The primary goal of the Distribution Control System was to eliminate operator errors that caused blending of different chocolate recipes or spilling of expensive chocolate product. A strong secondary motivation was to provide a system that could aid a new operator in learning the operation rapidly and without mishap.
The entire distribution network comprises of 65 tanks with load cells, 63 PLC controlled pumps, 109 PLC monitored valves and about 300 valves that are not monitored (except by the operator). None of the valves can be controlled through the PLC. The control system would need to monitor high levels based on a tank selection made by the operator and then switch off the appropriate pump when the high limit in that tank was reached. The delivery of chocolate is in effect a dynamic process where multiple pumping operations can be going on at the same time and where one pump can service many tanks depending on operator preference. This control requirement alone is a challenge beyond the capacity of any PLC or MMI product currently available.