So, Who’s Really in Charge? The Many Hands That Control a PLC
2. The Programmer
At the heart of PLC control lies the programmer. This is the individual (or team) responsible for writing the code that dictates the PLC’s behavior. They use specialized programming languages, like Ladder Logic, Function Block Diagram, or Structured Text, to create a set of instructions that the PLC executes in a continuous loop. It’s like writing a recipe for the PLC to follow.
The programmer needs a deep understanding of the process being controlled. They need to know how the various sensors and actuators interact, what the desired outcomes are, and how to handle potential errors or unexpected situations. Think of them as the architect designing a building, ensuring everything works together seamlessly.
Their work involves not just writing the code, but also testing and debugging it. This is a crucial step to ensure that the PLC behaves as intended and doesn’t cause any unexpected (and potentially catastrophic) problems. They are also the ones that decide which signals from field devices such as proximity sensors are used to control the action of an output device, such as a valve. It’s like a trial run for the entire system.
A programmer often works with software developers to create a Supervisory Control and Data Acquisition system (SCADA). This allows human machine interface (HMI) to visualize and interact with the PLC process. This is crucial for real time process control.
3. The Engineers
While the programmer writes the code, engineers play a crucial role in defining the overall control strategy and ensuring that the PLC is properly integrated into the system. They’re the ones who determine what sensors and actuators are needed, how they should be wired, and how the PLC should be configured to communicate with other devices.
Engineers are also responsible for troubleshooting problems and making adjustments to the system as needed. They might fine-tune the PLC’s parameters to optimize performance, or they might diagnose and repair hardware failures. Think of them as the construction workers who bring the architect’s plans to life.
They are responsible for testing the PLC programs and hardware integration to make sure the desired system operation is working properly. They usually work together with the programmer to make sure both systems are aligned. The engineer will also create documentation that shows how the system is wired for reference.
Often the engineers are also in charge of the safety of the machine. They ensure that the proper safety circuits are used to make sure no one is injured while the machine is running. These safety checks include light curtains, e-stops, and safety scanners that stop the machine if someone enters a dangerous area.
4. The Operators
In many cases, the control doesn’t stop with the programmer and engineers. Operators, the people who work with the machinery on a daily basis, can also exert control. They use Human-Machine Interfaces (HMIs) — touchscreens, buttons, and other controls — to monitor the system’s performance, make adjustments, and respond to alarms.
While operators don’t typically modify the PLC’s code directly, they can influence its behavior by changing setpoints, enabling or disabling certain functions, or overriding automatic controls. Think of them as the drivers of a car, who can steer and control the speed within the limits set by the car’s design.
They also do visual inspections of the machine to identify any problems such as leaks or loose parts that can effect the performance of the process. They are then able to report the issues to the appropriate people for maintenance and repairs.
Modern HMI systems also allow operators to view historical data such as alarms. The data can then be analyzed to resolve any reoccurring issues within the PLC control system.