Saturday, April 16, 2016

A Better Load Cell for Weighing Heated, Vibration Prone Process Vessels

Heated Tank with KIS load cells
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 an 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%.

load cell issues
Load cell performance problems causes.

BLH KIS sensor
BLH KIS sensor
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.

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 Instrument
BLH Instrument
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.

The video below gives an excellent view inside the KIS design and why its ideal for process vessels.