Advanced Distributed Modular Data Acquisition

Авторы: Eric Lyness, Steven Marlow – Mink Hollow Systems Inc
Источник: NIDays08 - Professional Development Conference for Engineers and Scientists. CUSTOMER CASE STUDY BOOKLET.

THE CHALLENGE

NI CompactRIO has met and exceeded the five challenges of VISION compliance and proved it can easily fit into the ATC process for testing vehicles for the United States Army.

Products:

CompactRIO

Industries:

ATE/Instrumentation, Transportation, Government/Defense, Aerospace/Avionics

THE SOLUTION

Creating a flexible, mobile data-recording system that easily replaces an established, custom-built system using commercial off-the-shelf (COTS) hardware to reduce maintenance costs.

Aberdeen Test Center (ATC) at Aberdeen Proving Grounds in Maryland conducts 80 percent of the United States Army automotive testing for wheeled and tracked vehicles. Traditionally, one of the primary tools for in-vehicle data acquisition was a custom-built portable device called the “white box.” Designed several years ago by engineers at ATC, the white box communicates with the vehicles’ computers and records a variety of measurements as the vehicle drives along a course. Test requirements define the measurements, which vary based on the type of vehicle being tested and the purpose of the test. For example, the measurements for a tank are very different from measurements for a Humvee.

Over the years, ATC has built hundreds of white boxes, adding features and tailoring the boxes to new test requirements that arise. The expense of maintaining hundreds of boxes and making modifications for new testing requirements led ATC to look for COTS replacements.

The CompactRIO system proved to be a perfect fit for the specifications, because it easily accommodates the most common instrumentation used for in-vehicle testing including GPS (via RS232) and a controller area network (CAN) bus for communication with the vehicles’ computers. Low-power consumption, large storage capacity and portability make it ideal for in-vehicle testing, but most importantly, it is versatile and can fit into the larger system.

A System with a VISION

ATC required that the device fit not only into the vehicles but also the larger enterprise-wide data system used for many years to track testing. This system, called the Versatile Information System Integrated Online (VISION), specifies a data path that tracks all measurements from the vehicle to the ATC VISION database, and then to the Internet where vehicle suppliers, ATC test engineers and government contracting officers can view the test results.

For the CompactRIO platform to be a viable solution, it needed to be VISION-compliant. To be compliant, the CompactRIO system had to address the following five challenges:
• Respond to user datagram protocol (UDP) commands from ATC’s client software
• Host a web interface for test operators to enter metadata for each test
• Perform time-based GPS synchronization among multiple CompactRIO systems
• Generate universal unique identifications in VISION format

Meeting the Challenges

Two principal concerns drove the system design: efficiency and expandability. System efficiency was surprisingly challenging. Although streaming GPS and CAN data is not an especially difficult task for CompactRIO, the task of efficiently parsing the data and repackaging it in the VISION format was an issue. By moving some of the parsing and packaging algorithms to the FPGA on the CompactRIO, we could meet the throughput demands of the system.

For ATC, one of the most attractive features of the CompactRIO implementation was its expandability. With more than 50 off-the-shelf I/O modules already available and the option to design custom modules if necessary, CompactRIO can easily adapt to new test requirements. This is even more useful if the software is designed to be scalable.

To develop the system for ATC, Mink Hollow Systems chose a highly modular approach. Several independent processes, with varying priority levels, run in parallel on the real-time controllers and communicate via queues. A high-priority data acquisition loop reads the XML configuration file, formatted according to existing ATC standards, to determine the I/O used in the test. The data acquisition (DAQ) loop then dynamically launches the necessary I/O-specific modules, such as GPS or CAN. If a particular test does not require a certain type of I/O such as CAN, the CAN module is not launched. As new physical modules, such as analog inputs, are added, corresponding dynamically loaded software modules can also be added with minimum impact on the existing code.

Adata recorder loop receives all data for storage and is designed to load a file type specific module that formats and writes the data to a disk that can be selected at run time. The VISION-compliant BLOB format is just one possible format. In the future, plug-in modules can easily be added for TDMS, HDF5, or other arbitrary file formats.

Lower-priority loops include the web-server loop, a data-socket loop, and a time-server loop. The web-server loop and the socketserver loop provide feedback to operators on computers connected via the Ethernet port of CompactRIO, which means the operator can enter metadata about the test and verify that the system is acquiring data properly. The time-server loop performs events at low rates, such as updating the CompactRIO clock to GPS time once per minute.

CompactRIO has met and exceeded the five challenges of VISION compliance and proved it can easily fit into ATC’s process for testing vehicles for the United States Army. ATC anticipates that over the next several years, it will gradually replace the existing white boxes saving enormous amounts of time and money in maintenance and update costs.