Product Technology Partners Ltd. is a leading provider of software solutions for today’s cutting-edge product developments. As a long-standing National Instruments Silver Alliance Partner with several certified LabVIEW and NI LabWindows™/CVI software developers, including a LabVIEW Architect and the UK’s first LabVIEW Champion, we were approached by our customer to develop and implement a software solution for a motor and gearbox endurance test rig based on LabVIEW. As part of the customer’s test strategy and commitment to maintain the highest quality guarantees, the rig had to perform automated, continuous control and measurement for many weeks to qualify each product.
We tested the motor and gearbox subassemblies against a torque distribution that was representative of a punitive use case and applied with a hysteresis brake for a controlled torque load. We measured various properties of the assembly, including rotational speed, current draw, temperature and measured torque throughout the test process.
The requirement for acquiring various signals, including analogue and digital voltages, thermocouple temperature, digital counters and electromechanical relay control (all at potentially different sampling rates), coupled with a harsh working environment led to our selection of NI CompactRIO. In our experience, CompactRIO is well-proven for industrial suitability, reliability and ease of programming with the LabVIEW environment. We chose an NI cRIO-9114 chassis and an NI cRIO-9022 controller with eight module slots. This hardware was sufficient for the range of measurements required, and offered adequate computational power to meet data acquisition, processing and logging requirements.
After we built the rig hardware, Product Technology Partners Ltd architected and refined a highly configurable software solution for reliable control and measurement while handling mass data logging with network synchronisation and off-loading. The rig is remotely located, so we implemented the Web Publisher Tool to publish the front panel to remote terminals for configuration, starting and stopping tests, and monitoring progress.
We configured the test system by importing settings from an Excel spreadsheet template containing the specific acquisition rates and calibration values for each channel, profile data for controlling the torque, test header data, email addresses for warning messages and other related parameters. The system stores the file on a common FTP server. Through the remote panel web interface, the operator can browse to the server file path and the code calls on the LabVIEW Internet Toolkit to find the remote file and import the contents.
The system calibrates and records the acquired data in sparsely populated comma-separated value (CSV) files. CSV was a customer requirement due to its readability, but it is typically inefficient when it comes to file sizes. Therefore, we implemented an indexed, sparsely populated approach to optimise space use and ease collation and data mining with tools such as NI DIAdem. The system synchronizes the data files and off-loads them to the remote FTP server location for data analysis and archiving throughout all operations. Test engineers are able to study the results while the tests are under way.
At all times, the user can access the remote panel from any web browser on the company network to review the progress of the test, inspect recently acquired data, check warnings or alerts and pause or stop a running test.
Endurance tests can take up to 12 weeks and complete at least 6,000 cycles of a test torque profile, so it is imperative that an engineer can review and confirm the test progression from the very beginning of test execution. In addition to reviewing the synchronised FTP server data, the system presents the last five minutes of measurements in analysis charts in the remote panel for an at-a-glance view to show that the test is performing as expected.
In addition to acquisition, calibration and data logging, the software also performs safety monitoring duties to ensure the system is operating within sensible boundaries. The system can quantitatively assess the high and low threshold ranges in the test-configuration file for both warning and alarm levels for each calibrated measurement. The system automatically sends an email notification to the test engineer when any channel falls within the defined warning range.
Additionally, for any channel in the alarm range, the system sends an email to security personnel and immediately stops the test rig. For example, if the gearbox temperature rises above 70 °C, the system sends a warning email to the test engineer. However, should it continue to rise above 100 °C, the system stops the rig and sends another email to both the engineer and security personnel, informing them of the hazard.
The system architecture adopts multiple parallel threads of execution and takes advantage of the Timed Loop priority property to ensure the critical code paths execute unhindered.
Early tests showed that the architecture was largely successful, but also that the demand on the CPU oscillated rapidly between low and high throughout the control and acquisition process loops. Using the NI Real-Time Execution Trace Toolkit we were able to study the CPU activity in fine detail and identify bottleneck areas in the code. Once identified, we staggered these code segments to help uniformly spread out the demand on the CPU. Most noticeable, however, was evidence of an increasing average CPU use with increasing test time, which was a consequence of needing to update the panel chart data with the latest measured values. Reducing the graph plot history size was the most effective measure for reducing long-term average CPU use.
We used National Instruments CompactRIO and LabVIEW to design and deliver a highly customisable subassembly endurance test solution capable of remote autonomous operation. The LabVIEW Internet Toolkit and Web Publishing Tool greatly simplified the task of implementing a remote interface and achieving networked data synchronisation to significantly reduce overall development cost and time.
Product Technology Partners Ltd.
Product Technology Partners Ltd
Tel: 01223 264445