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By Dr Bob Sandor
Even a Fender Guitar will sound dull and out of tune unless it is tuned regularly, similarly, to ensure its accuracy an analytical balance must be calibrated regularly. An analytical balance is used to measure the precision gravitational mass of an object which it does in conjunction with the gravitational pull exerted by the earth surface. However, the force of gravity varies depending on various factors. A key element of which is, altitude.
Calibrating an analytical balance compensates for the variation in altitude or other factors that cause a change in the gravitational force. Calibration is the process of calculating the errors in a device with reference to a standard and then correcting these errors. It is advised that your analytical balance be calibrated on installation and with every change in location. There are many external environmental factors that can cause unstable values to be displayed on your balance. Some of them are: an uneven surface, air-conditioning or heat vents placed close to your balance, doors or windows in close proximity to your balance causing temperature fluctuations etc. To avoid erroneous measurements, it is recommended to calibrate an analytical balance periodically.
Many modern analytical balances offer internal calibration motors where balances are automatically calibrated. Internal calibrating balances normally commence the calibration process on manual initiation. However, in certain situations like disconnection of the balance from its power supply or where there is a more than predetermined fluctuation in the temperature, a self-calibrating balance may calibrate itself. However internal calibration is an expensive feature and though it may have its benefits, it is not without flaws. An internal calibrating balance re-calibrates on power-up, if there is any defect in your balance, you will not be able to start-up your balance and it can lead to expensive repairs.
External calibration is done using test weights that are calibrated under strict laboratory conditions. Test weights that pass the calibration test are certified while those that fail are sent back to the lab for repair. ISO 9000 requires analytical balances to be calibrated using externally certified test weights. These certified test weights must be carefully handled and need to follow certain rigid and clearly defined procedures regarding cleaning and storage to ensure that they do not lose their precision. Many companies usually have quality control specifications that determine when and how test weights need to be recalibrated. In the absence of any strict regulation, it is suggested that test weights that are considerably used, be recalibrated every six months.
Analytical balances are calibrated depending on individual use and requirement. If you normally use your balance to calculate weights which is less than the full capacity of your balance, then you can calibrate your balance to a weight that is closer to your normal requirement. This will ensure that you get a much more accurate and precise reading. For instance, if your balance has a capacity to weight up to 300g, but your general requirement of weights is around 200g, then you can calibrate your balance to a maximum weight of 220g, to ensure that the weight reading is more exact.
It is recommended that you purchase certified test weights along with your balance itself as this will enable you to conduct in-house external calibration and save on the expenses of calling in an external calibration company.
About the Author: Dr. Bob Sandor is a Director at Tovatech, a leading North American supplier of
analytical balances
. When not busy running his company, he explores his fascination with the many aspects of various scientific & industrial devices. For more details on the above you can reach him through the
analytical balance
section of his website.
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