What is the difference between Laboratory Scales and Balances?
Scales and balances are both common laboratory instruments. While one measures mass and the other measures weight, since they're almost always used on Earth, they tend to have the same function: measuring how much of something we've placed onto the weigh pan. Weight = mass * gravity and since gravity is the same in most conditions, the differences between the actual functions of the two machines often go overlooked.
Traditionally, a balance had two pans and was literally used to measure masses of objects by balancing the two pans. Known weights were placed on one side and an amount of interest was placed on the other. A balance doesn't measure weight, but it does measure mass. The point is subtle but important and can be best explained by imagining how such a contraption would work on the moon. It would function just the same. This is because, while the weight of an object on the moon is one sixth what it is on Earth, the mass remains the same on either end of the balance.
Technological advances have allowed engineers to come up with improved balance that no longer require pans with known weights. An analytical balance now contains a load cell that is displaced when weight is placed on top of the pan. The amount of displacement is measured and a current is sent to the electronics of the balance, registering the displacement and measuring the mass of the object being weighed.
A scale, however, doesn't measure mass but weight. If you were to take a scale with you to the moon, it would tell you that you weigh one sixth what you did on Earth. That's because there are force gauges inside the scale that operate using Hook's Law. The amount of force on a spring is proportional to the amount of stretch in the spring. In a scale, there is no comparative measure that forces the scale to accurately compare the weight being measured to an independent weight, like there is in a traditional balance.
That's why most laboratory and science researchers use analytical balances for the highest possible precision. Scales tend to have a higher measurement range than analytical balances, however. For more information on whether a laboratory scale or analytical balance is best for your needs, feel free to contact us with your specific requirements.