. 241. 



