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Using industrial scales

Supplier: King Materials Handling By: Ron Mileham
30 August, 2011

Not the ones that the statue of Justitia holds outside most law courts.

I mean the common or garden variety that we all use sooner or later, be it for checking our own weight in the bathroom, to determining if the freight company is overcharging us.

There are a million ways (or should I say weighs) of getting to the same point. Most modern scales rely on something called a load cell. A load cell is a strain gauge. It is deformed by weight, and the deformity is measured electronically to give you the load weight.

What’s that got to do with the price of fish you say? Well, nothing really, except that it’s a mixture of art and science if you want to get it spot on. Which segues into why you need to get it right -- at times.

That time is when you are selling product by weight. Then your scales need to be Trade Approved. Even the ones that capture the weight of your toothpaste tube, as it flies through on a conveyor. Any under or overweight tubes are rejected and binned (for later recovery of the product).

When sending freight by the pallet load, you need to know that within say 5% your load weight corresponds with that of the weight on your invoice from the freight company. In this way, you have some control. If you don’t know your pallet load weights, you are open to misrepresentation (add to that correct load measurements).

Trade Approved scales are set up initially at the factory to be as accurate as possible within given tolerances. This is then tested again on site by either using approved weights, or if the weight load is too big, the truck and empty container is sent to an approved weigh station to determine the tare (empty) weight. Then, after filling the container with a known load weight, the truck is sent back to the weigh station in order to verify the final weight.

Trade Approved scales must be periodically checked for accuracy to ensure you always get a fair deal.

Scale types can include:

  • In-ground for trucks, where many load cells need to be calibrated to give an accurate holistic readout.
  • Crane scales, for determining loads on the end of crane hooks -- vital information if you don’t want to exceed the cranes lifting load limit. They are now able to be wirelessly received via a hand held display.
  • Counting scales, when you have a million items. Just weigh a few, then keep pouring until you get the weight you need -- very clever.
  • Under conveyor scales for in-line weighing.

Scales that fit onto forklifts have two options for weighing goods. One is to fit conventional load cells to the main carriage, then weigh the forks and whatever is on them through a sub carriage. The other is to measure the amount of  back pressure in the hydraulic lines. Both can be viewed as a digital or LED readout. Reading the hydraulic line back pressure in order to determine weight is also useful for any heavy equipment which uses hydraulics such as back end loaders with buckets.

Two Types of Scales: Counting & Pallet
The Counting Scale is a very handy scale for when you need to count out product, but by weight. Throw a pre-determined number of widgets onto the scale, say ten, then set the counter. Then set the finished or required quantity button. Continue to throw product onto the scale until the finished number comes up. Simple as that and far quicker than counting out product.

The Pallet Scale is pallet sized and sits on the floor of the warehouse. When a pallet load is ready for shipping, it is placed onto the scale and the weight shown on a display or printed out as a hard copy.