How to customize COTS test systems to application-specific data-acquisition solutions

BY Pat Cassady

By definition, commercial off-the-shelf (COTS) modular instruments, such as VME, PXI, VXI, CompactPCI, and PCI, at one time created automated test and measurement systems as general-purpose, programmable, and flexible systems sufficient to handle several different input ranges, types, speeds, and functions.

At first, these modular commercially available instruments may seem ready to meet the needs of instrument manufacturers or test system designers, yet 100 percent COTS tend to be inadequate for complex, commercial measurement. Often as not, these instruments are built into either a chassis or personal computer, and help build systems for research-and-development laboratories with techniques or information not previously available.

Nearly 90 percent of the money a company makes comes from sales of COTS modules; yet, an increasing number of buyers require some modifications to hardware or software to fit properly into the application, notes Steve Krebs of KineticSystems, a CompactPCI/PXI and VXI data acquisition module provider for test and measurement applications.

“We build flexibility into our cards so they can deal with multiple conditions,” Krebs says. “For instance, we have multiple input ranges on our cards. But we can’t anticipate everything, particularly in cutting-edge applications, so that’s where customization still enters into the equation.

“With modular instruments, there is this idea that you can buy different pieces from Vendor A, B, and C, stick them together in a system, and that will be it,” Krebs says. “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.”

Some customization can be handled by the customer’s engineering staff, but modifications can be a time-consuming, expensive activity that consumes resources and detracts from a company’s core activity. As a result, manufacturers are well advised to partner with instrument providers willing to semi-customize COTS products. Unfortunately, high-volume manufacturers are often only interested in providing off-the-shelf products and are ill equipped or unwilling to provide semi-customized products.

“Large instrument manufacturers claim to do it all. But if you need customization, they often refer you to third-party integrators or channel partners, and the way these parties generate revenue is to charge significantly for it,” Krebs says, adding that smaller instrument manufacturers are willing to provide semi-custom solutions free or at nominal costs.

PXI system for component testing

KineticSystems completed work for an automotive component testing application (CTS Automotive). 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 customer required a COTS solution to replace existing instrumentation for a lower cost and the same performance as its existing system. The ATE system was to be installed in multiple plants throughout the U.S., and later standardized for export to other countries, including China.

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 as a custom solution, was a proprietary, non-standards-based system no longer supported by its manufacturer. Later, the system was updated with VXI components from KineticSystems, 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,” Krebs says. “Now, they were interested in a more economical solution that took less real estate and that they could standardize on globally.”

KineticSystems was able to satisfy the requirements with a PXI-based solution. The company supplied 4 modular, off-the-shelf instruments in a rack-mounted enclosure. Each CP246 is a flexible, 8-channel CompactPCI/PXI module with signal conditioning and A/D converter.

The customer also wanted to perform more frequent calibration of the instruments in its own metrology labs. Typically, calibration is performed annually at KinectSystems’ facility. However, calibrating in house would minimize downtime and expense. In response, Kinetic Systems 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 built-in flexibility to perform ad-hoc data acquisition experimentation without having to write any code. It was achieved through KineticSystems’ SoftView configurable data-acquisition software, which provides access to all of an instrument’s capabilities and features through a simple point-and-click GUI. KineticSystems further customized SoftView to include the ability to specify modules as master/slave to allow for simultaneous acquisition of multiple transducer signals between multiple modules—a feature now standard in the SoftView software package.

Laser instrument systems

Some advantages of purchasing a COTS module is to reduce costs and time-to-market, and to allow a company to focus its abilities on the design of the complete measurement system and not instrument manufacturing.

This was the case for a U.S. manufacturer of laser instrument systems for specialized inspection at electrical and geological sites. The manufacturer had been dedicating valuable resources to engineering its own digitizer card in house, which was expensive and time-consuming, and distracted personnel from its core competence—the laser optical system itself. Although commercial digitizers were available at the time the product was initially created, FPGAs (field-programmable gate arrays) that perform on-board signal processing on a COTS digitizer were not.

Later, when the product started to take off, the manufacturer decided to incorporate an off-the-shelf digitizer into its system. GaGe, a manufacturer of high-speed PCI/PCI Express digitizers, had just released one of the first digitizers with FPGA programmability that performed many of the functions the manufacturer required. After some research, the laser manufacturer selected a 12-bit, high-speed digitizer from GaGe.

Almost immediately, it was clear that the FPGA was not large enough for the application, so GaGe worked with the customer to add another, larger FPGA. The larger FPGA was from the same FPGA family and was pin-compatible with the original. Consequently, GaGe was able to enlarge the FPGA without changing the circuit board, which would have entailed much higher costs. The manufacturer realized belatedly that the digitizer they had developed in house was also equipped with low-speed A/D, D/A, I/O to capture analog temperature measurements, activate motors, and turn the various devices on and off.

To add these elements, GaGe partnered with KineticSystems to deliver what became a 2-board solution: the digitizer and a PXI DAQ data-acquisition board from KineticSystems modified to operate from a USB port that provided the additional functions.

Laser instruments used to monitor conditions in remote locations operated off solar-powered rechargeable batteries, creating a strict power budget. Working with the customer, GaGe removed unnecessary components on its cards and reduced power consumption by 50 percent. “Because our board is general-purpose, we had multiple input ranges and multiple channels, and the customer only required one,” says Andrew Dawson of GaGe. “We removed a channel and the amplifiers, which resulted in a significant reduction in the power required.”

Another element had to be addressed: the duration of the trigger pulse used to activate the laser beam. Although adequate for most applications, the standard trigger pulse on the GaGe board was too short in duration for this specific application, causing the laser to activate intermittently and, therefore, unreliably. GaGe engineers modified the card to extend the duration of the trigger pulse. GaGe also adapted the boards to be mounted horizontally, instead of vertically, and provided special board stand-offs to meet mounting requirement. “Although, by itself, each of these modifications might appear minor, the ensemble of modifications provided the customer with a complete, application-specific solution,” Dawson says.


Pat Cassady is president of Dynamic Signals LLC in Lockport, Ill. Visit the company online at www.dynamicsignals.com.

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