Accurate Weighing Results in Difficult Plant Environments

Accurate Weighing Results in Difficult Plant Environments
Accurate feeding, batching and metering of bulk solids begins with precision weighing. In 1976 Coperion K-Tron introduced the process industry’s first truly digital load cell using advanced vibrating wire weighing technology.

After over five decades and six generations of innovation and development, Coperion K-Tron’s Smart Force Trans­ducer (SFT) technology continues to set the standard for the industry. Advanced single-wire design, high resolution, internal force reduction, and 90% fewer parts combine to provide the highest possible levels of performance and reliability.

Consider a loss-in-weight feeder operating in a typical plant environment. Feed rate control is achieved by continuously weighing the entire feeding system, then controlling the rate at which the system loses weight by adjusting motor speed or vibrator amplitude to achieve the desired setpoint. The total load applied to the weighing system is the sum of the actual weight of the feeder and bulk material plus the variable force contributed by in-plant vibrations. No matter how accurate its scale system is, a loss-in-weight feeder is worthless if the weight readings are tainted by vibrations. Many feeders stand in the midst of harsh industrial activity, making its ability to accurately measure the actual loss in system weight crucial to its performance. Possible agents of measurement contamination include shock, vibration and other perturbations such as drafts, and even convective air currents.

Achieving high gravimetric feeding performance on the process line requires discriminating between weight data and the contaminating effects of inertial forces induced from such ambient influences. Coperion K-Tron’s exclusive dynamic digital filtering algorithm con­tinuously identifies and extracts spurious inertial components from the weight measurement, even in severe process environments. Thanks to this digital filter SFT load cells are able provide accurate, stable and reliable digital load mea­surement under a broad range of operating conditions.

Coperion K-Tron’s advanced vibration filtering algorithm ensures an accurate weight signal.
Coperion K-Tron’s advanced vibration filtering algorithm ensures an accurate weight signal.

 All 100% digital SFT load cells are designed to never need in-field calibration. The weight of the feeder is captured, linearized and temperature compensated 450 times per second with zero data loss at the measuring point inside the SFT. At the same time, the 64-bit wide data registers used in the newest software versions provide mathematical data resolution in parts per billion, resulting in significantly higher calculation accuracy and a stable scale resolution of 1:8’000’000 (or 1 part of 8 million) in 20ms. This allows the physical sample data from the SFT vibrating wire to be processed more precisely. The Coperion K-Tron KCM-III feeder controller utilizes the full capacity of the SFT weighing technology, receiving weight signal input from the SFT load cell every 20ms. That means the feeder can adjust output speed, based on new weighing data, at a rate of up to 50 times per second.

All of these recent enhancements provide even better noise filtering, less weight shift under vibration and near-instant response to changing process conditions, such as setpoint or bulk density fluctuations. This advanced weighing technology together with the fast feeder control result in extremely high short-term accuracy, despite challenging environments.

This article is published by

Innovative and Sustainable Bulk Material Processing Solutions.

Coperion and Coperion K-Tron are system and equipment suppliers, including extruders, feeders, pneumatic conveying and components, who understand the importance of process efficiency. We design, develop, manufacture and maintain systems, machines and components for the plastic, ...

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