Säätöpiiri

Säätöpiiri, in Finnish, refers to a control circuit or control loop that regulates a physical quantity in a system. It is a feedback-based subsystem that ensures a process variable follows a desired reference. A typical säätöpiiri comprises a sensor or transducer that measures the process variable, a controller that computes a corrective signal, and an actuator that implements the adjustment. The feedback path compares the measured value with the setpoint to reduce deviation (error).

Operation and architecture: In closed-loop säätöpiire, the controller continuously uses feedback to adjust the output. Open-loop configurations act without feedback, relying on accurate models or fixed commands but are more sensitive to disturbances. Controllers can be analog or digital, hardware-based or software-based.

Common controller paradigms include proportional-integral-derivative (PID) controllers, on-off control, state feedback, and more advanced digital strategies such as model predictive control or fuzzy logic. Actuators convert the controller signal into physical action, for example motors, valves, or power electronics; sensors provide real-time measurements; and the plant is the system being controlled.

Applications: Säätöpiire are used across industries and domains, including process automation, heating, ventilation and air conditioning, motor control, robotics, and power electronics. They aim to achieve criteria such as stability, fast response, low steady-state error, and robustness to disturbances and noise.

Design and analysis: The design of säätöpiire draws on control theory, using models of the plant, transfer functions, and frequency response analysis. Tools such as root locus, Bode plots, and Nyquist diagrams help ensure stability. Real-world implementations must address sensor noise, nonlinearity, delays, and saturation.