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Just How Important Is Calibration?

When and why you should calibrate your balance

by Adam Equipment
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The question of calibration frequently arises with a new balance, and the answer is simple: most manufacturers recommend calibration before the first use. And if you use your balance at all, regular calibration is critical.

There are many reasons a balance needs to be calibrated. Variations in the environment can make a difference, and just the simple process of shipping can affect the mechanics of the balance.

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Let’s say the ambient temperature in a room changes more than two degrees Celsius. Before you think about performing any high-precision measurements, you need to calibrate your balance. Fluctuations in barometric pressure can wreak havoc with the results produced by a balance that hasn’t been calibrated. And if your locale has a different gravitational force than that of the factory producing the balance, calibration is absolutely necessary for precise measurements.

They might seem insignificant, but even small changes can mean big differences in results.

The gravity of the situation

Gravity is not the same everywhere on Earth, as our planet is not a perfect orb. Every place in the world is positioned differently to “magnetic north.” This variation results in slight gravitational differences, depending on a particular location’s altitude compared to sea level. If the balance is moved to a place where the gravitational pull is greater or less, it will display a different value, as the force will vary.

If you stand at either of the Earth’s poles, you are slightly closer to the center of the Earth than if you stand on the equator. As you move closer to the center of the Earth, the force due to gravity will be slightly greater. As you move away from the center, it decreases. Therefore, if you climb a mountain, you move farther from the Earth’s center and the effect of the gravitational force is less. This is important, because balances measure the force of gravity that is pulling the mass toward the center of the Earth.

Balances react differently to changes in location. A less-sensitive balance, one that is readable to 1.0g for example, may not be able to measure a change in gravity when it is moved from one place to another. Highly sensitive lab balances will more readily display differences in gravitational forces. On the most sensitive analytical lab equipment, such as five-place, semi-micro balances, it is possible that a very small difference in location can cause large changes to the balance’s calibration.

For example, an analytical laboratory balance capable of weighing 100g, readable to 0.0001g, can detect very miniscule changes in gravity. If the balance is calibrated with a 100g mass and then moved upstairs three floors, the change in gravity will cause the balance to measure the 100g mass as 99.9970g, or 0.0030g less because it is farther away from the center of the Earth. If the balance moves north by 1,000 meters (1km), it will measure the same 100g mass as 100.0007g, an increase of 0.0007g, because it has moved closer to the North Pole. If it moves south by 1,000 meters, it would be measured 0.0007g less. If it moves east or west it would stay the same, as it is the same distance to the center of the Earth.

Types of Calibration

Some balances are equipped with internal motorized calibration, and while this feature might cost more, it’s convenient and helpful. Since internal calibration is extremely easy, users might tend to calibrate more regularly. Most balances with internal calibration also offer external calibration, which is a fairly simple process, but requires more effort by the user.

During external calibration, a previously determined weight is always used to set the balance’s parameters, guaranteeing the results. For example, when a one-kilogram mass is used as the standard and placed on a balance, its force will always read as 1,000g. Any other weight that is placed on the balance will be measured against this standard.

Different standards (weights) used to calibrate might provide different readings. Previously purchased calibration weights aren’t the same as those used during the initial factory calibration, and a small variation can make a big difference in your results.

In some instances, balances must meet specific traceability requirements for ISO purposes or to adhere to other regulations. These situations necessitate the use of certified calibration weights. Traceable calibration can be accomplished as long as certified weights are used in the procedure, and balance service companies specialize in calibration certification.

To achieve optimal precision and consistency in measurements, users should always adhere to operation and maintenance guidelines recommended by the manufacturer.