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Balance check

How to Select the Correct Test Weights and Weight Class

| Editor: Marc Platthaus

Mettler Toledo offers a wide range of stainless steel test weights from 50 µg to 5000 kg.
Mettler Toledo offers a wide range of stainless steel test weights from 50 µg to 5000 kg. (Source: Mettler Toledo)

Laboratory technicians often don't know which test weights and weight class they should choose to check the performance of their balances and scales. The free Mettler Toledo GWP Recommendation service specifies the correct test weights and weight class based on the degree of accuracy you need to satisfy your specific process tolerances.

Routine testing of balances and scales between scheduled calibrations helps to detect non-conformance with weighing process requirements early to maintain accuracy. However, for reliable testing, it is important to select the correct test weights while ensuring adequate testing frequency, test methods/SOPs, warning/control limits, and user training.

To help you select test weights, Mettler Toledo offers a free service called GWP Recommendation. Using the scientific principles of Good Weighing PracticeTM, the recommendation relies on your answers to a quick series of questions including the maximum capacity of the weighing device, the weighing tolerance, the safety factor, and environmental conditions. Based on this input, your GWP Recommendation will specify the correct test weights to check the performance of your device.

What requirements do you need for the balance check?

According to USP chapter 41 and Mettler Toledo Good Weighing Practice (GWP), performance tests should be done at <5% of the balance capacity for repeatability testing and at <100 % of the balance capacity for sensitivity and eccentricity testing. To meet these requirements more easily and eliminate the cost of maintaining a larger weight set, Mettler Toledo offers Carepacs.

According to the global weighing standard GWP two test weights are sufficient for balance routine testing: For repeatability testing the recommended test weight is ~5 % of the device's capacity. For sensitivity and eccentricity testing the test weight should normally be 100 % of the device's capacity for laboratory balances and 33 % of the device's capacity for industrial scales. Both weights are rounded down to the next OIML/ASTM denomination.
According to the global weighing standard GWP two test weights are sufficient for balance routine testing: For repeatability testing the recommended test weight is ~5 % of the device's capacity. For sensitivity and eccentricity testing the test weight should normally be 100 % of the device's capacity for laboratory balances and 33 % of the device's capacity for industrial scales. Both weights are rounded down to the next OIML/ASTM denomination. (Source: Mettler Toledo)

The comprehensive Carepac solution offer you only the essential tools you need to put balance routine testing into practice. They provide the user with two carefully selected test weights, a calibration certificate, and accessories including tweezers and gloves for safe, professional weight handling.

Carepac sets, available in three box sizes with twelve combinations different nominal values, support the testing of balances up to 8 kg and the verification of tolerances down to 0.03 %. A third, customer-specific test weight can be added when required; however, two weights generally allow you to obtain trustworthy results.

Mettler Toledo test weights themselves are available as OIML or ASTM single weights or weight sets from 50 µg to 5000 kg. Made of the finest quality austenitic steel to offer the highest resistance to corrosion, all test weights are supplied in a robust, easy-to-clean case to protect the each weight’s integrity.

When required, test weights are delivered with a calibration certificate from a Mettler Toledo calibration laboratory that is produced in accordance with ISO / IEC 17025 requirements to fulfill metrological traceability requirements.

Here you can learn more about how the high-quality test weights and Carepacs.

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