LINEAR MEASUREMENT

AKHIL KRISHNAN G

LINEAR MEASUREMENT

• The term linear measurement is applied to

the measurement of length , diameter ,

thickness , internal and external dimensions

In directDirect

Non Graduated(outside/inside calipers,

surface gauge) Graduated (steel rule, vernier

caliper)

STEEL RULE

• It is a line measuring instruments

• It is made form hardened stainless steel

• They are available in 150,300,600.1000 mm

• Least count is 0.5 mm

VERNIER CALIPER

• Suitable to measure diameter of circular parts

• Accuracy is 0.02 mm

• It is made from alloy steel

• Consist main scale, vernier scale , depth bar ,internal and external measuring jaws.

VERNIER HEIGHT GAUGE

• Used to measure the height, and scribing lines on components

• Principle is similar to vernier caliper

• Least count is 0.02

VERNIER DEPTH GAUGE

• Used to measure the depth of holes ,slots etc.

• Principle is similar to vernier caliper

• Least count is 0.02

MICROMETER

• Its accuracy is 0.01

• For each revolution of thimble the spindle advances a distance equal to the pitch

• Different types are outside , inside , screw thread, depth gauge

POTENTIO METER

• It is an electromechanical device

• Consist of a variable resistive element , slider and circuitry

• Movement of the slider over the resistive element causes the change in resistance

Winding wire : Alloys of copper nickel, silver plantinum

• Winding former : made of ceramic materials

• Slider : made of tempered phospher bronze

Advantages

• Less expensive

• Large amplitude measurements are possible

• High electrical efficiency

• Disadvantages

• Poor dynamic response

• Poor resolution

• More wear

LVDT

• Its an electromechanical device.

• It consist of one primary and two secondary coils wound over a winding former

• Secondary windings have equal number of turns and they in out phase with each other

• Input supply is given to primary

• Displacement to be measured is connected with central core

• The amount of voltage change is proportional to the linear displacement of core

• At central position of the core , the net effective voltage is 0

• Advantages

• High range

• Less friction

• Low hysteresis

• High sensitivity

• Less power consumption

• These transducer tolerates high degree of shock and vibrations without any effects

• Disadvantages

• Sensitive to external magnetic fields

• Performance may affected by vibrations

• Performance may affected by temperature

CAPACITIVE TRANSDUCER

• Capacitance C = 𝑁−1 𝐴𝐾∞

𝑑

• Where N = no of plates

• A = effective area

• K = di electric constant

• ∞ = proportionality constant

• d = distance between the plates

• Capacitance is ability to store energy in the form of charge.

• By varying K A d, we can change the capacitance and this change is used to detect the displacement

Capacitive transducer with change in area b/w the

plates

• Capacitance is proportional to the effective area of plates

Capacitive transducer with change in

distance b/w the plates

• The capacitance is inversely proportional to the distance between the plates

• Advantages

• Require extremely small force

• Extremely sensitive

• Good frequency response

• Resolution is small

• Require small power for operation

• Can be used for application where inductive

transducer fails.

• Disadvantages

• Need insulation

• Non linearity

• Temperature sensitive