Application Notes

This application provides an option for adding control hardware to an existing Airbus 5VAC power system by interfacing DC control signals and lamp test inputs to illuminated pushbutton switches. Relay buffering is used to isolate the controls allowing the annunciators to be driven by the Airbus AC lighting Bus.

This solution uses a standalone NEXSYS Module containing an Electronic Latch (EL1) and a Pulse/Timer (PT1). A 1K resistor is used to ensure the mission power input line is pulled to ground when off which enables the PT1 to detect the transition to ON when engaged. The Terminal Block simplifies the wire splicing requirements. The example also requires an external power relay. The PT1 is always energized via battery power to ensure mission power is detected when it is turned on.

This application provides a delayed electrical system startup. A 20 second power up delay occurs following activation of mission power assuring primary avionics systems have completed power up and have stabilized before auxiliary systems power up. The auxiliary systems depend upon the stability of primary systems for calibration and correct power up.

This example demonstrates a power switchover function in the event of a master power failure. The application has an automatic switchover function when voltage drops below defined levels. Also, the switchover may be forced by manually latching an alternate action switch. Hysteresis is also defined to compensate for voltage fluctuations due to changes in electrical load.

This circuit detects a fuel tank over fill condition. When an over fill occurs a limit switch trips and a blinking advisory is initiated. The Blink mode continues until the over fill is corrected resetting the limit switch. The circuitry for this system is self-contained in a single indicator body.