Advancing the design of the Blade Compressor
29 December 2015
Understanding the real world performance of a novel compressor design and validating the theoretical analysis underpinning it led Midlands based Lontra to invest in multiple test beds that were capable of measuring many channels at high and low speeds simultaneously.
Lontra, founded in 2004, is a fast-growing Coventry based firm that licenses IP to technical and commercial partners. The company’s flagship innovation is the Blade Compressor, a patent protected, compact, double-acting rotary compressor that improves efficiency in energy-intensive industries. For some companies, the running costs of air handling applications can reach six figures or more. Lontra’s Blade Compressor delivers a 20 percent performance gain for significant efficiency savings.
The company expanded its headquarters recently by adding two new buildings plus a third chamber for prototype testing. One challenge was finding a suitable data acquisition system to manage large channel counts and log at fast acquisition rates to sample data every rotational degree of the compressor up to speeds of 4,500rpm. These data were necessary to achieving efficiency improvements as well as validating predictions that formed the basis for previous design iterations. Lontra’s senior development engineer, Carl Godden takes up the story:
“It is almost unheard of for a company our size to have testing facilities of this quality and capability. While we’re a relatively small firm, we’re focused on developing and licensing our IP, so we need world class data.
“Most test bed specific systems fail to satisfy our requirements; they’ll offer large channel counts but without the high-speed acquisition capability required to monitor pressure waves during the compressor cycle.
“With some large channel count systems the ability to log at, say, 25kHz requires another low-channel-count, high-speed system to be used alongside during testing, which is not ideal.”
With this in mind, Lontra chose National Instruments’ (NI’s) robust and portable CompactDAQ system, which initially allowed the DAQ to be transferred between two test beds that existed at that time. The company added modular C Series data acquisition cards to support pressure, temperature, voltage, and current sensors, while an NI 9401 card was used as an angle encoder input to read positional data. LabVIEW development software delivered the flexibility required for measurements and post processing.
In order to understand the pressure dynamics within the compressor, Lontra realised that it required more channels, and this pointed the company toward the modular PXI platform. However, this meant that a generic test bed code was needed, which could run the two systems. That’s when NI Alliance Partner, Wiresmith Technology became involved, with Wiresmith’s James McNally joining the group to assist in the development of the software.
According to Carl Godden, Wiresmith provided an easy working relationship with good feedback on ideas and prompt turnaround times on development. They tracked the work backlog effectively to prioritise the correct items without losing sight of additional ideas and features.
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. Meanwhile, 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 expansion capabilities meant that, despite using multiple I/O cards in both systems, the majority of the advanced synchronization abilities of the chassis were configured automatically for faster development and great 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 the different hardware, the majority of code could be reused as both systems integrate easily with LabVIEW via 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.
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 a deeper understanding of the system and to push the efficiency higher.
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 to provide continuous background logging so that long-term running trends can be analysed.
Another key area of the software that needed to be flexible and scalable was the user interface. Here, Lontra took advantage of an xControl provided on the LabVIEW Tools Network by Saphir called XTabs. A dynamic, tab-based user interface was developed, so technicians could add as many displays as required for the amount and type of data they needed to view. Each tab becomes a separate loop in the LabVIEW code, to which data is sent through user events. The Mission System Control Suite was also exploited in order to give the displays a more modern feel.
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 set-up times significantly, increasing overall test efficiency.
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