﻿ Electromagnetic relays: types, device and principle of work

# Kinds of electromagnetic relays

The relay is the element of the automatic device which at impact on its entrance of the external physical phenomena skachkoyoobrazno accepts value of output size.

Device of the electromagnetic relay.

These values, most often, output size has 2: for example, in the elektroyomagnitny relay of 2 steady conditions of contacts - closed and opened.

The electromagnetic relay reacts to change of any certain parameters short circuit or razmykayoniy the contacts

Contacts of the relay join in the chain which
exercises control or control of the devices which are switched on in the power chain for switching (for example, exercises control of contactors and др).

Principle of operation of electromagnetic relays.

Relays can work under the influence of the most different faktoyor: electric current, light energy, liquid pressure or gas, fluid level, etc.

On the way of accession distinguish primary, secondary and intermediate relays.

Primary relays turn on directly in the chain the upravleyoniya.

Secondary relays turn on through measuring transforyomator of current or tension.

Intermediate relays work from executive bodies of other relays and intend for the usiyoleniye and reproduction of the signal, i.e. distribution of impact on several chains.

Key parameters of the relay are:

• ratings - current, tension, time and other sizes which relays are expected;
• the operation size, i.e. that value of parameter (current, tension, time and so forth) at which there is the automatic operation of the relay; the relay reacts to that parameter on which it was manufactured;
• relay setting - value of size of operation at which this relay is adjusted (the relay has the quantity of the settings fixing operation size in certain limits).

Figure 1. Electromagnetic relay.

Electromagnetic relays are characterized by the following osnovyony parameters:

• tension (current) of retraction, i.e. the smallest znacheyoniy tension (or current) on relay coil clips, at koyotory the anchor is involved;
• tension (current) of falling away - the greatest value of tension (or current) on relay coil clips at which there is the falling away of the anchor;
• in coefficient of return of the relay - the relation of tension (current) of falling away to tension (current) of retraction.

Electromagnetic relays on response time (tcp) happen: inertialess (tcp <0,001 sec.); high-speed (tcp <0,05 sec.), normal (tcp = 0,05 +-0,15 sec.); slowed down (tcp = 0,15 +-1 sec.) and the timing circuit which have time srabatyvayoniyatsr> 1 sec., and it is possible to regulate it.

The relay consists usually of 3 elements: 1) perceiving, 2) intermediate and 3) executive.

1. Perceiving (sensitive) reacts on vkhodyony parameter and will transform it to physical quantity, neobkhoyodimy for operation of the relay; the sensitive elemet is, the nayoprimer, the relay coil.
2. The intermediate element compares the transformed size to the standard. And on reaching the preset value transfers the vozdeyyostviye of the perceiving element to executive. Promezhutochyony components of contact relays are the counteracting springs and dampers. Dampers are used to calm of fluctuations of mobile parts, and in the timing circuit - for the polucheyoniya of the set endurance of time.
3. The effector influences the managed chain; executive components of contact relays are contacts.

Figure 2. The MKU-48 relay executed in the casing.

Let's consider the device of the electric relay working by the electromagnetic principle (fig. 1). The relay consists of sleduyuyoshchy main parts: the anchor 3 which is the mobile part, the core 2 which is the motionless part of the relay coil l got on the magnetic conductor core; the closing contacts 6, the 5th the disconnecting contacts of the spring 7.

At turning on of the coil the anchor of the relay is attracted, and the rod, soyediyonenny with it, 4s metal bridges closes or disconnects the corresponding contacts.

The low-current electromagnetic relays used earlier only in the field of communication find all bolyyoshy application in automatic equipment. This results from the fact that slabotochyony (telephone) relays have the pin count several times bigger, than in normal electromagnetic relays; it allows to reduce the total quantity of the relay in the scheme. Besides, such relays consume small currents thanks to what they can work with datchiyoka which are not expected big currents (for example, poluproyovodnikovy thermo - and photoresistance).

Let's consider 2 types of the relay which found the most mass application.

The RPN relay of the direct current (the relay flat normal) is the electromagnetic one-bobbin relay with the flat core. It is intended for switching of electric circuits in razyolichny schemes of stationary devices. Current of operation of these relays is very small - about several tens milliampere. The package of contact units of the relay consists of one or several groups, each of which consists, in turn, of the set of contacts (from 2 to 5); combinations of contacts can be the most different. External wires are connected to the ends of tails of springs by means of soldering.

For alternating current circuits RPP relays of the analoyogichny device are issued.

Figure 3. The scheme of the polarized relay.

The MKU-48 relay represents the multicontact relay. Konyostruktivno relays in the casing and without casing are issued. External wires are connected to the relay without casing by means of soldering. Contact units of the relay are carried out with different kombinayotion of contacts. For example, the relay for alternating current of napryayozheniy 220 V is produced with the pin count from 2 to 8; at the same time relays with 2, 4 and 8 closing contacts are issued; with 2 zamyyokayushchy and 2 disconnecting contacts; with 4 disconnecting konyotakta, etc.

The working current of the relay is small: for some relays it makes 0,0045 A. Power consumption of the relay> or = 5 W. On rice 2 pokayozano the MKU-48 relay device with the casing.

The polarized relay represents the electromagnetic relay at which the direction of the peremeyoshcheniye of the anchor depends on the direction of the magnetizing current. Unlike the normal electromagnetic relay, poyolyarizovanny has 2 directions of travel of the anchor; it is in addition supplied with permanent magnets.

Key diagram of the konstrukyotion of the polarized relay of the predstavleyon in fig. 3 Main parts are the magnetizing coil 4 creating the magnetic flux of Fe in the steel core 5 and constant magyonit 3, the forming magnetic flux of Fp. The magnetic flux of Fe passes through the steel mobile anchor 2 and branches on 2 flows of Fe:2, one of koyotory matches, and another is opposite in direction to the magyonitny flow of the permanent magnet. On the end of the anchor there is the average contact which is becoming isolated depending on polarity of the pilot signal in magnetizing coils, with the left or right motionless contacts 1.

In the absence of the pilot signal and, therefore, the potoyok of Fe, on the anchor set to neutral position deystyovut identical attractive forces at the left and on the right.

If to give in the relay winding the pilot signal in the napravleyoniya, shown in the drawing, then in the right rod of the magnet flows and Fp will develop as they will match, and the resulting flow will increase:

in the left rod magnetic fluxes will be subtracted:

and the general flow in the right rod will turn out more magnetic flux in the left rod (Ф'> F"). As a result the anchor of the relay priyotyantsya to the right and will close the right contact. If to change the signal polyaryonost, then the anchor of the relay will be thrown on the left contact.

For those whom more complete information interests you can download or esteem  on the website "Reference Book on Low-current Relays".