How can you distinguish between control system types?

1 Open-loop control systems

An open-loop control system is one that does not use feedback to adjust its output based on the input. It only relies on a predefined set of rules or commands to perform a task. For example, a toaster is an open-loop control system that heats the bread for a fixed amount of time regardless of the actual temperature or crispiness. Open-loop control systems are simple, cheap, and easy to implement, but they are also prone to errors, disturbances, and uncertainties.

2 Closed-loop control systems

A closed-loop control system is one that uses feedback to measure the output and compare it with the desired input. It then adjusts its output accordingly to minimize the error or deviation. For example, a thermostat is a closed-loop control system that senses the room temperature and switches the heater on or off to maintain a set point. Closed-loop control systems are more accurate, stable, and robust than open-loop control systems, but they are also more complex, expensive, and difficult to design.

3 Linear control systems

A linear control system is one that follows the principle of superposition, which means that the output is proportional to the input and the sum of the outputs is equal to the sum of the inputs. For example, a voltage divider is a linear control system that produces an output voltage that is a fraction of the input voltage. Linear control systems are easy to analyze, model, and design using mathematical tools, such as differential equations, Laplace transforms, and state-space methods.

4 Nonlinear control systems

A nonlinear control system is one that does not follow the principle of superposition, which means that the output is not proportional to the input and the sum of the outputs is not equal to the sum of the inputs. For example, a diode is a nonlinear control system that produces an output voltage that depends on the polarity and magnitude of the input voltage. Nonlinear control systems are more realistic, versatile, and adaptive than linear control systems, but they are also more challenging, unpredictable, and chaotic.

5 Continuous-time control systems

A continuous-time control system is one that operates on continuous signals that vary smoothly over time. It can have any value within a range at any instant of time. For example, an analog watch is a continuous-time control system that displays the time using a continuous movement of the hands. Continuous-time control systems are natural, smooth, and precise, but they are also susceptible to noise, interference, and distortion.

6 Discrete-time control systems

A discrete-time control system is one that operates on discrete signals that change only at discrete intervals of time. It can have only certain values at certain instants of time. For example, a digital watch is a discrete-time control system that displays the time using a discrete sequence of digits. Discrete-time control systems are artificial, convenient, and efficient, but they are also limited, approximate, and quantized.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?