Repeatability and reproducibility are two common terms used by engineers which confuse a lot of engineers. Repeatability and reproducibility are used to define the precision of any instrument or equipment.
Today in this article we will try to clearly understand repeatability and reproducibility in a detailed way so that in the future these terms do not create any kind of confusion for us.
Repeatability
Repeatability is defined after measurements are taken under certain conditions like
- Same instrument/equipment
- Same person
- Same condition
- The same method of measurement
- Same place
Hence, we can conclude that when measurements are taken by the same instrument/equipment, by the same person who follows the same method of measurement at the same place, then this method is known as repeatability.
We can take an example of measurement of the output by a 24 VDC power supply unit using Multimeter. We need to test the repeatability of the power supply unit.
Here an engineer is measuring the output voltage of a 24 VDC power supply unit. The readings are taken from the same terminals every time and also the temperature of the room is kept at 25 degrees centigrade.
The engineer takes 10 different measurements at intervals of 1 minute. The below table shows the readings taken by the engineer. (The Multimeter used is a certified and recently calibrated Multimeter)
| Measurement 1 | 24.03 |
| Measurement 2 | 24.02 |
| Measurement 3 | 24.04 |
| Measurement 4 | 24.03 |
| Measurement 5 | 24.05 |
| Measurement 6 | 24.02 |
| Measurement 7 | 24.02 |
| Measurement 8 | 24.03 |
| Measurement 9 | 24.04 |
| Measurement 10 | 24.03 |
From the above table, it is clear that the maximum deviation we are getting is 0.05 VDC.
This much voltage deviation is acceptable by the system using this 24 VDC. Hence, we can say that our 24 VDC power supply unit is producing a repeatable output.
This way we can also say that repeatability is the way of measurement that is used to build confidence in a particular instrument or equipment which is used in any plant or industry or other location.
We will take another example of a pressure transmitter. We assume that the range of the pressure transmitter is 0 kg/cm2 to 50 kg/cm2.
Now if we want to do a repeatability test of the pressure transmitter, then we will apply some pressure say about 30 kg/cm2 about 10 times to the pressure transmitter using the same hand pump, at the same location and within a short period to keep ambient conditions constant.
Below are the readings of the pressure transmitter.
| Measurement 1 | 30.05 |
| Measurement 2 | 30.05 |
| Measurement 3 | 30.04 |
| Measurement 4 | 30.03 |
| Measurement 5 | 30.04 |
| Measurement 6 | 30.06 |
| Measurement 7 | 30.01 |
| Measurement 8 | 30.06 |
| Measurement 9 | 30.05 |
| Measurement 10 | 30.04 |
From the above measurement table, we can conclude that the pressure transmitter is producing repeatable outputs.
Reproducibility
Reproducibility is defined after measurements are taken under certain conditions like
- Same instrument/equipment or different instrument/equipment
- Different person
- Different condition
- A different method of measurement
- Different place
Hence, we can conclude that when measurements are taken by the same instrument/equipment, by a different person who follows a different method of measurement at some other place, then this method is known as reproducibility.
We should also select different timings for doing this test. Again, we take the same example of the 24 VDC power supply unit.
In this case, we will ask different people to conduct the test. We will also install the power supply unit at different locations having different temperatures.
Also, we will measure the output voltage of the 24 VDC power supply using different Multimeters (The Multimeters used are certified and recently calibrated Multimeters) at different time intervals.
Doing this will help us know whether the 24 VDC power supply units made by a company or an industry are producing the same outputs every time under different conditions or not.
This measurement test will give confidence to the makers of the 24 VDC power supply unit that the 24 VDC power supply units made by them is working everywhere in most cases.
In this case, also, we can take the example of the pressure transmitter. Here, we will install the pressure transmitter at different locations and we will give the same pressure every time but using a different hand pump or another pressure-generating device.
The person giving the pressure should also be different and the testing should be done at different intervals of time like in the day, in the evening, and night.
If every time we get some kind of output, then the pressure transmitter is producing reproducible outputs.
This way repeatability and reproducibility can be used in two different ways to check the instrument or the equipment.
EndNote
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