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.