Islamic University of Gaza
Industrial Engineering Department
EIND3102: Measurements Lab
 Metrology
is the science of measurement,
embracing
both
experimental
and
theoretical determinations at any level of
uncertainty in any field of science and
technology. ”International Bureau of Weights and
measurements (BIPM)”
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 Measurement
is the process of determining
or finding the size, quantity or degree of
something .
 The principle dimensional measurement is
length; secondary measurement is angle and
curvature. You can describe shape without
describing size, but not the reverse.
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Measured Quantity
Units
Symbol
Length
Meter
m
Mass
Kilogram
Kg
Time
Second
s
Temperature
Kelvin
K
Electrical Current
Ampere
A
Quantity of substance
Mole
mol
Luminosity
Candela
Cd
Plane angle
Radian
rd
English unit
Value
Miles
1mile=1760yard
Equivalent value
in SI
1 mile = 1.609 km
Yard
1 yard = 3 ft
1yd = 91.44 cm
1 ft = 12 in
1 ft = 30.48 cm
Foot
Inch
in
1 in = 25.4 mm

Four methods of measurement:
1.
Direct method. compare the quantity directly with the
primary or secondary standard.
1.
Indirect method.
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1.
Comparison method: the comparison of an
unknown quantity to a known quantity called a
standard using Dial Indicator.
1.
Coincidence method.
 Measuring
instruments are measuring
devices that transform the measured
quantity into an information, either
analog or digital.
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
The
functions
instruments are:
1.
2.
3.

of
the
measuring
Indicating function
Recording function
Controlling function
The
applications
of
the
measuring instruments are:
1.
2.
3.
Monitoring of processes and operations
Control of process
Experimental engineering analysis
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
Measuring Instruments Types:
1.
2.
3.
4.
Angle measuring Instruments: e.g. Angle
gauges; Divided scales; Sine bar with slip gauges;
Autocollimator; and Tool Maker Microscope.
Length measuring Instruments: ex: Steel
rule; Caliper; Micrometer; and comparators.
Instruments for surface finish: surface
roughness measurements.
Instruments for deviations: Coordinate
Measuring Machine (CMM).
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
Measurement Applications
1.
2.
3.
4.
Plate Work: The layout and
inspection performed from a surface
plate. The primary purpose of a
surface plate is to provide a
reference plane.
Coordinate Measurement
Statistical Quality Control
Inspection:
Verification
of
conformity to a standard.
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Resolution:
It is the minimum value that can be measured when
the instrument is gradually increased from non-zero
value.
 Repeatability:
The degree of closeness with which a given value may
be repeatedly measured under same conditions.
Reproducibility:
The degree of closeness with which a given value may
be repeatedly measured under different conditions.

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Gaging:
It is not measurement, but a form of inspection
and sorting.
 Tolerance:
The two extremes within which an actual part
dimension must lie.

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They are a necessity in any testing environment
that requires linear dimensional accuracy and/or
calibration of measuring tools, such as
micrometers and calipers.
 They are precision ground and lapped measuring
standards. They are used as references for the
setting of measuring equipment such as
micrometers, sine bars, dial indicators (when
used in an inspection role).
 Gage blocks are manufactured to precise gagemaker tolerance grades for calibrating,
checking, and setting fixed and comparative
gages.

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
Calibration of a measuring instrument
It is the process of determining the values of the
quantity being measured corresponding to a
pre-established arbitrary scale.

Advantages of calibration:




Optimizes resources.
Assures consistency.
Ensures
measurements
(and
perhaps
products) are compatible with those made
elsewhere.
Eliminate or reduce bias in the user's
measurement system relative to the
reference base.
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 Accuracy
is the agreement between a
measured value and the true value.
 Precision also called reproducibility or
repeatability, the degree to which further
measurements or calculations show the same
or similar results.
 Instrument precision is usually associated
with the number of digits displayed on the
output, i.e., its resolution.
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 Accuracy
indicates proximity to the true value,
precision to the repeatability or reproducibility
of the measurement
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High precision, but
low accuracy
High accuracy, but
low precision
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 Precision error is
Error is
the random error.
Inaccuracy or
Uncertainty.
 Accuracy error is the  Precision error is
measured value minus the reading minus
the average of
the true value.
readings.
 Accuracy
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 Measurements
Errors :
Is the difference between the true value of the size and
the value found by measurement.



