Issues with ethernet parametric testing in a production enviroment

Ethernet is an emerging communication technology in the avionics industry. There are many advantages to utilizing Ethernet that include a very high data rate, some noise immunity, weight savings, and commercially available equipment. Some of the disadvantages include extra line replaceable units (LRUs) on the plane (Ethernet switches) and added difficulties in aircraft wiring. This new technology brings with it many challenges in an automated test equipment (ATE) environment including, signal distortion, connector repeatability, and expensive measurement equipment. Rockwell Collins' traditional ATEs utilize a switch system to simulate the avionics environment for LRU testing which limits the quantity of I/O stimulus required. This switch system was not designed to support 100Base-TX Ethernet switching for parametric testing. A new switch system, interface panel, and an updated oscilloscope had to be designed into the ATE. Signal distortion: There were two main issues realized after integration: impedance mismatches due to different cables and connectors and excess loss which needed to be quantified. These issues made it very difficult to make repeatable and accurate measurements on the waveform. Connector repeatability: The Ethernet connector available on the commercial market is the RJ4S. This connector is very unreliable and wears out easily in a production/field environment due to the need for a reconfigurable ATE that can be capable of testing multiple test products with multiple test adapter cables. Expensive equipment: The required parametric tests (physical layer) for 100Base-TX Ethernet at the reference plane (LRU shipside connector) per ARLNC 664 are as follows: Differential Signal, UTP, zero-peak Signal Amplitude Symmetry (positive/negative) Rise and Fall Time (10% and 90% levels) Rise and Fall Time Symmetry Duty Cycle Distortion, peak-to-peak Transmit Jitter (HLS) Overshoot. The test equipment required for these Ethernet measurements adds extra cost to the ATE that was traditionally not required. This new scope adds multiple issues with repeatability, accurate measurements, and integration issues within an ATE environment while attempting to maintain backwards compatibility. This presentation will review Rockwell Collins' experience in implementing Ethernet parametrics in a production environment, the pros and cons, and screen shots of the Ethernet waveforms before and after being switched through the ATE.