A relay (English name: relay) is an electrical control device. It is an electrical appliance that causes the controlled quantity to undergo a predetermined step change in the electrical output circuit when the input quantity (excitation quantity) changes to the specified requirements. It has an interactive relationship between the control system (also called the input loop) and the controlled system (also called the output loop). Usually used in automated control circuits, it is actually an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit.
There are three basic forms of relay contacts:
1. The two contacts are disconnected when the moving-on (normally open) coil is not energized, and the two contacts are closed after energization. It is indicated by the pinyin prefix "H" of the ligature, and the letter "M" in the selection number of the permanent relay.
2. The two contacts of the movable-break (normally closed) coil are closed when the coil is not energized, and the two contacts are disconnected after energization. It is indicated by the hyphenated pinyin prefix "D", and the letter "B" in the selection number of the permanent relay.
3. Conversion type This is a contact group type. This kind of contact group has three contacts in total, that is, the middle is a moving contact, and the upper and lower are static contacts. When the coil is not energized, the movable contact and one of the static contacts are disconnected and the other is closed. After the coil is energized, the movable contact moves to make the original open into closed, and the original closed into the open state, reaching the converted state. purpose. Such contact groups are called changeover contacts. It is indicated by the pinyin prefix "z" of the word "zhuan", and no letter in the selection number of the permanent relay indicates the conversion type.