Metrology-8-Metrology Errors

Question 1

What is accuracy of a measuring instrument?

Answer 1

The accuracy of a measuring instrument indicates the deviation of the
reading from a known input. The accuracy of an instrument indicates how well it agrees with the true value.

Question 2

What is the precision of a measuring instrument?

Answer 2

The precision of a measuring instrument indicates its ability to reproduce
a certain reading with a given accuracy.The precision of an instrument refers to the dispersion of measurements.

Question 3

What is the sensitivity of a measuring instrument?

Answer 3

The sensitivity of a measuring instrument is the ratio of the instrument
scale change to the change in the measured variable.

Question 4

What is the error of a measuring instrument?

Answer 4

The error of a measuring instrument is the quantified deviation between
the instrument reading and the known input.

Question 5

What is the uncertainty of a measuring instrument?

Answer 5

The uncertainty of a measuring instrument is the deviation between
readings when a known reference value does not exist.

Question 6

What are the two categories that measuring instrument errors can be divided into?

Answer 6

Systematic errors remain constant or change in a regular fashion in
repeated measurements of one and the same quantity. Corrections
can be introduced to remove the error.
Random errors are differences between the results of separate
measurements which cannot be predicted individually

Question 7

What are the potential sources of random error?

Answer 7

• Human errors
• Environmental errors
• Equipment errors

Question 8

What are Airy points used for?

Answer 8

The Airy points are used for two-point support and make the end faces of
the beam parallel, where A = 0.5577 L

Question 9

What are Bessel points used for?

Answer 9

The Bessel points are used for two-point support, and minimize the
change in the overall length, where B = 0.559 L

Question 10

What is Thermal expansion?

Answer 10

All materials will contract and expand when subject to changing
conditions and temperatures.
All materials have a coefficient of thermal expansion (α), although
these will not necessarily be linear with temperature.
a =
Expansion/Original length x temperature change
Linear Expansion = L{1+ ( angle1- angle 2)}

Question 11

What is ABBE’s rule?

Answer 11

Maximum accuracy may be obtained when the standard scale and the
work piece are aligned on the same line of measurement

Question 12

What is parallax error?

Answer 12

• Parallax is the change in the apparent relative positions of objects when
  viewed from different positions.

Question 13

What are inclination errors?

Answer 13

Inclination errors are due to the incorrect positioning of measurement
transducers, especially when measuring internal dimensions.
If the internal micrometer is inclined in the axial direction of the pipe/tube,
positive measurement errors will be produced.
If the micrometer is inclined in the lateral direction, then negative measurement
errors will be produced.