MECHANICAL BALANCES

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Mechanical Analytical Balance

An analytical balance weighs to .0001 g or 0.1 mg. In this course, these balances will be the ones to use where the most accurate weighings are required.

This mechanical balance has a built in set of weights. These weights sit on a rack which is suspended from the same point on the beam as the pan. This beam is supported by the main fulcrum and balanced at the other end by a counterweight.

In weighing, weights are physically removed from the rack to compensate for the mass of the material on the pan. This is done by turning one or both of the knobs on the left side.

Since the smallest weight which can be removed is 1.0000 g and the accuracy of the balance is .0001 g , how does this balance do it?
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Triple Beam Balance

This mechanical balance takes its name from the three beams along which the 1, 10 and 100 g weights run. It is a very rugged balance but at best it is readable to .01 g.

The 10 and 100g weights must be set in notches which are multiples of these weights. The one gram weight is on a continuous scale divided to .1 g.

Note: this balance uses only three weights to measure all masses up to about 600 g. The effect of each of these weights is changed by varying its distance from the balance's fulcrum.

RWK 1997