Timing circuit: device and principle of work
To ensure the correct functioning of schemes of automatic control, often happens it is necessary to carry out operation of separate devices in the certain sequence with the soblyuyodeniye of the necessary intervals of the vremeyona. The timing circuit is for this purpose intended.
Timing circuits work or by the principle of the mechanical zamedyoleniye and are produced with primeneyoniy pendulums or elektrodvigayotel, or by the principle of elektroyomagnitny delay.
Mayatniyokovy relays give endurance of time within 1-15 sec., dvigatelyyony - up to 24 h, the relay with elektromagyonitny delay - up to 5 sec. Relays with electromagnetic zamedleyoniy produce only for work in control circuits of postoyoyanny current, this relay works by the principle of increase in time of the spayodaniye of the magnetic flux in magnityony system at shutdown of the relay.
Let's consider the device and the scheme of inclusion of the electromagnetic timing circuit of the RE-500 type which finds broad application at automation of the electric drive. This relay (fig. 1) consists of the coil 1, motionless magnitoprovoda2, anchors 3, the reguliyorovochny screw 5, traversy6 with interlock contacts and the sidehaul spring 4.
In the place of contact of the core with the anchor neyomagnitny laying is placed, it serves for prevention of possible sticking of the anchor to the core, in the absence of laying the otyobrasyvayushchy spring can not overcome the holding effort of the permanent magnetism of the core, and the relay will not be switched-off.
The anchor is involved under the influence of the flow created katushyoky 1, got on the core. On the anchor it is strengthened the traverse 6 with mobile contacts of bridge type which form the closing contacts of the relay.
For improvement of conductivity contacts are produced with sereyobryany pads.
Time from the moment of giving of the impulse for the relay coil to the srabayotyvaniye of contacts is called endurance of time of the relay. Reguliroyovany excerpts of time it is made within each type of the relay by change of thickness of non-magnetic laying and the tension of the sidehaul spring by means of the adjusting screw 5. The laying less tension of the spring, the more vyyoderzhka of time of the relay is thinner. Besides, the endurance of time for the relay of the vreyomena RE-511, RE-513 and RE-515 can be received the next ways: 1) short circuit of the coil; 2) shutdown of the relay coil.
Short circuit of the coil
At turning on of the RV relay the anchor priyotyagivatsya very quickly (time of the zayoryad of the relay 0,8 sec.). At shutdown the endurance of time is created, at the same time shutdown of the relay can осуществляться both by the rupture of the chain of the coil, and by its short circuit (fig. 2a). The endurance of time at the zakorachiyovaniye of the coil turns out for the sleyoduyushchy reason. (And, therefore, the srabatyyovaniye of contacts of the relay) it is necessary for falling away of the anchor that the flow in magnetic system disappeared or decreased up to the certain size, as occurs at the termination of the power supply of the relay coil, i.e. at its shutdown.
If to shunyotirovat the relay coil (for example, parallel inclusion of any contacts of other intermediate IS relay), then the self-induction vsledyostviye in the contour formed by the relay coil and konyotakty IS is supported some time current. Therefore, the magnetic flux and the attractive force of the anchor to the core will fade gradually too. R resistance has to be provided in the chain of the coil for prevention of the short zamyyokaniye (if in this chain there are no other consumers).
Shutdown of the relay coil
At shutdown of the relay coil it is possible to reach also slowed-down falling off of the magnetic flux in the magnetic conductor (fig. 2). The distinguished dampers are for this purpose applied. The damper is called the thick sleeve, vypolnenyony of copper or aluminum which is got on the general the serdechyonik with the involving coil. This sleeve creates the secondary circuit. At disappearance of the main magnetic flux at IS razyomykaniye in the sleeve current which according to the Lenz rule aims to support the main flow is induced. The more mass of the damper, the more endurance of time of the relay. The damper role odnoyovremenno carries out as well the aluminum basis of the relay. Razyolichny ranges of endurance of the relay (0,3 — 5,5 sec.) are reached due to application of additional removable dampers.
It must be kept in mind that the RE-500 relay is intended for the direct current, and alternating-current engines it turns on in the control circuit via rectifiers.Top