Testing Business Jet Primary Power Distribution Boxes
To design and build a facility to test a Business Jets primary power distribution box specified by customer supplied documentation.
A National Instruments rack mounting 19” PXI based computer is used with dedicated I/O, to control all sensors, actuators, switches, relays etc. A multiplexor I/O system is used to route various test points from the product under test to cards in the PXI chassis, including serial communications, ARINC, RS232 and RS422. Various power supplies for high and low current testing and connections using Virginia Panel Corporation Mass interconnect solutions.
The equipment was to be floor standing to dock trolley units capable of accepting left and right handed versions of the distribution box. The trolleys were to allow distribution boxes to be easily hooked up outside the test system and wheeled into a garage type construction and effectively parked inside.
A self test adapter, capable of identifying faults on the boards of the PXI chassis should also be provided and constructed to allow access for maintenance/repair.
The first step was to keep all instrumentation and rack mount power supplies in a single equipment rack beside the garage and put high current switching and measurement devices inside the garage above and around the docking area.
To allow full mobility it was necessary to divorce the equipment rack from the garage. To permit easy connection a VPC G6 interface was used. This allowed the signal wiring from the instrumentation and low current power supplies to be disconnected from the garage. This concept would also be useful for the self test requirement as a self test adapter could be fitted to the VPC interface when the garage was disconnected.
To make the facility fail safe it was necessary to create a fully functional emergency stop & interlock circuit consisting of emergency stop buttons located at various points around the system; door & panel interlock switches; temperature switches; smoke detectors, due to the possibility of the unit under test being manufactured incorrectly and watchdog timers to allow the system to shut down if the PXI chassis crashes and holds on to a load longer than the prescribed time.
To provide suitable cooling of the equipment, a widened 19’’ rack was adopted. This allowed the required air flow using high air flow DC fans. These were strategically situated throughout the rack and due to the high currents generated inside the system, (1125A @28Vdc max), we needed to thermally divorce the high current supplies using a thermal barrier foam.
How the solution was Implemented
Starting with electrical drawings and equipment list a 3D model of the equipment rack and garage was made using solid edge modelling software. By modelling all of the equipment it helped to ensure that all the required components fitted together correctly.
The structure of the equipment rack started with a 19” rack on wheels. To this rack was added shelving to hold the power supplies, PXI Chassis and test equipment. In addition installed custom made panels and facia plates to the front and sides of the rack were installed to hold various electrical components. Once the equipment was installed into the rack, the wiring of the 3 phase power distribution and safety circuits were completed and the custom cable assemblies from the instrumentation to the VPC interface added.
Due to its size the Garage had to be designed and constructed using extruded aluminium section. The frame was installed with thick fibreglass panels on the sides and a aluminium base and top to maintain stability. Large doors in the front and back and internal panels to fix electrical components were added. The unit was the completely hard wired using wire gauges from 0.24mm sq to 150mm sq.
Both of the trolley’s were designed around each Unit Under Test to allow precise alignment of the high current connections to the distribution box terminals. Storage for the signal harnesses and terminal tools was also provided inside the trolleys.