| 摘要 |
<p>726,200. Time switches; thermal switches. CART, P. Jan. 5, 1953 [Jan. 23, 1952], No. 314/53. Class 38 (5). A switch controlled conjointly by a timing device and by a thermostat influenced by the apparatus, e.g. a water heater, controlled by the switch, comprises, Figs. 1, 4, a synchronous motor 1 driving through a shaft 1<SP>1</SP> and a friction clutch (Fig. 3, not shown) a cam 3 having a pair of similar surfaces extending through 180 degrees connected by steps B, B'. The cam 3 is rotated through 180 degrees in a time (e.g. eight hours) which is slightly less than that available for energizing the water heater during the night. A pair of studs 14 on a contact-carrying arm 11 are held against the cam 3 by a spring strip 12, the contact 13 cooperating with a contact 8 on an arm 7 biased by a spring strip 10 against a screw 9 carried by the rod 6 of a thermostat. Thus as the temperature of the water heater increases, the thermostat tube 5 expands to raise the contact 8. When the motor 1 is started the studs 14 are at the foot of the steps B, B<SP>1</SP> and-unless the water heater temperature is excessively low-the contacts 8, 13 are open. The arm 11 is gradually raised by the cam 3 and eventually the contacts 8, 13 close to energize the water heater connected to terminals 17, 18. The thermostat may then function to open the contacts which are then closed again by the cam 3. A plate 19 is driven by the cam 3 through a spring strip 21 fixed to the latter and engaging the plate with its free end, a pin-and-slot connection limiting the relative movement possible between the plate and cam. When the cam has rotated through nearly 180 degrees the plate 19 is arrested by a spring arm 16 held in position against its own resilience by an armature 15 on the arm attracted by the field of the stator of motor 1. The friction clutch thus begins to slip and the cam 3 remains in the position where the studs 14 are at the feet of the steps B, B'. De-energization of the motor releases the armature 15 and permits the plate 19 to be moved by the strip 21 so that when the motor is next started to repeat the cycle the arm 16 engages the end of the plate and enables the cam to be rotated by the motor. In a modification, Figs. 5a 5b, the plate 19 is omitted and, instead, the cam 3 has a pair of teeth 23 which co-operate with the longer one of a pair of contact-carrying strips 22 insulatingly mounted on the arm 16. The contacts 22 complete the circuit to the motor 1 and are shunted by a resistance (Fig. 6, not shown). When the cam 3 has rotated 180 degrees as previously described, a tooth 23 engages the longer strip 22 to open the contacts 22 and stop the motor 1, the current through the shunting resistance being insufficient to drive the motor but sufficient to retain the armature 15. When the motor supply is interrupted the armature 15 is released and the contacts 22 re-engage. Hence when the motor is next energized to repeat the cycle the longer strip 22 engages the inclined trailing edge of the tooth 23 and the cam 3 may be rotated. According to another arrangement, Fig. 7, the contact 13 is raised throughout the cycle by a bimetal strip 30 heated by a coil 29 energized by a variable voltage tapped off from a potentiometer 25 by an arm 28 rotated through 360 degrees by the motor 1 for each cycle. A disc 31 with a single tooth 23 is rotated by the motor 1 to open contacts 22 as described with reference to Figs. 5a, 5b.</p> |
