Devices

Last Updated: 3 months ago2024-12-26 ; Contributors: AhmedThahir, web-flow

Sensors (Input)

Devices that - detect the state of a physical environment - quantitatively provide a corresponding output as an electrical/optical signal

Characteristics of Sensors

	Meaning
Static	After steady state condition, how the output of a sensor change in response to input change	Range	Highest and lowest value that can be sensed
		Resolution	Smallest change in input that can be sensed
		Sensitivity	Ratio of incremental change in response of system wrt incremental change in input
		Error	Difference between true and measured value $u = y_m-y$
		Accuracy	$1-E[u]$
		Precision	$\sigma(u)$
		Linearity	Deviation of sensor curve from particular straight line
		Drift	Difference in measurements from a specific reading when kept at that value for long period of time
		Repeatability	Deviation between measurements in a sequence under same conditions
Dynamic	Properties of system's transient response to input How well sensor responds to changes in input	Zero-order system	Output shows a response to input signal with no delay
		First-order system	Output approaches final value gradually
		Second-order system	Output response oscillates before steady state

Classification

Aspect	Class	Meaning	Example
Activity	Passive	Cannot independently sense input	Accelerometer Temperature Water-level Soil moisture
	Active	Can independently sense input	Radar Sounder Laser altimeter
Signal Type	Analog
	Digital
Direction of Quantity	Scalar	Only magnitude	Speedometer
	Vector	Magnitude and direction	Accelerometer Gyroscope

Sensor Fusion

Combining measurements of the same quantity from multiple sensors, to obtain a combined information with lower uncertainty than any of the individual sensors. Using multiple sensors for the quantity also allows us to verify each sensor wrt others.

If we have $s$ sensors, $$ \begin{aligned} \mu_\text{S} &= \left( \sum \limits_s^S \dfrac{\mu_s}{\sigma^2_s} \right) \sigma^2_{S} \ \sigma^2_\text{S} &= \dfrac{1}{\sum \limits_s^S \dfrac{1}{\sigma^2_s} } \end{aligned} $$ where $S$ refers to the combination of all the sensors

Effectors (Output)

Devices that perform some action such as emitting light, sound, motor, etc

Sensors

• Motion
  • Gyroscope
  • Radar
  • Magnetometer
  • Accelerometer
• Acoustic
  • Ultrasonic
  • Microphones
  • Geophones
  • Vibrometers
• Environmental
  • Temperature
  • Humidity
  • Pressure
  • Infrared
• Touch sensors
  • Capacitive
  • Infrared
• Image Sensors
  • Thermal
  • Camera
• Biometric
  • Fingerprint
  • Heart rate
  • Face recognition
• Force sensors
  • Pressure
  • Strain
• Rotation sensors
  • Encoders

Actuator

• Motor
• Valve controller
• LED light

Classification

Class	Subclass	Example
Electric	Linear	Electric Bell
	Rotatory	Motor
Fluid Power	Linear	Cylinder, Piston
	Rotary	Cylinder, Piston
Chain	Linear	Sprockets, sections of chain
Manual	Linear	Gearboxes Wheels
	Rotatory	Levers Handwheels

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