Always the measured value of an instrument cannot be an actual value or true value. If the measured value is very close to the true value, we call it to be a very accurate measuring system. So one must have an idea, how much the measured value is close to the actual value. Before using the measuring data.
If the measured value is no closer to the standard value, it is counted as an error.
The term error in a measurement is defined as:
Error = Instrument reading – true reading
Instrument Error are classified into three categories:
Gross errors arise due to human mistakes. such as mistake of recording the measured data in calculating a derived measured. Careful reading and recording of the data can reduce the gross errors
Random errors , cause of such errors are clearly unknown and they affect the readings in a random way
Systematic errors affects all the reading in a particular fashion. Calibrating the instruments with standard measurement can reduce the error. Zero error is an example for systematic error. Environment can be the cause of systematic error
Zero error can simply say as, A device is showing a particular value even if there is no input to the device is a Zero error.
For a device Zero errors are linearly changing, so that it can be calibrated.
What is Calibration:
A process where known inputs are applied to a measuring system and the output are observed and compared with the standard instruments derived from comparison with the primary standards kept at Standard Laboratories.
Calibration can be done for all points of measurements. Actual measurement can be obtained from look-up tables. This type of calibration is known as software calibration.
Calibration is done at different points of measurement, instead of calibrating at each points particular points are selected and calibrating those points expecting that error for the whole range of measurement would remain within a small range. These types calibration is known as Single-point, Two-point, There-point calibration. Based on the number of points which are calibrating.