Weigh module general installation guidelines

Applying force to load cells

Load cell that use strain gauges are sensitive enough to detect very small changes in weigh. The tick is to make sure that they react only to the weigh you want to measure,not other forces. To get accurate weight  reading,you must carefully,control how and where weigh is applied to a load cell.Ideally, a load cell should be installed so that the load the load is applied vertically throughout the entire weigh range(see figure 5-1)

To attain that ideal,the weigh vessel and load cell support would would need to be level,parallel,and infinitely rigid.when a tank scale and its structural supports are designed and installed carefully,it is possible for  the scale to approach an ideal loading application.when a scale is not  installed properly,there are several types of  fores that can affect its accuracy.the following sections describe loading problems commonly encountered in tank scales application.

Angular loading

Angular loading occurs when a force that is not perfectly vertical is applied to a load cell.This diagonal force can be defined as the sum of its vertical component and its horizontal component.In a well-designed weigh module application,the load cell  will sense the weight(vertical force)but will not sense the side load(horizontal force)

Figure 5-2a and figure 5-2b show a weigh module application with the load cell anchored to a foundation.I n figure 5-2a,the force exerted by the tank’s weight is perfectly vertical.In figure 5-2b,the force is applied at an angle.The vertical component(F)of this angular force is normal to and sensed by the load cell;it is equal to the force applied in figure 5-2a.the horizontal component (side load)=F*Tangent θ

Figure 5-3a and Figure 5-3b show how angular loading would affect a load cell anchored to the tank that is being weighed.figure 5-3a shows an ideal installation with a perfectly vertical fore.In figure 5-3a,the force (FN) that is normal to and sensed by the load cell would be less than the vertical force(F) applied to the load ell in the ideal installation.In this case,FN=F*cosine θ.

Eccentric loading

Eccentric loading occurs when a vertical force is applied to a load cell at a point other than its center line(see figure 5-4).this problem can be caused by thermal expansion and contraction or by poorly designed mounting hardware.You can avoid eccentric loading problems by using a weigh module system that will compensate for expansion and contraction.

Side and End loading

Side and loading occur when horizontal forces are applied to the side or end of a  load cell (see figure 5-5 ).they can be caused by thermal expansion and contraction,by misalignment,or by vessel movement due to dynamic loading.Side and end forces can affect the linearity and hysteresis of the scale.For static loading applications,use a weigh module system with a self-aligning load pin suspension.

Torsional loading

Torsional loading occurs when a side force twists a load cell(see figure 5-6).It can be caused by structural deflection,system dynamics,thermal movement,or mounting hardware misalignment.Torsional loading will reduce a system’s accuracy and repeatability.To avoid this problem,always follow proper structural support and installation guidelines,and use weigh module that compensate for tank movement.