By Dr. Pramit Sarma

Precision scales and balances are available in a wide range, depending on their application. The weighing ranges vary from fractions of a milligram for lab and analytical balances, to several kilograms for a precision scale. In order to use them well, it is necessary to know that they are functioning correctly. This requires the process of calibration. Calibration of a digital balance can vary depending on the make, the model and the weight range. However, most of the basic procedures of calibration are similar.

See that the surface on which the analytical balance rests is completely flat. Keep all wireless devices at least ten feet away or switched off. Lab and analytical balances need to be in a tightly temperature-controlled, dust and static free environment. Mains electric power must be clean and stable, while batteries must be fully charged. The lab analytical balances need handling with gloves on. The tolerance to environmental and hygiene variations depends on the application. Lab analytical balances are delicate, while industrial scales are robust by design. Calibration is required for several reasons – most commonly after taking a number of measurements, after a specified time-period, due to unacceptable changes in the power supply or environment, or after restarting following a power shutdown.

If the analytical balance’s electric power was off, turn it on. Allow a minute or so to pass to allow the electronic circuits to warm up. The simplest form of calibration for the user is with a self-calibrating analytical balance. Such a device has internal motor-driven weights used in a preprogrammed combination to calibrate the analytical balance across the full weight range with a single push of the auto-calibrate button. In case manual calibration is required, there are two main ways of performing calibration. One is with a single external test (or calibration) weight, and the other is with a set of weights (typically three). It is important to ensure that the test weights themselves are in good shape, or they may need replacement.

The program mode of the lab balance must be set to ‘calibrate’, with a display depending on the particular balance used. For simple or singleton calibration, place the test weight gently on the balance. Let it stabilize a few seconds and then activate the calibration. The display will clearly show when the calibration has ended. For less sophisticated use, this is sufficient. For high precision across the minimum to maximum weight capacity of the balance, typically a set of three weights in special 1:2:4 ratios are used. The smallest weight should be near the minimum reading, while the sum of all three should be near the maximum. It allows seven evenly spaced weights for calibration. These seven calibrations allow high precision across the full span of the balance. It ensures the best possible linearity of measurement for the analytical balance.

Recalibration at some point is always required. The frequency of recalibration depends on the type of balance and its application. Usually, once properly calibrated, a single test weight recalibration suffices. With self-calibrating balances, it depends on the predetermined method used by the balance itself. Once calibrated, the analytical balance is ready to provide weight measurement with high accuracy.

About the Author: Dr. Pramit Sarma is a consummate geek with an abiding love for technology innovation! At Tovatech he indulges in his passion for high precision engineering & scientific equipment. Tovatech is a leading North American supplier of analytical balances. For more details on this article please visit the analytical balance section of Tovatech’s website.

Source: isnare.com

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