Calibration Criteria for Analytical Balance

Weighing is a basic operation in any analytical laboratory. It is possible to run a laboratory without modern analytical instruments but it is not possible to carry out analysis without a weighing balance. Weighing is an essential requirement for preparing sample solution, reagents, titrants, precipitates,etc. The accuracy of your results will largely depend on the accuracy of your analytical balance. Precautions for correct weighing of samples discussed the need for calibration amongst other factors.

Calibration against certified standard weights will give you the confidence on your weighings. Regular calibration will guarantee the correctness of your results along with those precautions you should take in preparing your samples.

Balance calibration validates the weight readings provided a regular calibration schedule is followed. Recommended balance calibration schedules are discussed in this article.

Self Calibration

Self calibration is a simple exercise which takes less than a minute and should be done every time before using the balance

Do the self-calibration by pressing ‘cal’ key. Balance will go into automatic self-calibration mode and following display will appear:

Calibration

Start of Self Calibration

Calibration With 0 Weight

End of self calibration

 

After self-calibration is over display will show 0.000 or 0.0000 or 0.00000 g. The balance is then ready for use.

After performing self calibration calibrates the balance using standard weights of 0.02 gm, 0.05 gm, 0.2 gm, 1.0 gm, 10 gm and 20 gm to cover the average range of weighings that you’re likely to perform during the day.

Acceptance criteria: The observed weight should be within +/- 0.1% of the value of standard weights.

Weekly Calibration

In addition to self calibration eccentricity calibration is carried out.

Eccentricity refers to the recorded differences in readings when the same weight is placed at different positions of the pan e.g. center, top, bottom, left or right.

Top Top Position

Top Position

Right Position

Right Position

Center Position

Center Position

Left position

Left position

Bottom Position

Bottom Position

 

The standard weights taken for calibration are 0.01 gm, 0.1 gm, 5gm and 50 gm.

Acceptance criteria: the RSD of eccentricity for observed readings should not exceed 0.6%

Monthly Calibration

Monthly calibration needs to be carried out as per weekly calibration schedule but covering a wider range of standard weights:

0.01 gm, 0.02 gm, 0.05 gm, 0.10 gm, 0.20 gm, 0.50 gm, 1.00 gm, 2.00 gm, 5.00 gm, 10.00 gm, 20 gm, 50gm, and 100gm.

Acceptance criteria: the observed weight should be within +/ – 0.1% of the actual value

It is true that calibration takes your valuable time but the accuracy and consistency of your readings is guaranteed every time provided you use and handle your balance with the required care.

About Dr. Deepak Bhanot

Dr Deepak Bhanot is a seasoned professional having nearly 30 years expertise beginning from sales and product support of analytical instruments. After completing his graduation and post graduation from Delhi University and IIT Delhi he went on to Loughborough University of Technology, UK for doctorate research in analytical chemistry. His mission is to develop training programs on analytical techniques and share his experiences with broad spectrum of users ranging from professionals engaged in analytical development and research as well as young enthusiasts fresh from academics who wish to embark upon a career in analytical industry.

Comments

  1. Mohamed Kamal says:

    If that possible to get the reference of the accepted criteria for balance verification.

  2. aly reda says:

    thanks for this important article
    i have a question, i have certified standard weights like ( 1 -2 -5 -10, ……. gm ) with error and expanded uncertainty and the analytical balance used also have with error and expanded uncertainty for this weights so my question here is how to calculate the acceptance range for each one?

    • In such case you have to take the combined uncertainty using the formula given in renowned texts.Add the squares of different uncertainties and take the square root.

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    I am hoping to check out the same high-grade blog posts by you later on as well.

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