The analytical lab balance has been around for 60 years now; and during that period it has been steadily evolving. Leading equipment manufacturers developed continuous innovation to enhance 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 first analytical balance, manufactured in 1945 had a single pan. The first major breakthrough occurred in 1971, when the nanogram balance set the world record for precision weighing. This was actually used to weigh the rocks that astronaut Neil Armstrong brought back from the moon. Then, in 1974, Mettler produced its PT1200 scale, the industry’s first fully electronic precision balance. It had a capacity of 0 to 1,200 grams and sensitivity to 0.01 grams. And so it went on. The up-to-date analytical balances need just the touch of a key for automatic motorized leveling; and have a resolution of 61 million digits and are top-loading with a motorized draft shield.

Equal arm balances have become practically obsolete and nearly all analytical balances today are electronic. These balances can be either single pan or two pans. Single pan balances do not function on the traditional principle of balancing the substance to be weighed against a standard set of masses. Its mass is computed through load cells following the principles of electromagnetic force compensation.

Here is how it works. Once the test sample is put on the analytical balance pan (can be on a weighing paper), the load cell is displaced from its original position; and the vertically downward force exerted by the “weight” displaces the coil, which causes the load cell to start a current and return a compensation circuit. This current is converted to a voltage and uses electronic circuitry and appropriate software to attain proper calibration and display the measured weight.

Two-pan analytical balances use a precision chain and a multi-weight carrier activated by dials. In line with the internal weights on a carrier, the precision chain serves the same function as traditional weights. The difference is that the operator does not need to open the glass enclosure to add weights, as long as they do not exceed 100 g. Therefore, once the measured weight is within 100 milligrams of the desired weight, he just dials in the incremental weight required. This obviates the necessity of opening the balance case to arrest the beam . He also does not need to physically add standard weights, then release the beam and observe its swing before closing the case. For recurring operations, this can result in considerable time savings.

The principle utilized by some direct reading analytical balances is constant load balance. It has the beam, ring weights and pan at one end, where the materials to be weighed are placed.  The balance weight, load, is located at the other end. When a substance is put on the pan, it disturbs the balance that is, it disrupts the equilibrium. Hence, in order to reestablish balance equilibrium, the corresponding amount of weight is removed. Then the microscale in the balance reads the projection and shows the correct value. In order to increase the efficiency and reduce vibrations of the balance, the operating knob is generally located in front on the base of the balance. This also allows 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.