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MARCH/APRIL 2023

BELT TENSION AND PLACEMENT

How They Impact Accuracy

Todays electro mechanical weigh scales are both dependable and accurate. With the help of precision load cells, speed sensors, self calibration and electronic integrators, measurements can be easy and reliable.

That being said, hardware is not the only factor affecting a weigh belt scale's accuracy.

Belt Tension

Conveyor tension that is too high can lead to bridging (when product bonds together and forms an arch above the discharge outlet of a hopper, silo or other container). In this case, the scale is unable to weigh the entire belt and material, resulting in an underestimation of the tonnage.

If the conveyor tension is too low, the belt may sag, causing material to shift, skewing the numbers. Generally, a 2% sag is optional. After that, even a small 1% variation from the optimal tension can alter the scale's accuracy and repeatability by as much as 10%.

Placement

The reliability of your weigh scale is heavily impacted by it's placement on the conveyor line.

DON'T install the scale near the conveyor loading point. Turbulence leads to poor performance and accuracy. Wait to weigh materials until they completely settle, at least one or two conveyor idlers away from where turbulence stops. For the same reason, avoid installs near the conveyors head pulley or tail pulley.

DO install the conveyor belt scale in an area with constant belt tension. Because it acts as a force on the scale, belt tension is factored out during calibration. Tension variations will affect accuracy. If belt tension variances are a continuing problem, talk with your belt scale manufacturer about a tensioning device.

DON'T install on a steep incline.  Angles of more than 15 deg greatly increase the chance of material roll back, causing the material to be weighed multiple times. Inequality between belt speed and material feed velocity may also cause roll back.

DON'T install the belt scale where the conveyor forms a convex or concave curve. The belt could lift up from the curve preventing a solid, empty belt zero balance.

DO  isolate the belt scale from vibratory equipment.  The vibration from crushers, vibratory feeding equipment and hammer mills can negatively affect the belt scale. 

DO consider weather conditions.  Temperatures variations can cause the conveyor belt to lengthen or shorten, affecting the tension of the belt and the accuracy of the scales. In winter, the belt may contract and stiffen. Run the belt empty for 10-15 minutes to make it more pliable. In summer, the belt may expand, requiring more maintenance.

Tecweigh offers several models of Weigh Belt Feeders using NTEP approved load cells. They are available in capacities ranging from 500 to 1,000 pounds per hour with custom designed feeders for even greater capacities.

Quick, easy, and safe calibration utilizes self-storing calibration weights that eliminate bulky chains or awkward hang-on weights. The weights are specifically sized for the required application to provide accurate calibration.

WY-15 Single Idler Conveyor Belt Scale

Tecweigh's WY15 Single Idler Conveyor Scale utilizes two NTEP approved bending-beam load cells. With rigid all-welded construction the WY15 is more reliable, more durable and easier to use than competitors' scales.

WY-10 Single Idler Conveyor Belt Scale

A highly dependable, rugged belt scale. The weather-tight one-piece construction keeps your line rolling even in the most extreme conditions: dust, dirt and harsh weather. The WY10 utilizes LVDT load sensor technology. LVDT load sensors simply can’t be overloaded and are far less susceptible to damage from lightning strikes, making blown load cells a thing of the past.

HY-15 Hybrid Belt Scale

The HY15 Hybrid Belt Scale incorporates Tecweigh's electronics package with a less costly modular scale frame. The compact, low profile design is suitable for many conveyor applications (including mobile units).

Made with heavy-duty cold rolled steel, the HY15 will withstand harsh environments. With two (2) NTEP approved strain-gauge load cells, the HY15 offers a single-idler accuracy of ½-1%. The dual-idler HY25 model provides an accuracy of ¼-½%.

The Hybrid Belt scales come with a complete installation kit, mechanical overload protection, signal conditioning enclosure, calibration weight brackets and speed sensor,.

For mobile applications, the HY15 offers a unique weighing design. One module is a rigid mount from the idler to the load cell, with the other incorporating a forgiving spherical bearing to greatly reduce drift problems caused by flexing structures.

Optional features include wireless communication, multi-scale processor, printer, remote displays and more. Tecweigh’s WP25 weight processor, or any other Tecweigh processor, makes your HY15 or HY25 a complete weighing system.

For help choosing a Weigh Belt system with features that integrate right into your existing system, contact your TEC Representative or visit Tecweigh.

Watch a Tecweigh Belt Scale Installation from Start to Finish.

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