How to choose the relay correctly? One is to "know the enemy", that is, the object controlled by the relay must first have a thorough investigation and a thorough understanding of the nature and characteristics of the controlled loop and the requirements for the relay. Secondly, the various characteristics of the relay itself—principle, use conditions, technical parameters, structural and technological characteristics, specifications and models, etc., should be fully grasped and carefully analyzed; Comprehensive consideration of performance, availability and economy, so as to correctly select and use relays. The principle of correct selection of relays should be:

(1) The main technical performance of the relay, such as contact load, action time parameters, mechanical and electrical life, etc., should meet the requirements of the whole system;
 (2) The structure type (including installation method) and external dimensions of the relay should be able to meet the needs of the conditions of use;
(3) Economically reasonable.