Calibration of Analytical Balance – Answering the ‘HOW’s

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This is a guest post from Kevin Hill,  head of the marketing efforts at Quality Scales Unlimited in Byron, CA.
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An analytical balance is a highly sensitive lab instrument that is designed to accurately measure mass. They have a readability range between 0.1mg – 0.01mg. They are meant to detect very fine increments of the materials being weighed. Even the slightest breeze or vibration can affect the readings.

Analytical Scale Calibration using a set of standard weights

How to Calibrate an Analytical Balance?

Analytical balance calibration is important if you want accurate readings of the materials being weighed every single time.


Internal Calibration

It must be performed as per the manufacturer’s instructions. It may involve switching on the calibration scale and allowing it to warm up.

Next, press the key for ‘auto calibrate’. The internal calibrations will first display a ‘no weight’ measurement. After that, it may require a specified standard check weight to be placed on them.

External Calibration

The external check is done for three factors:

1. Drift: Normally, a 10mg standard weight is used to carry out a drift check. You have to record ten measurements with the 10 mg weight to observe any variations in the results. If there is a variation or a ‘drift’, it should not exceed the mean value by more than ± 0.2 mg.

The mass value cannot vary above 0.01mg, thus making the criteria of the actual mass value of 0.1%.

2. Measurement Uncertainty: Place 10mg external weights on the balance pan. Note 10 measurements for the weights. Next, carry out the required calculations to determine the measurement uncertainty by multiplying standard deviation by 3, and dividing that by the actual mass value.

The measurement of uncertainty should not exceed 0.001.

3. Performance Check: Place 1 mg, 2 mg, 5 mg, 10 mg, and 20 mg calibration standard weights separately on the top pan after the auto calibration process. Note the measurements in the performance check log.

These measurements should remain within 0.1% of the actual mass value of each weight.

How Often Should You Calibrate the Analytical Scales?

The frequency of analytical scale calibration depends on a number of factors:

a) Manufacturer’s Recommendations

If the manufacturer has recommended a frequency of calibration, then adhere to it. Some recommend calibration a few times a month, others recommend on a weekly basis.

b) Environment the Scales are Kept in

If the scales are kept in an environment that contains fluids, dust or any substance that can build up on the scale, you need to calibrate more often. All these elements affect the readings. 

Similarly, if the scales are located in a place that has vibrations, mechanical shock or static electricity, the reading would be affected.

Consider calibrating the scales regularly to prevent these factors from affecting the readings.

c) Frequency of Scale Usage

If you use scales every day, then wear and tear will occur faster as compared to scales that are used once a week.

Calibration should be done more often if you use the scales more frequently.

d) Importance of an Exact Weight to your Business

The frequency of calibration is also dependant on how important accurate weights are for your business.

If you cannot afford even the slightest inaccuracy in the reading, then you will have to calibrate on a daily or weekly basis. For instance, in the case of medical equipment or pharmaceutical product, even the slightest inaccuracy can be dangerous.

Contrarily, if it is alright for the results to differ by 1% of the actual readings, the frequency of calibration can be less.

Additionally, troubleshoot immediately if you notice any deterioration in the accuracy at any time.

In Conclusion

It is critical that you monitor and calibrate the analytical balance frequently. You can use automatic internal calibration or calibrate the balance with external weights. Regardless of the method, ensure that the calibration is done at the right time.

Author Bio:

Kevin Hill heads the marketing efforts at Quality Scales Unlimited in Byron, CA. Besides his day job, he loves to write about the different types of scales and their importance in various industries. He also writes about how to care for and get optimized performance from different scales in different situations. He enjoys spending time with family and going on camping trips.

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