PRESENTATION ON

“DIFFERENT TYPES OF STRAIN GAGES”

PRESENTED BY

BHOSALE SURAJ UTTAMRAO

M.E.(CIVIL-STRUCTURE) SEM-I

UNDER THE GUIDANCE OF

Prof. Dr. A.N. BAMBOLE

APPLIED MECHANIC DEPT.

SARDAR PATEL COLLEGE OF ENGINERRING, ANDHERI (W), MUMBAI.

� TYPES OF STRAIN GAUGES :-

� MECHANICAL � MECHANICAL

� OPTICAL

� PNEUMATIC

� ACOUSTICAL

� ELECTRICAL

� MECHANICAL STRAIN GAUGES:-

� The mechanical devices are generally known as extensometer and are used to measure strain under static or gradually varying loading condition.

� PRINCIPLE:-

� Extensometer is usually provided with two knife edges.

� They are clamped firmly in contact with the test component at a specific distance.

� When the test component is strained, the two knife � When the test component is strained, the two knife edge undergoes a small relative displacement.

� This displacement is amplified through a mechanical linkage and magnified displacement or strain is displayed on a calibrated scale.

Demountable Mechanical Strain Gauge

Different types of Mechanical strain Gauge:-

a) Berry strain gauge

� Lever arm and dial gauge.gauge.

� Measure a strain down to 10microstrain over a 50mm gauge length.

B) Johansson Extensometer

� Torsion tape stretched between knife edges.

� Half end is twisted in one direction, while other half in other other half in other direction.

� Measure a strain down to 5microstrain over a gauge length of 50mm.

c) Huggenberger Extensometer

Sets of levers are been used in this to magnify the displacement.

Formula for measurement = L1L2/a1a2

Ratio Gauge length range

300-2000 6.5 to 100 mm

Sensitivity as high as 10microstrain.Suitability: - Where large height does not pose problems of mounting.

Scratch Gauge

Scratch Gauge

� Scratch gauge:-

� Minimum strain that a scratch gauge can sense is about 100microstrain.

� Suitability: - compact in size, weight =30g, attached to weight =30g, attached to almost any surface with

� Clamps, screws or adhesive bonding.

� Tuckerman’s Optical Gauge:-

� Auto-collimator is used which carries a source of a parallel beam of light and an Optical system with reticle to measure the deflection of the reflected ray.

2) Optical Gauges:-Mechanical-Optical Gauges:-

Combination of mechanical and optical levers is used to amplify the relative displacement between knife edges.

the reflected ray.� Lozenge functions as movable

knife edge.� In this system, any relative motion

between the component and the auto-collimator will not affect the measurement.

� Sensitivity is 2microstrain.� Available in wide range starting

from 6mm.� It can reliably measure both static

and dynamic strains

Optical strain Gauge

Advantage:-• Reduced wiring as compared

to electrical strain resistance.to electrical strain resistance.• Light weight as compared to

others.• Insensitivity to

electromagnetic interference.

�Photo elastic

strain Gauges:-

� Components- a strip of plastic with reflection backing with ‘Frozen-in’ fringes pattern.pattern.

� Polaroid/Quarter sheet.

� Graduated scale is there for measurement.

� Sensitivity -50microstrain.

Pneumatic strain Gauge• Pneumatic Strain

Gauges:-

• Magnification upto 100000 and gauge lengths as small as 1mm are possible to achieve in these gauges.

• They are sensitive, robust and • They are sensitive, robust and reliable. Suitable for both static and dynamic strain measurements.

Acoustic Strain Gauge

Acoustic strain Gauge

� Acoustic Strain Gauges:-

� Frequency of vibration in test gauge is measured by comparing it

with fundamental natural frequency of the wire.

�

� Sensitivity:- 0.5microstrain

� Advantages: - Long-term reliability.

� High accuracy.

� Facility for remote measurement.

� Chiefly used at: - Reinforced Concrete structure, dams, steel structure.

� Electrical Gauges:-

� INDUCTANCE GAUGES

� CAPACITANCE GAUGES� CAPACITANCE GAUGES

� ELECTRICAL RESISTANCE GAUGES

Inductance Strain Gauge

� a) Inductance Strain Gauge:-

� In this Linear variable differential transformer (LVDT) used.

� Two coils Primary and Secondary are used is attached to one edge and movable magnetic core is connected to the other.

� Movement of the core in one direction away from the null position produces an output from the null position produces an output alternating voltage proportional to the displacement from the centre

� Suitability – used over a wide range of temperature below 0 to elevated temperature.

� Sensitivity – range 0.02 to 0.15 V/mm displacement per volt of excitation applied to the primary coil.

� Limitation – magnetic fields, size and mass

Capacitance strain Gauge

� Capacitance Strain Gauges:-

� Capacitance changes occur due to axial sliding of an outer cylinder relative to two concentric inner cylinders.

� Temperature compensation is achieved by using rod.

� Function satisfactorily upto 800 C.

� Sensitivity – 1microstrain.

THANK YOU