This document discusses various tools used for linear measurement. It describes steel rules, vernier calipers, micrometers, and other tools that can directly measure length, diameter, thickness and other linear dimensions. It also discusses transducers that convert linear displacement into an electrical signal, including linear variable differential transformers (LVDTs) and capacitive transducers. LVDTs and capacitive transducers allow linear measurements to be monitored electronically.

1. LINEAR MEASUREMENT
AKHIL KRISHNAN G

2. 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)

3. 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

4. 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.

5. VERNIER HEIGHT GAUGE
• Used to measure the height, and scribing lines
on components
• Principle is similar to vernier caliper
• Least count is 0.02

6. VERNIER DEPTH GAUGE
• Used to measure the depth of holes ,slots etc.
• Principle is similar to vernier caliper
• Least count is 0.02

7. 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

8. 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

9. Winding wire : Alloys of copper nickel, silver
plantinum
• Winding former : made of ceramic materials
• Slider : made of tempered phospher bronze

10.  Advantages
• Less expensive
• Large amplitude measurements are possible
• High electrical efficiency
• Disadvantages
• Poor dynamic response
• Poor resolution
• More wear

11. LVDT
• Its an electromechanical device.

12. • 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

13. • 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

14. 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

15. Capacitive transducer with change in area b/w the
plates
• Capacitance is proportional to the effective area
of plates

16. Capacitive transducer with change in
distance b/w the plates
• The capacitance is inversely proportional
to the distance between the plates

17. • 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