| 摘要 |
949,784. Thermal switches; control of A.C. motors. TEXAS INSTRUMENTS Inc. May 20, 1960 [July 29, 1959], No. 17951/60. Headings H2B and H2J. In a switch similar to that of Specification 941,873 a snap-acting thermally responsive electrically conductive member is mounted in cantilever fashion. A normally-closed contact 82 is mounted on a bifurcated bimetal strip 70 connected by its two legs to terminals 30 and 40. Upon heating, the strip 70 bends downward to open contacts 82, 24 and, if the heating current continues, then pushes an insulating button 100 on a spring blade 90 to close contacts 98, 44. When used as a start relay for a split-phase motor, the start winding is connected between terminals 20 and 40 and the main winding between terminals 30 and 40. Thus, both the starting current and the main current flow through the bimetal element 70 until the contacts 24, 82 open, when the main current only continues to flow therethrough. Continuance of this main current causes contacts 44, 98 to close and short out the bimetal element 70 to protect it from overheating. When the element 70 cools, it allows the spring blade 90 to rise, and since the main current is still flowing, the contact 98 continues to cycle, maintaining the bimetal element 70 just above the reset temperature. The operating temperature can be adjusted by turning screw 60 to move the terminal 40 (and contact 44) longitudinally and thus vary the tension of the bowed snap-action bimetal leg 76. By setting the operating temperature high, the switch is made relatively independent of ambient temperature changes. |
