A sensor turns a physical condition into information.
A device may indicate that a target is present, that a mechanism has reached a point or how far something has moved. These are different kinds of information.
A simple switch gives discrete states. A measuring sensor or encoder can provide more detailed information, depending on its design.
Different ways of detecting a target.
- Mechanical switchA moving part operates contacts.
- Inductive sensorDetects a nearby metallic target without contact.
- Optical or magnetic sensorResponds to light or a magnetic target.
An optical sensor may use a beam being interrupted or reflected. A magnetic sensor may respond to a magnet passing it. Each method has its own target, range and environmental requirements.
Detection and interpretation are separate steps.
The output goes to a controller or another circuit. That system interprets the information alongside other inputs before deciding what to do.
Output type, supply requirements and the meaning of each state must match the receiving circuit. Two sensors that detect metal may still have incompatible outputs.
One signal does not describe the whole lift.
The controller receives a marker signal. It may also need direction, movement information and other conditions to identify position correctly and decide the next action.
A door-closed indication is not automatically proof of a locked door. Likewise, a general-purpose position sensor is not automatically a safety-rated device.
Targets and surroundings matter.
Alignment, target material, operating distance, contamination and damaged wiring can affect detection. An intermittent signal may involve the target or connection rather than a failed sensor alone.
These are principles for understanding reports, not instructions for adjusting detectors. Later lessons will show how position feedback works alongside the drive and lift controller.
A closer look
Switching sensors often have hysteresis: their turn-on and turn-off points differ slightly to avoid chatter at the boundary. Response time and repeatability also matter. These properties are different from the precision of a complete lift positioning system.
Check your understanding
Does a sensor changing state mean the controller must move the lift?
Reveal the explanation
No. It provides one piece of information. The controller must evaluate the other required conditions before issuing a movement command.