Definition of finder relay: finder relay is an automatic control device whose output will jump when the input (electrical, magnetic, acoustic, optical, thermal) reaches a certain value. Finder relay is a commonly used control device in our life. In a popular sense, it is a switch that turns off or on when conditions are met. The switching characteristics of finder relay are widely used in many control systems, especially discrete control systems. On the other hand, because the electronic circuit is designed and used for a certain purpose, it ultimately needs to be connected with some more or less.

Finder relay is an electronic control device, which has a control system (also known as input circuit) and a controlled system (also known as output circuit). It is usually used in automatic control circuits. In fact, it is an "automatic switch" that uses a small current to control a large current. Thus, it plays the role of automatic regulation, safety protection and circuit conversion in the circuit.

Finder relay contacts have three basic forms:

1. The two contacts of the dynamic closing type (type H) coil are open when not energized and closed when energized. It is represented by the phonetic prefix "H" of the compound word.

2. The two contacts of the dynamic break type (type D) coil are closed when it is not powered on, and the two contacts are disconnected when it is powered on. It is represented by the hyphen speech prefix "d".

3. Conversion type (Z type) this is the contact group type. This contact group has a total of three contacts, namely a moving contact in the middle and a static contact in the upper and lower parts. When the coil is not powered on, the moving contact and one of the static contacts are disconnected and the other is closed. After the coil is powered on, the moving contact moves to make the originally disconnected contact close and the originally closed contact become disconnected, so as to achieve the purpose of conversion. Such contact groups are called transfer contacts. It is represented by the phonetic prefix "Z" of the word "Zhuan".