Patent GB-1319468-A (GB)
Title: Temperature control systems
IPC: C03B7/06
Filed: 1970-09-25
Abstract: 1319468 Automatic temperature control CORNING GLASS WORKS 25 Sept 1970 [26 Sept 1969] 45719/70 Heading G3R  An automatic control system maintains the temperature of molten glass in a forehearth 10 at a predetermined temperature and in addition ensures that the temperature in each half of the melt (i.e. as heated by gas burners 11a 11b respectively), has the same value or alternatively that the temp difference has a predetermined value or is within a predetermined differential temp range there being a "dead band, " eg determined by operational amplifiers, within which no control is effected. Drive units 29a, 29b each having forward and reverse windings, position valves 30a, 30b respectively, to control the burners' heat output in accordance with signals from the control system. Potentiometers (not shown) on respective drive units signal back to a comparator unit 28 the degree of opening of a respective valve. A radiation pyrometer 13 senses the melt temperature and its electrical output is compared with a pre-set desired value in a unit 20 the amplified error signal output of which is fed to a controller 22. The controller includes relays K3 K4 the contacts of which under equilibrium conditions i.e. when the error signal is zero, are opened and closed intermittently at equal mark/ space ratios. If the melt temperature is too high the error signal is such that K3 passes longer current pulses than K4, and vice-versa. The pulses from K3 are fed to the reverse windings of the drive units 29a 29b via contacts 40, 41 and 38, 39 of relays K2, K1 respectively, in the comparator unit 28, while the shorter pulses from K4 are passed to the forward windings via the remaining relay contacts. Thermocouples 12c, 12d sense the temperature of respective halves of the melt and their amplified outputs are fed to the summing junction of an operational amplifier 26a together with an adjustable bias voltage from a potentiometer 32. If it is desired that there should be no temperature difference then the bias is omitted but if one side of the pool of molten glass is to be at a higher temperature than the other the bias is pre-set accordingly to the desired temperature differential. The output of 26a is fed to a proportional controller 27 and to a differential amplifier unit 26b (which may comprise four separate differential amplifiers two of which are used as limiters to prevent control action above and below pre-set positive and negative levels respectively). The output of 26b is fed to the comparator 28 together with the valve position signals from the drive unit pots. If the temp sensed by thermocouple 12c exceeds that sensed by 12d, or alternatively if the actual temperature differenetial differs from the desired value thereof, a resultant signal, is produced which energizes relay K2 thereby opening its contacts 40, 41 and 42, 43. Thus pulses will be supplied only to the forward winding of drive unit 29b and the reverse winding of 29a. Valves 30a 30b will therefore be driven toward their closed and further open positions respectively until the pre-set desired conditions are re-established.