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Localizing Diagnostic Testing of Relay Driver Circuits

IP.com Disclosure Number: IPCOM000043416D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Bonn, RM: AUTHOR [+4]

Abstract

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.

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Localizing Diagnostic Testing of Relay Driver Circuits

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. If the bit is low, then current flows through the coil and the entire relay driver circuit and coil are proven to be operational. The device interface, shown in Fig. 2, is an AC-coupled, isolated interface. It provides good impedance matching and noise rejection and is less susceptible to EMC problems than other forms of serial transmission lines. In Fig. 3, this disclosure adds a relay, making it possible to perform diagnostic "wraps" on the logic and driver/receiver circuitry without depending on or disturbing the device at the opposite end of the cable. However, successful completion of this wrap test does not ensure that the pulse transform...