Customizing COTS testing systems: From off-the-shelf to a total solution
By definition, the off-the-shelf modular instruments (VME, PXI, VXI, CompactPCI, PCI, etc.) used to create automated test and measurement systems are designed to be general purpose, programmable and flexible enough to handle a variety of input ranges and types, speeds, and functions.
At first blush, these modular, off-the-shelf instruments may seem ready-to-go for instrument manufacturers’ or test system designers’ needs. However, 100 per cent COTS are generally inadequate for complex, commercialized measurement systems. Often these instruments, built into systems within a chassis or PC, are used to build systems that are used in a laboratory or R & D environment, with techniques or information that was not previously available.
“We build flexibility into our cards so they can deal with multiple conditions,” says Steve Krebs, of KineticSystems, a company that manufactures CompactPCI/PXI and VXI data acquisition (DAQ) modules for test and measurement applications. “But we can’t anticipate everything, particularly in cutting edge applications, so that’s where customization still enters into the equation.”
Although nearly 90 per cent of the company’s revenue comes from off-the-shelf module sales, Krebs notes than an increasing number of customers require some level of hardware, software or firmware modifications to fit the application.
“With modular instruments there is this idea that you can buy different pieces from Vendor A, B and C and stick them together in a system and that’ll be it,” says Krebs. “But once you put these modules together in a chassis, there can be issues with interoperability, input ranges, synchronization, signal amplitude or conditioning and other performance characteristics.”
And while an engineering staff may be able to handle some customization, modifications can be a time-consuming, expensive activity that consumes resources and detracts from a company’s core activity.
That’s where some customization from the product manufacturer can come in handy. KineticSystems recently installed an automotive component testing application. The system was for an automotive component level development and testing division of a large company that supplies products to many different industries.
The project involved an upgrade of the company’s current data acquisition system for testing component-level assemblies for automobiles, in this case accelerator pedals. The company required a COTS solution to replace existing instrumentation for lower cost and the same performance as its existing system.
The ATE system was to be installed in multiple plants throughout the United States, and later fully standardized for export to other countries.
The testing process involves temperature-controlled test chambers to simulate the worst-case component environments. The accelerator pedals are mechanically cycled 24 hours a day for up to several months while the data acquisition system records the position and monitors the motion profile to ensure the pedal is performing as designed. In some instances, stress is also measured on the component under test.
The original ATE system developed for this purpose was a proprietary, non-standards based system no longer supported by its manufacturer. Later, the system was updated, but was still largely proprietary.
“Every time they purchased a new system they made incremental improvements, but never came up with a standardized solution they could easily duplicate,” says Krebs. “Now they were interested in a more economical solution that took less real estate and that they could standardize on globally.”
The answer was a PXI-based solution, using four modular off-the-shelf instruments in a rack-mounted enclosure. Each instrument was a flexible 8-channel CompactPCI/PXI module with signal conditioning and ADC.
The company also wanted to perform more frequent calibration of the instruments in its own metrology labs. Typically, calibration is performed annually at the instrument supplier’s facility. However, calibrating in house would minimize downtime and expense, so the team developed a standalone software application to perform periodic calibration with pre-calibration and post-calibration report generation for NIST traceability.
The customer also required the ATE to have the built-in flexibility to perform ad-hoc data acquisition experimentation without having to write any code. This was achieved through configurable data acquisition software, which provides access to all of an instrument’s capabilities and features through a simple point-and-click GUI.
The software was further customized to include the ability to specify modules as master/slave to allow for simultaneous acquisition of multiple transducers signals between multiple modules.