Mixing System Requirements

White Papers:
Prev | Cadbury Chocolate Project Review | Next

# 3. Mixing System Requirements

The goals of the mixing control system were to increase total output from the mixing system, prevent accidental mixing of different recipes and reduce the variability in the final product.

Since there were two mixers feeding a single conveyor to the refiners, the greatest improvements in production would be realized by interleaving the processing stages at the mixers; i.e. one mixer could be discharging product while the other mixer was mixing ingredients.

All earlier efforts to produce a control system for the mixing operation had been attempted using Microsoft DOS(r) and Windows(r) as the operating system and windowing environment. Attempts were made to use programs such as MS-Excel(r) and InTouch(r) as the control program and user interface. All of these early attempts proved to be very disappointing. The DOS/Windows approach was both highly unstable and almost completely incapable of controlling the system and was too slow to respond to the changes in the production equipment. The programs chosen to control the mixers were far too restrictive in their functionality and were not capable of controlling two mixers that were usually at different stages of a batch cycle.

A Siemens PLC provided low level control of valves and motors in the system. Control information was accessed through a serial line connection to the PLC. Serious problems were caused when the MS-Windows environment would preempt the PLC communications program. At best this resulted in very slow communication, as the link had to be reestablished. More often, the break resulted in loss of process data. When data was lost, the operator would have to run the system in manual mode for the rest of the cycle and the InTouch screens became a purely monitoring system. One of the consequences of these early attempts was that the operators found they were running the system in manual mode most of the time and so became quite familiar with the way the InTouch graphics operated. Management requested that if at all possible, the InTouch screens should be kept as part of any solution that we proposed.

Prev | Home | Next
Chocolate Mixing System | Up | Mixing System Solution

Copyright 1995-2002 by Cogent Real-Time Systems, Inc.