Linear measurement systems in instrumentation and control, vernier calipers, linear displacement transducers,

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
Direct In direct
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 =
푁−1 퐴퐾∞
푑
• 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