part 1

Instrumentation measuring life easuring MassAn object’s mass is measured using a balance.The most common type of balance is an electronic balance in which the balance pan is placed over an electromagnet(Figure 2.2). The sample to be weighed is placed on the sample pan, displacing thepan downward by a force equal to the product of the sample’s mass and the acceler-ation due to gravity. The balance detects this downward movement and generates acounterbalancing force using an electromagnet. The current needed to produce thisforce is proportional to the object’s mass. A typical electronic balance has a capacityof 100–200 g and can measure mass to the nearest ±0.01 to ±1 mg.Another type of balance is the single-pan, unequal arm balance (Figure 2.3). Inthis mechanical balance the balance pan and a set of removable standard weights onone side of a beam are balanced against a fixed counterweight on the beam’s otherside. The beam itself is balanced on a fulcrum consisting of a sharp knife edge. Addinga sample to the balance pan tilts the beam away from its balance point. Selected stan-dard weights are then removed until the beam is brought back into balance. The com-bined mass of the removed weights equals the sample’s mass. The capacities and mea-surement limits of these balances are comparable to an electronic balance.instruments for measu