Why is Balance and Scale Calibration Important?

1. What is balance calibration and why should I calibrate?

The second part of the question triggers another one: "Why would you want to weigh at all if your balance is not calibrated?" Balance or scale calibration is essential to achieve accurate weighing results. Ignoring this important service activity turns measuring into guesswork. In other words, it is negligent to weigh with a non-calibrated balance or scale. The accuracy of balances and scales becomes less reliable over time. This is the result of normal wear and tear caused by regular use and external factors such as mechanical shocks or hazardous environments. This may lead to a rather quick degradation or deterioration over a longer time. Periodically scheduled balance calibration in combination with frequent routine testing greatly enhances the life time of your balance or scale and its weighing accuracy.

But what is calibration? In simple terms, calibration is a quantitative comparison. To check the reading of a balance or scale, a reference weight is placed on the pan. The error is defined as the difference between the measured value (the reading) and the true value (the reference weight). The question whether this error is trustworthy or not, will be outlined below. At the end of balance calibration, a certificate is created, which reports the balance or scales readings and compares them to a reference value. Applied tolerances result in a Pass/Fail statement.

2. What are the benefits of balance calibration?

Calibration, performed by an authorized provider offers the following benefits:

• Cost savings. Calibrated equipment allows sound decision making, which avoids waste, rework or product recall.
• Reliable measurements. Using calibrated equipment assures that measurements made in one place are compatible with those made in another. Results from any balance in the process will be accurate and reliable, as will the final product.
• Compliance. Calibration facilitates smooth passing of internal and external audits.
• Detection of aging equipment. All equipment ages over time and critical components may sustain mechanical stress or wear and tear. Drift cannot always be eliminated but it can be detected through periodic calibration.
• Process and profit improvement. Interpretation of calibration results according to defined tolerances improves processes and ultimately increases profit.

3. How often do I have to calibrate my balance, and what are the risks of not calibrating?

A calibration certificate reports results at the time the calibration was performed. In many cases the responsible person assumes that the calibration is valid for a year. This leads to the wrong conclusion that a calibration interval of one year is sufficient.

Ideally, calibration intervals are defined following a risk-based methodology, for example what is the probability of something going wrong and how high is the impact? A high impact and high probability corresponds to a high risk, which requires a shorter calibration interval. Otherwise a low impact and a low probability results in a low risk, allowing intervals to be extended.

To forgo calibration is a high-risk strategy. Hidden costs and risks associated with the un-calibrated balance or scale could be much higher than the cost of calibration itself. Using non-calibrated equipment can lead to production problems such as:

• unscheduled downtime
• inferior product quality
• process and audit issues
• product rework and recalls

Environmental changes can also lead to undetected drift or increasing random errors which degrade performance. Periodically scheduled calibration along with routine testing (see below) is the best way to reduce calibration-related risk.

4. Which tolerances apply to balance calibration?

Tolerances determine whether a balance or scale behaves "well enough" to meet a particular set of process requirements. Tolerances set the criteria to issue a Pass/Fail statement. Tolerances can stem from a variety of sources, including legal agencies, manufacturing industries, and the process itself.

Legal tolerances protect consumers but do not consider specific producer requirements. Optimizing process tolerances that are applied to measuring instruments can have a large impact on process profitability.

5. Is there a difference between calibration and adjustment?

Yes, there is an important difference. Unfortunately, the terms "calibration" and "adjustment" are often confused.

Calibration

The International Bureau of Weights and Measures (BIPM) and the Joint Committee for Guides in Metrology (JCGM) have produced a valuable tool to assist with the standardization of weighing terms called the International Vocabulary of Metrology (VIM). In it, item 2.39 defines calibration as an aspect of how a balance operates:

"Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication."

In other words, a balance or scale is calibrated to understand and document how it behaves. The above definition also clearly states that the derivation of measurement uncertainty is an integral part of calibration. A balance calibration without a statement of measurement uncertainty is incomplete and becomes a spot check at best.

Adjustment

While the calibration states how a balance or scale behaves, adjustment of the device changes its behavior. Adjustment is defined in the VIM as follows:

"Set of operations carried out on a measuring system so that it provides prescribed indications corresponding to given values of a quantity to be measured."

Therefore, adjusting a balance or scale means modifying its indications in a way that allows them to correspond – as much as possible – to the quantity values of the measurement standards applied.

6. My scales are legal for trade, do I still need to calibrate?

The goal of legal metrology is to ensure fair trade and to protect consumers. When the scale is used in trade or a legally controlled application, it must be set up, verified and sealed in accordance with local Weights & Measures regulations. For an assessment of test results and to apply a Pass/Fail criterion, legal norms such as OIML or Handbook 44 are referred to. These norms allow quite large tolerances, meaning that the risk to give away material is also quite high. You can avoid this by having an authorized service technician calibrating your scale, and by applying your own process tolerances. In a nutshell, you are not obliged by law to calibrate, but it is in your best interest to do so. Benefits of this approach are:

• You improve your weighing process, and are still compliant with requirements of legal metrology
• You will generate higher profits through less material give-away