Page:The Bell System Technical Journal, Volume 1, 1922.pdf/23

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DIRECT CAPACITY MEASUREMENT
23

The excess of one direct capacity C12 over another C55 is readily determines by connecting terminals 1 and 5 to corner D, terminals 3, 4, 7, 8, . . . to corner C or A, and then balance with terminals 2 and 6 on A and C, respectively, and repeat, with their connections reversed.

Potentiometer Method, Fig. 3

The required direct capacity C12 is balanced against one of its associated direct capacities, augmented by a standard direct capacity

Fig. 3—Potentiometer Method for Direct Capacity

C1, and the measurement is repeated with the required direct capacity and standard interchanged. Let R′, R″ be the resistance required in arm A B of the bridge for the first and second balance, then, S being the total slide wire resistane and G1 the grounded capacity of terminal 1:[1]

This ratio method requires for the bridge a variable or slide wire resistance and a constant condenser, and it may be employed as an improvised bridge, when sufficient variable capacity is not available for the Colpitts method. Not being a substitution method, however,

  1. See appendix, section 3.