ion Error, Standards and Dimention Analysis

8/14/2019 ion Error, Standards and Dimention Analysis

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Instrumentation andmeasurement

Types of error

Measurement standardsDimension analysis


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1.0 Type of ErrorsGross ErrorsSystematicallyEnvironmental

Gross Errors

Refer to errors due to human mistake in readinginstruments and recording and calculating measurementresults. Example 1: read the temperature as 31.5C while the actual

reading may be 21.5C Example 2: read 25.8C and record as 28.5C Prevention: read and record carefully, and taking the

average of several reading


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Systematic Errorsa) Instrumental errorsi) Due to inherent shortcoming in the instrument Inherent due to their mechanical structure. They may be due to improper calibration, construction,manufacturing limitation, orfaulty instrument.

Example: If the spring (use for producing controlling torque)of a permanent magnet instrument has become weak, thedevice will always read high.

Overcome methods by:- Recalibrated carefully- Apply correction factors after determining the instrumentalerrors- Proper maintenance, use and handling of instruments


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Systematic Errors ii) Due to misuse of instrument

Example: Failure to adjust the zero of instruments Using leads of too high resistance (when measure

low R value)

Measuring an ac signal which beyond the instrumentbandwidth response.

Overcome methods by:

- Recalibrate system carefully

- Using the right instrument for the particularapplication


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Systematic Errors iii) Due to loading effect of instruments

Due to the internal resistance of the device Due to the active filters effect of the device

Leakage of current or voltage

Improper ground or reference

Loading effect cause inaccuracy of measurement -Can be avoided by using appropriate instrument orusing them intelligently. Example: using a voltmeterwhich has a relatively high resistance compared to theload resistance.


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b) Environmental Errors Effect due to the temperature, pressure, humidity, dust,

vibrations or external magnetic or electrostatic fields.

Overcome methods

i) Keeping the conditions as nearly as constant as possible.

Example: temperature can be kept constant by keeping the

equipment in a temperature-controlled enclosure.

ii) Use equipment, which is immune to these effects

Example: variations of resistance with temperature can beminimized by using the materials, which have a very lowresistance temperature co-efficient


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b) Environmental Errors iii) Employ techniques, which eliminate the effects of

disturbances

Example: effect of humidity & dust can be entirelyeliminated by hermetically sealing the equipment

iv) Apply computed correction

2 (c) Observational Errors

The errors that introduced by the observer

i) Parallax error using a wrong method in observingthe values

ii) Reaction time different instantaneous reaction ofthe people. Ex: Watch timer


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2.1 Standards terms Dimension- defines some physical characteristics.

Example, Length, volume,

velocity, heat and etc.

Unit is a standard or reference by which adimension can be expressed numerically

SI unit The international system of units - It isbased on seven well-defined base units (meter,kilogram, second, ampere,

Kelvin, Mole, Candela) and two supplementary,dimensionless units (Radian,

Steradian)


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2.2 Fundamental and secondaryunits

There are five fundamental units or base units:

a) Meter (m), L

b) Kilogram (Kg), M c) Second (s), T

d) Ampere (A), I

e) Kelvin (K), q Secondary units are the product of fundamental units

For eg : Area ( L2)- m2, Newton, Kgms-2 and etc


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Derived Units


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2.3 Symbols and notation


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2.4 Equation and numbering It is important to have a right concept to write an equation. For

an example:

Y=MX + C Where M and C are the constants. X and Y are the variables.

X is always refers as the input/ changes to the system. (Alwaysput at the right side of

the equation.)

Whereas,

Y is always refers as the result/effect that cause by the

changing of the X. (Always put at the left side of the equation and also always as a single

term)


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2.5 Dimension analysis It is necessary condition for correctness that

every equation be balanced dimensionally. For example:

Newton, F(N) = mass M(kg) X accelerationLT-2 (ms-2) = [M][L T-2]

= [MLT-2] Unit for force = N = kg ms-2

ion Error, Standards and Dimention Analysis

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