|Definition:|| equipment used to prevent unsafe operation, protect personnel, and prevent hazards
Note 1 to entry: Interlocks may be single-channel, double channel or multi-channel.
Note 2 to entry: Single-channel interlocks use a single channel of sensors, logic units and an actuation item such as a contactor or relay.
Note 3 to entry: Double-channel interlocks use two channels of equipment and sensors, arranged so that each channel is capable, on its own, of preventing the unsafe condition or state. The channels may consist of two sets of essentially identical equipment. An alternative is two different channels which perform the interlock functions differently, or two similar channels, one in normal operation and the other in backup operation to prevent an unsafe condition or state if the first channel fails.
Note 4 to entry: Multi-channel interlocks use several channels of equipment and sensors. They are arranged so that each channel is capable, on its own, of preventing the unsafe condition or state. One failed channel cannot block actions which prevent unsafe conditions or states. Use of multi-channel systems can provide benefits such as allowing on-line maintenance and avoiding the need for a channel bypass.