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
Q. Explain Crystal Oscillator The frequency of a crystal-controlled oscillator is held constant to a high degree of accuracy by the use of a quartz crystal. The frequency depen

In this design, there are 24 line finders. If any of the 100 subscribers has to get access to any of 24 two-motion selectors, it is necessary that every line finder is capable of r

fast decoupled program

A 3-phase transmission line is 200km long. The line has a per phase series impedance of 0.25+j0.45 Ω/km and shunt admittance of j7.2 μS/km. The line delivers 250MVA, at 0.6 lagging

There is a limitation on the size of data. Most Microprocessor does not maintain floating-point operations.

Thevenin' s Theorem Thevenins Theorem states: "Any linear circuit containing several energy source and resistances can be replaced by just a Single Voltage in series with a

Q. Assumption of capital asset pricing models? 1) Investor; s objective is to maximize the utility of terminal wealth: investor aims at maximizing the utility of hi9s wealth r

Management Process of Balanced Score Card The BSC (Balanced Score Card) proposes four a new management processes which separately and in combination, contributes to linking lo

Q. Find idealized expressions for the active and ohmic states and sketch the universal characteristics of an n-channel enhancement MOSFET operated below breakdown.

List the different types of flags affected by the arithmetic and logic operations. Carry flag, Auxiliary carry flag , Parity flag, Sign flag, Zero flag