Fatigue Rated Universal Load Cells

Features

The structure of the load cells are simple and compact, consisting of an inner loading hub and an outer supporting flange bridged smoothly by a uniformly continuous solid shear web, avoiding structural stress risers. Strainsert gages are installed and sealed inside small gage holes along the neutral axis of the web. Low deflection and high natural frequency of the load cells are obtained, along with high resistance to extraneous forces. Mechanical and dynamic properties of load cells are fully tabulated.

Long fatigue life (one billion cycles) and stability of the Load Cell is mainly due to low strain levels the shear gages are subjected to ±500µe FS for completely reversed “C/R” rating and 750µe FS for unidirectional “U/D” rating at ±2-mV/V and 3-mV/V nominal output signal levels respectively.

Linearity and symmetry of output signal in tension and compression are obtained by equal straining of all shear gages in the bridge circuit of the Load Cell.

Barometric or hydrostatic pressures, or vacuum environment do not produce erroneous output signals in Load Cells.

Allowable loads that fatigue rated Universal load cells will withstand for one billion cycles without failure are tabulated under Uni-directional (U/D) and Completely Reversed (C/R) load headings.

In specifications the relation is stated as (U/D) = 150%(C/R).

Allowable intermediate loads between uni-directional (U/D) and Completely Reversed (C/R) loads can be read off the limit chart (see limit chart below), where (C/R) FS Fatigue Load Rating is defined as ±100% at one billion cycles. Peak tension and peak compression, as well as mean tension and mean compression, loads are also given in % (C/R) FS.

Overload allowance in Fatigue Rated Load Cells can only be made at the expense of fatigue life. However, when the required service life of a load cell is less than one billion cycles, advantage may be taken of the reduced fatigue life and the cell may be rated at higher peak loads, per overload factors given in the below specifcations. Once this overload is applied, however, even for a few cycles, fatigue life of the cell must remain at the reduced value. Thus peak load ratings corresponding to one billion cycles should not be exceeded if long fatigue life is an important consideration for the load cell. The load capacity and corresponding life of a Fatigue Rated Load Cell is stated below. In the following example consider the below case:

FFL (180/±120) U (C) – (3/±2) SPKT

Where Uni-directional (U/D) Rating is 180,000 lbs., and completely reversed (C/R) Rating is ±120,000 lbs.
From limit chart intermediate ratings are available. Say at +50% (+60,000 lb) Mean Tension Load
Allowable peak tension load is +133% of 120,000 lbs. = +159,600 lbs.
Allowable peak compression load is -33% of 120,000 lbs. = -39,600 lbs.
All at one billion load cycle fatigue life. If, on the other hand, required service life of the load is only one million load cycles, then, from overload allowance chart all load ratings can be increased by an overload factor of 1.10, thus:
(U/D) = 1.10 X 180,000 = 198,000 lbs.
(C/R) = 1.10 X (±120,000) = ±132,000 lbs.
At +50% (+60,000lbs) Mean Tension Load, the allowable peak tension = 1.10 X 159,600 = +175,560 lbs.
The allowable peak compression = 1.10 X (-39,600) = -43,560 lbs., All at one million load cycle fatigue life

Some Features Include:

Specifications

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