Benefits of CompactRIO
FPGA and processor
Perhaps the greatest benefit of CompactRIO is the FPGA/processor combination. Because the FPGA is reconfigurable, the achievable data rates and sampling accuracy are comparable to most state-of-the-art scopes. We can perform real-time calculations and outputs with no processor delays. Once the data is time-stamped and buffered, the processor advantages come into play. Software engineers can take advantage of the full breadth of the processor’s flexibility to achieve extended and remote FPGA operation and manage large data sets. The buffered data can be retrieved and written to a USB drive, making its storage capabilities comparable to a laptop. The GPS signal is monitored and recorded. Scripts are run to post process, erase non-trigger data, and prepare the data for analysis. Daily tasks are performed and automated FTP uploads to a server can be executed each evening.
Rugged and reconfigurable
CompactRIO exceeded all our environmental requirements. It handles a temperature range of -40°C to 80°C, so we mounted the unit externally in an electrical compartment. Its small footprint and excellent vibration/shock resistance allowed for easy, semi-permanent installation.
CompactRIO is highly customizable. We knew we needed to conduct multiple phases of investigation, and the ability to reconfigure the system to hone in on potential problem areas was a significant benefit. After performing preliminary voltage analysis, we discovered that it would be beneficial to monitor two current signals. Adding these two signals was a very simple task. Using a CompactRIO with swappable input modules, we could monitor almost any conceivable input.
CompactRIO offers multiple data access options. We could use a router to access the data over a network via wireless downloads or manually access the data via a removable USB drive. To make project development manageable, we did not implement wireless downloads at first. We recorded data to the flash drive and personnel accessed it once a week by shutting off the program, removing the USB drive, and swapping it with a new one. We are currently working with RTD to implement daily, automated FTP transfers to a server, which will save time and make the data more quickly accessible.
To effectively measure and record the transients, we needed to implement a sample rate >10,000 Hz. Vehicle diagnostic data is only available every millisecond, so a 1,000 Hz rate is sufficient. A third sampling rate of 50 Hz can be added if temperature readings are necessary. The FPGA easily accommodates these different rates and writes the data to a buffer. A fourth rate of 1 Hz was needed for the GPS input, and was handled in the processor.
Another benefit of CompactRIO is the video processing. We originally planned to handle and record the video in the CompactRIO FPGA. However, as the project progressed, we realized the CompactRIO could not handle the buffering we required at the specified resolution. We bought a digital video recorder (DVR), but then ran into difficulty synchronizing the video in the DVR with the CompactRIO data. They had different internal clocks, and due to natural clock drift, we could not rely on them for our required synchronization level. The solution here was simple. We bought an NI 9401 bidirectional digital input module to plug into the CompactRIO chassis. As the system records the voltages, the FPGA runs a simple algorithm to determine if a voltage transient is occurring. If it finds one, it sends out a binary signal to the DVR via the NI 9401. This occurs in real time with no processor delays. The DVR records the binary signal as a trigger with the video file, so we only have to download the video files that show active triggers, which reduces video storage and download times. This also helps us perfectly synchronize the video data with the CompactRIO voltage and GPS data by aligning the triggers.