Different Types Of Scales And Balances In The Laboratory
Laboratory Balances are precise scales for measuring very small differences in quantity
, or moisture levels in analytical samples. Originating in ancient Egypt, the balance scale used a beam with a scale cup on each end, balanced on a fulcrum in the centre.
A known weight could be placed in one cup, and then a measure of any substance could be put in the other. Additional amounts could be added or subtracted until the scales were in balance.
Balance beam scales are still the standard for weights and measures. New certified proof weights (those used to check the accuracy of a scale) are verified against the master weights on a balance beam scale.
The middle fulcrum is known as the center-balance; there is also the off-center balance, which will allow for the weighing of heavier objects without the need for significantly heavier balance weights. Modern scales will make the conversion calculations for you.
Balances measure gravitational mass rather than compression force. Although on earth we tend to think they are (and for the most part, react) the same, mass does not change with the environment. The easiest illustration of the difference between mass and weight is an astronaut. In space, an astronaut has no weight, but he must still maneuver his mass.
At first, he will push off a wall to move across a space as if he had the same weight as on earth. He will find he is now moving MUCH more quickly than he intended; when he tries to stop, he thinks he will have the same over-reaction, only to find he has to use even more energy to stop.
His mass was moved with much more force than it would have on earth, and so needs an accompanying increase in power to stop.
Since balances measure mass rather than weight, you will not get a different value if you are on a mountaintop or Death Valley; the North Pole or the equator.
There are three primary types of laboratory balances in use today:
There are top-loading/open balances whose main use is weighing samples or ingredients; measuring amounts for chemical recipes, or comparing relative densities.
Analytical balances are designed for concise measurement of extremely small quantities. The more sensitive the reading, the more self-calibration that comes as a standard for the balance. Those that weigh in micrograms (1/1000th of a gram) have built in sensors that will recalibrate if temperature or humidity is outside their pre-set range.
They also have a clear outer casing that will reduce contamination by dust or air flow. To further reduce fluctuations, samples should be weighed at room temperature.
Moisture balances have a heat source (usually a high temperature light such as a halogen bulb) to measure the amount of moisture released by a heated sample (most commonly as a percentage).
Some balances used for testing larger samples heat it with microwaves instead. It has applications in food, pharmacology, environmental, chemical, industrial and beverage industries. Almost any product (or one of its components) manufactured today has been tested for moisture content using some variety of this balance.
by:Andrew Long
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