A hoist system for critical loads incorporates improved safety technology
to monitor various possible fault conditions. For example, a
command-not-operated function causes braking of the hoist when an encoder
detects one of a group of conditions including a lack of load movement
when a movement command is issued by the operating system, failure of
encoder feedback, or failure of a control circuit. An uncommanded motion
function also causes braking of the hoist when an encoder detects one of
a group of conditions including load movement without a movement command
issued by the operating system, or reverse directional movement of the
load from a directional movement command input by the operating system.