| 摘要 |
<p>832,428. Control of D.C. motors; controllers. B.T.U. (MANUFACTURERS) Ltd. Oct. 8, 1957, No. 31450/57. Class 38 (3). [Also in Group XXXV] An electric motor 1 which drives a fan for forcing air through a heat-exchanger into a space to be heated is connected in series with a resistor 2 adapted to be short-circuited by time-delay contacts 71 for a period after the motor has been switched-on so as to ensure that the motor is started and then operated at low speed. A thermostatic switch 3 is located in the space to be heated, contacts 31, 33 being engaged when the temperature falls, and contacts 32, 33 when it rises. A further thermostatic switch 4 prevents the motor from being started until the temperature of the heat-exchanger has risen to a predetermined value, whilst a time switch 5, renders the system inoperative during the night, for example. A manual switch 6 has alternative positions for " high-speed heating," " lowspeed heating " and " cooling," and, in the first and third positions of the switch, the resistor 2 is short-circuited so that full voltage is applied to the motor when the appropriate switches are closed. Thus, when the switch 6 is in its first position, the motor is energized to provide warm air when switches 4, 5, and contacts 31, 33 are closed. When the manual switch is in its third position, cool air is provided during the periods that switch 5 and contacts 32, 33 are closed. If the system is set for " low-speed heating " however, the resistor 2 is short-circuited by the contacts 71 only during the initial starting period. The time-delay unit 7 may comprise a bimetallic strip heated by a coil connected to terminals 72, 73. In a modification, the contacts 71 are part of an electromagnetic relay having coil 80 and change-over contacts 74. When voltage is applied to terminals 72, 73, a capacitor 75 is charged through rectifier 76 so that a timing capacitor 78 is charged through resistor 79. When the voltage across the capacitor 78 reaches a predetermined value, coil 80 becomes effective to open contacts 71 and change-over the contacts 74, whereby the capacitor 78 is discharged through resistor 81. The coil 80 is still energized however, through resistor 79 and the relay is held in its operated condition. As soon as the power supply is disconnected from the terminals 72, 73, the capacitor 75 discharges through resistor 79 and coil 80, so that the relay is quickly released.</p> |
