GB936050A - Improvements in or relating to process control apparatus - Google Patents

Abstract

936,050. Electric correspondence control. WEST INSTRUMENT Ltd. April 10, 1962 [April 17, 1961], No. 13802/61. Class 40 (1). An apparatus for controlling the duration of a process in accordance with the output from means 10 responsive to a physical characteristic such as temperature, comprises means comparing said output with a quantity which is periodically varied between values corresponding to an upper and a lower limit of the said characteristic at a rate to give two or more cycles of variation in the minimum treatment time, and a timing device such as motor 21 which operates only during periods when the magnitude of said output exceeds that of the comparison quantity. The duration of a process is varied in accordance with temperature within a range bounded by the minimum and maximum temperatures at which the treatment can be carried out, so that the duration is a maximum when the temperature is at its minimum value, and vice versa. The output from a thermocouple or a resistance thermometer 10 energizes a temperature controller not shown, and determines the position of a pointer 11 which moves over a scale 12, a corresponding member 17, and a contact 18 which co-operates with a contact plate 19 carried by a member 14. The member 14 is carried cyclically between the upper and lower scale values suitable for the process by a motor driven cam 15, the shape of which is determined by the required process temperature/duration relationship, and the periodicity of which is such that at least 20 cam revolutions are performed in the minimum permissible process time. A motor 21, which drives the programme disc of a process timer 22, is energized from a supply 20 and through switch member 17 only when the latter is " up-scale " of the swept pointer 13. Thus the timer will not be energized when the pointer 11 and member 17 are below the minimum value of the swept range of pointer 13 but once this minimum value is exceeded by the pointer 11, then the energization period of the timer will increase. The rotation of the programme disc thus integrates all those periods of time during which the pointer 11 is " up-scale " of the swept pointer 13 and after a predetermined rotation terminates the process by, for instance, effecting the removal of the object under treatment from the furnace.