Automatic FPGA Reprogramming in an Expandable Data Acquisition System

This article, written by Dr Richard Thomas of Product Technology Partners Ltd, describes the development of a low-cost, versatile, high-performance industrial data acquisition and logging system with automatic reprogramming to handle “plug and play” style reconfiguration. It involves the integration of commercial off-the-shelf National Instruments hardware and novel programming techniques to conceive a complete turn-key system that provides high-performance, robustness and scalability at a lower cost than competitive bespoke systems.

With an interest in improving their existing industrial product range, Webtec Products came to us for the development of a new high-performance hydraulic data logging and reporting system. In collaboration with NI, we conceived a product based upon Webtec’s existing system that uses commercial off-the-shelf NI hardware and software development tools. We employed NI’s CompactRIO technology, incorporating the Xilinx FPGA chip for high-speed digital and analogue signal acquisition coupled with the determinism of a Real-Time operating system for data collection, processing, storage and analysis. In combination with this was the design of a powerful PC-based LabVIEW application for control of the CompactRIO system.

The result was the C2000 system - a complete instrumentation, display, logging, storage and reporting solution that substantially simplifies the hydraulic testing and certification process. Fully scalable up to 64 inputs, the system includes sensors to measure all hydraulic parameters such as flow, pressure, temperature, speed, contamination and torque.

The C2000 was required to acquire data from any combination of both 4-20 mA current and 5V (TTL) frequency signals. The need for reliability in an industrial environment pointed to the CompactRIO series of deterministic Real-Time chassis with FPGA technology, and the NI C series 9203 and 9411 measurement cards, perfectly suited to providing for high-speed acquisition across multiple channels with extreme industrial ratings.

As each C2000 system would be tailored to meet Webtec’s individual customer requirements, it was necessary for the system to cope with any number and arrangement of possible 9203 and 9411 modules. We therefore developed a module-detection algorithm that reports the customer’s chosen arrangement of C series modules, and uploads an appropriate bitstream from a library of precompiled FPGA codes.

With this “plug and play” style technology, a user that requires more channels can simply insert an additional C series card into any available slot on the CompactRIO chassis, and know the system will automatically detect the new module at power up. This information is also propagated up to the controlling LabVIEW application, which will automatically reconfigure itself and provide the user with immediate access to the new hardware channels (see Figure alongside).

The system Real-Time software independently performs each data logging task, processing and storing the acquired data on the CompactRIO storage card in a custom binary format for maximum performance, whilst simultaneously streaming reduced-rate data up to the PC to provide a live feed within the LabVIEW application.

The complementary PC application was written in LabVIEW 8.6, and through the use of LabVIEW server and the built in .NET and ActiveX interfacing tools, it provides operators with a feature rich and highly customisable user interface to the system. Communications with the Real-Time system are established over a LAN network, providing a high-speed and reliable data transmission protocol between the two systems.

The user interface panels are fully customisable, allowing operators to create and position digital and analogue indicators and text decorations with just a few mouse clicks. Each configuration can be saved and reloaded as required. This ultimately provides operators with a method for easily crafting however many personalised user interfaces they may need, each tailored to suit their individual logging requirements (See Figure alongside). These programmatic modifications were all made possible through the use of LabVIEW server and multiple-dynamic event registration. Another customisable feature is the test report tool that allows an operator to include company logo images and custom data fields, tabulated data and a graphical representation of the data.

To perform a log test, the operator will first configure their connected sensors for type, engineering unit, calibration details, deadband zone and display precision. Live readings are continually displayed in each of the operator’s customised user interface panels, with historical data shown graphically. Acquired data is then presented for inspection subsequent to each log test, before a PDF report is generated at the click of a button and displayed within the application using the Adobe PDF Reader ActiveX plugin. From here reports can be saved for future reference, or printed directly from within the C2000 application.

Analysis tools allow data from two tests to be combined and displayed together on a single chart for comparison and further report generation. Data files can be saved in either a native C2000 binary format, or exported as a comma-separated-value (CSV) format for import and further analysis in third-party spreadsheet packages. Plus, as the C2000 is designed to be networked, a supervisor can access test files from a different computer for emailing or printing additional reports.

So, to summarise...

Commercial off-the-shelf NI hardware and novel programming techniques were brought together to conceive the C2000 - a complete turn-key data acquisition and logging system that provides high-performance, robustness and scalability for the hydraulic measurement industry.

The development of techniques for self-reprogramming of the CompactRIO FPGA enabled the design of a “plug and play” style system capable of automatically adapting to hardware module changes. This versatility provides for a highly scalable system capable of evolving with the operator’s growing measurement needs.

To complement the hardware, a feature-rich LabVIEW application was developed with user customisable user interfaces, designed to communicate with the CompactRIO across a network for the remote control and operation of measurements. Features were included for the analysis and reporting of logged data, using the .NET and ActiveX tools of LabVIEW.

Acknowledgements: Webtec Products Ltd is a UK based manufacturer of hydraulic components and specialist hydraulic test equipment for the Industrial, Mobile and Agricultural Industries.