The description of mechanical, hydraulic, and pneumatic designs are followed by the discussion of electronic load cells—their design variations, features, accessories, and the more recent advances that have occurred in their designs. The discussion begins with the topic of strain gauge-type load cells. The reader should be aware that strain-gauge-type sensors, circuits, and electronics have already been discussed in other sections of this volume (Sections 5.7, 7.19, and 7.21). For this reason, some of the points that were already made will not be repeated here.The use of mechanical, hydraulic, and pneumatic weight sensors is declining in most areas except in the laboratory, where high-precision mechanical balances are still widely used. However, even in the case of these devices, electronic sensors are often used to operate digital displays or to provide memory and computer compatibility. In industrial application, mechanical platforms or truck scales are often combined with electronic load cells to operate remote displays or to provide computer compatibility.The number of load cells required is determined by the plane view geometry of the supported structure—hopper, tank, or silo. The main considerations include cost and accuracy. Cost can obviously be reduced by lowering the number of load cells used. On the other hand, if a load cell is not placed under each point of support, the total load is not being measured; therefore, if the load distribution is not symmetrical between points of support, the reading will be in error. Three points fully define a plane, so the ideal number of supports for uniform load distribution is three.When calculating the tare weight of the empty vessel, one must include any additional equipment attached to the vessel, such as agitators, valves, and filters.

that contributes to the weight that the empty vessel (including its accessories) will exert on the load cells. Examples of anticipated dynamic loads are vessels with crane buckets and vessels with horizontal agitators. Assuming for these cases K = 1.25, one can provide an extra capacity for sizing, resulting in a higher capacity load cell selection. A higher capacity load cell will perform better under repeated impact loads or high cycle fatigue.The lower plate is connected to the active weighing platform, thereby transmitting the weight through the links and upper plate to the top of the load cell. The load cell is supported by a base plate, that rests on the foundation or ground structure. The base plate also serves to absorb heavy side loads when the horizontal deflection of the weigh-bridge exceeds the clearances provided between the base plate and the cutout portion of the lower plate. The height of the adapter assembly can be adjusted by a center screw, enabling the equal distribution of total load among the several load cells in a given installation. The structure provides a highly flexible load cell adapter assembly, which transmits virtually no side loads to the load cell caused by differential expansion of the weighing structure relative to the ground structure. The side loads that are transmitted to the load cell are from weigh-bridge deflections, imposing angular loads on the load cell. These are minimized by appropriate structural design of the weighbridge.

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