15. The result of measuring is :
( 3 mm + ( 7 x 0.1 ) mm ) = 3.7 mm
16. 0 cm 2 cm1 cm
0 10
Main Scale
Vernier Scale
X 0.1 mm
Least Count = Value of the smallest division on MS/
Total number of division on VS
L.C = 1mm / 10 = 0.1 cm / 10 = 0.01cm
17. 0 cm 2 cm1 cm
0 4 862 10
Main Scale
Vernier Scale
X 0.05 mm
29. Dial Caliper
The dial Caliper
has seven main
components:
a slide scale,
lock screw,
thumb adjustment
wheel, measuring
jaws (inside &
out), dial with
measurements of
0.001 inch, depth
rod and a bezel.23
37. Description of the Spherometer
• Instrument that measures the surface power (D)
associated with the lens surfaces.
31
38. Functional Principle
Supporting the legs on the lens surface, the
movement of the center leg, is translated to the
scale, giving the value of the surface power of the
surface.
Positive value in
convex surfaces.
Negative value in
concave surfaces.
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39. Zero error
Adjustment or Calibrating the instrument to zero:
When placing the instrument on a flat polished surface,
the scale must mark 0.00 D.
If not, all previous measurements will be affected by
this value.
The measurement will be a result of the following
equation:
Psur: Value given by spherometer when place on flat
surface.
Psph: Value given by spherometer when placed on one of
the curved surfaces of the lens.
surPspherePP
43. Galvanometer
• The galvanometer is the "classic" device to
measure current
• Based on the fact that a wire carrying current
in a magnetic field feels a force
43
44. • The current flows through a coil in a
magnetic field
• The coil experiences a torque proportional to
current
• The movement of the coil is "opposed" by a
spring
• The deflection of the needle is proportional
to current
44
34
35
36
45. • Rsh = "shunt" resistance
• The current I divides itself between the
coil and the shunt
– I = IC + Ish
• By Ohms's law, Vab = IC RC = Ish Rsh
• Ish = IC (RC/Rsh)
• I = IC + Ish = IC (1 + RC/Rsh)
If RC and Rsh are known, measuring IC is
equivalent to measuring I
• Furthermore, I is still proportional to IC, which is
proportional to the deflection of the needle
• Thus, by "switching in" different shunt resistances I
can effectively change the "range" of my current
measurement
37