| 摘要 |
<p>1,184,543. Automatic temperature control systems. DUNLOP CO. Ltd. April 18, 1967 [April 23, 1966 (2)], Nos. 17856/66 and 17857/66. Heading G3R. A temperature control system for a de-icing heater having a resistance which varies with temperature comprises means for sensing changes in the heater resistance and a control means for reducing the power supplied to prevent the heater temperature rising above a determined level. The heater H is connected to a transformer voltage winding Vw and an opposing current winding I w which at the determined temperature reverse the phase of the secondary winding Sw output which through transistors Q1-Q3 and Q4-Q6, delays the firing angles of thyristors SCR1, 2 in proportion to the excess temperature. An over heat protective circuit, Fig.3, (not shown) comprises a transistor amplifier connected to winding Sw operating a relay which disconnects the supply and illuminates a warning lamp. In another arrangement voltages are derived from a heater having two sections of differing characteristics, Figs. 5 and 6 (not shown). A 3- phase star connected heater arrangement is described having thyristors in two mains leads, Fig. 7 (not shown). The output of winding Sw alternatively can be arranged through a variable ratio timer to cut-off the thyristors periodically for a determined time and an auxiliary circuit is arranged to operate at a higher temperature should the normal circuit fail. A low temperature circuit is also incorporated which at low temperatures periodically interrupts the supply when warming up the heaters. This circuit also incorporates thermistor detectors to cut-off the power at a determined thyristor temperature. An arcing detection circuit may be incorporated comprising three current transformers (T52-T54, Fig. 7, not shown) whose outputs are amplified in transistors (Q52-Q54, Fig. 9, not shown), and compared to cut-off power on inequality of current flow. This circuit is disabled if the inequality is due to an open circuit of one of the heaters.</p> |
