10 September 2010- Laboratory balance scale is used to measure weights of different substances. In a laboratory, a balance scale is widely used to get the most precise measurement of the mass of an object. There are different scales and balances used in a laboratory, which weigh chemicals, acids and substances of extreme sensitivity. The balance is composed of two pans balanced on a fulcrum to determine the weight of an object. While the object to be weighed is put on one pan, weights are put on the the other pan. When both the pans come at a same horizontal level, we get the weight of the object. In other words, when the weights on both the pans come at an equilibrium point, the total weights in the other pan display the weight of the object. Thus a laboratory balance scale indicates an equilibrium of two masses by exhibiting a balance between a quantity of unknown mass and a known quantity of mass. The basic components of the traditional
laboratory balance scales are made up of the following components. However the moderns versions of lab balances are digital.
Balance Scales
Beam
The beam represents the fulcrum at the top of the mechanism. It must be friction-free. As such, there is a knife-edge support for balance at the beam's midpoint
Scale Pans
These are pans made of metal or plastic and they hold the masses being compared. One pan is balanced on a knife edge at both sides of the pillar.
Pillar
The pillar is the center support. At the top, the pillar has the horizontal beam and the vertical scale-and-pointer indicator are supported at the pillar's front. There is a horizontal leveling rod at the base.
Stirrup
The stirrup in a laboratory scale supports the scale pan. For each pan, there is one stirrup, which affixes the pan to the beam.
Balancing Screws
There are balancing screws along with threaded metal rods , one on each end of the beam. These screws hold the stirrups to the beam and help in balancing the pans.
Plumb Line
The scale is fixed to the front of the pillar and the pointer or needle at the top. It displays on the beam when equilibrium is reached. The needle must be pointing to the center on the beam when the measuring starts and also when equilibrium is achieved.
Leveling Screws
The leveling screws help in leveling the instrument by enabling the user to adjust the balance scales to the plumb line. They are found on either end of a rod below the scale marker.
Arrestment Knob
This knob is found at the center of the leveling rod at the base of the pillar. This knob helps in raising and lowering the beam.
Weights
Lastly, the balance scale should have the standardized metric weights. These weights are usually available in 9 sizes ranging from 1 mg to 500 mg. These weights establish the control mass. They are placed in the scale pan on the right side of the scales and the object to be measured is placed in the left pan.
