| 摘要 |
A radio frequency heater has a timing circuit operable to switch off the radio frequency signal after an elapsed time. The heater may be used for curing resin woodworking adhesives. Closure of a trigger switch 18 energises a relay coil 19 thereby closing contacts 14 and 21. Contacts 14 control application of current to an RC timing circuit 39-42 and Schmidt trigger 35, and contacts 21 control current supply via a delay circuit 44 to a solenoid coil 26 operating a switch controlling application of RF current to heating antennae. Delay circuit 44 ensures that current is not applied to the antennae before valves in an RF generator have warmed up; circuit 44 may have a similar form to the heating period timer. At the end of the timed heating period, trigger circuit 35 energises relay coil 29 which has normally open self-holding contacts 28 and normally closed contacts 22 in the circuit of solenoid 26. The heater is thus latched in an off state until switch 18 is opened then reclosed. The time has RF filter elements 12, 13, 16, 37 and may be screened against RF interference. <IMAGE> |
