Transcript Slide 1 - UniMAP Portal

SHAIFUL NIZAM MOHYAR
UNIVERSITI MALAYSIA PERLIS
SCHOOL OF MICROELECTRONIC ENGINEERING
2007/2008
Definition of a Transducers
 Transducer is any device that converts
energy in one form to energy in another.
 Convert electrical energy to mechanical
displacement.
 Convert non-electrical physical quantity to
electrical signal.
e.g. temperature, sound or light to an
electrical signal.
Definition of a Transducers
 Function of transducer
To sense the presence, magnitude, change in
and frequency of some measurand.
To provide an electrical output, when
appropriately processed and applied to a
readout device.
electrical output
measurand
Excitation
Classification of Transducers
 Transducer can be classified according to their
application, based primarily on their physical
quantity, property or condition to be measured.
 1) Passive transducers
 require an external power.
 Their output is a measure of some variation,
such resistance and capacitance.
 2) Self generating transducer
 do not require an external power.
 they produce analog voltage or current when
stimulated by some physical form of energy
Selecting a Transducers
 Transducer has to be compatible with its application
1) Operating range – should maintain range
requirements and
good resolution.
2) Sensitivity – must be sensitive enough to allow
sufficient
output.
3) Frequency response and resonant frequency –
is the
transducer flat over the needed range.
4) Environment compatibility - corrosive fluids, the
pressures,
shocks and interactions.
Selecting a Transducers
5) Minimum sensitivity – minimally sensitive to
expected stimuli
other than measurand.
6) Accuracy – subject to repeatability and calibration
errors.
7) Usage and ruggedness - mechanical and electrical
intensities
versus size and weight.
8) Electrical – what are signal-to-noise ratios when
combined
limitations.
with amplifiers and frequency response
Resistive Transducers
 Also called displacement transducer.
 to detect and transmit the physical position of
mechanical parts via electrical signals
Strain Gauge Transducers
 a passive transducer
 Uses electric resistance variation in wires to sense the strain
produced by a force on wires.
 Measuring weight, pressure, mechanical force, or
displacement.
 A tensile stress tends to elongate the wire and thereby
increase its length and decrease its cross sectional area
Capacitive Transducers
 capacitive transducers can be made to be self-contained units.
 Some transducers work by making one of the capacitor plates
movable, either in such a way as to vary the overlapping area or
the distance between the plates.
 Other transducers work by moving a dielectric material in and out
between two fixed plates to detect and transmit the physical
position of mechanical parts via electrical signals
Differential Capacitive Transducers
 have 3 wire connections: one wire for each of the "end" plates
and one for the "common" plate.
 implementation in a bridge circuit
Differential Capacitive Transducers
 This bridge circuit is similar in function with strain gauges: it is not
intended to be in a "balanced" condition all the time, but rather the
degree of imbalance represents the magnitude of the quantity
being measured.
Inductive Transducers
 Inductive transducers may be either of the self
generating or passive type.
 The self generating type utilizes the basic electrical
generator principle, a motion between a conductor
and magnetic field induces a voltage in the
conductor (generator action).
 A tachometer is an inductive transducer that
directly converts speed or velocity into electrical
signal.
Variable Inductive Transducers
 this device is a transformer :
 primary winding powered by an external source of AC voltage,
and two secondary windings connected in series-bucking fashion.
 It is variable because the core is free to move between the
windings.
 When the core is centered and both windings are outputting the
same voltage, the net result at the output terminals will be zero
volts.
Thermocouple Transducers
 The Thermocouple is a thermoelectric temperature sensor
which consists of two dissimilar metallic wires
 These two wires are connected at two different junctions, one for
temperature measurement and the other for reference
 The temperature difference between the two junctions is detected
by measuring the change in voltage across the dissimilar metals
at the temperature measurement junction
Thermocouple Transducers
 Low cost.
 No moving parts, less likely to be broken.
 Wide temperature range.
 Reasonably short response time.
 Reasonable repeatability and accuracy.
Thermistor Transducers
 Have great resistance at low
temperatures but when they warm
up their resistance decreases rapidly.

Current can then flow through
them.
 When the thermistor is warmed up
by the hair drier its resistance drops.

As its resistance drops, current
flows into the base of the transistors
allowing the LED to light.
Assignment
Design and explain the operation of a
system that can control the level and the
temperature of water in a tank.