| 摘要 |
An electrically operable power switch (2) is connected between a power supply (3) and a power consuming device (1). A safety circuit (4) is arranged to monitor at least one safety-related condition of the power consuming device (1), the safety circuit controlling the energisation of at least one relay (6) in dependence upon the monitored condition. A first set of contacts (5) controlled by the relay is connected to supply power to the safety circuit, and a second set of contacts (7) controlled by the relay is connected to enable or disable the power switch. The first set of contacts (5) comprises at least two contacts arranged to be switched simultaneously and connected in series such that the supply of power to the safety circuit (4) is maintained except during switching of the contacts. The safety circuit (4) comprises an energy storing circuit arranged to maintain the energisation of the safety circuit for a period of time at least as long as the period of time required for the first set of contacts (5) to switch, and the second set of contacts (7) is arranged so as to disable a power switch (2) if the safety circuit (4) is deenergised. |
