There are three basic forms of relay contacts

(1) The dynamic closing type (normally open, H-type) coil is disconnected when the two contacts are disconnected, and the two contacts are closed after the power is turned on. It is represented by the pinyin prefix "H" of the word "he".
(2) The breaking type (normally closed, D-type) coil is not powered on when the two contacts are closed, and the two contacts are disconnected after the power is powered on. It is represented by the phonetic prefix "D" of the word "broken". [6]
(3) The conversion type (Z type) is the contact group. This contact group has a total of 3 contacts, that is, the middle is a moving contact, and the upper and lower are a static contact. When the coil is not energized, the moving contact is disconnected from one of the static contacts, and the other is closed; After the coil is powered on, the moving contact moves, so that the original disconnected state is closed, and the original closed state is disconnected, to achieve the purpose of conversion. Such a group of contacts is called a transfer contact. It is represented by the pinyin prefix "Z" of the word "turn".