Every test manager dreams of creating the ultimate reusable tester, and it's sometimes possible to design one tester to cover all the applications in a facility. PXI, with its modular architecture and wide range of available modules, has helped Dr. Eric Smitt, a senior electrical engineer for Lockheed-Martin Space Systems (Cape Canaveral, FL), create such an adaptable beast for a reasonable cost.

The Lockheed system is best described as a "tester tester." That is, it is a piece of test equipment that tests ATE built to test other equipment.

"We're basically making a lot of highly accurate DC and resistance measurements," Smitt said. "We're generating strings of pulses at a certain amplitude and a certain frequency, and with certain bit patterns. These signals go into the test equipment, which looks at them to determine whether they are correct, and sends a test result back to my unit."

This 6U PXI chassis has 20 slots and includes an embedded controller. Courtesy of Geotest.

• Analog measurement modules measure voltage, current, and resistance. Smitt's chassis contain DMMs and a digital scope module.
• Timing measurement modulesmake it possible to measure timing of events—as signaled by leading and falling pulse edges—to within milliseconds or nanoseconds.
• Signal source unitsconsist of pulse generators and reference voltage sources.
• Programmable resistance modulesconsist of switchable ladders of precision resistors. There are two of them: One presents high-precision (0.1%) 200-W resistors to the UUT; the other presents 0 to 750 kV in 1-V steps.
• Power sourcesprovide regulated power at levels up to 33 V at 33 A. There are two such high-power units slaved together. Smitt used GPIB to bring these resources under the control of the PXI embedded controller. A smaller power supply fits into the chassis. Its two outputs can source 0 to 30 V at 5 A, and each has programmable voltage and current limits.
• Power sinkscan load the UUT at power levels up to 1400 W at 30 V, essentially indefinitely.
• Programmable switchesprovide hardware flexibility. Ten programmable switching modules provide nearly 1000 relays to match resources with the ports where they are needed.

The Lockheed system's real flexibility, however, comes from the fact that all of these resources are controllable over the same PXI bus, which is an extension of the embedded controller's PCI bus. "We have sufficient instrumentation to provide almost any type of measurement we have to make," Smitt asserted. "The operators never see any of the instrumentation. The only thing they have access to is the software. They have to follow the canned routine implemented by our test program."

PXI was not a trivial choice for the Lockheed Martin engineers. "We had to do a big cost-benefit analysis on architectures," Smitt recalled. "We looked at the VME, we looked at VXI, looked at GPIB, and we looked at PXI. We found that the most cost-effective and most serviceable architecture through the life of our program was PXI."