Everything you need to know about precision, accuracy, and calibration Visaya Weekly – Episode 22

Hello, guys, this is German once again from Visaya.

We are halfway through 2017 and maybe is time to check our new year’s resolutions!

So I wanted to cut on the beer, eat healthier and lose a couple of pounds. Even if the value in the digital weight looks nice, it seems too good to be true! 

Is my digital weight working properly? How can I check this?

To Explain this in need to introduce two concepts:

Accuracy and Precision

When playing darts the closest your shot is to the bullseye the more accurate the shot is!

Precision, on the other hand, refers to how close set of measurements are to each other. You may see that all the shots are grouped in a section of the board, but if the are away from the bullseye they are still inaccurate.

So how can I check if my weight is accurate and precise?

If you want to check the accuracy of the digital weight you have to use an object with a known weight, like for example the kilogram standard in platinum-iridium and then compare the difference between these values.

Of course, there are no perfect measuring instruments and there are accepted ranges of error depending on the measuring principle and application.

The process of checking this error is called calibration.

Let’s see another example

The Orangina Suntory company in France produces some of the most popular refreshment drinks like Schweppes and Orangina.

They use a combination of vortex, magnetic and Coriolis flowmeters in order to measure and handle fluids like water, steam and the delicious finished products.

For a week or 15 days a year the line is shut down for maintenance activities and during this time they perform the calibration in all these instruments.

Working together with Endress+Hauser, they installed a calibration rig that is able to calibrate the flowmeters in the plant with the same accuracy than on a laboratory.

By using reference flowmeters that are more precise than the ones used in the plant they are able to compare the flow value during the test and make sure that the instruments are working within the appropriate range of accuracy or error.

If the instruments are out or the range and the error are higher than accepted there are several actions that can be undertaken like adjustment and compensation of the error with a transmitter or controller.

It’s good to clarify that calibration and adjustments are two separate things.

Calibration allows us to know how the instrument is behaving, whereas adjustment changes the behavior of the instrument.

And know that I have calibrated and adjusted my digital weight I think I have to adjust my diet if I want to be part of the next Orangina commercial.

As always thank you for watching, remember to subscribe. Till next week.

Oh, I almost forgot to tell you guys a nice fun fact. I mentioned before that you need a kilogram standard to check the accuracy of the scale. However, scientists of the National Institute of Standards & Technology are developing a new method to calculate it. You can check it out in the video below.

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