1. Recap
1. The degree of closeness of the measured value of a certain quantity with its true value is known as a) Accuracy b) Precision c) Sensitivity 2. Error of measurment is a) True value- Measured value b)Precised value- True value c) Measured value - Precision

2. 3 The ability by which a measuring device can detect small differences in the quantity being measured by it, is called its a) Damping b) Sensitivity c)Accuracy 4. The following is an internationally recognized and accepted unit system a) MKS b) FPS c)SI

3. Identify the iamge

4. MECHANICAL STRAIN GAUGE
Wedge and screw magnification
Simple mechanical lever magnification
Compound magnification system
1. Berry strain gauge
2. The Tinius Olsen strain gauge
Compound lever magnification
1. Huggenberger extensometer
2. Porter- Lipp strain gauge
Magnification by rack and pinion
Combined lever, rack and pinion magnification

5. Compound Lever Magnification
It is classified into two categories
a) Huggen berger strain gauge
b) Porter Lipp strain gauge
In this system magnification is composed of one or more levers in series

6. Porter- Lipp strain gauge

7. Description
These type of gauges are very sensitive to any vibration that may occur in the structure under test.
The natural frequency of these gauge is rather low
The gauge length of this gauge is 25mm and magnification 300
Advantages:
Compactness
Extreme light weight
Readings can be taken directly

8. HUGGENBERGER EXTENSOMETER

9. Description It consist of frame C which supports the lever system.
a is a fixed contact point.
b is a rhomb which is movable point
Rhomb b is integral with arm h
When there is change in length resulting in rotation of arm h and transmits through link d supported with knife edge m and n

10. -Contn
The readings are noted in scale f are converted to actual strain using the multiplication factor
Multiplication factor= l1 l2 /a1 a2
Spring is used to hold the points a and b in contact with test piece.

11. The magnification may vary from 300 to 2000 depending upon the model.
The gauge length varies from 12.5 to 25 mm
Advantages:
Small size
High magnification factor

12. Magnification by Rack and Pinion
The rack and pinion principle with various types of gear trains is employed in this type.
The dial indicator consist of gear train actuated by rack which follows the motion to be measured.

13. Dial gauge Indicator

15. Combined Lever, rack and pinion magnifaction

16. Description
This type is a combination of lever and rack and pinion system.
The Whitte more strain gauge is developed in 1928
The motion between two frame members is measured directly in dial indicators.

17. OPTICAL STRAIN GAUGE Marten’s mirror extensometer
Tuckerman optical strain gauge

18. Marten’s mirror extensometer

19. Tuckerman optical strain gauge