| 摘要 |
<p>1,140,043. Control systems for electricallyheated apparatus. SIEMENS ELECTROGER€TE G.m.b.H. 2 March, 1966 [2 March, 1965], No. 9241/66. Heading H2H. An electrically-heated device, e.g. a hotplate element 1, is controlled by a rectifier bridge 2 and semi-conductor controlled rectifier 3 whose firing instants (and hence the temperature of the element 1) are determined by the setting of the R.C. network 5 of a conventional oscillator 4, which is detuned by a resistor 6 to allow continuous energization of the element 1 up to a temperature in excess of the desired (set) temperature. When the excess temperature is reached, a voltage divider including a temperature sensitive resistor 8 causes firing of a semi-conductor controlled rectifier 7, which short-circuits the resistor 6 to allow the oscillator 4 to control the element 1 at a lower power level sufficient to maintain the desired temperature. Resistor 6 may be omitted and the capacitive part of the network 5 shorted out by the contact (10) of a relay (11) until the latter is energized at the excess temperature, Fig. 3 (not shown). The oscillator may be replaced by a transistorized phaseshifter (14) having part of its capacitance bridged by the semi-conductor rectifier 7, Fig. 4 (not shown), or having a resistor bridged by the relay contact, Fig. 5 (not shown), this last embodiment including protection against overheating in the form of two positive temperature coefficient resistors which operate at different temperatures to successively decrease the power. If a cold pot is applied to the element 1 when at its desired temperature, the supply may be temporarily interrupted, automatically or manually, to reset the control circuit and so permit continuous energization to be resumed.</p> |
