Internal or External Calibration: Which is Right for You?

What is calibration?

Calibration is a process of ensuring and maintaining the accuracy of a weighing instrument in alignment with a standard or accepted range of results. Therefore weighing scale calibration is considered the process of correcting, determining and checking the scale is meeting its known or assigned accuracy. It can either be achieved by internal calibration or through external calibration that requires the use of calibration weights.

Why does a balance need to be calibrated?

It is essential that balances and weighing instruments are regularly calibrated to ensure that weighing results are consistent. For example, commercial products that are sold by weight or specify a weight on the label are required by law to meet the advertised weight. If your scale is misaligned, your weighing results will also be similarly in-accurate, and you may be liable. Furthermore, a lack of product standardisation may negatively impact company reputation.

Calibration is crucial to increasing a weighing scale or balance’s longevity. It is also a necessary process to ensure valid data during rigorous testing. Frequent calibration ensures the balance is linear in its precision, allowing for more experiments with less chances of errors (who wants to work all day only to realise their results aren’t valid?).

How is a weighing scale or balance calibrated?

There are several ways in which to calibrate a balance or scale, however it is most common to use approved weighing scale calibration weights or test weights. There are wide variety of calibration weights available which range from 1g up to large kilogram increments. When testing your balance, it is best weighing practice to use a full set of weights that are comparable with your scale or balance’s weight capacity and level of accuracy.

You will also need to ensure that your test weights are trade approved by your region’s metrology association (e.g OIML, ASTM etc) in order to certify that a weighing scale or balance is an accepted trade approved scale.

For more specific information about the processes of scale and balance load cell calibration, please see our sister site The Measurement Shop UK's ultimate guide to load cells.

What is the difference between internal and external calibration?

External calibration:

External calibration means that the calibration process is manual. To calibrate a balance or scale externally, the user must have a set of approved weighing scale calibration weights that should be kept in top condition.

The scale calibration weights are put on the balance or scale and their mass or weight set as the standard. So if your weight is 1kg, you would set the weight on the scale as 1kg. It is important that the weights are bought from a trusted source (scale and balance manufacturers usually have an accessory tab on the website with a set of weights being one of the option). The weights should be maintained with care to ensure they do not lose or gain mass, which would render them invalid.

There are many tutorials that are often made by weighing equipment manufacturers; check the website or social media channels related to your brand for tutorials on how to perform proper external calibration on selected product models. The process should be quick and easy. Here is a demonstration, courtesy of Adam Equipment, on calibrating a Nimbus balance:

Internal calibration:

Internal calibration allows the weighing scale or balance to calibrate itself, often automatically without needing manual input from its users or calibration weight sets. There are various degrees and technologies used to ensure precision that change depending on model, make and price range. Some balances even allow you to set calibration at specific times or intervals (for example, during lunch or in the morning before people come to work, or even every couple of hours). They also allow for the scale or balance to be calibrated with a single button press. These balances have built-in calibration weights, often motor driven.

Adam and A&D models ending in an "i" are a good indicator for internal calibration. Some products that have internal calibration include the A&D FZ-i Series Precision Balances and the Kern ABJ-NM Analytical Balance.

Is it possible for internally calibrated weighing scales to be calibrated externally as well?

Generally speaking, yes. Most scales and balances with internal mass use a smaller reference weight, therefore they can be calibrated to their full capacity using external masses.

Which option is best for you?

The importance of balance calibration should not be underestimated, and it is crucial to weigh up the pros and cons of internal and external calibration before choosing your balance.

While external calibration tends to be less expensive (even when accounting for the purchase of calibrating weights), it also diverts time, staff and resources.

External calibration requires optimal settings and proper care not only for the balance or scale but for the weights as well. It is still quick and easy to do, it just requires diligence to maintain optimal calibration. Internal calibration is better suited if the conditions change often and you do not have the time or resources to keep calibrating the balance manually.

Internal calibration can account for changes in temperature, stability, movement, time and even improper power off of the scale or balance. However, models with internal calibration are usually more expensive.

Our advice

Overall, your decision should consider whether or not your duties allow you to frequently calibrate the balance manually and your budget. If you have time to calibrate the balance and it is not preventing you from accomplishing other tasks, manual calibration might save you some money.

1. Weighing conditions - If the conditions change too frequently or if you do not have enough time to calibrate your balance, internal calibration’s cost is offset by the time it will save you. Of course, just as maintaining and checking your calibration weight is important for external calibration, you should check that internal calibration is functioning optimally after prolonged use.
2. Digital versus manual - Some people trust external calibration more because there are less electronics that can malfunction while others think internal calibration is more precise because it does not rely on a physical standard that can be compromised.
3. Frequency of use - If you use the balance or scale for extended periods of time, in various different conditions and need continuous measurements, a balance with internal calibration might be better for you as it allows you to continue your work without having to stop to calibrate the balance.

If you have any questions on scale and balance calibration or any of the internal or externally calibrated scales we have on offer, please Get In Touch.

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