Patent GB-1353070-A (GB)
Title: Control systems for furnaces or melting tanks
IPC: G05D23/19
Filed: 1971-10-21
Abstract: 1353070 Controls for glass melting furnaces CORNING GLASS WORKS 21 Oct 1971 [22 Oct 1970] 48962/71 Heading C1M [Also in Division G3] In an electrically heated vertical glass melting furnace, Fig. 2, mutually opposed pairs of lower glass contact electrodes 32A-32F, Fig. 4, are connected to respective supply circuits 36A-36C. The power supplied to each circuit is measured by watt measurers, or Hall effect devices 48A-48C whose outputs connected in series, representing the actual power supplied via the lower electrodes, is fed to modifier device 50. A thermocouple 58 provides an actual furnace temperature signal to a controller 62 whose set point dial 64 allows a desired temperature to be seen. The D.C. output of controller 62, which is so adjusted as to give zero voltage output at the centre of a defined temperature range, and give symmetrical control about such zero point, is linearly combined in modifier 50, with the lower electrodes actual power signal, controller 52 maintaining the resultant at a value set on dial 54 by controlling the output of supplies 36A-36C via power amplifier 56. Control of upper electrodes, Fig. 3 (not shown). -Upper electrodes (28A-28F) are supplied in the same manner as for the lower electrodes, the actual power signal from watt measurers 38A-38C power being fed directly to controller (40) to maintain the power supplied to the upper electrodes constant. Alternative arrangements of upper electrode control loop.-(1) Signals proportional to the actual power supplied to upper and lower electrodes (V<SP>1</SP>, V<SP>11</SP>), Fig. 6 (not shown), are provided by potentiometers (76, 78) and the upper electrode controller (40, 42) is now set to control upper electrode power until the corresponding error voltage (Ve) is zero. Thus the ratio of the powers dissipated in the upper and lower electrodes is kept constant. (ii) The signal representing the actual power supplied to the upper electrodes is fed to modifier (50A), Fig. 7 (not shown), of the same form as modifier 50, in which it is linearly combined with a signal from controller arrangement (84, 86) [dial (86) being set to zero] representing an error voltage (Ve) derived as for alternative (i) above. The linear combination provides an actual value control signal to upper electrode loop controller arrangement (41, 42), Fig. 3 (not shown).  Modifier device 50, see Fig. 5 (not shown).-The D.C. output from controller 62 opposes the D.C. for example battery supply (68), the potentiometer (66) being set such that (V2) is zero at the centre of the operating temperature range. Attenuator (70, 72, 74) is adjusted to set the degree of effect that the temperature signal is to have on the lower electrode power control loop. Glass melting furnace, Figs. 2, 4.-Perforated batch feeder 16 is continuously agitated to feed batch material 18, which forms the furnace cover, Molten glass 20 is continuously withdrawn through orifice 22 whose furnace opening is raised above that of sump orifices 26. The control system may be applied to a horizontal furnace with rear and front electrodes replacing the upper and lower electrodes, material being added from the rear. The furnace may be heated by a combination of flame and electrical heating.