4.2.4 Force sensors
(i) Strain gauges:
The principle of this sensor is that the
elongation of a conductor increases its
electrical resistance.
(ii) Piezoelectric sensor: A
piezoelectric material has a
phenomenon known as piezoelectric
effect.
iii) Current-based detection: Since the
torque provided by an electric motor
is a function of the current consumed,
its measurement, along with known
engine characteristics, provides
torque detection.
4.3 External sensors
4.3.1 Type of contact
i) Limit switch: A limit switch is
constructed much like the common
light switch used in homes and offices.
4.3.2 Contactless type
i) Proximity sensor: Proximity
detection is the technique used to
detect the presence or absence of an
object by means of a non-contact
electronic sensor.
a) Inductive proximity sensor: All
inductive proximity sensors consist of
four basic elements, namely:
• Sensor coil and ferric core
• Oscillator circuit
• Detector circuit
• Solid state output circuit
b) Capacitive proximity sensor: A
capacitive proximity sensor works
much like an inductive proximity
sensor.
ii) Semiconductor displacement
sensor: The semiconductor
displacement sensor uses a
semiconductor or laser light emission
diode (LED) as a light source, as well
as a position-sensitive detector (PSD).