Main keywords for this article Factors Affecting Weighing System Performance. Special Installation Requirements. Shock and Vibration. Pressure Unbalance. Live to Dead Connections.
Factors Affecting Weighing System Performance
Satisfactory performance of an electronic weighing system is dependent upon the ability of the system to work properly while operating under the influence of a wide variety of mechanical and environmental conditions. The following factors can affect the weighing system performance:
Shock and Vibration
If a situation occurs where shock can be applied to the 8 modules, then this abrupt change in weight on the system must be taken into consideration when selecting the weight modules for the weighing system. Otherwise the transient loads may damage the load cells.
Vibration can also adversely affect the weighing accuracy of a system by preventing the weight instruments from coming to rest. Vibration can come from 2 sources – external to the weight scale and internal within the scale. External forces are normally foundation vibration and environmental vibrations. Internal forces are normally vibrations which are generated inside the vessel by spilling of the liquid or agitation. The effects of wind induced vibration are difficult to predict. If high accuracy is required, it is recommended that the weighing system be shielded from wind. If the vessel is to be located outdoors, it should be designed so that the vertical components of force caused by wind are minimized.
When designing tank and hopper scales, the possible effects of pressure unbalance between the top of the scale and the bottom of the scale must be considered. If there is a pressure difference between the top side live projection of the weighing system and the bottom side live projection of the weighing system, then this unbalance will act as a vertical force on the weight scale and produce a weighing error.
Live to Dead Connections
Vessels usually require supply connections for bringing material into and taking it out of the container and for pneumatic, hydraulic, or electrical supply of associated equipment on the container, such as agitators and electric heat tracing cables and piping. These supply connections can affect the weighing accuracy of the system unless flexible piping connections are properly made.
Tanks or hoppers which are constructed of steel can be expected to expand or contract at approximately one thousandth of an inch per foot over a temperature variation of 100 degrees F. In normal weighing systems, it is necessary to carefully evaluate the effect of expansion on the weighing system.
Weighing tanks or hoppers which are installed outdoors should, as far as possible, be protected against atmospheric conditions such as rain, snow, ice, wind, and rapid temperature changes. Rain water, snow, or ice must not be able to accumulate on a weighing system. If ice forms, considerable error can result. Standard weight modules are compensated for operation over a temperature range and high temperature weight modules are also available. Special precautions must be taken; however, where weight modules will be subjected to temperature exceeding these limits.
Special Installation Requirements
The accuracy and optimum performance of a weighing system, while obviously a function of the weight modules and instrumentation, is also dependent upon the vessel design, support structure, piping attachments, lateral restraint system, and proper selection of weight module accessories. Therefore, weighing system accuracy is inherently tied to the degree of attention given to the mechanical details.