Different types of errors in measurements

1. Errors in Measurement System

2. Definition
*An error may be defined as the difference
between the measured value and the actual/true
value.
*The actual/true value is the average value of an
infinite number of measured values.
*Measured value is the estimated value of true
value that can be found by taking several
measured values during an experiment.

3. Calculation of % error
*Absolute error = measured value - exact value
= ‫׀‬VA - VE ‫׀‬
*Relative error = [measured value - exact value] /
exact value
= ‫׀‬VA - VE / VE ‫׀‬
*Percentage error = [measured value - exact value] /
exact value x 100%
*Percentage error = ‫׀‬VA - VE / VE ‫×׀‬ 100%

4. Types of Errors in Measurement System

5. Gross Errors
*Gross errors are caused by mistake in using instruments
or meters, calculating measurement and recording data
results. (human errors)
*Such errors may end up in calculation of the final results,
thus deviating results.

6. Systematic errors
*Systematic errors occur due to fault in the measuring
device.
*Usually they are called as Zero Error – a positive or
negative error.
*These errors can be removed by correcting the
measurement device.

7. Systematic errors are classified into
*Observational Errors: These occur due to wrong
observations or reading in the instruments. (most
common parallax error)
*Environmental Errors: These occur due to some
external conditions of the instrument. (change in
temperature, humidity etc.)
*Instrumental Errors: These occur due to wrong
construction of the measuring instruments.

8. Instrumental errors may occur due to:
*Hysteresis or friction.
*Loading effect and
*Misuse of the instruments.

9. Random errors
*Random errors are caused by the sudden change in experimental
conditions. These errors are due to unknown causes.
*They are generally accumulation of a large number of small effects
and may be of real concern.
*These errors can be analysed statistically.
*Noise can cause random errors in measurements.
Hence, it is important to know the types of errors and minimise them
so that measured data is interpreted properly.

10. The End