| 摘要 |
<p>988,106. Temperature alarms. SPECIALTIES DEVELOPMENT CORPORATION. Dec. 21, 1962 [Jan. 3, 1962], No. 48374/62. Heading G4N. [Also in Division H3] A temperature responsive system comprises an element having an electrical resistance which varies in response to temperature variations from a normal value, a monitoring device responsive to a first predetermined value of resistance for giving an indication a predetermined time after the resistance passes through the value; and an inhibiting device which prevents the indication being given if the resistance reaches a second predetermined value in less than the predetermined time interval. As described, the system comprises a trigger circuit 12 in which transistor 32 is normally conducting and transistor 34 normally cut off. With a slow variation in resistance of the temperature sensitive element 10, due to a rise in temperature, the bias on the base of the transistor 32 changes to switch it off and charge capacitor 54. After a time determined by the capacitor charge circuit, transistor 34 becomes conducting operating relay 35 to initiate an alarm over contacts 52 and to open contacts 72. A further rise in temperature switches off transistor 55 in a second trigger circuit 14, but transistor 56 is prevented from conducting by the open contacts 72 in its collector circuit. With a rapid change in resistance of element 10, due to a fault condition, trigger circuit 14 switches before relay 35 operates and transistor 56 conducts clamping the base of transistor 34 so that relay 35 will not operate and no alarm is initiated.</p> |
