Principle of Analytical Balance – How the Modern Electronic Balance Works
The analytical lab balance exists since 1945; and during that period it has been steadily evolving. Leading analytical balance manufacturers developed continuous innovation to improve its performance. The ultimate goal is to increase the accuracy and precision of the analytical lab balance and to make it more dependable for researchers.
The earliest analytical balance had a single pan, and was manufactured in 1945. The first major breakthrough occurred in 1971, when the nanogram balance set the world record for precision weighing. This balance 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 precision balance that was fully electronic. It had a capacity of 1,200 grams and sensitivity of 0.01 grams. Then further advancement continues. The latest 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.
Equal arm balances have become practically obsolete and nearly all analytical balances today are electronic. They can be either single or double pans. An electronic single pan balance does not work on the usual way of balancing a material to be weighed against standard masses. The mass is computed by load cells which utilize the principles of electromagnetic force compensation.
Here is how it works. When the substance is put on the analytical balance pan (usually on a weighing container), the load cell is displaced from its original position; and the coil is displaced by the downward force, which causes 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 accomplish suitable calibration and show 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 glass enclosure need not be opened to add weights, as long as they are less than 100 grams. Therefore, 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 . It is also not required to physically add additional weights, then release the beam and observe its swing before closing the case. This can save time for repeated weighing operations.
The principle utilized by some 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 located at the other end. When a substance is put on the pan, it disturbs the balance i.e. it upsets 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 provides the right 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 personnel 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.
