Fault diagnosis apparatus and fault diagnosis method of multi-channel analog input/output circuit

A fault diagnosis method for a multi-channel analog input/output circuit including:

• a signal source for generating and transmitting plural types of signals;
• a first switching circuit having at least two or more switches, said signals from said signal source being supplied to said switches;
• an analog-signal conversion unit to which outputted signals from said first switching circuit are supplied;
• and a diagnosis-voltage input unit into which test voltages are inputted,
• said fault diagnosis method, comprising the steps of:
• inputting said test-voltage values from said diagnosis-voltage input unit into a multiplexer and an A/D converter which constitute said analog-signal conversion unit, said multiplexer having plural channels, said A/D converter converting outputs from said multiplexer into digital signals, said test-voltage values being different from each other for each channel of said multiplexer;
• and
• judging whether said multiplexer is at fault or said A/D converter is at fault by making comparisons between said digital voltage values and said test-voltage values inputted, said digital voltage values being outputted for each channel of said multiplexer.

A fault diagnosis method for a multi-channel analog input/output circuit which includes a signal source for generating and transmitting plural types of signals, an analog-signal conversion unit and a diagnosis-voltage input unit, said analog-signal conversion unit including:

• a first switching circuit having at least two or more switches, said signals from said signal source being supplied to said switches;
• a multiplexer having plural input channels, said outputted signals from said signal source being supplied to said input channels via said first switching circuit;
• an analog/digital converter for converting analog signals from said multiplexer into digital signals;
• and an output processing circuit to which said digital signals from said analog/digital converter are supplied, said diagnosis-voltage input unit including:
• a test-voltage input circuit for generating plural test voltages;
• a digital/analog converter into which said test voltages are inputted;
• a demultiplexer into which outputs from said digital/analog converter are inputted, said demultiplexer having plural output channels;
• and a second switching circuit to which outputs from said demultiplexer are supplied,
• said fault diagnosis method, comprising:
• a first step of setting each switch of said second switching circuit ON in a state where each switch of said first switching circuit is set OFF, and causing said plural voltages to be generated from said signal source in a state where said test voltages are fixed at 0 V;
• a second step of judging whether or not output voltages from said output processing circuit are equal to 0 V in said set states at said first step;
• a third step of judging that said switches configuring said first switching circuit are in ON-stuck states, if, at said second step, it is judged that said output voltages from said output processing circuit are not equal to 0 V;
• a fourth step of setting each switch of said second switching circuit OFF in a state where each switch of said first switching circuit is set ON, and causing said plural voltages to be generated from said signal source in said state where said test voltages are fixed at 0 V, if, at said second step, it is judged that said output voltages from said output processing circuit are equal to 0 V;
• a fifth step of judging whether or not said output voltages from said output processing circuit are equal to 0 V in said set states at said fourth step;
• a sixth step of judging that said switches configuring said first switching circuit are in OFF-stuck states, if, at said fifth step, said output voltages from said output processing circuit are equal to 0 V;
• a seventh step of setting each switch of said second switching circuit ON in said state where each switch of said first switching circuit is set OFF, and switching said test voltages into plural steps, and causing said plural voltages to be generated from said signal source, if, at said fifth step, it is judged that said output voltages from said output processing circuit are not equal to 0 V;
• an eighth step of judging whether or not said output voltages from said output processing circuit are equal to said test voltages in said set states at said seventh step, said test voltages being inputted such that said test voltages are switched into said plural steps;
• a ninth step of judging that said multiplexer or said analog/digital converter in said multi-channel analog input/output circuit is not operating normally, if, at said eighth step, it is judged that said output voltages from said output processing circuit are not equal to said test voltages inputted;
• and
• a tenth step of judging that said multi-channel analog input/output circuit is operating normally, if, at said eighth step, it is judged that said output voltages from said output processing circuit are equal to said test voltages inputted.