When and Why You Should Calibrate Your Balance
The answer is simple: if you use your balance at all, regular calibration is critical. The question frequently comes up when a balance is initially purchased. A new balance operator’s manual almost always recommends calibration before use.
There are many reasons a balance needs to be calibrated. The simple process of shipping can cause small changes to the mechanics of the balance. These small changes can mean big differences in your measuring results. Variations in barometric pressure can also affect the results you get from a precision or analytical balance. If your locale has a different gravitational force than the location of the factory producing the balance, calibration is necessary.
Location, Location, Location
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 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 will be less. 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 pulling the mass toward the center of the Earth.
Different balances will react differently to a change 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 location to another. More sensitive balances, such as those found in laboratories, will more readily display the difference in gravitational forces. On the most sensitive laboratory 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 add to the purchase price versus a balance with external calibration, it’s a convenient feature to have in a precision or analytical balance. Since internal calibration is extremely easy, it may mean the balance will be calibrated on a timely basis. Most balances with internal calibration also offer external calibration. External calibration is a fairly simple process, but requires more effort on the balance owner or user. During external calibration, a previously determined weight is always used to set the balance’s parameters, guaranteeing its results. For example, when a one-kilogram mass is used as the standard and is placed on a balance, its force will always read as 1000g. Any other weight that is placed on the balance will be measured against this standard. Some balance owners may have calibration weights that are slightly different from those used to initially calibrate the balance at the factory. Using different standards (weights) to calibrate a balance can result in different readings.
Depending on the use of the balance, the calibration may need to be traceable for ISO purposes or to meet other requirements. In this instance, a certified weight should be used to calibrate the balance. In the United States, the National Institute of Standards and Technology is the industry group that certifies weights for calibration. A traceable calibration can be done through a balance service company that specializes in calibration certification, or it can be done by the balance owner providing they buy a certified weight to be used in the calibration process.
For the best results, all balances should be calibrated regularly with use, if the local ambient temperature changes more than the specification allows, if the balance is moved, and if the balance will be used for making high-precision measurements.
About Adam Equipment
Adam Equipment manufactures and distributes a full selection of precision balances and scales for the lab, education, industrial, food, health/fitness, animal/veterinary and jewelry markets. The company is headquartered in England and has offices in the United States, South Africa, Australia and China. Founded in 1972, Adam is proudly celebrating its 40th anniversary in 2012. Since its inception, Adam has provided its customers with the winning combination of speed, performance and value. For more information about the company and its products, contact: firstname.lastname@example.org.
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