DAR ES SALAAM INSTITUTE OF TECHNOLOGY LECTURE NOTES TRANSDUCER AS INPUT ELEMENT TO THE INSTRUMENTATION SYSTEM Prepared by Lihakanga.R
DAR ES SALAAM INSTITUTE OF TECHNOLOGY
LECTURE NOTESTRANSDUCER AS INPUT ELEMENT TO THE INSTRUMENTATION SYSTEM
Prepared by Lihakanga.R
ObjectiveUpon completion of this lecture you will
be able to Understand basic idea on instrumentation systemKnow what is transducer.Know when transducer is considered as sensor.Know when transducer is considered as an actuator.Know how to select suitable transducer when designing .Know basic operation of widely used mechanical transducers.
Content
Basic instrumentation system. Classification of transducers. How to select transducer. Mechanical transducers.
Basic instrumentation system
Basic instrumentation cont… Transducer-Is the device that convert one form
of energy to another form. Sensor (Input transducer)-Is the device that
converts the physical/non physical quantity to be measured into electrical signal so it can be processed or transmitted electronically.
Signal conditioning circuit- this include amplifier, signal converter circuit, comparator, filters and circuit that carry out mathematical operation.
Actuator (output transducer)-A device that converts the modified electrical signal into non electrical signal.
Classification of transducers
Passive transducer (externally powered).
Active transducer (internally powered).
Passive transducers Resistive transducersPotentiometric device-Positioning of slide by an external force
varies the resistance in potentiometer or bridge. -used to measure pressure, displacement.Resistance strain gage-resistance of wire/semiconductor is
changed by elongation or compression due to externally applied force.
-used to measure force, torque, displacement.Thermistor-resistance of certain metal oxide with negative
temperature coefficient of resistance varies with temperature. -used to measure temperature.Photoconductive-resistance of a cell change as circuit element
varies with incident light. -used as photosensitive relay.Resistive hygrometer-resistance of conductive strip change awith
moisture content -used to measure relative humidity.
Passive transducer cont…. Capacitive transducersDielectric gage-variation in capacitance by change in dielectric. -used to measure thickness, liquid level.Capacitor microphone-Sound pressure varies the capacitance btn fixed
plate and movable diaphram. -used I measuring speech, music, noise.Variable capacitance pressure gage-distance btn two parallel plates is
varied by externally applied force.Used to measure displacement, pressure. Inductive transducersReluctance pick up-reluctance of magnetic circuit is varied by changing
the position of iron core of the circuit. -used to measure pressure, displacement, vibration, position.Differential transformer-the differential voltage of two secondary windings
of a transformer is varied by positioning the magnetic core through an externally applied force.
-used to measure pressure, force, displacement, position
Passive transducer cont….. Voltage/current transducerPhotoemmisive cell-electron emission due to
incident radiation on photo emissive surface.
-used to measure light, radiation.Hall effect pick up-potential defference is
generated across semiconductor plate (germanium) when magnetic flux interacts with an applied current.
-used to measure magnetic flux, current.
Active transducerPhotovoltaic cell-voltage is generated in a
semiconductor junction device when radiant energy stimulates the cell.
-used in light meter, solar cell.Piezo electric pick up-an emf is generated when
an external force is applied to a certain crystalline material such as quartz.
-used to measure sound, vibration, acceleration, pressure change.
Moving coil generator-motion of of a coil in a magnetic field generates voltage.
-used to measure velocity, vibration.
How to select transducer What is the physical quantity to be measured? Which transducer principle can best be used to measure this
quantity? What accuracy is required for this measurement? -Fundamental transducer parameters. -Physical condition. -Ambient condition. -Environment condition. -Compatibility of the associated equipment. Reducing the total measurement error -Artificially controlling environment to minimize error. -Simultaneously monitoring the environment and correcting data
accordingly.
Mechanical Transducers
Potentiometric
Mechanical Transducers cont…
Capacitive
Mechanical Transducers cont…
Inductive (LVDT)
Mechanical Transducers cont…
Strain gauge
END OF THE LECTURE
THANK YOU.