Abstract: An isolated voltage door latch for an appliance that includes a controller and a door contact. The controller is configured to control an electrical load device within the appliance based on a control signal. The door contact is configured to trigger transmission of a sensing signal to an electrical load actuator electrically coupled to the electrical load device. The sensing signal is transmitted to the electrical load actuator via a door latch circuit in a first instance in which the door contact is in a closed state. Furthermore, the electrical load device is configured to be activated in a second instance in which the sensing signal and the control signal are received by the electrical load actuator.

Abstract: A high reliability instrument system includes means for applying a test condition to the instrument and for determining whether the instrument properly responds to the test condition, and means for inhibiting the generation of an instrument output in response to such testing. This provides verification that most of the instrument system components, but not the system output, are properly functioning. The system further includes means for overriding the output-inhibiting function when it is desired to test the entire instrument system including the system output. The instrument system may include a gap-type ultrasonic instrument, with the test condition comprising a pulse applied to one crystal, the effects of which are detected at the other crystal to determine sensor integrity. The system is preferably configured as a two-wire on-off instrument system, in which application of the test condition at a transmitter is controlled by signals applied to the two-wire signal loop at a remote receiver.