Solid-state relays (SSR) have no moving parts or switching contacts allowing them to turn on and off faster and providing longer service lives than mechanical relays. They use semiconductors that activate when an input voltage is applied and are unlikely to be disturbed by environmental factors like shock, vibration, and electronic noise. General purpose solid-state relays are suitable for applications that are not exposed to hazardous or harsh conditions. Hazardous-location solid-state relays can be used in environments where flammable gases, liquids, flyings, and other combustible materials are present. Time-delay solid-state relays operate at specific times to turn power on and off to downstream circuits. Proportional controllers provide precise control of their output load and are used with single-phase applications that require fast or timely responses.