Sensors and Transducers
A sensor detects a physical quantity. A transducer converts one form of energy or information into another. In mechatronics, sensors close the loop between mechanical motion and electronic control.
Learning Objectives
By the end of this lesson, you should be able to:
- classify common mechatronic sensors;
- distinguish accuracy, precision, resolution, repeatability, and latency;
- choose analog, digital, incremental, or absolute feedback;
- plan calibration and fault detection;
- avoid sensor placement mistakes.
Common Sensor Types
| Quantity | Sensor examples | Typical output |
|---|---|---|
| Position | potentiometer, encoder, LVDT | voltage, pulses, serial data |
| Speed | tachometer, encoder derivative, Hall sensor | pulses, frequency |
| Force/weight | strain gauge, load cell | millivolt bridge |
| Proximity | inductive, capacitive, optical | switch, analog, IO-Link |
| Temperature | thermistor, RTD, IC sensor | resistance, voltage, digital |
| Current | shunt, Hall sensor | voltage or digital |
Sensor Specifications
Resolution is the smallest detectable step. Accuracy is closeness to the true value. Repeatability is the ability to return to the same reading under the same condition. Latency is delay between physical change and reported value.
A control loop often cares more about repeatability and latency than absolute accuracy.
Signal Chain
Placement Matters
A motor encoder measures motor shaft motion. If there is gearbox backlash or belt stretch, the load may not be where the motor says it is. A load-side encoder improves accuracy but may need better protection and cabling.
Calibration and Faults
Practical systems need a known reference. Examples include a home switch, calibration weight, precision resistor, gauge block, or known temperature point.
Fault checks include open circuit, short circuit, out-of-range reading, stuck value, impossible rate of change, and disagreement between redundant sensors.
Common Mistakes
- Choosing high resolution but ignoring noise.
- Placing the sensor before backlash when load position matters.
- Forgetting cable shielding and strain relief.
- Using an analog sensor without checking ADC reference and input range.
- Filtering so heavily that control response becomes unstable.
Summary
Sensors make mechanical state visible to electronics. Choose them by measured quantity, range, accuracy, repeatability, latency, environment, signal chain, placement, and fault behavior.
Further Reading
- Honeywell and TE Connectivity sensor application notes.
- Texas Instruments sensor signal conditioning resources.
- National Instruments sensor fundamentals tutorials.