Automatic plant shutdown equipment

Control equipment for industrial plant operating from a main power source and having a first control operable to connect said plant to said main power source and a second control operable at intervals during the working of said plant, said equipment comprising:

• a first detector coupled to detect the operation of said first control and operable to provide an output indicative thereof;
• a second detector coupled to detect the operation of said second control and operable to provide an output indicative thereof;
• a timer unit, coupled to receive said outputs from said first and second detectors and comprising a first timer operable to commence a first timing operation in response to the receipt of said output from said first detector and in response to the receipt of said indication from said second detector, and operable to provide a first output indicative of said first timing operation not having endured for longer than a first predetermined period;
• a first relay switch, operable to connect said plant to said main power source if and only if said timer unit is in the course of providing said first output, said first predetermined period being longer than the maximum interval between successive operations of said second control,
• whereby, if said plant is being worked and said second control is being operated, said plant remains connected to said main power source but if said equipment ceases to be worked and said second control ceases to be operated, said plant is shut down by disconnection from said main power source.