Test Methods of Scale Calibration

If your business relies on weighing scales in any way, it is essential that they are calibrated regularly. Just like any other mechanical and electrical device, scales are subject to the wear and tear of time. As a result, accuracy slips happen.

When a weighing scale exhibits even a slight inaccuracy, it can significantly impact your business. This is where calibration comes in. It plays an important role in ensuring that you achieve the level of accuracy and precision your business needs.

So, how do you know that your weighing scale is calibrated?

Test Methods of Scale Calibration

Below are the most common tests performed to ensure that your weighing scale is accurate and calibrated.

1. Eccentricity Test

Some scale users tend to place the item on different areas of the load receptor, thus, yielding varying results. The eccentricity test shows the effect of placing on multiple ranges the single test load.

To do this, you should prepare a test load that weighs about ⅓ of the maximum scale capacity. Using the test load, perform the eccentricity test on weighing instruments with multiple ranges using the highest range.

2. Tare Test

What is tare weight?

Sometimes referred to as “unladen weight,” tare weight is the mass of an empty container, such as a box, plastic, can, vessel or canister. This test aids in determining the net weight of the would-be content of the container.

The tare test is applied for items that need a container for accurate and precise weight measurement. Let’s say your business involves selling liquid seasoning. Naturally, you need containers like bottles or jars for your product. In this case, your weighing scale should ensure that it passes the tare test after filling the containers with the seasoning.

3. Repeatability Test

Essentially, the repeatability test aims to ensure that the scale yields the same measurement for multiple tests. The test involves the same item and weighing scale under constant conditions and similar handling.

Depending on the type and capacity of the weighing scale, repeatability tests can be performed at least 3 to 5 times per scale. For example, you are using a platform scale with a maximum capacity of 1,000Kg.

To do the test, you can use a load weighing about 350Kg and place it on the load receptor at least five times. Make sure to place the item in the same location of the load receptor for the entire repeatability test. At most, you should get the same reading for all repeated loading.

4. Discrimination Test

By using the load discrimination test, you can find out if the weighing instrument is capable of tracking even the slightest changes in load while altering its registration accordingly. This test can be conducted using the same load in the repeatability test.

Before doing the test, make sure to know the category of your scale, either class 1-2 or class 3-4. This way you will know whether to use the actual scale interval (d) or verification scale interval (e) during the test.

5. Weighing Test

The purpose of the weighing test is to determine the accuracy and precision of the scale using a set of decreasing and increasing weight loads. In most cases, the smallest test load should be 10% of the maximum capacity of the weighing instrument. You should also use 5 to 10 test loads of varying increasing or decreasing weight intervals.

Linearity

By using different areas of the load receptor during the weighing test, the linearity or non-linearity of the results show whether the scale measures equally and accurately throughout the given range.

Hysteresis

This is the difference in the measurement readings when a single test point of the load receptor receives an increasing or decreasing weight.

6. Variation of Indication Over Time Test

Regular use and aging can lead to scales losing their accuracy over time. Particularly, analog scales may suffer from rusting, and electronic scales may experience malfunctions. In either case, you should expect some reading inaccuracies.

To prevent this from happening, make sure to schedule a regular calibration involving a variation indication over time test with a trusted scale and load cell provider near you. The test includes a variation indication involving moisture build-up and temperature changes.

7. Magnetic Interaction Test

Another test applied to ensure that you are using a calibrated scale is the magnetic interaction test. This involves the gauging of the magnetic field dispersal on different weighing scales.

Generally, it tests the magnetic interaction between a scale and a test load. The magnetic interaction test aims to eliminate any possible magnetic impact on the scale’s accuracy and precision. This may include any force field that can affect a metal weighing pan.

8. Minimum Weight Test

Lastly, a minimum weight test is applied to ensure calibrated scales. However, this test is generally required in pharmaceuticals and science laboratories. The main purpose of this test is to identify the smallest possible load that can be measured while still achieving accurate and reliable results.

Scale calibration is crucial to most businesses, especially when weight matters to their customers. The 8 tests mentioned above can greatly help maintain and ensure that your weighing instruments provide accuracy and precision at all times.