SHAIFUL NIZAM MOHYARUNIVERSITI 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 transducerTo 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.

measurand electrical output

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 with amplifiers and frequency

response limitations.

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 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

Capacitive Transducers

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.

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

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.