| 摘要 |
<p>1293132 Automatic temperature control systems GULTON EUROPE Ltd 11 Nov 1969 [12 Nov 1968] 53660/68 Heading G3R In a temperature control system in which an error signal plus P.I. or P.I.D. terms provides a first output signal to control heating power, when the heating power is less than a determined part of the maximum e.g. 20%, a second output signal derived from the first signal controls cooling power incrementally from a minimum to a predetermined level as the heating power falls. The cooling power may rise to a maximum value as the heating power falls to zero, or the cooling power may increase to a maximum outside the range of heating values. Where cooling power requirement is greater than that of the heating, the arrangement may work oppositely, so that the heating signal is generated in the lower ranges of the cooling power signal. The signal characteristics may be linear or non linear and may be artificially adjusted to a desired pattern. In a plastics processing machine 10, a signal from 9 thermocouple 12 is applied together with a set point signal 19 to a comparator 18 which is connected to a three term controller amplifier 20 which through a pulse generator fires a thyristor arrangement. The thyristors may be controlled with variable angular delay, or proportional groups of complete half cycles may be passed through a heater 11. The output from amplifier 20 is in the form of pulses substantially equal to and synchronised with pulses of mains frequency in a manner known per se e.g. as disclosed in Specification 1021425. The pulses are also fed to a pulse counter and diode pump 25, detailed in Fig.4 (not shown) which provides an input proportional to heating power to an integrator 26 having an output current varying linearly e.g. 0-10mA in a manner inversely to heating power, which is applied to a motor 28 actuating a valve 15 coupled to a feedback potentiometer (not shown) connected in a positional feedback circuit in unit 27. Amplifier 26 also actuates a fan motor relay which energizes a fan just as the amplifier output departs from zero. An over temperature alarm 71 is energized on failure of the cooling system and another signal may be provided when the cooling is at a maximum value to indicate that the range of operation is incorrect. The circuit given in Fig.4 (not shown) provides zero output at the determined level, e.g. 20% heating power and maximum output at zero heating but other ranges are envisaged in the Specification. The circuit has a time constant of 20 seconds hence gives a steady output for intermittent input. Other types of controller e.g. pneumatic may be employed and on/off proportional control may be used in place of the continuous proportional control described.</p> |
