The Evolution & Principle of Analytical Balances
The analytical lab balance exists since 1945; and it has been steadily evolving during that period. Leading equipment manufacturers developed continuous innovation to improve its performance. The aim is to increase the precision and accuracy of the analytical lab balance and to make it more reliable for researchers.
The earliest analytical balance, manufactured in 1945 had a single pan. In 1971, the first major advancement took place, when the nanogram balance made precision weighing attainable. This balance was actually used to weigh the rocks that astronaut Neil Armstrong brought back from the moon. Then, Mettler produced its PT1200 scale in 1974, which was the industry’s first fully electronic precision balance. The Mettler balance had a capacity of 1,200 grams and sensitivity to 0.01 grams. Then further advancement continues. The newest analytical balances feature touch keypads for automatic motorized leveling; and are top-loading with a motorized draft shield and a resolution of 61 million digits.
Almost all analytical balances today are electronic where previous models of equal arm balances have become outdated. These balances can be either single or double pans. Electronic single pan balances do not work on the traditional principle of balancing the substance to be weighed against a standard set of masses. The mass is computed through load cells following the electromagnetic force compensation principle.
This is how it works. Once the test sample is placed on the analytical balance pan (usually on a weighing container), the load cell is displaced from its original position; and the vertically downward force exerted by the “weight” displaces the coil, causing the load cell to produce a current and return a compensation circuit. This current is converted to a voltage and uses electronic circuitry and appropriate software to achieve proper calibration and display the measured weight.
On the other hand, two-pan analytical balances use a multi-weight carrier activated by dials, and a precision chain. In line with the internal weights on a carrier, the precision chain has similar function with traditional weights. The difference is that the personnel does not need to open the glass enclosure to add weights, provided they are less than 100 g. Once the reading reaches to within 100 mg of the desired weight, he just dials in the incremental weight required. So it does not necessitate to open the balance case to arrest the beam . He also does not need to add standard weights, then release the beam and observe its swing before closing the case. For repeated operations, this can result in considerable time savings.
The principle utilized by other direct reading analytical balances is known as constant load balance. It has the beam, ring weights and pan at one end, where the objects to be weighed are placed. The balance weight, load, is at the other end. When a substance is put on the pan, it breaks the balance i.e. it upsets the equilibrium. Hence, in order to reestablish balance equilibrium, it is necessary to remove the equivalent amount of weights. The microscale in the balance then reads the projection and provides the right value. In order to reduce vibrations and increase the efficiency of the balance, the operating knob is generally located in front on the base of the balance. It will also allow the users to comfortably work on the balance for longer.
This article was written by Firoze Hirjikaka, a retired Civil/Structural Engineer with a graduate degree from London University. He explores his passion for scientific & engineering equipment at Tovatech a leading American supplier of analytical balances. For more information on this article visit the Tovatech site from any of the above links.
