Load Cells: The Vital Component in Precision Weighing

A load cell is a transducer or a sensor that converts force into an electrical signal. In industrial weighing applications, it's a critical and core component used to measure weight or force.

The most commonly used types of load cells in industrial applications are strain gauge load cells, which work on the principle of piezoresistance. When a load or force is applied to the strain gauge, it deforms or changes shape. This change in shape causes a measurable change in the electrical resistance. The change in resistance is proportional to the load applied, meaning the more significant the load, the larger the change in resistance.

This change in resistance is usually minimal, so it's converted into an electrical signal using a Wheatstone bridge configuration. The signal is then amplified and converted into a digital form by an analog-to-digital converter. This digital signal can be interpreted and displayed on a readout device, such as a digital display or a computer.

In industrial weighing applications, load cells are ubiquitous, with applications including weighing scales, industrial scales, batching scales, and load-testing machines. They can measure loads ranging from tiny (a few grams) to large (hundreds of tons).

Load cells are robust and reliable, capable of withstanding harsh industrial environments. They can handle extreme temperatures, high levels of vibration, and other challenging conditions. Additionally, they offer high precision and accuracy, which are critical in many industrial applications.

In addition to their use in weighing, load cells measure tension, compression, and shear forces, making them versatile tools in many industrial processes. They play a significant role in quality, inventory, and process control in various industries, including manufacturing, agriculture, food processing, pulp & paper, power generation, transportation, and construction.

BLH Nobel is a leading weighing and force measurement solution provider, including load cells, weighing modules, and process control equipment. The company is renowned for delivering precision, reliability, and durability, particularly in harsh industrial environments.

KIS Weigh Modules, adeptly deployed on dynamic process vessels amidst harsh, sanitation-intensive areas, have mastered the art of thriving amidst grime and grit. Their performance remains uncompromised and exceptional, even in the most challenging conditions riddled with corrosive acids, potent industrial cleaning agents, acidic vapors, and abrasive granulated powders.

Part of the remarkable performance of the BLH Nobel KIS is its ingenious cylindrical design. KIS beams can be maneuvered within the module's infrastructure, aligning precisely with the direction of the applied weight. The modules feature cylindrical, electro-polished stainless steel, forming an almost friction-free surface, allowing the module yoke to glide effortlessly during thermal expansion and contraction periods.

 

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(508) 351-6200

Understanding Load Cell Overload

When you're talking about load cells in process weighing, what does safe and ultimate overload mean, and how strong are load cells?

The ultimate strength relates to the function as a load cell and not the mechanical strength. The mechanical strength of the load cell is even higher. 

For a load cell, there is generally three capacity limits:  

The nominal capacity of one 100%: Let's say we have a 100-pound load cell. This is the limit or capacity of the load cell. Note the load cell should not be subjected to higher forces under regular use. If the application needs to measure higher loads, then a larger load cell should be used.

The safe load usually is 200 percent of the rated capacity: Let's say with the 100-pound load cell this would be 200 pounds. If the load cell is occasionally subjected to more than 100 percent but less than 200 percent, nothing happens to it, and it will work. If repeatedly subjected to more than 100%, the load cell can be damaged due to fatigue.

The ultimate load is usually 300 percent of rated capacity or 300 pounds for a 100-pound load cell. If the load cell is occasionally subjected to a load greater than 200 percent but less than 300 percent, the load cell will be subjected to a zero shift. However, in most cases, the load cell can be recalibrated and repaired. If subjected to more than 300 percent, the bonding of the strain gauges will most likely be damaged beyond repair. The function of the load cell is damaged, and it should be scrapped. 

As a reminder, this refers to the function as a load cell and not the mechanical part. The mechanical strength of a load cell varies but is often in the range of 400 to 1 000 percent. It should also be noted that there's a fatigue limit for a load cell that generally is 133 of capacity. 

Cost Effective, Speedy Force Calibration System from BLH Nobel

A BLH Nobel customer's manufacturing process included multiple critical tanks that required regular weight calibration. The largest, a reactor, weighs 60 tons. Traditionally, they calibrated the vessels by filling them with water, a laborious and expensive process. It took a week for each tank.  Aside from filling the tanks, each must be emptied and rinsed. Finally, calibration required thorough drying before resuming production. 

BLH Nobel developed a method to elevate the vessels and read the weight change at various stages of the process. This video demonstrates that method.

BLH Nobel's solution allows the calibration of a weighing vessel, silo, or tank in a fraction of the time compared to using flowmeter or weighbridge calibration. BLH Nobel jacks the tank using hydraulics instead of loading with weights or flowmeter. Typically they measure the result in several points and verify the weighing result. BLH Nobel's method is often carried out without modifying the existing frame or structure, as most already have a suitable jacking point at each load cell.

For more information about this weighing calibration process or any BLH Nobel products in New England, contact AP Corp. Call (508) 351-6200 or visit https://a-pcorp.com.

Process Weighing, Web Tension, and Force Control Systems Applications in Pulp and Paper Production

BLH Nobel is a leading supplier of specialized pulp and paper measuring devices. Over the years, they've built a strong understanding of pulp and paper manufacturers' process problems. Be assured that BLH Nobel has the best solutions to maximize productivity and performance.

DOWNLOAD THE BLH PULP & PAPER APPLICATIONS GUIDE HERE

Pulp and Paper Applications

• State-of-the-Art Instrument for Weighing and Force Measurement
• Web Tension Measurement Unit
• Dynamic Resultant Force Measurement
• Refiners Position and Pressure Control
• Paper Rolls, Pulpers and Coating Kitchen

AP Corp.

https://a-pcorp.com

508-351-6200

Load Cells for Weighing Vessels in Hot and Vibration Prone Areas

Most load cells are designed to handle vertical force and cannot discern errors introduced from side loading and/or torque loading. In real world conditions, though, load cells see much more than vertical loading, and unfortunately, can output erroneous values. While they are excellent for static weighing situations, such as scales, load cells typically can’t handle the rigors of process vessel applications.

A case in point is a chemical manufacturer with several, existing three cubic meter batching tanks. It was decided the tanks needed modifications to provide more accurate weighing of the individual ingredients. The existing load cells were experiencing errors due to thermal expansion of the vessel, and the resultant side loads from expansion. Additionally there was a problem with vibration in the plant. A better solution was needed, and whatever the solution would be, the customer made it clear the new weighing system must provide system accuracy in the range of ±0.1%.

An approach to deal mechanically with the thermal cycling while using the same type of load cell was discussed. It involved several mechanical modifications that required significant and costly structural changes.

BLH KIS

Another suggestion was to evaluate a unique load cell design that was particularly tolerant against thermal expansion, vibration, and high lateral forces - the BLH Nobel KIS series.  The KIS load cell offered some obvious advantages over rebuilding the tanks supports and frame, namely time and expense. Beyond the short installation time and easy modification, the KIS also offers excellent reliability and accuracy.

BLH Controller

The customer decided to “take the easy way out” and just replace the old, error-prone load cells with KIS load cells. Installation and start-up was very easy, taking very little time. After installation, the customer was pleasantly surprised by the high accuracy of the new KIS load cells, despite the thermal expansion of the vessel and the inherent vibration.

For more information on BLH Nobel products in New England and Upstate New York contact A-P Corp. Call them at (816) 353-6550 or visit them at https://a-pcorp.com.