JPS5855533B

PURPOSE:To secure the fault diagnosis for the signal converter circuit through a simple method by varying the reference voltage of the comparator circuit and then securing the same state when the pseudo input signal is applied equivalently. CONSTITUTION:Voltage veriable setting circuit 100 consists of switch elements 17 and 18, inverter 21 plus resistors R5 and R8, and then varies reference voltage ES of comparator circuits 1a-1n via pseudo input set signal 19 sent from the computer. In other words, the two active states of the external contact are taken into the input terminal of one side of comparators 1a-1n in the form of the scale of the voltage signal, and reference voltage ES set to the middle of the two voltage signals is applied to the input terminal of the other side. Then voltage ES is changed to the voltage level different from the steady state, and the output of the comparator at that time is compared with the data set previously to carry out the fault diagnosis. Thus the state identical to that obtained by applying the pseudo input signal equivalently is secured, ensuring the fault diagnosis for the signal converter circuit through a simple method.