Sheela.PLecturer / EEE

Proud to be a Electrical Engineer

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Sensor Technology

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TRANSDUCER• Transducers convert one form of energy into

another

• Sensors/Actuators are input/output transducers

• Sensors can be passive (e.g. change in resistance) or active (output is a voltage or current level)

• Sensors can be analog (e.g. thermocouples) or digital (e.g. digital tachometer)

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Necessity of Transducer

Ruggedness

Linearity

Repeatability

High Stability and Reliability

Good Dynamic Response

Convenient Instrumentation

Residual Deformation

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Selection of Transducer

• Physical quantity to be measured

• Transducer principle –suitable for the quantity to be measured

• Accuracy in the measurement

• I/O characteristics transducer with the recording system

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Advantages of Transducer

• Amplification and Suppression can be done easily.

• Mass-inertia effects are minimum

• No friction effects present during –indication quantity.

• Measuring systems controlled with least power.

• Output can be easily received, transmitted & processed before measuring.

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Sensing Element

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Sensing Element

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Active Transducer

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Passive Transducer

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Active & Passive

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Analog Transducer

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Digital Transducer

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Bourdon Tube

• Bourdon tubes are known for its very high range of differential Pressure Measurement in the range of almost 100,000 psi (700 Mpa).

• It is an elastic type Pressure transducer.

• Eugene Bourdon in the year of 1849.

• Various forms

C type

Spiral

Twisted Tube

Helical05/01/23 EEE 15

Bourdon Tube

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Bourdon Tube Working

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Bourdon Tube

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Bellows

• Bellows is used for pressure measurement, can be made up of cascaded capsules.

• Expanded or contracted axial by changes in pressure.

• Materials Commonly used :

Brass

Bronze

Beryllium copper

Alloys of nickel & copper

Steel 05/01/23 EEE 19

Bellows

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Bellows Working Principle

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Load Cells

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Strain Gauges:

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Strain Gauge Working Principle

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Thermistor

• Thermal Resistors- Semi conductor device.

Negative Temperature Coefficient

Positive Temperature Coefficient

• Room Temperature resistorΩ is 100 Ω to

10M Ω normally at 80 C⁰

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Types of Thermistor

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PTC & NTC

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Metal Resistance Thermometer

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Digital Encoding Transducer

• A digital optical encoder is a device that converts motion into a sequence of digital pulses.

• By counting a single bit or by decoding a set of bits, the pulses can be converted to relative or absolute position measurements.

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Shaft Encoder

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Optical Encoder

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