Differentiate between accuracy and precision, Electrical Engineering

Q. With suitable example differentiate between accuracy and precision.

 Sol. Accuracy :  Accuracy is the closeness with which instrument reading approaches the true value of the particular quantity to be measured, that is, accuracy of a measurement means conformity to truth. The accuracy of an instrument is measured in terms of its errors. The most important characteristic of an instrument or measurement system is its accuracy. It is generally expressed as a percentage of either true value or full scale value.

     Mathematically, accuracy on the basis of true value, Vt  is given by:

Accuracy =

 

Accuracy =

 

Where Vmax  and Vmin are the maximum or minimum final reading or results obtained after applying all the known corrections to all the various indicated readings and Vis the true (actual) magnitude of input.

Accuracy of a measurement means conformity to truth.

Precision: Precision refers to the degree of agreement within a group of various measurement or readings of the same parameter of variable.

As seen above, accuracy and precision have totally distinct meanings. Let us illustrate this using following examples:

1.   Consider an instrumentation system where the temperature of boiling water at 100?c is being measured using a thermometer. Suppose that four reading are taken using the same thermometer and they are : 100.4?c, 100.3?c, 100.5?c and 100.3?c

2.   Consider the case of two voltmeter 'A' and 'B' measuring the voltage at the same point with respect to ground. Assure that the true value of voltage is 50 V while the two voltmeters indicate the values as shown below when four consecutive reading are taken.

No. or Readings

Voltmeter 'A'

Voltmeter 'B'

Voltmeter 'C'

1.                            50V                       48.5V                                 50.1V

2.                            50.2                      48.5V                                 50.1V

3.                            48.8V                    48.5V                              50.80V

4.                            50.1V                    48.52V                             50.1V

 

It is clear from above that voltmeter 'A' reads very close to the true value of 50 V. However, there is an agreement between the four readings.

On the other hand, voltmeter 'B's' reading are not very close to true value of 50 V. But all the values are very close to each other or same. We can conclude from above that voltmeter 'A' is fairly accurate  but not precise while voltmeter 'B' is not accurate and precise.

If we consider of third voltmeter 'C' which reads 50.1, 50.1, 50.80, 50.1 for the same true value of 50 V, then we can say that voltmeter C is both accurate and precies.

Sensitivity : The sensitivity of the instrument is the ratio of the change in output (response) of  the instrument to the change of input or measured variable.

It denotes the smallest change in the value of a measured variable to which instrument responds. Sensitivity is an important property of the instrument which is determined by design. The numerical value of the sensitivity is influenced by the requirement of instrument application. The choice will be decide by the smallest subdivision desired by the conditions of the test treatment.

Sensitivity and responsiveness are frequently confused, as in speaking of thermometer which is sensitive to 0.1 °c. In accordance with the definition of the two terms, it is correct to say that the thermometer will respond to a change in ± 0.1°c.

Posted Date: 7/12/2012 7:05:20 AM | Location : United States







Related Discussions:- Differentiate between accuracy and precision, Assignment Help, Ask Question on Differentiate between accuracy and precision, Get Answer, Expert's Help, Differentiate between accuracy and precision Discussions

Write discussion on Differentiate between accuracy and precision
Your posts are moderated
Related Questions
What is an assembler? Assembler: An assembler or macro-assembler usually forms a part of the operating system. This translates an assembly language program in machine languag

#question.draw the block diagram pf digital storage oscilloscope and briefly discuss about each block

project for solar panel for farms in Saudi Arabia

Explain the construction of a MOSFET. Draw the symbols and diagrams of both P-channel and N-channel MOSFET. As JFET and MOSFET also have source, drain and gate. Its gate is ins

design a single phase distribution circuit from a supply point to a load

Q. Show that the block diagram of Figure can be reduced to the form of Figure. Find G eq (s) and H eq (s).

Describe the physical properties and uses of the Brasses. Brass - It is an alloy of copper and zinc along with 60 percent copper and 40 percent zinc. Its properties are- 1.

What do you understand by Bezier surface ? Discuss Determine the equivalent bicubic formulation of a closed and open cubic B-spine surface. a) What do you understand by solid

(a) Provide examples of intentional electromagnetic sources and examples of unintentional sources. (b) Describe the process of the formation of lightning. (c) Reduce each of

how a combination clipper works?