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BELL SYSTEM TECHNICAL JOURNAL 



Fig. 12 — {A) Circuit for measuring the contact noise of a parallel assemblage of re- 

 sistance elements. (B) The equivalent a.-c. circuit of {A). 



ous value of a.-c. voltage experienced across the impedance Z — which is 

 the input impedance of a measuring circuit — is 



€ = ei - iiRx 



^n ^n^n — tZj , 



where 11,12 • • • *n are the respective fluctuating currents flowing because 

 of the generator action of the fluctuating contact resistances. Also 

 we have 



i = ii + ^2 • • • in- 



R.^Z\ 



€ 



Y' 



The noise power dissipated in Z, and thus measured by the measuring 

 device, is defined in the usual way as e^/Z, where e- is the mean square 

 voltage across the impedance Z and is defined as 



c2 = hmit (1//) 



Jo 



■Mt. 



