Sensors - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 16

is split into two beams. One of the two beams crosses through one of the beams,
which is deformed by the pressure. This deformation changes the light's properties.
The two beams are combined and brought to a photodiode. Different propagation
speeds create a phase shift between these beams which is detected at the diode.

2.4.3 Position and Motion Sensors

Position sensors play an important role in a wide variety of applications. Numerous
ways of detecting position are available, ranging from simple contact sensors to more
complex contact-free ones. Position measurement can either be relative (displacement
sensors) or absolute, linear or angular.
All types of position sensors have their own advantages and drawbacks; thus, it
is important to choose the right type of the sensor for the given application.

2.4.4 Resistive Position Sensors

Resistive position sensors are better known as potentiometers. In various forms,
these sensors have found applications from volume adjustment knobs and sliders on
radios to industrial machine slide sensing. A potentiometer is simply a resistor
whose resistance changes based on the position of a movable part.

2.4.5 Limit Switches

Limit switches are the simplest of position sensors. They are electromechanical
contact devices. A limit switch consists of a number of switches. When the moni-
tored object comes into contact with one of the switches, this switch is activated.

2.4.6 Magnetic Position Sensors

Magnetic Position Sensors are noncontact position sensors that are magnetic-fields-
generated or affected by target objects.
The magnetic field is a vector quantity that has both magnitude and direction.
Scalar magnetometers measure only the total magnitude. Others measure the magnitude
of the component of magnetization along their sensitive axis (unidirectional sensors).
Vector magnetic sensors have two or three bidirectional sensors.