Methods of Measurement
Measurement can be determined as to find object’s size, length, weight, capacity or other aspects.
It completely depends on the instrument and parameter
There are some tricks and techniques to find target measurement.
According to accuracy required for the measurement divided into six different methods.
Methods of Measurement
The following are the different methods for measuring a physical variable.
1. Direct Method
2. Indirect Method
3. Comparative Method
4. Substitution Method
5. Null Method
6. Fundamental Method
Direct Method
In this method, the value of the quantity of target is directly measured by comparing with standard.
It includes an only simple mathematical calculation to find out results.
Examples:
Measurement of Length of cloth with Scale
Measurement of Resistance by Ohms Meter
Measurement of Length using Vernier Caliper
Measurement of Voltage using Voltmeter
Measurement of Resistance by Ohms Meter
Measurement of Length using Vernier Caliper
Measurement of Voltage using Voltmeter
Indirect Method
When the direct method is not possible for measurement, the Indirect method is used.
In this method quantity is measured by mathematical relationship of know parameters.
Examples:
Measurement of Volume by measuring Mass and Density
(Volume=Mass/Density)
Measurement of Speed by measuring Distance and Time
(Speed=Distance/Time)
Measurement of Temperature by using RTD or Thermocouple
The output of ‘RTD’ and ‘Thermocouple’ is in ‘Ohm’ and ‘millivolt’ respectively. This is converted into temperature respective standard conversion tables.
Measurement of DC Current by using shunt(Resistance)
(Ohms Law V=IR i.e. I=V/R) I is current, V is Voltage, R is Resistance
Comparative Method
In the comparative measurement method, the quantity to be measured is compared with the known value of the same quantity.
Examples:
(Volume=Mass/Density)
Measurement of Speed by measuring Distance and Time
(Speed=Distance/Time)
Measurement of Temperature by using RTD or Thermocouple
The output of ‘RTD’ and ‘Thermocouple’ is in ‘Ohm’ and ‘millivolt’ respectively. This is converted into temperature respective standard conversion tables.
Measurement of DC Current by using shunt(Resistance)
(Ohms Law V=IR i.e. I=V/R) I is current, V is Voltage, R is Resistance
Comparative Method
In the comparative measurement method, the quantity to be measured is compared with the known value of the same quantity.
Examples:
Comparing of Sound Level meter with reference sound level meter
Comparing of Lux meter with reference Lux Meter
Comparing of Voltmeter with a reference Voltmeter
Substitution Method
The substitution measurement method involves the replacement of the value of the quantity to be measured with the known value of the same quantity.
In this method, the quantity to be measured is measured by direct comparison on an indicating device by replacing the measuring quantity with some other known quantity that produces the same effect on the indicating device.
Example:
Calibration of weights by Substitution method
Null Method
In the null measurement method, the quantity to be measured is compared with a known quantity, and the difference between these two is made zero i.e. Indicator Indicates Zero reading.
Null measurement techniques achieve greater accuracy.
Example:
Measuring unknown resistance using Wheatstone bridge
Fundamental Method
In the fundamental measurement method, the measurement is based on the measurement of the base quantities used to define the quantity.
The quantity to be measured is directly measured and linked with the definition of that quantity.
Examples:
Measurement of the temperature by fixed point apparatus
Measurement of voltage by Josephson Junction
Measurement of time by cesium atomic clock
Measurement of length by using Iodine Stabilize Helium-Neon laser
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