Systematic Error and Random Error in Metrology and What Are the Reason for It
No matter how careful you are, there will always be an error in physical quantity measurement. This “error” is a part of measuring process. They are mainly classified into Systematic error and random error.
What is the systematic error in metrology?
The systematic error is defined as the type of error that deviates by a fixed amount from the true measurement. Systematic error is reproducible inaccuracy and that are consistently in the same direction. So, it cannot be eliminated by taking a large number of readings and then averaging them. But This type of error is controllable in both magnitude and direction, can be assessed and minimized by good analysis.
In a series of measurements, systematic error is constant or proportional to the true value. So, it is also called controllable errors. However, it is very difficult to identify the systematic error.
In order to assess the systematic error and then minimize it, it is important to know the source or reasons for systematic error. The reasons for systematic errors are
- Calibration error
- Ambient condition
- Deformation workpiece
- Other avoidable errors like datum errors
What are random errors in metrology?
The random error provides the measure of random deviation that happens when a physical quantity measurement is carried out repeatedly. When a series measurement of physical quantity is done under similar conditions, the result varies unpredictably from one measurement to another. They are variable in magnitude and direction but cluster around the true value.
Since the variation is unpredictable, the specific cause for random deviation cannot be determined. Following are likely to be the reason for random error.
- Error in operator’s judgment in taking reading from engraved scale deviation, and operators’ inability to taking the reading because of fluctuation while taking measurement.
- Play in the linkage of measuring instruments. Noise in measuring instruments.
- Positional error associated with object and standard arising due to small variation in setting.
- Presence of transient fluctuations in friction of measuring instrument.