Data acquisition system, in effect, requires integration of:

Sensor/transducer for measurement of physical variables

Signal-Conditioner/transmission circuitry, that enables conversion of signal outputs from transducers to a readable form for Data Acquisition/interface modules.

The Data Acquisition Hardware comprising Multiplexer, Amplifier, A/D Converter, Buffer Memory, etc. to digitisethe analog signals for CPU.

Computer/CPU to process the digital data for data processing, display, outputs (control), storage, transmission, etc.

What is transducer?

The device which converts the physical form of signal into electrical form.

Types of Transducer:-

Displacement

Force & Pressure

Temperature

Light Sensors

Others

Strain Measurement

Strain Gauge

Piezoelectric Transducer

Pressure Measurement

Gravitational Pressure Transducer

Manometers

Elastic Pressure Transducer

Diaphragm

Capsule

Bellows

Bourdon Tubes

Definition:-

Strain Gauge is a passive, Resistive transducer which converts the mechanical elongation and compression into a resistance change.

Construction:-

There are many types of strain

gages. Among them, a universal strain

gage has a structure such that a grid-

shaped sensing element of thin

metallic resistive foil (3 to 6μm thick) is

put on a base of thin plastic film (15 to

16μm thick) and is laminated with a

thin film.

Construction:-

Construction:-

Operating Principal:-

Wheatstone Meter Bridge

Wheatstone Bridge Using Strain Gauge

Construction:-

Operating Principal:- In capacitive pressure sensor, one of these

metal plates is permitted to move in and out.

Capacitance between them changes due to varying distance between the plates.

The movable plate is connected to a diaphragm which senses the pressure and then expands or compresses accordingly.

The movement of the diaphragm would affect the attached metal plate’s position and capacitance would vary.

Construction:-

Operating Principal:-

Piezoelectric crystals develop a potential difference (i.e. voltage is induced across the surfaces) whenever they are subjected to any mechanical pressure.

Attached to the crystal is a horizontal shaft to which a diaphragm is connected.

Whenever the diaphragm senses pressure, it pushes the shaft down which pressurizes the crystal and voltage is produced.