Errors pertains to measurement not to an
instrument.
Error = True Size – Actual Size
True Size: is the theoretical size obtained through
measurement. This type of size is free from any type
of error. It is the guide for measuring many properties
such as accuracy of an instrument.
Actual Size: is a measured size with permissible
error. It refers to the minimum acceptable size of a
sample.
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
There are two general categories of error:
systematic (or bias) errors and random (or
precision) errors.
Errors
• Systematic
• Random
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 Systematic
errors (also called bias errors)
They are consistent, repeatable errors. For
example, suppose the first two millimeters of a
ruler are worn off, and the user is not aware of
it. Everything he or she measures will be too
short by two millimeters – a systematic error.
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Systematic errors arise for many reasons. Here are just a few:
 Calibration Errors: due to nonlinearity or errors in the calibration
method.
 Loading or Intrusion Errors: the sensor may actually change the
very thing it is trying to measure.
 Spatial Errors: arise when a quantity varies in space, but a
measurement is taken only at one location (e.g. temperature in a
room - usually the top of a room is warmer than the bottom).
 Human Errors: arise if a person consistently reads a scale on the
low side, for example.
 Defective Equipment Errors: arise if the instrument consistently
reads too high or too low due to some internal problem or
damage.
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 Random
errors
They are unrepeatable, inconsistent errors,
resulting in scatter in the output data.
The random error of one data point is
defined as the reading minus the average
of readings.
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There are many other errors, which all have technical names,
as defined here:
 Zero Error: The instrument does not read zero when the
input is zero. Zero error is a type of bias error that offsets
all measurements taken by the instrument, but can usually
be corrected by some kind of zero offset adjustment.
 Linearity Error: The output deviates from the calibrated
linear relationship between the input and the output.
Linearity error is a type of bias error, but unlike zero error,
the degree of error varies with the magnitude of the
reading.
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Sensitivity Error: The slope of the output vs.
input curve is not calibrated exactly in the first
place. Since this affects all readings by the
instrument, this is a type of systematic or bias
error.
 Resolution Error: The output precision is limited
to discrete steps (e.g., if one reads to the
nearest millimeter on a ruler, the resolution
error is around +/- 1 mm). Resolution error is a
type of random or precision error.

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Hysteresis Error: The output is different, depending on
whether the input is increasing or decreasing at the
time of measurement. This is a separate error from
instrument repeatability error.
 Instrument Repeatability Error: The instrument gives a
different output, when the input returns to the same
value. The reasons for the differences and the
procedure to get to that value are usually random, so
instrument repeatability error is a type of random error.

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

Drift Error: The output changes (drifts) from its
correct value, even though the input remains
constant. Drift error can often be seen in the zero
reading, which may fluctuate randomly due to
electrical noise and other random causes, or it can
drift higher or lower (zero drift) due to nonrandom
causes, such as a slow increase in air temperature in
the room. Thus, drift error can be either random or
systematic.
Parallax: This error can occur whenever there is
some distance between the measuring scale and the
indicator used to obtain a measurement. If the
observer's eye is not squarely aligned with the
pointer and scale, the reading may be too high or
low (some analog meters have mirrors to help with
this alignment).
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Environmental factors: Be aware of errors
introduced
by
your
immediate
working
environment. You may need to take account for
or protect your experiment from vibrations,
drafts, changes in temperature, electronic noise
or other effects from nearby apparatus.
 Reading
Error: describes such factors as
parallax, interpolation, or optical resolution.
 Loading Error: results from the change of the
measurement instrument when it is being used.
 Effect of support.
 Dirt.

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Errors due to Vibrations.
 Metallurgical Effects.
 Contact Point Penetration.
 Errors due to Deflection.
 Errors due to Looseness.
 Errors due to Wear in Gauges.
 Errors due to Location.
 Errors due to Poor Contact.
 Errors due to Impression of Measuring Stylus.

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