Brief:
You have been commissioned by a multinational confectionery company to design a control panel for the colour coating process of a new production line, figure 1. Uncoated confectionery arrives along 8 separate conveyor belts. The confectionery then passes through coating (1), drying (2) and storage (3) stages, prior to packaging.
The process has the following monitoring and control requirements:
1) Colour Coating
a. Level indicators for each of the 8 coloured coating tanks. The levels must normally be maintained between 40-45 litres.
b. Controls for the inlet valves of each of the 8 coloured coating tanks, to regulate the levels of coating in the tanks. These require frequent and fine adjustment by the operator to vary the inlet flow.
c. Temperature indicators for each of the 8 coloured coating tanks. The temperature in the tanks is thermostatically (i.e. automatically) controlled to remain between 55-58ºC, but must be monitored. If the temperature falls outside the critical region (55-58ºC) the conveyer belt for that colour must be stopped manually as the coating will be substandard.
2) Drying
The coloured coating is dried by cool air, pumped through the 8 conveyor belts by a single large dryer. Although the dryer operation is automatic, a warning is needed on the control panel to indicate the rare situation in which a dryer failure occurs.
3) Storage Tanks
a. Temperature indicators for each of the 8 storage tanks. Temperature is important and thermostatically controlled to be between 2-15ºC. If the temperature moves outside this range for any conveyer the belt must be stopped by the operator.
b. Level indicators for the volume of confectionery in the storage tanks. The storage tanks are emptied automatically, but a warning is needed to indicate if the level rises above 80 litres. A belt will need to be stopped manually if the level exceeds 100 litres.2
4) Start Up and Shut Down
a. Controls to start and stop individual belts, as required by production circumstances.
b. Separate controls to start or stop the full process. These initiate an automated sequence that gives an orderly start-up or shut-down.
c. A control for stopping the full process in an emergency.
