| 摘要 |
A control system for maintaining the diameter of drawn glass tubing includes signals from two diameter measuring means, one where the tube is hardened and one where the tube is still in the plastic state, the first signal being compared with a standard signal to give a third signal for comparison with the second signal, the resultant variations giving a signal used to vary the pressure in the interior of the tube in the plastic zone. As shown, tubing is drawn from a reservoir 11 of molten glass through the annular orifice between a tank 12 and bell 13 which is constantly provided with air pressure from a fan 20 to form the tubing. The diameter measuring means in the plastic zone comprise hollow pressure conducting tubes 14, 15 inside and outside the tube which transmit pressures to a differential pressure gauge and transmitter 16 which emits the second signal, proportional to the pressure difference, to a preset pneumatic pressure controller 18, any variations from the preset value operating a pneumatic motor valve 19 to adjust the internal pressure in the tubing in the internal zone by regulating the bleeding of air from the system. The controller 18 is variably preset from a diameter sensing unit 21 which gives the first signal to a controller 22 which is compared with a predetermined <PICT:0943305/C1/1> standard signal 23 to give the third signal which presets the controller 18. To avoid variations in this third signal due to only minor variations or a short length of defective tubing, the controller 22 is set to respond to low frequency variations in tubing diameter which controller 18 is set to respond to high frequency variations in pressure. A third sensing device may be used to give diameter variations after the tubing has cooled to room temperature and a signal therefrom may be used in place of the standard signal 23. The tubing gauge disclosed in Specification 905,307 may replace the tubes 14, 15 for measuring the diameter in the plastic zone.
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