FEATURE DATA ACQUISITION Using DAQ to advance designs In order to increase understanding of Lontra’s double acting rotary blade
compressor and advance the design, multiple test beds were developed which were capable of measuring many channels simultaneously at high and low speeds through a portable system based on NI CompactDAQ
B
ased in Coventry, Lontra licenses IP to technical and commercial partners,
with its flagship innovation being the Blade Compressor, a patent protected, compact, double acting rotary compressor that improves efficiency in energy- intensive industries such as water treatment and industrial compressed air. When the company added two new
buildings and a third test chamber to its facility for engineering prototyping and testing, it needed a data acquisition system that would be capable of managing large channel counts and log fast enough to sample data every rotational degree of the compressor up to speeds of 4,500rpm. To meet demands, the company
selected the robust and portable NI CompactDAQ system. This initially enabled the company to transfer the DAQ between the two test beds that existed at that time. Modular C Series data acquisition cards were then added to support pressure, temperature, voltage, and current sensors; and an NI 9401 card was used as an angle encoder input to read positional data. At the facility, the company needed to
improve understanding of the pressure dynamics within the compressor and a new model compressor, which required more channels. This drove interest toward the modular PXI platform. A generic test bed code was then needed that could run the two systems. So, the company contacted James
McNally from Wiresmith Technology, an NI alliance partner, to assist with the software development.
CAPTURING SAMPLES At the heart of the system is the DAQ hardware. The CompactDAQ and the C Series modules delivered the required signal conditioning for thermocouple, platinum resistance thermometer (PRT), pressure, voltage, and current measurements. In PXI, the NI SC Express range provided
signal conditioning for temperature and pressure measurements whilst multifunction DAQ cards offered the more regular voltage and current requirements. The NI-DAQmx driver’s channel
16 MARCH 2016 | INSTRUMENTATION
expansion capabilities meant that despite using multiple I/O cards in both systems, the majority of the advanced synchronisation abilities of the chassis were configured automatically for faster development and confidence in the final solution. Calibration support was added through the use of NI-DAQmx scales and a local database based on SQLite, so the technicians could apply system-level calibration to the measurements. To give immediate design feedback, some of the channels also calculate the real-time efficiency of the compressor under test. Despite different hardware, the
majority of code could be re-used as both systems integrate easily with LabVIEW through the NI-DAQmx driver. A hardware abstraction layer was developed with LabVIEW object oriented programming to include the few required changes in a single software application, reducing the support burden of two separate code bases. The DAQ subsystem captures samples at 25kHz and passes them into a couple of data paths: 1. The high-speed path transmits data at the full rate to angular graph displays and the high-speed logging module. When the operator chooses to, he can start a high-speed log to a TDMS file to capture transient tests. This delivers the additional information needed for Lontra to understand the system and push the efficiency higher.
2. The other data path down samples the data to 10Hz using the built-in processing functions in LabVIEW. This is then used to update the displays as well as provide continuous background logging so that long-term running trends can be analysed. As the user interface also needed to be flexible, the company took advantage of an xControl provided on the LabVIEW
Tools Network by Saphir called XTabs. This enabled a dynamic, tab-based user interface to be set up so technicians can add as many displays as required for the amount and type of data they need to view. Each tab becomes a separate loop in the LabVIEW code.
THE BENEFITS Lontra now possesses a generic test code to run on all of its test bed systems. The code requires minimal user input by technicians and engineers and reduces test setup times significantly, increasing overall test efficiency. Carl Godden from Lontra commented: “Thanks to our world-class CAD, and analytical modelling facilities and test bed labs, our very first production prototype is still running today with our first customer. The system based on CompactDAQ ensures we can continue to refine our simulations, helping us expand the range of applications for our award winning Blade Compressor.” Of additional benefit, the flexibility
of the configurable user interface means the company can create specific individual tests dependent upon the scope of work being carried out. Furthermore, the additional ability to load stored calibrations into individual test configurations and flag any out of range calibrations has assisted with ensuring consistent, accurate traceable data, which is vital for the development of Lontra products.
National Instruments
www.ni.com
Blade Compressor is a patent protected, compact, double acting rotary compressor that improves efficiency in energy-intensive industries such as water treatment and industrial compressed air
In PXI, the NI SC Express range provided signal conditioning for temperature and pressure
measurements whilst multifunction DAQ cards offered the more regular voltage and current requirements
Authors: Carl Godden, Lontra –
http://lontra.co.uk James McNally, Wiresmith Technology –
www.wiresmithtech.com
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