Sensors actuators and automation in practice
How an automatic system measures, thinks, and acts
Behind Every Automatic System — From a Simple Thermostat to a Robot Arm in a Factory — Lies the Same Basic Chain: Something Measures a Condition in the Outside World, Something Interprets the Measurement and Decides What Should Happen, and Something Executes That Decision Physically. The Three Links are Called Sensor, Control and Actuator, and Understanding the Interplay Between Them is the Core of the Trade Control and Automation.
§The sensor — the system's eyes and ears
A sensor converts a physical quantity — temperature light pressure distance movement — into an electrical signal the controller can work with. Some sensors provide an analog signal that glides smoothly with the measurement while others provide a pure digital signal — present or absent above or below a limit. The choice of sensor type depends on what is to be measured how precisely it should be measured and what environment the sensor must be in.
| Sensor type | Measuring tool | Typical use |
|---|---|---|
| Temperature sensor | Heat grades | Thermostats, cooling, process monitoring |
| Fotocelle/lyssensor | Light intensity or presence of light | Street lights, alarms, counting equipment |
| Proximity sensor | Distance or whether something is present | Robots, access control, safety |
| Pressure sensor | Pressure in liquid, air or mechanical | Pumps, hydraulics, process systems |
| Accelerometer | Movement, vibration, inclination | Alarms, industrial monitoring, electronics in vehicles |
§From raw signal to reliable measurement
A sensor signal is rarely ready to use right out of the box. It often needs to be amplified because it is weak filtered to remove noise and — if the controller is digital — converted from analogue to digital through an analogue-to-digital converter (ADC). This signal conditioning is a classic electronics task: a poorly treated signal gives a controller that responds incorrectly regardless of how good the sensor itself is.
§The steering — the decision
Steering can be a simple electronic circuit, a microcontroller or an industrial PLC (programmable logic controller), depending on the complexity of the task. What they have in common is that they read sensor signals, compare with a desired state, and calculate what should happen. A simple control just switches on or off at a limit value; a more advanced control — for example a PID regulator — adjusts continuously and gradually to hit the desired point without overreacting.
§The actuator — the hands that perform
The actuator is the part that converts the control's decision into physical action: a motor that rotates, a relay that connects power to, a valve that opens, or a solenoid that moves a mechanical part. Actuators often require far more power than the electronics controlling them, and therefore there is almost always an intermediary — a relay or a power transistor — that allows a weak control signal to connect or disconnect a far more powerful current.
- 01Electric motor — rotates, runs or pumps.
- 02Relay – lets a small signal switch a larger power circuit
- 03Solenoids — move a mechanical part linearly, often to open or close
- 04Valve — controls flow of air, water or other fluids
- 05Light-emitting diode/lamp — visual feedback, often part of the system itself
§Feedback — the closed loop
What really makes a system 'automatic' rather than just remote controlled is feedback: the sensor measures the result of the actuator's action and the control constantly adjusts based on the new measurement. A thermostat that turns off heat at the right temperature and turns it back on when temperature drops is the simplest example of such a closed loop — and the principle appears in everything from air conditioning to robot control and production equipment.
“An automatic system is no smarter than the loop it measures and acts in — the better the sensor and actuator work together the more reliable the result.”
— Professional view on automation