Balance Calibration – what are the options?
Balances are relied on in most laboratories and industrial sites for a range of experiments and everyday quality control or operational work.
Keeping your balance regularly calibrated is essential to ensure the readings they give are accurate. This does not need to mean a costly visit from an external contractor, as many balances are easily calibrated in house.
When should a balance be calibrated?
Balances need to be calibrated in the location they will be used in. This is partly to avoid variations in gravity (as this changes in different locations and could give noticeable changes to sensitive analytical balances) and partly to avoid any knocks in transport which can disturb the sensitive internal elements of the balance.
Any balance should be calibrated when it is first opened and sited, any time it is moved, and at regular intervals during use. How regular is up to you, as this will vary a lot depending on factors including the accuracy you require, any standards or regulations you need to adhere to, how much the balance is used, or how much the temperature varies at the site.
How to calibrate a balance yourself
Most balances will allow you to calibrate them in a few simple steps – the user manual for your particular model should detail how to do this.
Normally a single weight of at least 50% of the balance’s maximum capacity should be used – for example for a balance of 800g maximum capacity, a 500g calibration weight should be used, or for a 400g capacity a 200g weight should be used. The manual of the balance may recommend a specific weight, so consult this for a guide.
Always wear synthetic gloves or use tweezers to handle the calibration weights, as the oils naturally found in skin can affect the results.
Choosing a weight classification
Calibration weights are made in different classes of accuracy, as defined by the OIML (International Organisation for Legal Metrology).
Class E2 weights offer high precision for analytical balances – the maximum permissible error at 1kg is ±1.6mg. These weights are available as single weights or as sets which include a range of sizes for additional checks or sites where a range of balances are used. They can also come with a UKAS calibration certificate when proof of their accuracy is required.
Class F1 weights are a slightly lower accuracy for sites that don’t require maximum precision – the maximum permissible error at 1kg is ±5mg. These are available as single weights and can have a basic calibration certificate to prove their accuracy.
Balances with internal calibration
Another option to consider is balances which have internal calibration. This removes the need to buy and store a calibration weight separately, and removes the need for careful handling as the weight is kept enclosed in the balance workings.
Depending on the model the internal weight is either moved into position for calibration automatically by a motor, or manually by a sliding switch. For example the Adam Nimbus range of balances are available with or without internal calibration to suit all preferences.
Some advanced models will also automatically re-calibrate at set time intervals, or when changes in the room temperature are detected. Select Ohaus models including the Discovery and Explorer ranges include this AutoCal™ function.
Try the links above to find out more about lab or industrial balances, calibration weights and certification for calibration weights, or contact us with any questions you have about lab or industrial weighing