BRIDGE METHODS OF MEASURING IMPEDANCES 



4. Product Arm Type — Product Imaginary 

 If {ZbcZad) is imaginary, then 



= ^^c + Oad = ± 90°. 

 That Is 



ZbcZad = Zbc/Yad = JRbc/Bad = JXbc/Gad- 



Substituting equation (16) in equation (6) 



BabRbc BabXbc 



459 



and 



RcD = 



XcD = 



Bad Gad 



GabRbc _ GabXbc 

 Bad Gad 



(16) 



(17) 



(18) 



For this type the components of Zcd are balanced by components 

 of Yab 90° out of phase, that is Bab will balance Rcd and Gab will 

 balance Xcd- 



The relations given in these equations are summarized in Table I. 



TABLE I 

 Bridge Types 



1 These values may be derived by using admittances in place of impedances and 

 vice versa throughout. 



Actual Bridge Forms 



The fixed arms may be made up of simple resistances or reactances 

 or of complex impedances provided they meet their phase require- 

 ments. Since the choice of complex impedances has no practical 

 advantages over simple reactances or resistances, the choice of fixed 

 impedances should obviously be made on the basis of the simplest 

 practical type. So they will be limited for the present to simple 

 resistance, capacitance, and self inductance. 



