TOPIC 2
Least Count, Sensitivity , Precision and Resolution of Instrument
Least Count of Instrument
The smallest value that can be measured by a measuring instrument is called its least count.
Measured values are good only upto this value.
A Vernier scale on caliper may have a least count of 0.02 mm while a micrometer may have a least count of 0.01 mm.
Relation between Least Count and Precision of Instrument :
The least count of a measuring instrument is the smallest change in the measured quantity that can be resolved on the instrument's scale.The least count is related to the precision of an instrument; an instrument that can measure smaller changes in a value relative to another instrument, has a smaller "least count" value and so is more precise. Any measurement made by the instrument can be considered repeatable to no less than the resolution of the least count. The least count of an instrument is inversely proportional to the precision of the instrument.
Sensitivity of an Instrument :
* It is ratio of Change in output of the Instrument to the change in input or measure quantity.
* The Sensitivity of an Instrument should be High.
* Example. Consider a pressure sensor that has a measurement range of 0–100 PSI and an output range of 0–5V. Its sensitivity is .05 Volt/PSI.
* The sensitivity of an instrument says nothing about the quality of an instrument. This is typically established by the instrument’s accuracy and precision.
It is closeness with which an instrument reading approaches the true value of the quantity being measured. The measured quantity may be different from true quantity due to effects of Temperature, humidity etc.
Precision :
The term " Precise " means clearly or sharply defined . Precision is defined as the closeness between two or more measured values to each other.
Note : Accuracy and Precision are two independent terms.
Resolution :
Precision :
The term " Precise " means clearly or sharply defined . Precision is defined as the closeness between two or more measured values to each other.
Note : Accuracy and Precision are two independent terms.
Resolution :
If the input is slowly increased for some arbitrary value , it will be found that the output does not change at all until a certain increment is exceeded , this increment is called Resolution.
In other words it is the smallest change in a measured variable to which an instrument will respond.
In other words it is the smallest change in a measured variable to which an instrument will respond.
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