PE2-4.2 Sensors: Proximity, Motion, Force, Flow & Light
You can classify sensors and select among inductive and capacitive proximity sensors, tachogenerators, optical encoders, strain gauges, tactile, ultrasonic and laser flow sensors, level sensors and photodiodes.
Learn each sensor by the physical principle it exploits, because that predicts its failure modes better than any specification table: an inductive proximity sensor detects metal only, a capacitive one detects almost anything and drifts with humidity. The strain gauge is the one to know properly since it underlies load cells, pressure sensors and torque measurement, and it is nearly always used in the bridge circuit configuration for the drift-rejection reason. Optical encoders introduce the absolute-versus-incremental distinction that recurs throughout motion control.
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Definition and classification of sensors
What counts as a sensor and the families they fall into. The classification predicts what a new device will be like before you read its datasheet.
Inductive and capacitive proximity sensors and their applications
Detecting presence without contact, by two different physical principles. Which one works depends on what the target is made of, which is the practical point.
Tachogenerator and optical encoders
Measuring rotation, by generating a voltage or by counting marks. The encoder gives position as well as speed, which is why it dominates.
Strain gauge as a force sensor
Measuring force through the deformation it causes. The bridge circuit from the measurement topic is what makes the tiny resistance change readable.
Fluid pressure and tactile sensors
Two more mechanical quantities, one of which is a whole field on its own. Tactile sensing is where robotics and this subject meet.
Flow sensors: ultrasonic and laser
Measuring flow without obstructing it, which is why these two methods exist. Both infer flow from something else, which is the idea to notice.
Level sensors: ultrasonic and capacitive
Measuring how full something is, by two principles with different failure modes. Foam and coating on the vessel wall defeat them differently.
Light sensors: photodiodes and their applications
Detecting light, and the range of things that reduces to. Many sensors above are optical underneath, which is worth realising.
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