Relay
■ Overview
A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. Relays allow one low-power circuit to switch a second higher-power circuit which can be completely separated from the first. There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical. When input (eg. Voltage, ampere, temperature) reaches a preset value, a relay switches on or off the controlled circuit for adjustment, protection or changeover. Relays have advantages of quick action, good stability, long service life, small volume, and thus are widely used in equipment for power protection, automation, measurement, remote control, communications, etc.
■ Contact materials
Solid Type: pure silver or AgCdO, AgZnO or AgSnO2
Clad Type: specially engineered to save cost, typical materials are：
| AgCdO/Cu | Main composition is AgCdO; stable contact resistance. |
| AgNi/Cu | Cd-free, better arc erosion resistance than AgCdO, excellent anti-welding resistance under large current. |
| AgZnO/Cu | Higher thermostability than AgCdO, good electrical erosion resistance, nontoxic, and pollution-free. |
| AgSnO2/Cu | Most promising substitute for AgCdO material; excellent arc erosion resistance and anti-welding resistance. |
