Case Studies

Advancing the design of the Blade Compressor®

by Lontra and James McNally


Increasing understanding of the performance of a revolutionary blade compressor in real world environments to validate the theoretical analysis and advance the design of Lontra’s Blade Compressor®, refining its performance across multiple industry applications.

The Solution

Creating multiple test beds capable of measuring many channels at high and low speeds simultaneously through a smaller portable system based on CompactDAQ for existing test cells and a test cell based on PXI with double the channel counts ready for future designs, joined together by LabVIEW software that can run on either hardware platform.

Test Bed Expansion

The first 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 4,500 rpm. The data gathered could be used to help the company’s development, increase efficiency even more, and validate predictions that were the basis for the earlier concept design.

“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,” said Carl Godden, Test and Development Manager at Lontra. “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 25 kHz requires another low-channel-count, high-speed system to be used alongside during testing, which is not ideal. The NI hardware and software justified itself, it covered all the requirements on our measurement chain all in one system.”

With this in mind, we chose the CompactDAQ system. This robust, portable system initially allowed us to transfer the DAQ between the two test beds that existed at that time. We added modular C Series data acquisition cards to support pressure, temperature, voltage, and current sensors. We used an NI 9401 card as an angle encoder input to read positional data. LabVIEW development software delivered flexibility on measurements and post processing.

We needed to improve understanding of the pressure dynamics within the compressor and a new model compressor, which required more channels. This drove our interest toward the modular PXI platform. We then had to provide a generic test bed code that could run the two systems.

Our NI field engineer advised us that our requirements and expertise would benefit by getting assistance from an NI alliance partner. We contacted James McNally from Wiresmith Technology to assist with the software development. Wiresmith Technology 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.

System Design

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 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. We added calibration support 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, we could reuse the majority of code as both systems integrate easily with LabVIEW through the NI-DAQmx driver. We developed a hardware abstraction layer 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 25 kHz 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 10 Hz 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 we can analyse long-term running trends.

Another key area of the software that needed to be flexible and scalable was the user interface. Here took advantage of an xControl provided on the LabVIEW Tools Network by Saphir called XTabs. We could set up a dynamic, tab-based user interface 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, which we send data to through user events. We also leveraged the Mission System Control Suite to give the displays a more modern feel.

Solution 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.

Godden concludes,

“It took Thomas Edison 10,000 prototypes to perfect the lightbulb. James Dyson improved on that with just 5,000 for his vacuum cleaner. 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.”

The flexibility of the configurable user interface allows us to create specific individual tests dependent upon the scope of work being carried out. 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.

The complete hardware and software packages offered by NI in conjunction with Wiresmith Technology have increased our test efficiency and accuracy. Lontra can also further develop and optimise data analysis simulation techniques for future product design. The ability to correlate simulations against improved quality test data will ensure future Blade Compressor® simulations are optimised; thus, reducing design and development time and time to market for the Warwickshire-based company.

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