Transducers (lecture notes)
Transcript of Transducers (lecture notes)
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Lecturer: Jomo N. Gill
MEASUREMENTS ANDINSTRUMENTATION
ELE 4101
LECTURE IX
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CONCEPTS TO BE EXAMINED
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- Transducers
General classes of transducers
Variable parameter analog transducers
Resistive transduction
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TRANSDUCERS
All physical quantities measured with electronicinstruments are first converted into signalvoltages, which can in turn be amplified or
otherwise made into suitable form for recording orindication. As used in instrumentation, the termtransducer denotes the devices used to make thisconversion.
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Transducers use almost all knownelectromechanical principles to convert themeasured quantities into their electrical analogs.
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GENERAL CLASSES OF
TRANSDUCERS
Transducers are classified into four main groups:
- self-generating analog- variable parameter analog
- frequency or pulse generating
- digital
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contd
Analog transducers produce an electrical outputsignal that is a proportional continuousmeasurement of the input signal variations.
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Pulse rate transducers produce voltage pulseswhose frequency or random pulse generation rateis proportional to the input parameter variations.
Digital transducers produce a unique codedvoltage or current form for each discrete valuesensed.
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VARIABLE PARAMETER
ANALOG TRANSDUCERS
These produce an output which is a proportional
fraction of an original resistance, capacitance orinductance.
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The changes in resistance, inductance or
capacitance caused by the physical phenomenonbeing measured, are translated into correspondingvoltage or current effects. These are thenconverted into an output signal.
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contd
The conversion requires auxiliary circuitry. TheWheatstone bridge and its variations are
commonly used.
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RESISTIVE TRANSDUCTION
The variation of resistance is one of the mostcommon transduction principles. The resistance ofa resistive element can be varied by severalmethods, including:
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- sliding a wire along a rheostat
- applying mechanical stress
- varying light intensity to a photosensitivematerial
- changing its temperature
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Resistive transduction is used by:
- displacement transducers
- strain gauges- resistive temperature devices (RTDs)
- thermistors
- photoconductive devices
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POTENTIOMETERS
The potentiometer or slidewire resistor relies onrotation or mechanical displacement of a sliding
contact to determine the value of the resistanceoutput. They are used in the direct measurementof linear and angular displacement and motion.
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Potentiometers also find application as the sensingelement in many transducers designed to measurepressure, acceleration, force, and liquid level.
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The resistive element consists of either woundwire, or a ribbon of deposited carbon film,platinum, or other compound.
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Inside a potentiometer Schematic diagrams
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VARIOUS TYPES OF
POTENTIOMETERS
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