Localizing Diagnostic Testing of Relay Driver Circuits
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Diagnostic testing of analog circuits usually requires a switch or relay to functionally "switch" an analog net. A disadvantage in using a switch is that manual intervention is required to open/close the circuit. The disadvantage in using a relay is that the actuating coil itself may be defective (open), thereby influencing the results of the diagnostic test. Using the design shown in Fig. 1, a defective relay actuating coil is detected by using the coil as a pull-up device to the relay coil driver and by feeding the coil driver output back to the system as a status bit. In this arrangement, the diagnostic software samples the status bit prior to actuating the relay. If the bit is high, then the coil is not open. After actuating the relay, the bit may be sampled again.