DFB ratio bias device is an auxiliary unit of DDZ-III electric combination instrument. It can be used to enlarge, reduce signal according to ratio and also can be used in the occasion which can change the zero contact arbitrarily. In addition, DFB-type ratio bias devices can be used as a non-indicating DGB ratio control system. Because of the input voltage (or current) signal and the output current (or voltage) signal, it also can be used in the occasions where need voltage- current converting or current - voltage converting. The ratio factor of meter is 0.3～3.