MEASURMENT- measurment is a process or the result between rhe quantities.
METHODE OF MEASURMENT - The methods of methode may be brodaly classified into two categories.
1.DIRECT METHODE- In these methods, the unknown quality is directly compared against a standered. The result is expressed as a numerical number and a unite.
Direct methods are quite common for the measurment like lenth, mass and time.
2. INDIRECT METHODS- in engineering applications, for measurment purposes indirect methods are required because the measurment by direct methode are not always possible, feasibal and praticable. These methode in most of the cases are inaccurate because they involve human factors. They are also less sensitive. Hence, direct methode are not preferred and are rarely used.
CLASSIFICATION OF INSTRUMENT-
1.ABSOLUTE INSTRUMENT- The instruments which gives the value of parameter in terms of physical constant of instrument.
These instruments based on their operations on the indirect methodology of measurment and are generally used as standred instrument in calibrating are tangent galvanometer and Rayleighc's current balance.
2. SECONDARY INSTRUMENTS- These instruments gives the value if measurment directly and their operations based on directly methodology of operations.
these instrument are used for day to day used in the industry.
in comparison to secondry instrument absolute instrument are higly accurate as they contain less number of moving parts resulting in lower opration consumption powe
3. ANALOG INSTRUMENT - The instruments whose output various continusly with respect to time, while maintainig constant relationship with the input.
4.DIGITAL INSTRUMENT - The instrument whose output various directly with respect to time while maintaining a constant relationships with the input.
Analog instruments can be further classified as deflecting and null deflectin instrument.
DEFLECTING INSTRUMENT - the instrument which give the value of parameters under measurment in term of deflection of a pointer away fram the zero position.
5.DEFLECTING INSTRUMENTS - The instruments which give the value of parameter under measurment in term of deflection of a pointer awaty from zero position.
6.NULL DEFLECTION INSTRUMENT - these instrument indicate the end of their measurment with zero deflection. bridge circuit
6.INDICATING INSTRUMENT - these instrument give the instantaneous value of measurment parameter eg. ammeter, voltmeter.
7.INTEGRATING INSTRUMENT - these instrument maintain a contain record of measurment over a specifiex period of time eg. Energy meter.
8.RECORDING INSTRUMENT - These instrument gives the total sum of electrical power consumption ovar a specified period of time eg. recording voltmeter.
ERRORS ANALYSIS-error is defined as the deviation of the true value from the desired value. it is expressed either as absolute value.
STATIC ERROR-it isdefinid as the difference between the true value of the variable and The measured value of the varible.
TYPES OF STATIC ERROR-They are sub divide as follows:
1. gross errors
2.systematic errors
3. random error
1.GROSS ERRORS-.These errors are due to human mistake ib reading instrument, recording and calculation measurment result.
gross errors may be of any amount and therefore their
mathematical analysis is immopable, however, they can be adapating two means they are-
1.More care should be taken in reading should be taken for quality.
2.SYSTEMATIC ERRORS-
Systematic error (also called systematic bias) is consistent, repeatable error associated with faulty equipment or a flawed experiment design. These errors are usually caused by measuring instruments that are incorrectly calibrated or are used incorrectly. However, they can creep into your experiment from many sources, including:
A worn out instrument. For example, a plastic tape measure becomes slightly stretched over the years, resulting in measurements that are slightly too high,
these errors arise due to following three main reason-
A person consistently takes an incorrect measurement. For example, they might think the 3/4″ mark on a ruler is the 2/3″ mark.
3. RANDOM ERRORS- Random errors in experimental measurements are caused by unknown and unpredictable changes in the experiment. These changes may occur in the measuring instruments or in the environmental conditions.
The probable reeors is determined from the formula -
probabal errors =0.6745.standred deviation
in pratice, the number of observations is finite.
The Gaussian normal distribution. m = mean of measurements. s = standard deviation of measurements. 68% of the measurements lie in the interval m - s < x < m + s; 95% lie within m - 2s < x < m + 2s; and 99.7% lie within m - 3s < x < m + 3s.
The precision of a measurement is how close a number of measurements of the same quantity agree with each other. The precision is limited by the random errors. It may usually be determined by repeating the measurements.
