The pulse relay is most widely used in the field of railway automation. Such a device commutes with its contacts networks and circuits of various capacities under loads of a different nature - inductive, capacitive, active, or combinations thereof. The relay windings can be connected to cable or overhead lines, rail circuits with high levels of interference of various kinds and subject to lightning discharges.
The impulse relay is used in systems and networks of railway automation mainly as a receiver of impulses of rail circuits, which control the rail lines on 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 movement of trains. The pulse relay is also installed both in unheated special relay cabinets and in relay rooms with appropriate heating.
Let us consider in more detail the device of such a device. The principle of operation of a pulse type relay and the design of the device are based on elements such as a permanent magnet, a coil with an armature with movable contacts inside, four pole tips of the magnetic circuit, and adjusting screws. The anchor is fixed on a metal base. The pulse relay of the plug type has a contact system consisting of fixed and movable 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 relay parts are located under a transparent cap with a handle.
A small-sized pulse relay is used as a track relay in rail pulse circuits operating on alternating current. Inside it there is a panel with a rectifier of four silicon diodes. This device has some disadvantages: a large mass and dimensions (more than two kilograms - this is a lot for a protective or regulatory type device).
Currently, an inexpensive relay with a changeover contact using a mercury magnetically operated reed switch (sealed contact) is used as the main relay in railway automation.
Reed switches are contact springs that are made of special magnetic material and placed in a glass ampoule. This ampoule is filled with an inert gas, or a vacuum is created in it to reduce the likelihood of sparking or corrosion of the contacts. A pulse relay with a sealed switching contact has its positive aspects, such as small dimensions, low cost, high speed, easy operation, high reliability. However, there are 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 a pulse relay with a reed switch, additional external heating is required.