Repeatability in measurement is a vital aspect when it comes to precision in measurement. Along with reproducibility, you get two aspects of precision to analyze. They show how consistent a repeated measurement is. As a result, it generates a reliable measurement.
Learning about measurement repeatability is not only important in the field of metrology but also in instrumentation. The quality of the measuring instrument can matter in repeatability. You are expected to design high reliability of measurement system that has good resistance against environmental condition changes.
So, What is Repeatability in Measurement?
Repeatability is the level of how consistent the measuring results that are performed:
- by the same person/operator,
- at the same time (in a relatively short period of time),
- in the same site,
- using the same measuring instrument,
- measuring the same object,
- under a replicated measurement method.
In comparison with the reproducibility test, the operator, measurement interval, environment, and measurement methods are subjects to change.
By performing a repeatability test, you will find the standard deviation after the statistical calculation.
The measurement repeatability is factored by these 4 factors:
- Measuring Instrument Quality. A precision measurement device will lead to good repeatability, then lead to precise measurements. This precision comes from highly resistant material or high-end sensors.
- Operator Expertise. A measurement error such as a random error can happen due to the operator’s incapability in reading the measurement result. As a result, it adds a greater difference in value in the reading.
- Data-Collection Error.
Easiest Example of Repeatability in Measurement
The easiest repeatability test that you can do is by performing zero reading. You can try it with linear precision measuring tools such as dial caliper, digital caliper, dial indicators, test indicators, micrometers, and many more.
Make sure to fulfill the repeatability condition. You have to use the same measuring tool, the same procedure (the same applied pressure, etc), the same place (laboratory, machine shop, outdoor, etc), and the same operator (you).
Perform zero reading several times within 10 minutes. If you get the same zero reading after a number of tests, it means good repeatability.
The experiment can be easier if you use the digital models. Choose the one that provides data transfer. This model allows the reading automatically transferred to the spreadsheet on your computer or tablet.
The Importance of Repeatability in Measurement
Imagine that you are a quality control. Your job is to make sure that the end products are under specific dimensional size. In this case, the operator, place, measuring tools, and time are the same. The only subject to change is the object to measure itself. Then, the problem raises up. The measuring tool shows variance in reading. Which is the wrong one? Your measuring tool or the end products?
This is the reason why a repeatability test is at least important to perform, to guarantee that there is no wrong with your measuring tool.
Surely, if your measuring tool doesn’t have enough repeatability, you cannot trust the measurements. Perhaps, almost all the end products are produced out of dimensions you want. It could be just a small part among the entire products. In the end, you cannot repair the end products. You lost money.
There is no reason to separate precision from accuracy. Without precision, accuracy can be nothing. They have to pair to give a trusted measurement result. And when it comes to precision in measurement, two factors that have to include: repeatability and reproducibility.
In the case of repeatability, multiple measurements are performed identically by the same operator, place, method, instrument, and time. This test will generate a variance in results. The further calculation is done to get the repeatability standard deviation.
When it comes to calibration, repeatability test is included to get the uncertainty value. Along with other uncertainty values, the documentation of the total calculation result can be seen in the certificate. You can then read how repeatable your instrument is.