Typical Electronic Scale Configuration

This section describes how a typical scale is configured for the purposes of establishing a common terminology and understanding:

A. Platform/Hopper

Whatever it is that the scale is supposed to weigh, there has to be a method of supporting or holding the item to be weighed so all of the force of gravity on the item is transmitted to the load cells. Typically either a steel platform (say for trucks) or a hopper (for bulk materials) is used. The platform or hopper is totally mechanically isolated from all surrounding structures so that it is totally supported by the load cells. It is important that there are no mechanical connections to the surrounding structure, other than through the load cells.

B. Load Cells

One or more load cells is used to measure the force on the scale. Typically 3 or more load cells are used in a heavy capacity scale. If less than 3 load cells are used then some sort of mechanical checking arrangement is used to stop the scale from tipping over, which will cause in-accuracies unless it is a very small scale. Each of the load cells have a capacity rating in terms of the maximum load they are designed to measure, stated in pounds or Kg, which must be greater than the total weight of the platform/hopper plus the weight of the item being weighed. These load cells are wired to a weight indicator via a J-Box. C. Junction Box – Each load cell has a 4 wire cable coming from it. Two of these wires are used to provide power to the load cell (excitation), and two return a voltage reading proportional to the weight on the cells (signal). All four cells are wired in parallel in a junction box located near the scale. From this junction box a single cable returns to a weight indicator.

D. Weight Indicator

This generally mounted remotely from the scale itself, in an area where the weight can be viewed on the indicator display. A Six conductor cable from the load cell junction box connects to the Excitation, Sense and Signal leads on indicator. The Sense leads are jumpered to the Excitation leads either in the junction box, or at the indicator to allow the indicator to correct for Excitation voltage changes. The purpose of the Indicator is to digitize the low level signal voltage from the load cells and convert it to a displayed weight, and to optionally communicate that weight to other devices such as PLCs or remote displays.