Page 365 - The Mechatronics Handbook

18

Sensor and Actuator

Characteristics

18.1 Range
18.2 Resolution
18.3 Sensitivity
18.4 Error
18.5 Repeatability
18.6 Linearity and Accuracy
18.7 Impedance
18.8 Nonlinearities
18.9 Static and Coulomb Friction
18.10 Eccentricity
18.11 Backlash
18.12 Saturation
18.13 Deadband
18.14 System Response
18.15 First-Order System Response
Joey Parker 18.16 Underdamped Second-Order System Response
University of Alabama 18.17 Frequency Response

Mechatronic systems use a variety of sensors and actuators to measure and manipulate mechanical,
electrical, and thermal systems. Sensors have many characteristics that affect their measurement capa-
bilities and their suitability for each application. Analog sensors have an output that is continuous over
a finite region of inputs. Examples of analog sensors include potentiometers, LVDTs (linear variable
differential transformers), load cells, and thermistors. Digital sensors have a fixed or countable number
of different output values. A common digital sensor often found in mechatronic systems is the incremental
encoder. An analog sensor output conditioned by an analog-to-digital converter (ADC) has the same
digital output characteristics, as seen in Fig. 18.1.

18.1 Range

The range (or span) of a sensor is the difference between the minimum (or most negative) and maximum
inputs that will give a valid output. Range is typically specified by the manufacturer of the sensor. For
example, a common type K thermocouple has a range of 800∞C (from -50∞C to 750∞C). A ten-turn
potentiometer would have a range of 3600 degrees.

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