“FMSS” stands for Force Measurement Suspension System. A Force Measurement Suspension System is an interposed active structure, consisting of one or more articulated members, placed between the load receptor (hopper, platform, weigh suspension, etc.) and a load cell. FMSS functions as a selective “force” filter in the sense that it can discriminate between forces representative of the desired net load measurement (both magnitude and direction) and all other undesirable extraneous forces such as vibration. The load cell in each case experiences a pure tension force, free of all destructive side loading components. The particular configuration of FMSS chosen for an application depends on the type of equipment and the known physical interfacing problems that it presents.
The configurations consist of:
- Various constant sensitivity platforms (Flexure and cable scales)
- Graded sensitivity weighbridges (conveyor belt scales)
- Lateral torque transmitting devices (Model “D”)
Specific functions that a properly selected Force Measurement Suspension System provides under appropriate applications:
A) Provides adjustable mechanical TARE balancing of dead loads (typically as high as 200 times NET Loads), thereby enabling the full utilization of the available load cell force range (Load Cell Utilization Factor). The resulting maximization of the measurement signal reduces signal transmission problems, enhances zero temperature stability, reduces susceptibility to moisture migration, and lessens dependency on high quality terminal connections. The adjust-ability of TARE balancing permits future changes in the dead load equipment, such as that required by a new volumetric feeder or a larger hopper.
B) Reduces deflection of load receptor to fraction of load cell deflection. On Conveyor Scales and Weigh Belt Feeders, this means less sensitivity to belt tension effects. On Loss-In-Weight Feeders, this means less sensitivity to inlet/outlet flexible connections and “weigh loops wiring.”
C) Reduces zero shifting as a result of foundation distortion. This is a major and poorly understood problem in conveyor weighing in particular. Aside from well known “belt errors” generated through the load receptor side of the system, significant zero shifts can occur through the foundation side of the system if the supporting frame structure underneath yields under load or settles over time. Loss In Weight feeders are particularly sensitive to foundation distortion owing to their reliance on exceptionally high measurement resolution and frequent load sampling. Thayer Scale’s “Cable Scale Suspension Systems” have proven effective where the weighing system is hung from overhead structures, supported on wheels, or moved about by forklift.
D) Provides preferred access location of load cell for inspection or removal. Load receptor does not have to be disturbed. Very important on conveyor scales, where the re-alignment of idlers necessitated by load cell removal is a dreaded task, or on Loss In Weight feeders, where there is oftentimes a need to remove the volumetric feeder and its connections first.
E) Simplifies the application of Test Weights for calibration checking. The FMSS can be configured to accept automatic means for applying and storing weights initiated from a remote location. This is a preferred system where quality control procedures dictate “Calibration Status” printouts on production reports.
F) Provides for lower signal velocity and acceleration under dynamic conditions. In conveyor weighing, a multiple idler FMSS having a symmetrical sensitivity gradient across the longitudinal axis of the scale can provide accurate weighing at speeds in excess of 500-600 fpm. This is possible because as material rapidly crosses the suspension system, the force experienced at the load cell is changing at a relatively slow rate.
G) Negates the effects of vibration. Weigh feeder and belt scales can be subjected to vibration produced by many different sources. In standard design weighing systems this vibration is transferred through the support structure into the load cell and the electronics reads this vibration (motion) as meaningless weight variations. FMSS technology makes the load cell virtually immune to the detrimental effects of vibration.
Load Cell Utilization Factor
The performance of a load cell and its associated instrumentation is specified on the basis of the load cell’s rated output. If the load cell is supporting a quantity of dead weight (i.e. hopper, screw feeder) then the mount of range left to do the job of weighing is only a fraction of the load cell’s rated output. The situation is further aggravated by the limited availability of conventional load cell capabilities. The percentage of a load cell’s rated output reserved for the actual job of weighing material is called the Load Cell Utilization Factor.
Permitting a condition to exist wherein the Load Cell Utilization Factor is a mere 20% (not unheard of, or even uncommon), results in drift, non-repeatability and temperature induced shifts that can be as much as 5 times worse than what is stated on specification sheet describing the transducer and measuring system.
At Thayer Scale, we custom build our load cells (See LC-137) with capacity ranges that step up in fine increments. Our applications computer can pick the best load cell for the job; one that will have a range that is ideally suited to the service it will perform. This, in combination with our cable suspension system which mass counterbalances the dead load of the hopper and screw feeder, enables us to reach a 90 – 100% load cell utilization factor on all applications.
Thayer’s FMSS technology also increases OVERLOAD capacity when using Strain Gauge Load Cell’s operating at the same Utilization Factor (UF%).
Typical Thayer FMSS Configurations
Thayer Scale is well known for its proprietary “Flexure Plate” and “Flexure Cable” Force Measurement Suspension Systems, which are available in a number of capacity ranges and configurations to suit the unique needs of the principal classes of continuous weighing and feeding equipment.
The FMSS can be configured to provide other outstanding benefits, depending on the particular needs dictated by the type of weighing equipment employed.