University Park, Pa. -- A wire testing technology developed by Penn State engineers was used to diagnose the recent fuel-sensor problem that delayed the launch of the Space Shuttle Discovery.
The original technology, known as time domain reflectometery (TDR), is considered the benchmark for test methods used for troubleshooting installed wires and cables. NASA technicians used the Penn State TDR to collect data on the intermittent low-fuel sensor in Discovery's external tank.
N. Scott Deno, a research engineer with the College of Engineering's Electronics and Computer Services (ECS) group, said TDRs are excellent tools to examine wiring that's in hard-to-reach places.
"TDR is a single-ended test which makes it particularly well-suited for characterizing installed wiring," he explained. "The instrument injects a voltage into a cable. As the pulse travels down the cable, it encounters impedance discontinuities producing voltage reflections. The instrument captures these reflections as a function of time. The resultant waveform, or signature, is then analyzed for the presence of faults or defects."
The development effort behind the TDR began in the 1990s when Penn State teamed with CM Technologies of Coraopolis to create the Industry Standard Architecture (ISA) version of the device. The effort was led by Paul Hulina, now an associate professor emeritus of electrical engineering. The 1990s design allowed high resolution signatures to be acquired and stored on the host computer for analysis. Technology developed during that effort was integrated in all Penn State TDR designs and patented by Hulina.
In 2000, ECS began developing a smaller version of the device that could be used in a computer's Personal Computer Memory Card International Association (PCMCIA) slot. In addition to trying to shrink the TDR card, the Penn State team had to cope with the limited amount of power available from a PCMCIA slot.
The new version can be used with a laptop computer or a personal digital assistant.
"We enhanced the existing ISA design and were able to use that to produce a higher bandwidth device in a much smaller form factor by using newer technology components," Deno said.
NASA purchased seven of the new PCMCIA TDR cards in 2002 from CM Technologies for troubleshooting wire problems on the International Space Station. Two Penn State TDR cards, which have passed NASA's battery of tests for use in space, are slated to be sent to the station on the next shuttle flight. According to Greg Allan of CM Technologies, their first task will be to troubleshoot a problematic audio line on board the station.