Select the type and parameters of the relay contacts according to the load
The contact directly connected to the controlled circuit is the contact system of the relay. Long-term practice in foreign countries and China has proved that about 70% of faults occur on the contacts. In addition to the close relationship between the structure and manufacturing factors of the relay itself, failure to properly select and use it is also one of the important factors. And most of the problems are caused by the user's actual load requirements being different from the rated load of the relay contacts.
1. Determine the contact combination form according to the control requirements, such as whether it is normally open or normally closed contact or changeover contact;
2. Determine the number of contacts and the number of groups according to the number of controlled circuits;
3. Determine the relevant parameters of the contact according to the nature of the load and the size of the capacity, such as rated voltage, current and capacity, and sometimes the requirements for contact resistance, jitter time, distributed capacitance, etc. need to be considered. Regarding the rating of contact switching, electromagnetic relays generally specify its nature and size. Its meaning refers to the magnitude of the current that the contact can switch within a specified number of actions and under a fixed voltage and frequency. This load value is determined by the structural elements of the relay. In order to facilitate assessment and comparison, only resistive loads are generally specified.