Impulse relay is most widely used in the field of railway automation. Such a device switches with its contacts networks and circuits of various capacities under loads of a different nature - inductive, capacitive, active, or combinations thereof. Relay coils can be connected to cable or overhead lines, track circuits, which have high levels of various kinds of interference and are subject to lightning discharges.
The impulse relay is used in systems and networks of railway automation mainly as a receiver of impulses of track circuits that control rail lines at stages and stations. In difficult and unstable conditions, the main task of this device is a clear and reliable trouble-free operation in the field of telemechanics and railway automation to ensure the safety of work and train traffic. The impulse relay is also installed both in unheated special relay cabinets and in relay rooms with appropriate heating.
Let's consider in more detail the device of such a device. The principle of operation of the pulse type relay andthe design of the device is based on such elements as a permanent magnet, a coil with an armature placed inside with moving contacts, four pole pieces of a magnetic circuit, and adjusting screws. The anchor is fixed on a metal base. The plug type impulse relay has a contact system consisting of fixed and moving contacts. Such a system is designed for several tens of millions of switching operations at a current of up to several amperes and a voltage of several tens of volts. All parts of the relay are under a transparent cap with a handle.
Small-sized impulse relay is used as a travel relay in track impulse circuits operating on alternating current. In it, inside the case, there is a panel with a rectifier of four silicon diodes. Such a device has some drawbacks: a large mass and dimensions (more than two kilograms is a lot for a protective or regulatory type device).
At present, an inexpensive relay with a changeover contact using a mercury magnetic reed switch (sealed contact) is used as the main relay in railway automation.
Reed switch are contact springs made of a special magnetic material and placed in a glass ampoule. This ampoule is either filled with an inert gas or vacuumed to reduce the chance of sparking or corrosion of the contacts. An impulse relay with a changeover sealed contact has its positive aspects, such assmall size, low cost, high speed, easy operation, high reliability. However, there are also some disadvantages. For example, such a relay is difficult to use in winter due to the effect of low temperatures on mercury. Therefore, for a device such as an impulse relay with a reed switch, additional external heating is required.
