IFD:Sensors

From Medien Wiki

Sensors can be categorized by many aspects. Intuitively the most unique property of a sensor is what's it obviously detecting. For example everybody would know that a temperature sensor is measuring the physical temperature. And also what an air pressure sensor is made for. In these examples the physical method and our common understanding of the sensor is identical.

However there are also sensors which aren't that obvious. What is a touch screen measuring? Touchscreens are detecting touch, but they are measuring pressure or presence - or even resistance or capacitance. So the touch screen is more an applicance of an other type of sensor.

Many technical related people will regard the physical method of measurement as most clearly identifying. However this isn't true as well as there are many sensors which are already a fusion of many sensors. (for example an inertial motion unit has a compass, gyroscopes, temperature sensor and and accelerometer). Thus it can be very hard to find a specific sensor.

To design electronic devices using a sensor the electric interface of the sensor plays a main role in using- and sometimes also when selecting a sensor. Some are very simple to interface and need almost no effort, while others are very precise and need a special interface.

All three: application, physical method and electric interface are important - and there may be more properties to categorize sensors.

Interfaces

Sensors can be interfaced via:

  • Resistance
  • voltage
  • current
  • capacitance
  • frequency (pulses per time)
  • digital protocols (serial and parallel)
  • pwm (lenth of on/off period - duty cycle)
  • switch (connection is open and closed)
  • open collector (almost identical to a switch)
  • logic level (high / low)
  • other...

Physical property measured

  • Pressure or Tension
  • Voltage
  • Current
  • Magnetism / magnetic fields
  • Bend / flex / Radius / curvature
  • Position
  • Length / distance
  • Presence
  • Orientation
  • Light
  • Conductance (resistance)
  • Sound / ultrasound / air pressure
  • Sound in fluids or pressure in fluids
  • Shear
  • Angle

Applications

Uncountable - thus incomplete:

location (2d, 3d), eye position, movement, forces and deformation, presence, ambient measurements. switches and buttons. incremental input (rotary or linear sliders, etc.)

Common Examples

  • tablet writing: location + pressure
  • mouse: location + digital pressure + wheel
  • touch screen
  • inertial tracking
  • GPS tracking
  • Joystick
  • Piano Keyboard

List of Sensors

Sensor Physical Electrical
Bend and flex stress or curvature Bending Resistive
Reed switch Magnetism Switch
Photo transistor Light, broad spectrum Transistor, current
Photo diode Light, broad spectrum Diode, reverse current
LDR (Light dependant resistor) Light, broad spectrum Resistive
PIR: passive infrared movement detector Movement of differently warm objects Open collector / Voltage / Switch
Pyroelectric Sensor Changes in Temperature Transistor, current
FSR Force sensing Resistor Pressure Resistive
NTC Temperature Resistance
PTC Temperature Resistance
Temperature Sensor, integrated Temperature Voltage
Hall Sensor Magnetic fields analog / digital voltage.
Electret microphone Pressure (sound) in air. Voltage (integrated amplifier)
Piezo disk or transducer deformation, sound in solids and fluids, Voltage
Strain gauge Pressure and tension Resistance
Peltier element Temperature difference bewtween 2 surfaces Voltage + Current
Vibration Sensor (piezo) Acceleration (by inertia) Voltage
MEMS Acceleration Sensor Acceleration PWM / Analog voltage, i2c, ...
Rotary encoder Rotation, infinite Switch
Rotary encoder Rotation, infinite, absolute Open collector, digital
Potentiometer, rotary Rotation, limited
Potentiometer, hotpot Pressure Resistive
Potentiometer, slider Linear position Resistive
Touch, Capacitive (Button) Presence various
Touch, Capacitive (Slider) Position and Presence various
Touch, Capacitive, 2D Position 2D and Presence various
Touch, Resistive, 2D Position 2D and Pressure various
CCD array Light digital or analog video
Stepper motor rotation, infinite Voltage, digital (pulses)
Infrared (IR) Distance Sensor (Sharp) Distance Voltage
Ultrasonic Distance Sensor (Parallax Ping) Distance (to parallel surface) digital

Links

http://www.rn-wissen.de/index.php/Sensorarten