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Gross Error/Human Error
Cause :
Human mistakes in reading/using instruments
May also occur due to incorrect adjustment of the instrument and the computational
mistakes
Problem :
cannot be treated mathematically
cannot eliminate but can be minimized
Example :
E.g.: Improper use of an instrument.
This error can be minimized by taking proper
care in reading and recording measurement
parameter.In general, instruments change ambient
conditions to some extent when connected into a complete circuit.
Solution :
Therefore, several readings (at three readings) must be taken to minimize the effect of ambient condition changes.
FOR EXAMPLE
Example of reading resistor value using multimeter
Systematic Error
WHY ?
Due to shortcomings of the instrument (such as defective or worn parts, ageing or effects of the environment on the instrument)
Classification
Static :
caused by limitations of the measuring device or the physical laws governing its behavior.
Dynamic :
caused by the instrument not responding very fast enough to follow the changes in a measured variable
Types :
Instrumental error (mechanical structure) Environmental error
Observational error
1) Instrumental Error
Cause
Inherent while measuring instrument because of their mechanical structure (e.g.: improper calibration or faulty instruments, friction in the bearings of various moving component, irregular spring tension, stretching of spring, etc.)
Solution
error can be avoided by:
Proper maintenance
selecting a suitable instrument for the particular measurement application
apply correction factor by determining instrumental error
calibrate the instrument against standard
2) Environmental Error
Cause
Due to external condition effecting the measurement including surrounding area condition such as change in temperature, humidity, barometer pressure, etc.
Solution
Depending on the cause few solution to avoid the error are as follow:-
• use air conditioner
• sealing certain component in the instruments
• use magnetic shields
• New calibration under local condition
3) Observational Error
Cause
• introduced by the observer
• most common : parallax error and estimation error (while reading the scale)
• E.g.: an observer who tend to hold his head too far to the left while reading the
position of the needle on the scale.
Solution
• User read the scale according to the correct position
Random Error
Cause :
• due to unknown causes, occur when all systematic error has accounted
• accumulation of small effect
Solution :
Can be avoided by:
• increasing number of reading
• use statistical methods to obtain best approximation of true value
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1.7 Error In Measurement
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