With recent changes, the NCWM has facilitated the development of a new class of certified-for-trade weighing solutions.

August 20, 2020

4 Min Read
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Image courtesy of Thayer Scale

David Hyer, president and general manager, Thayer Scale

First published in 1949, the National Institute of Standards and Technology (NIST) Handbook 44 is updated annually at the conclusion of the annual meeting of the National Conference on Weights and Measures (NCWM). For more than 70 years, it has “provided the specifications, tolerances and other technical requirements for commercial weighing and measuring devices as adopted by the NCWM. Manufacturers refer to these standards for proper design and performance. Service agents and regulatory officials use the standards for ensuring compliance of design, installation, performance, and use.”

For weighing equipment manufacturers, the National Type Evaluation Program (NTEP) Certificate of Conformance demonstrates that the product listed has passed a rigorous set of factory and field-testing procedures validating adherence to the Handbook 44. These procedures are developed and administered by one of five sectors, according to the application: Belt Conveyor Scale Sector, Grain Analyzer Sector, Measuring Sector, Software Sector, and Weighing Sector. The technical policies, checklists, and test procedures are updated annually and published in NCWM Publication 14.

Recent Developments
Like any standards committee, the NCWM has the daunting challenge of maintaining the integrity of existing standards while supporting the development and adoption of new technologies and advancements in the industry. In the case of NCWM, the additional burden of ensuring the safety and integrity of the nation’s weighing systems, including the ability to transact business upon these systems, creates a unique responsibility. As a result, the rate of change to these standards is slow and deliberate.

In the continuous weighing field, and more specifically the Belt Conveyor Scale sector, two recent developments are worthy of note. These developments pave the way for new weighing solutions that could dramatically improve the effectiveness and economic viability of a series of applications.

1. Introduction of a 0.1% Certified-for-Trade Belt Scale Accuracy Class
First introduced in 1969, the certified-for-trade belt scale has been a reliable and effective conveyor scale, enabling the transaction of business while loading or unloading ships, railcars, or conveying a wide range of materials overland. Recent improvements in weigh-frame design, belt-tensioning systems (take-ups), calibration techniques, and manufacturing tolerances have improved the expected field performance of these high-accuracy belt scales to the point where a new class of accuracy can be achieved and reliably maintained. The introduction of a belt scale that reliably and certifiably demonstrates ongoing accuracy of 0.1% or better opens up a range of new applications that were not previously permissible at the lower accuracy (0.25%). One particularly important application is the weighing of grain for export. Until now, the only permissible weighing solution for grain shipments for export was the bulky and expensive garner system. These large, static weighing devices require a staging hopper, a weighing platform, and a take-away conveyor – resulting in significant time and expense in the loading process for grain. Now a 0.1% accuracy belt scale can be integrated into an existing belt conveyor eliminating the time and expense of a separate weighing stage.

2. Addition of the Weigh Belt as an Approved Belt Conveyor Scale
An overland conveyor is often an integral part of a material handling process flow. It is a highly efficient and effective means of moving aggregate, grain, sand, biofuel, and other materials. The addition of a certified-for-trade belt scale is an easy, proven way to equip the process with a means of conducting business without additional process steps. However, many material handling processes have no room for an overland conveyor, or safety or environmental conditions preclude the use of an unenclosed, environmentally uncontrolled conveying solution. In these environments, a weigh belt is often used to control flowrate or totalize material flow for inventory purposes or other internal metrics. In the past, a weigh belt was not permitted for use as a certified-for-trade weighing device. In the 2016 edition of Handbook 44, this was changed. The weigh belt is now considered a candidate for NTEP certification as a 0.25% accuracy device.

Next Steps
With these changes, the NCWM has facilitated the development of a new class of certified-for-trade weighing solutions. Look for product announcements from several vendors over the coming months as they roll out solutions that meet these new standards. Additionally, the NTEP committee will be developing new factory- and field-testing procedures that will ensure compliance with these new standards. These procedures will likely culminate in a future update to NCWM Publication 14.

David Hyer is president and general manager, Thayer Scale, Pembroke, MA. For more information, call 855-784-2937 or visit www.thayerscale.com.

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