Why does an error occur during a measurement

Measurement error

Definition: The measurement error is defined as the difference between the true or actual value and the measured value. The true value is the average of the infinite number of measurements and the measured value is the exact value.

Types of errors in measurement

The error can come from various sources and is usually classified into the following types. These guys are

  1. Gross mistakes
  2. Systematic errors
  3. Random errors

Their types are explained in detail below.

1. Gross mistakes

The gross mistake occurs because of the human error. As examples, it is assumed that the person using the instruments reads incorrectly or records the wrong data. Such a mistake falls under the gross mistake. The gross error can only be avoided by reading carefully.

For example - the experimenter reads 31.5 ° C while the actual reading is 21.5 ° C. This happens because of the neglect. The experimenter makes an incorrect measurement, and because of this, the error occurs in the measurement.

Such errors, as a rule, are very commonmeasurement. It is not possible to completely eliminate such errors. Some of the gross flaws are easily recognized by the experimenter, but others are difficult to find. Two methods can fix the gross error.

Two methods can fix the gross error. These methods are

  • The reading should be taken very carefully.
  • At least two measurements of the measurand should be made. The readings are taken by the different experimenter and at another point to correct the error.

2. Systematic errors

The systematic errors are mainly divided into three categories.

  1. Instrumental errors
  2. Environmental flaw
  3. Observation error

2 (i) Instrumental errors

These errors mainly arise for the three main reasons.

(a) Inherent shortcomings in the instruments - Such types of errors are built into instruments because of their mechanical structure. They could result from the manufacture, calibration, or operation of the device. These errors can cause the error to be read too low or too high.

For example - if the instrument uses the weak spring, it indicates the high measurand. The error occurs in the device due to friction or hysteresis loss.

(b) Misuse of the instrument - The error occurs in the device due to an error by the operator. A good instrument used in an unintelligent way can produce a tremendous result.

For example - misuse of the instrument can result in errors in setting the instrument zero point, poor initial adjustment, use of too high a resistance. These improper practices may not cause permanent damage to the device, but they do cause errors.

(c) charging effect - It is the most common type of error caused by the instrument during measurement work. For example, if the voltmeter is connected to the high resistance circuit it will give a misleading indication, and if it is connected to the low resistance circuit it will give the reliable indication. This means that the voltmeter has a load on the circuit.

The error caused by the loading effect can be overcome by using the counters intelligently. For example, if a low resistance is measured by the ammeter-voltmeter method, a voltmeter with a very high resistance value should be used.

2 (ii) Environmental Defects

These errors are due to the external condition of the measuring devices. Such errors mainly occur due to temperature, pressure, humidity, dust, vibration or due to the magnetic or electrostatic field. The corrective measures to eliminate or reduce these adverse effects are

  • The arrangement should be made to keep the conditions as constant as possible.
  • Use equipment that is free from these effects.
  • By using the techniques that eliminate the effects of these disturbances.
  • By applying the calculated corrections.

2 (iii) Observation Errors

Errors of this type are due to mistaken observation of the reading. There are many sources of observation errors. For example, the pointer of a voltmeter is reset slightly above the surface of the scale. So a mistake occurs (because of parallax), unless the viewing direction of the observer is exactly above the pointer. In order to minimize the parallax error, high-precision measuring devices with mirrored scales are provided.

3. Random errors

The error caused by the sudden change in the atmospheric state, such an error is called a random error. These types of errors are retained even after the systematic error has been eliminated. Therefore, such an error is also referred to as a residual error.