Object-Oriented Approach Facilitates Improved Control For Large-Scale Neutrino Experiment

Project Summary:

The Short-Baseline Near Detector (SBND) is the latest large-scale neutrino experiment at Fermi National Accelerator Laboratory (Fermilab), which will be used to analyze the properties of neutrinos, a family of elusive fundamental particles. The main volume of the detector consists of 112 tons of liquid argon, kept cold and pure by an elaborate cryogenic system, which is monitored and controlled via Ignition.

Problem:

One major opportunity for modernization and improvement on this project was the implementation of an object-oriented approach, including use of User Defined Types (UDTs). This stands in contrast to past projects, developed on another platform, in which every device (e.g., pressure sensor, control valve) had to be programmed individually with its own popup in the HMI.

Instead of adding custom features to select devices on an ad hoc basis, all devices needed a standard suite of features, permitting consistency and flexibility to our operators. For example, all transmitters (i.e., pressure, flow, temperature) should include scaling, filtering, simulation, error detection (open/short circuit), and trending. Furthermore, operators need dynamic alarms, ones they can enable, disable, and modify on the fly. On past projects, alarm management was handled by the PLC, resulting in a hardcoded set of alarms that was risky due to PLC restarts and laborious to change.

Solution:

The primary solution was a library of standardized objects, which Fermilab calls FermiPCL (Process Control Library). It includes heavy use of UDTs, both in the PLC programs and in Ignition. On the PLC side, instances of common function blocks pass information to each other in the form of UDTs, permitting them to share not only the process value, but also engineering parameters, error and simulation status, and the name of the object from which the value originates. On the Ignition side, Fermilab implemented a hierarchy of UDTs. This begins with a template UDT containing a common set of tags and parameters. The custom parameters, which are referenced by nested tags, identify the appropriate OPC item path, database, and alarm notification pipeline, such that these do not need to be configured on individual tags. Via inheritance, the template UDT then becomes the basis for 14 other UDTs, each of which corresponds to a function block definition in the PLC and has accompanying template(s) and a popup in Ignition. These UDTs each contain multiple instances of nested (and some nested-nested) UDTs, which correspond to the inputs and outputs of the function blocks in the PLC.

To address the challenge of creating UDT instances in Ignition, Fermilab created a tag administration window. It uses Python scripts to facilitate this process. Each of Fermilab’s PLCs has an onboard OPC UA server. In the window, one button runs a script that scans the OPC UA server for tags corresponding to function block instances and displays them in a table. Another button then creates the corresponding UDT instances. When it encounters custom function blocks — those not in the library — it creates a new UDT definition and instances as necessary.

Fermilab also moved alarm management out of the PLC and into Ignition. Ignition has alarm management features built into the base platform that meet industry standards, such as ISA-18.2, right out of the box. There is no need to burden the PLC with managing alarms. By way of the Alarm Notification Module, Fermilab can alert appropriate personnel when problems occur, so they know to login and make changes as needed.

Results:

With the FermiPCL set of UDTs, templates, and popups in place, along with the tag administration window, developing individual projects is now much easier. This is especially beneficial on a large-scale project, such as the Short-Baseline Near Detector cryogenic system.

Adding sensors, valves, and other devices to the system has become a breeze. Given the device has been added to the PLC program, Fermilab simply scans and creates the corresponding UDT instance with the tag administration window. From there, Fermilab can drag-and-drop the UDT instance from the tag browser onto the desired window to place an instance of the corresponding template. And it’s done. Absolutely no manual configuration of tags is required whatsoever.

The ultimate result has been satisfied operators and smooth operations. Operators are very pleased with the new features and freedom of control that they have on this latest project. When they request additions, whether it be a new device or some new functionality, Fermilab can satisfy their requests expeditiously.

Start Date: August 2022

Deploy Date: February 2024