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Principle of Analytical Balance – How the Modern Electronic Balance Works

The analytical lab balance has been around for 60 years now; and it has been steadily evolving during that period. All over the world, equipment manufacturers developed continuous invention to enhance its performance. The aim is to increase the precision and accuracy of the analytical lab balance and to make it more dependable for researchers.

The first analytical balance, manufactured in 1945 had a single pan. In 1971, the first major advancement took place, when the nanogram balance set the world record for precision weighing. This was actually used to weigh the rocks from the moon, which were brought back by Neil Armstrong. 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 0 to 1,200 grams and sensitivity to 0.01 grams. And so it went on. The newest 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.

Almost all analytical balances today are electronic where previous models of equal arm balances have become outdated. They can be either single or double pans. Single pan balances do not function on the traditional principle of balancing a material to be weighed against standard masses. Its mass is computed by load cells which utilize the electromagnetic force compensation principle.

This 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 coil is displaced by the downward force, which causes the load cell to generate a current and return a compensation circuit. This current is then converted to a voltage and uses electronic circuitry and appropriate software to accomplish proper calibration and show the measured weight.

On the other hand, 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 has similar function with traditional weights. The only difference is that the operator does not need to open the glass enclosure to add weights, as long as 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 . It is also not required to add standard weights, then release the beam and observe its swing before closing the case. For repeated weighing needs, this can save a considerable amount of time.

The principle utilized by other direct reading analytical balances is known as constant load balance. The beam, pan and ring weights are at one end, where the materials to be weighed are placed.  While the balance weight, load, is at the other end. When a substance is put on the pan, it breaks the balance i.e. it disrupts the equilibrium. Therefore, in order to restore the original balance equilibrium, the corresponding amount of weight is removed. The microscale in the balance then 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. 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.

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  • christine mercy

    when a substance is placed on the pan of the weighing  balance, a force is exerted by the substance or object thus opposing the gravitational force which thus corresponds to the mass of the object been weighed.

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