Time relay is an automatic switching device that uses electromagnetic or mechanical principles to realize delay control. When the input action signal is added (or removed), its output circuit needs to pass a specified accurate time to produce a jumping change (or contact action). It is an electrical component used on a circuit with a lower voltage or a smaller current to switch on or off a circuit with a higher voltage and a larger current. At the same time, the time relay is also a control appliance that uses the electromagnetic principle or the mechanical principle to realize the delay control. There are many types of it, including air damping type, electric type and electronic type.