TIP-3

Weigh Modules

Are the critical measuring device for your system, pricing is generally proportional to accuracy.

Care should be taken when selecting a module to give the accuracy and repeatability you are looking for.

Quite often the accuracy specifications is for the load cell only and does not include mounting hardware.

Economy shear beam weigh modules are often this way, as the module hardware design degrades accuracy.

Precision Assemblies High accuracy assemblies are factory trimmed to 0.1% or better Any off the shelf assembly will perform identical as the specifications are tested and written for the complete assembly, there is no degrade in module accuracy when installed. Only mechanical connections to your weighed vessel will degrade the accuracy. The module design has integral vessel restraint and expansion/contraction allowance with minimal affect on performance. Specifications for side load, uplift and overload are often 100% of rated capacity. (This is substantially higher than approximately 30% side loading for economy modules). Well suited for mixing applications or vibration, torsion, uplift, and or overload.
Mid Range Assemblies Designs vary and often have limited specifications for side load and uplift ratings. Care should be taken when selecting assemblies for agitated applications, side loading and vessel movement may become an accuracy and repeatability issue . The module shown includes vessel restraint for uplift and overload that is fixed to the measuring end of the load cell only and does not shunt across the cell to a fixed structure. Performance is much better than other styles that use bolts or rods that shunt across the load cell. The bolts or shunt often bind with vessel movement causing a load error and poor zero repeatability. Select modules with well matched load cell outputs to improve system performance.
Custom Assemblies Are usually a low cost solutions where hardware is attached to shear beams. Specifications are normally provided for cell only as the hardware reduces accuracy. Avoid modules that have a bolt or mechanical shunt across the cell unless always static. The restraints cause poor zero repeatability and/or span errors. When economy load cells are used they are typically matched 1%-5%, a trim card is suggested to match the cells to improve overall accuracy. Best suited for static weighing or a single support for empty/full level applications.

Last modified: 09/15/09 Send mail to info@iwsystems.ca with questions or comments