1. Selection of voltage and current
The selection should be based on the supply voltage of the control circuit and the maximum current that can be output, and then be selected according to whether the voltage and current of the controlled circuit are DC voltage or AC voltage. First, the rated operating voltage must be considered. The operating voltage must not exceed 1.5 times the rated operating voltage, otherwise a large current will generate heat and burn the coil. The current delivered to the relay must be greater than the pull-in current to ensure that the relay can work stably.
2. Selection of contacts
To determine what form of contact is needed for the number of groups of controlled circuits, it should be selected after comprehensive consideration. The selection should also consider whether the relay is short-term and intermittent, 8-hour or long-term.
3. For control relays, the return coefficient is generally required to be below 0.4 to avoid the self-release of the power supply voltage in a short time.
Use and maintenance of relays
1. to consider the installation environment of the relay
Changes in ambient temperature and humidity can deform parts of the relay, change sealing and insulation parameters, and reduce the reliability of the relay. Corrosive gas, vibration, and shock will cause damage to the relay's coil, contacts, and casing. Vibration and shock will also cause the relay to malfunction.
2. Method to improve the load capacity of relay contacts
When the load capacity of the relay contact can not meet the requirements of use, it can not be solved by using several pairs of contacts in parallel, because it is almost impossible to close and open several pairs of contacts simultaneously. Intermediate relays or contactors should be used to expand the load capacity of the contacts.
3. Periodically check the moving parts and connecting parts
Check whether the wiring is loose and corroded; whether the moving parts are stuck; whether the live parts such as coils have accumulated dust; whether the insulation of the electrical parts is reduced; whether the contacts and electromagnetic system are clean and the movement is normal.
4. Measures to solve the virtual connection of contacts
The so-called "virtual connection" means that in the control loop, due to the change of the contact resistance of the relay contacts, the actual voltage across the controlled coil is lower than 85% of the rated control voltage, resulting in control failure. It is difficult to find the virtual connection of contacts. Therefore, increase the control voltage as much as possible; to control large-capacity contactors, use intermediate relays to improve reliability; when the control circuit requires high reliability, the rated control voltage of 220V and above should be used.