The industry is conscious of the importance of quality and this has contributed to the increasing use of instrumentation for the automatic control of process machinery and for monitoring and recording performance.
The cooker and the press may be operated at controlled loads by level control of the material in their feed tubes. The temperature of the hot air going into the direct dryer is generally maintained constant by automatic adjustments of the fuel supply. Automatic temperature control, and even automatic fire extinguishers are also available. Stable operation of the ventilation system may be maintained through pressure control of the air in the exit compartment. Pressure deviations may be corrected by manually or automatically adjusting the air shutter in the exhaust tube.
Stickwater concentrators may, in practice, be fully automated. The finally extracted concentrate, the solubles, is continuously controlled for constant viscosity and signals of deviations from the setpoint act on the extraction pump, the revolutions of which are steplessly variable. Alterations in the extracted volume will in turn be automatically compensated for in the individual stages of the plant as these are furnished with level controllers acting on the valves and on transfer pumps between the stages.
Great efforts are being made to effect continuous measurement of the moisture content in the finished fish meal and, based on this, to arrive at complete automation of the whole operation by use of Programmable Logic Control systems. This development will be followed with great interest.