There are many types of time relays, and the following aspects should be considered when selecting them:
(1) Current type and voltage level For electromagnetic damping and air damping time relays, the current type and voltage level of the coil should be the same as those of the control circuit; for motor type and transistor type time relays, the current type and voltage level of the power supply should be Same as that of the control circuit.

(2) Delay mode The delay mode is selected according to the requirements of the control circuit, namely the power-on delay type and the power-off delay type.
(3) Contact type and quantity The contact type (delayed closing or delayed opening) and quantity are selected according to the requirements of the control circuit.
(4) Delay precision electromagnetic damping time relay is suitable for occasions with low precision requirements, and motor-type or electronic time relays are suitable for occasions with high delay precision requirements.
(5) Operating frequency The operating frequency should not be too high, otherwise it will affect the electrical life and even cause the delay action to be out of tune.