Types of Errors in Instrumentation

Error can be classified into three types:

  1. Gross error
  2. Systematic error
  3. Random error

These errors occur mainly due to human mistakes in reading instruments, recording and calculating instruments. So whenever human being is involved in measuring some gross error are definitely committed. These errors must be detected and eliminated as possible.

1. Gross error

The gross error can be explained with an example.
An experimenter made transpose the reading, while reading the value, i.e., the value may to be 25.8 degree Celsius whereas the experimenter by mistake may read it as 25.5 degree Celsius. This information is known as gross error.

The gross error can be avoided in two ways,
Great care should be taken in reading and recording the data
For very large number of values its approximate value between the readings can be considered.

2. Systematic error

The systematic error can be classified into three types

• Instrumental error
• Environmental error
• Observation error

Instrumental error:

The instrumental error occurs due to three reasons
• Due to inherent short comings of the instruments
• Due to the misuse of the instruments
• Due to the loading effect.

Inherent shortcomings

These errors are due to construction, calibration and operation of instruments or measuring devices. Due to this error the instruments may read too high or too low.

For example, if the spring of permanent magnet has become very weak, then the instrument will always read very high.

To avoid these types of error

• The procedure of measurement must be carefully planned.
• Correction factors must be applied after determining the instrument errors
• An instrument can be re-calibrated carefully.

Misuse of the instrument

When a good instrument is used in a unintelligent manner then it results in misuse of the instruments, thereby producing poor initial adjustment and zero adjustments.

Loading effect

The loading effect occurs due to improper use of the instrument for measuring work.
For e.g. a well calibrated voltmeter may well mislead voltage when connected across a high resistance circuit. Similarly when the same voltmeter is connected across a low resistance value then it may give more dependable reading.

Environment error

These errors are due to environment factors like change in temperature, humidity and variation in pressure. This kind of error can be avoided by providing proactive cover or shield to the instrument.

Observation error

These errors are induced only by the observer and most common error is parallax error. These parallax errors are introduced while reading a meter scale.

This is due to the line of vision observer, which is not exactly above the pointer to avoid this error highly accurate meters are provided along with minus scale.

3. Random error

These types of error remain after gross error and systematic error which can be totally reduced. These errors are due to small factors which changes very often from instrument to the other instrument. These errors are also due to unknown cases which are also called residual error.