The ‘weight’ is over for legal-for-trade weigh in motion

By |  November 8, 2021
Cardinal Scale’s Armor digital truck scale with SmartCell load cells is one equipment example that can soon be used as an in-motion single-draft scale. Photo: Cardinal Scale

Cardinal Scale’s Armor digital truck scale with SmartCell load cells is one equipment example that can soon be used as an in-motion single-draft scale. Photo: Cardinal Scale

When the calendar turns to 2022, aggregate producers and other operations shipping materials on trucks will have a new option to weigh their saleable products.

Until now, operations deemed “legal for trade” were limited to using a static scale, onto which a truck loaded with materials would drive up and get weighed – with the price determined based on the weight.

Thanks to a shift from the National Conference on Weights & Measures (NCWM) and new coding that’s going into the 2022 version of Handbook 44 – an annual guide dealing with specifications, tolerances and other technical requirements for weighing and measuring devices – operations will have the option to utilize full-length, single-draft, weigh-in-motion (WIM) scales to determine the weights and costs associated with their business. Each manufacturer will first have to undergo a test and certification process to be able to offer these WIM scales, however.

So, what does all of this mean for you? In short, this NCWM development provides what is viewed among some scale manufacturers as a quicker and safer way to gather critical information and conduct business. WIM scales have been in use for years in areas that do not include the sale of materials. Now, however, NCWM is allowing WIM scales to be used for legal-for-trade weighing.

As the name indicates, a WIM scale can obtain the weight of a vehicle loaded with material while the vehicle moves across it.

“It gets the weight in that small window of time when the truck’s back axle has pulled onto the end of the scale, and you’ve got the distance between the front axle and the other edge of the scale,” says Eric Golden, vice president of engineering services at Cardinal Scale. “That’s the amount of time you have to get the weight of the vehicle. As soon as the front axle leaves [the scale], your time is done.”

Consider, though, that NCWM will only allow legal-for-trade WIM scales to be full-length, single-draft static scales. These scales will either have to be retrofitted with the technology needed to weigh a truck while it’s in motion (if a producer already has said scale) or be purchased with that technology already installed if it’s a new scale, Golden says.

“You have to have a scale that has been certified as a static scale, and then this WIM application is like an endorsement,” Golden says. “If you have a driver’s license and you get a motorcycle endorsement, you still have to start with the driver’s license. Then, you get the motorcycle part. This is the same thing.”

Golden adds that this endorsement can be obtained during the same test that scales receive their static certification.

Speed & safety

Because a driver remains in the truck and trucks keep moving along the scale, WIM scales, in theory, can be safer and more efficient than static scales.

“For every weighment you do, if it’s saved you 30 seconds, that by itself is not a big amount,” Golden says. “But in aggregate, throughout the day where you’re constantly doing truck after truck, it’ll add up. If you’re doing hundreds of trucks a day, you’ll be able to get a whole lot more throughput if you don’t have to stop on the scale to get a static weighment.”

Along with the enhanced safety and efficiencies WIM scales provide, Southern Illinois Scale & Construction’s Brad Fryburger says WIM scales provide accuracy that is better than some may think.

“People that have worked on static scales [have said]: ‘You don’t want that. That’s not accurate,’” says Fryburger, who serves Southern Illinois Scale & Construction as general manager “Is it really [inaccurate]? Let’s weigh that same truck 100 times on your static scale, and then let’s go back and compare it to what it looks like when weighed 100 times [on an in-motion scale]. It’s really not [bad].”

Jack Kopanski

About the Author:

Jack Kopanski is the Managing Editor of Pit & Quarry and Editor-in-Chief of Portable Plants. Kopanski can be reached at 216-706-3756 or

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