By Eugene le Roux, FSAIRAC, and Eamonn Ryan
In the earlier parts of this series, we examined how centralised control systems integrate information from across a facility to create co-ordinated, intelligent operations. Let us now look a little closer at what happens between the point of measurement and the central control system itself.
Closed loops greatly improve accuracy and stability, but they also bring new challenges. Pvproductions | Freepik.com
At any given point in a process – be it a temperature sensor, a pressure transducer, or a flow meter – the signal produced is typically analogue. However, this raw signal is seldom perfect. It may be too small to be read accurately, non-linear in response, or contain electrical noise and interference. Before it can be interpreted by the central controller, it must therefore undergo signal processing.
This processing corrects and refines the sensor output so that a clean, stable digital signal of suitable scale can be transmitted. Only once that happens can the control logic at the central point make accurate, meaningful decisions. In essence, signal processing translates the physical world into digital information.
Now consider the reverse situation. The central control system must often command an actuator to perform some task – open a valve, start a motor or adjust a damper. The microprocessor’s output signal is small and digital, while the actuator usually requires a much larger analogue input. The digital signal must therefore be converted, amplified and supplied with appropriate power.
In addition to the signal wiring that connects the actuator and the control system, there must also be a power source – electrical, pneumatic or mechanical – to do the actual work. In many systems, a feedback signal is returned from the actuator to confirm position or performance, forming what is known as a closed-loop control system.
Closed loops greatly improve accuracy and stability, but they also bring new challenges. Each loop must be properly tuned so that it responds quickly without becoming unstable. Understanding this delicate balance between responsiveness and control is fundamental to every automated process.
The interaction of sensors, processors and actuators – each converting information between physical and digital forms – is what makes automation possible. It’s the invisible dialogue that keeps systems running efficiently and reliably.
