Your Guide to Accurate Measurements with Weighing Scales

 

Whether you are measuring ingredients for your favorite recipe, keeping track of your weight, or conducting scientific experiments, having an accurate weighing scale is crucial. In this blog, today we will break down the essential factors that determine the accuracy of your scale.

Many believe that readability and accuracy are one and the same. But there is more to it. We will help you unravel everything you need to know about scale accuracy.

 

What does scale accuracy mean? How well a scale can display the weight of a sample relative to the true weight of the sample. This is closely related to the combination of the display resolution and consistency of the performance of the scale.

 

We will focus on four key factors that play a significant role in determining whether your scale is accurate:

• Repeatability
• Reproducibility
• Calibration adjustment techniques
• Linearity 

An Overview of Scale Accuracy 

Scale accuracy refers to how well a weighing scale can provide measurements that are close to the true or actual weight of an object. In simpler terms, it determines how precise and reliable a scale is in displaying weight values.

 

To assess the accuracy of a scale, it involves considering factors like readability, repeatability, linearity, reproducibility, and calibration procedures. These factors collectively determine how close the scale's displayed measurement is to the real weight of the object being weighed. Accurate scales are essential for ensuring consistency, quality control, and safety in many industries and everyday tasks.

 

Readability: 

Readability or resolution or division size is the smallest increment by which the displayed measurement of a scale can change. Simply put, it tells you how precisely your scale can show weight changes.

 

You might think that a scale with a readability of 0.2 lb. is more accurate than one with a readability of 0.5 lb. However, it is crucial to understand that readability does not equate to accuracy. A scale with a readability of 0.2 lb. can display weight values more precisely than a scale with a readability of 0.5 lb. But accuracy is affected by multiple factors beyond readability.

 

Repeatability: 

Repeatability measures how well a scale consistently displays the same weight when the same load is placed on it repeatedly. Manufacturers often provide an estimated value for repeatability in their scale specifications.

 

To calculate repeatability, you can multiply the division size by the number of divisions specified. For example, a scale with a readability of 0.2 lb. and a specified repeatability of +/- 5 divisions would have an estimated repeatability of +/- 1 lb. In comparison, a scale with a readability of 0.5 lb. and a specified repeatability of +/- 1 division would have an estimated repeatability of 0.5 lb.

 

In this case, the scale with a 0.2 lb. resolution shows high precision but lower accuracy, while the scale with 0.5 lb. resolution exhibits lower precision but higher accuracy.

 

Linearity: 

Linearity is another crucial factor in scale accuracy. It measures how well a scale displays the correct weight value across its entire weight capacity range. Many manufacturers provide estimated linearity values to give you an idea of a scale's performance.

For example, a scale with a readability of 0.2 lb. and a 1,000 lb. capacity should ideally display 500.00 pounds when loaded with 500.00 pounds. If it does not, it has linearity errors. A non-linear scale may show deviations from the expected values at different weight levels.

 

Reproducibility: 

Reproducibility is the ability of a scale to consistently display the correct weight value over time, even when external conditions change. Factors like temperature fluctuations, changes in scale level, or overloading can impact reproducibility.

Manufacturers often provide values related to: 

• Temperature changes
• Overload protection 

These values help you assess how well a scale maintains accuracy when conditions are less than ideal. 

The Process of Calibration 

Calibration is the process of adjusting and verifying the accuracy of a measuring instrument to ensure that it provides precise measurements. Below is an overview of the process of calibration: 

Selection of Calibration Standards: 

Calibration starts by choosing appropriate calibration standards or references. These standards are devices or measurements with known and traceable accuracy, often provided by national metrology institutes. 

Preparation and Setup: 

Before calibration begins, the equipment and environment should be prepared. This may involve cleaning, stabilizing the temperature and humidity, and ensuring the device to be calibrated is in proper working condition. 

Adjustment (if necessary): 

In some cases, the measuring instrument may be adjusted to bring its readings closer to the reference standard. Calibration technicians or specialists perform these adjustments carefully to minimize any systematic errors. 

Comparison: 

The instrument being calibrated is then tested by comparing its measurements to those of the reference standard. This is done under controlled conditions to ensure consistency and accuracy. 

Data Collection: 

During the calibration process, measurements from both the device being calibrated and the reference standard are recorded. This data allows for a detailed analysis of any deviations and errors. 

Analysis: 

The collected data is analyzed to determine the accuracy and precision of the instrument being calibrated. This helps in identifying any systematic or random errors that need correction. 

Adjustment and Correction: 

If discrepancies are found, adjustments are made to the instrument being calibrated to reduce errors. This may include fine-tuning, modifying settings, or updating firmware or software. 

Traceability: 

Calibration records are maintained to ensure traceability, which means there is a documented and unbroken chain of comparisons from the instrument being calibrated to national or international standards. 

Documentation: 

A calibration certificate is issued, detailing the calibration process, results, and any adjustments made. It serves as proof of the instrument's accuracy and is often required for regulatory compliance and quality control purposes. 

Recalibration: 

Instruments should be recalibrated at regular intervals to ensure ongoing accuracy. The frequency of recalibration depends on factors like the instrument's usage, environmental conditions, and regulatory requirements. 

To Sum It Up 

Scale accuracy is not solely determined by the readability of the scale. To select the right scale for your needs and ensure accurate measurements, you should consider factors like repeatability, linearity, reproducibility, and the calibration procedure. Understanding your specific requirements and adhering to relevant industry and government regulations is also crucial.