Customizing COTS Testing Systems

KineticSystems was able to satisfy the requirements with a PXI-based solution. The company supplied 4 modular off-the-shelf instruments (KineticSystems Model #CP246) in rack mounted enclosure. Each CP246 is a flexible 8-channel CompactPCI/PXI module with signal conditioning and ADC. 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 ATE to have the built-in flexibility to perform ad-hoc data acquisition experimentation without having to write any code. This was achieved through KineticSystems' configurable data acquisition software, SoftView, which provides access to all of an instrument's capabilities and features through a simple point and click GUI. KineticSystems further customized its SoftView software to include the ability to specify modules as master/slave to allow for simultaneous acquisition of multiple transducers signals between multiple modules. This feature is now a standard offering in the SoftView software package. Insert: windtunnel-1wcap Laser Instrument Systems One of the advantages of purchasing COTS module is to reduce costs, 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, 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/PCIe digitizers, had just released one of the industries' first digitizers with FPGA programmability that performed many of the functions in firmware processing 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 then realized belatedly that the digitizer they had developed in house was also equipped with low-speed A/D, D/A, IO 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. Next, the manufacturer needed to address a unique low-power requirement. Because the laser instruments were used to monitor conditions in remote locations with no ready access to power, the units operated off solar powered rechargeable batteries. This created a strict power budget, not to exceed the power the solar panels could supply. Working with the customer, GaGe removed unnecessary components on its cards to reduce power consumption by 50%. "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 that had to be addressed was 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. Adding an external circuit would have solved the problem, but the customer rejected that solution because it would add to the cost. GaGe engineers modified the card to extend the duration of the trigger pulse. Finally, GaGe 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," says Dawson. EM Compliance Systems In another example from GaGe, a US manufacturer of electromagnetic (EM) compliance systems required 8-bit high speed digitizer. However, the customer required more memory than currently available on even the largest of GaGe's digitizers. This was an extraordinary requirement as GaGe offers some of the highest on-board memory in the industry, up to 4 GS/s. But the customer still needed more. GaGe solved the requirement with a two card solution, with each card's memory designed to fill in succession. Due to timing delays between cards, a special triggering signal was added to activate the second card when the first card was full. GaGe provided a procedure to figure out the delay between the two cards and provided its customer with custom software that could be used to easily align data acquisition between the two cards through a visual representation of the signals. The application also required a subtle adjustment to the sampling rate in order to cover the entire EM frequency spectra. According to the Nyquist Theorem, the sampling rate must be at least twice the highest analog frequency for completely accurate analog-to-digital conversion (ADC) of the signal. The GaGe card delivered a 2 GS/s sampling rate, but the customer wanted to be able to accurately identify signal frequencies up to 1 GS/s. To build in flexibility, the customer specified 2.1 to 2.2 GS/s sampling rate for the card. Because GaGe utilized fixed oscillators, it had to look elsewhere for a solution. Fortunately, GaGe's digitizers have a built in 10 MHz reference input as part of its standard reference circuitry that, multiplied by 200 provided the 2GS/s. GaGe modified the normally fixed reference input to be adjustable between 9 and 11 MHz so the sampling rate could be tuned to 90-110% of 2 GHz which delivered a 1.8 to 2.2 GS/s sampling rate. Because the GaGe digitizer was going to be utilized in a high vibration environment, the cards would be mounted in a spring-suspended chassis. Like all standard PC-based cards, an off-the-shelf digitizer is designed to attach to a slot at one end with the other end in open space. In a high vibration environment it was possible the card vibrate like a tuning fork, potentially damaging the card. GaGe addressed this issue with custom mounting brackets that secured the digitizer at both ends within the suspended chassis. The previous solution, despite its higher cost, utilized a spectrum analyzer that scanned at specific frequencies over the course of an event. This presented the possibility that the equipment could miss a non-compliant signal as it scanned through the various EM frequencies. GaGe's solution provides 100% coverage, capturing all the data at all frequencies over an 8 second event of interest. According to KineticSystems' Krebs, there is a limit to customization that should be expected from COTS products. "Once you get to the point of having a vendor create a new circuit board, you are really designing a fully custom product," says Krebs. "The expense goes way up, and you are no longer reaping the advantages of COTS modules." The bottom line is modular instrument manufacturers need to be able to deliver the best of both worlds: a level of customization at the price and timing of COTS products. www.dynamicsignals.com