• Transducer/sensor converts a nonelectrical quantity, measurand, into a
related electrical output signal
• Ideally there is a linear relationship
between the measurand and the output
• Sensors often need a source of
energisation, a power supply
• What’s the measurement made for?
– Information, to quantify the measurand
– Record, to provide a historical profile
– Control, use the information to control some process
• Sensor measurements are subject to errors
– Noise
– cross sensitivity, output changes because it’s
sensitive to other environmental variables
– Characteristic errors, deviation from the predicted
– Dynamic errors, non-ideal frequency or time response
• Important Characteristics
– Accuracy, usually expressed in %, variation
from the stated linear (or other relationship)
between measurand and output
– Resolution, smallest change in the
measurand that can be detected in the output
– Range, range of value of the measurand that
the sensor can accurately sense
• For any form of measurand there are always
several sensors that can be used, which one
depends on the application
• Similarly, many sensors can be used to sense
different measurands
• E.g: Temperature: thermocouple, resistance
thermometer, thermistor, semiconductor sensor,
infra-red thermometer……
• E.g: Strain gauge: strain, pressure, height,
displacement, velocity, acceleration
• Sensors generate analogue outputs such
as voltage or frequency
• Sensors generate digital outputs such as
pulses or digital data
Transducers/Sensors: Examples
• Linear displacement:
– Resistance
– Capacitance
– Electromagnetism LVDT (linear variable
displacement transformer)
– Ultrasonic
– Optical
– …………
Transducers/Sensors: Examples
• Temperature:
– Thermocouple
– Platinum resistance
– Thermistor
– Semiconductor junction
– Semiconductor thermometer
Transducers/Sensors: Exercise
• Use the rest of the lecture time for a web search
on the transducer type given:
1. Range of types available & typical devices (diagrams,
2. Accuracy, range, resolution
3. Measurand/output law (linear?, shown as a graph?,
4. Cross-sensitivity? Other important electrical
5. ???
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