Custom Automated Test System – Characterization of Heat Transfer System Thermal Performance

Challenge

Our client, ATSI, Inc., headquartered in Amherst NY, designs and builds complex structures and process systems, from industrial construction projects to mechanical systems for power engineering. A previous, long-standing Viewpoint customer that does research and design of thermal energy systems approached ATSI to engage in the build of a specialized test skid that would be used to assess and characterize a heat transfer system. Our long-standing end-customer requested a data acquisition subsystem based on LabVIEW.

Furthermore, the end-customer requested a subsystem that supported flexibility in the data acquisition by channel count and type, since the R&D nature necessitated adaptability. The overall test system needed to automate progress through a sequence of setpoints and ramps.

Solution

ATSI designed the automated control and sequencing with a Modicon PLC. Viewpoint augmented ATSI’s engineering resources to provide the data acquisition subsystem and setpoint sequence editing. This sequence was passed to the PLC for automated sequencing thought the setpoint list. Because our mutual end-customer did not provide explicit design details, we had flexibility to decide which aspects of the control and data acquisition needs would be automated by the Modicon PLC and which by the PC running LabVIEW.

Since Viewpoint had previously developed a similar application for our end-customer, with some of the required data acquisition needs, we chose to leverage and enhance that software platform for this project. That choice drove some of the other designs and defined the scope of work for Viewpoint and ATSI.

Some overall design decisions were:

• The LabVIEW application provided data acquisition, test configuration, and operator screens.
• The Modicon-based subsystems provided process control and safety.
• A PLC HMI for process system operation and status as well as control loop tuning.
• NI Compact DAQ (cDAQ) offered flexible PC-based acquisition channels for high sample rate historical data collection.
• A sequence editor on the PC defined the test setpoints, durations, and limits to pass to the PLC for execution.

The test configuration encompassed cDAQ channel configuration, PLC tag configuration, sequence editing, and graphical views on the acquired data. Some channels were acquired at slow rates, e.g., up to about 1 S/s for sensors measuring parameters such as temperature and flow, while others had fast rates, e.g., 1 kS/s to 10s of kS/s for sensors measuring parameters such as transient pressure and vibration. Handling the datafile storage and display of this wide range of data types and rates was important for the end-customer to compare and correlate the effects of changing operating conditions.

Data logging is configured by the sequence editor to occur on certain conditions such as immediately entering a new step, time delayed after entering a step, and activated by the PLC upon reaching stable setpoint control. This flexibility gave the end-customer management of when data collection occurred to ease the comparison and correlation of readings from selected sensors.

After the configuration is completed, the sequence is passed to the PLC. The operator starts the test on the PLC HMI and the PLC automates the test run. Data collected during the test run could be displayed in live graphs during testing, used for verification of setup and operation; post-test in stacked graphs and overlaid plots; and exported for specialized analysis, display, and review.

Benefits

The design of this system was driven largely by the need for flexibility. Sensors and channels could be added, the test sequence could be edited with a variable number of steps with editable execution features, and the data acquisition and storage permitted various rates and logging criteria.

These design choices offered the following advantages:

• As a partner of the team, Viewpoint acted as staff augmentation for ATSI by providing experienced engineers with expert LabVIEW and data acquisition capabilities.
• Flexibility of test sequences, including setpoints and their stabilization criteria.
• Tight integration between the Modicon PLC and LabVIEW-based PC enables critical control and safety to execute reliably and yet adjustably.
• Customized mechanical all-welded skid plugs into end-customer’s test article.
• Setup of data logging including configurable sample rates.
• Ability to add channels by plugging in supplemental DAQmx-based cDAQ modules.
• The LabVIEW application architecture is actor-based for straightforward inclusion of new data sources as needed in the future.
• New data sources are registered with the object-based data aggregator.
• The system handles multiple days of test execution
• The multi-pronged viewer allows verification checks while in setup an operation as well as post-test review.

System Overview

The custom automated test system supplied to the end-customer was a hybrid, made up of PC-based and PLC-based components coupled with the fluid-handling components on the skid. The hardware listed below includes only the data acquisition, control, and safety items, and only a high-level description of the mechanical aspects.