Errors & Types of errors
Error
An
error may be defined as the difference between the measured value and the
actual value.
Error = True value ~ Measured value
Types
of Errors
Generally
errors are classified into three types:
1) Gross Errors
2) Blunders
3) Measurement Errors
2) Blunders
3) Measurement Errors
Gross Errors:
Gross errors are caused by mistake
in using instruments or meters, calculating measurement and recording data
results.
The best example of these errors is
a person or operator reading pressure gage 1.01N/m2 as 1.10N/m2.
It may be due to the person’s bad
habit of not properly remembering data at the time of taking down reading,
writing and calculating, and then presenting the wrong data at a later time.
This may be the reason for gross
errors in the reported data, and such errors may end up in calculation of the
final results, thus deviating results.
Blunders
Blunders are final source of errors
and these errors are due to recording a wrong value while making a measurement.
These blunders should stick out like
sore thumbs if one person checks the work of another person. It should not be
comprised in the analysis of data.
Measurement Error:
The Measurement Error is the result
of the variation of a measurement of the true value.
The best example of the measurement
error is, if electronic scales are loaded with 1kg standard weight and the
reading is 10002grams, then the measurement error is = (1002grams-1000grams)
=2grams
Measurement
Errors are classified into two types:
Systematic error
Random errors
Systematic Errors:
The Systematic errors that occur due
to fault in the measuring device are known as systematic errors. Usually they
are called as Zero Error / a positive or negative error.
These errors can be detached by
correcting the measurement device.
These
errors may be classified into different categories.
Instrumental Errors
Environmental Errors
Observational Errors
Theoretical Errors
Instrumental Errors:
Instrumental errors occur due to
wrong construction of the measuring instruments.
These errors may occur due to
hysteresis or friction. These types of errors include loading effect and misuse
of the instruments.
In order to reduce the gross errors
in measurement, different correction factors must be applied and in the extreme
condition instrument must be recalibrated carefully.
Environmental
Errors:
The environmental errors occur due
to some external conditions of the instrument.
External conditions mainly include
pressure, temperature, humidity or due to magnetic fields.
In
order to reduce the environmental errors,
·
Try to maintain the humidity and
temperature constant in the laboratory by making some arrangements.
·
Ensure that there shall not be any
external electrostatic or magnetic field around the instrument.
Observational
Errors:
These types of errors occur due to
wrong observations or reading in the instruments particularly in case of energy
meter reading.
The wrong observations may be due to
PARALLAX.
In order to reduce the PARALLAX
error highly accurate meters are needed (i.e) meters provided with mirror
scales.
Theoretical Errors:
Theoretical errors are caused by
simplification of the model system.
For example, a theory states that
the temperature of the system surrounding will not change the readings taken
when it actually does, then this factor will begin a source of error in
measurement.
Random Errors:
Random errors are caused by the
sudden change in experimental conditions and noise and tiredness in the working
persons. These errors are either positive or negative.
An example of the random errors is
during changes in humidity, unexpected change in temperature and fluctuation in
voltage. These errors may be reduced by taking the average of a large number of
readings.
Sources of Error
The
possible sources of such errors are:
1. Small variations in
the position of setting standard and work piece.
2. Slight displacement
of lever joints of measuring instruments.
3. Operator error in
scale reading.
4. Fluctuations in the
friction of measuring instrument etc.
Comparison between Systematic
Errors and Random Errors
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Systematic
Errors
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Random Errors
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These
errors are repetitive in nature and are of constant and similar form
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These
are non-consistent. The sources giving rise to such errors are random.
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These
errors result from improper conditions or procedures that are consistent in
action.
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Such
errors are inherent in the measuring system or measuring instruments.
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|
Except
personal errors, all other systematic errors can be controlled in magnitude
and sense.
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Specific
causes, magnitudes and sense of these errors cannot be determined from the
knowledge of measuring system or condition.
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If
properly analyzed these can be determined and reduced or eliminated.
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These
errors cannot be eliminated, but the results obtained can be corrected.
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These
include calibration errors, variation in contact pressure, variation in
atmospheric conditions, parallax errors, misalignment errors etc.
|
These
include errors caused due to variation in position of setting standard and
work-piece, errors due to displacement of lever joints of instruments, errors
resulting from backlash, friction etc.
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