Abstract: Two theorems in linear circuits are presented and proved in this paper. One is the theorem of conservation of the node voltag sensitivity order, the other is the theorem of conservation of node voltage change order. Based on the theorems, a new approach——the hard and soft fault dictionary for analog circuits is presented. Only using one fault characteristic code, this method can determine hard or soft fault which is caused by any element parameter. The size of the dictionary only is half of the size of the former hard fault dectionary.

Key words: sensitivity, fault diagnosis, dectionary method