Relays operation pdf

Note that the above only applies to a series- parallel realization. In a later section it will be n shown that the function2Xk and its negative may be realized with 4 n-1 elements using a more general type of circuit. The function requiring the most elements using any type of circuit has not as yet been determined. The negative, of any network mayv be found by De Morgan's theorem, but the network must first be transformed into an equivalent series-paralael circuit unless it is already of this type.

A theorem will be developed with which the negative of any planar two-terminal circuit may be found directly. As a coro- llary a method of finding a constant current ci'rcuit equivalent to a given constant voltage circuit and vice versa will be given.

Let N represent a planar network of hinder- ances, with the function Xab between the terminals a and b which are on the outer edge of the network. For definiteness consider the network of Fig. Now let M represent the dual of N, as found by the following process; for each ccntour or mesh of N assign a node or junction point of M. For each element of N say Xk, separating the contours r and s there corresponds an element X' connecting the k nodes r and s of M. The area exterior to N is to be considered as two meshes, c and d, corresponding to nodes a and d of M.

Thus the dual of Fig. For the network of Fig. Incidentally, the easiest method of finding the dual of a network whether of this type or an impedance network is to draw the required network superimposed on the given network. Now, if Xab : 0, then there must be some path from a to b along the lines of N such that every element on this path equals zero. Bat this path repre- sents a path across M dividing the circuit from c to d along Wliich every element of M is one.

To open a relay a series connection is opened. The general con- stant-voltage system is shown in Fig. In a constant- current system the relays are all in series in the line. To de 4operate a relay, it is short circuited. The gen- eral constant-current circuit corresponding to Fig. If the relay Yk of Fig. If this is true for all the relays, we shall say that the constant-current and constant-voltage systems are equiv- alent.

The above theorem may be used to find equivalent circuits of this sort. For, if we make the networks N and M of Figs. X2 Constant I current M N source. Xn Yn Fig. As ha s been shown, any function represents explicitly a series-parallel circuit. The series-parallel realiza- tion may require more elements, however, than some other circuit representing the same function. In this section a method will be given for finding a cir- cuit representing a certain type of function which in general is much more economical of elements than the best series-parallel circuit.

This type of func- tion frequently appears in relay circuits and is of much importance. A function of the n variables X1 , X 2. Since any permutation of variables may be obtained by successive interchanges of two variables, a necessary and sufficient condition that a function be symmetric is that any interchange of two variables leaves the function unaltered.

We now give a theorem which forms the basis of the method of synthesis to be described. Theorem: The necessary and sufficient condition that a function be symmetric is that it may be speci- fied by stating a set of numbers a,, a2, This follows easily from the definition. For the ex- ample given these numbers are 2 and 3. For every selection of a set of numbers from the numbers 0, 1, 2, These give the "functions"l and 0 respectively.

The set of numbers a1 , a , The theorems concerning combinations of symmetric functions are most easily stated in terms of the classes of a-numbers.

For this reason we denote the class of a-numbers by a single letter A. If two differ- ent sets of a-numbers are under consideration they will be denoted by A1 and A 2. Thus 86 1, 2, 3. The negative of a set of a-numbers will be written A' and means the class of all the numbers from 0 to- n inclusive which are not members of A. Thus if A is the set of numbers 2, 3, and 5, and n s 6 then A' is the set of numbers 0, 1, 4, and 6. Theorem: Sn A' S A These theorems are useful if several symmetric functions are to be obtained simultaneously.

Before we study the synthesis of a network for the general symmetric function consider the circuit a-b of Fig. This circuit represents 83 2. If X 1, the line stays on the level marked 0; next hinderances X and Xf are encountered. If X 2 is aero, the line is switched up a level; if not, it stays at the same level. Finally reaching the right hard set of terminals the line has been switched up to a level representing the number of variables which are dqual to zero.

Terminal b is connected to level 2 and therefore the circuit a-b will be completed if and only if 2 of the variables are zero. Thus the function 33 2 is represented. If 33 0,3 had been desired, terminal b would be connected to both levels 0 and 3. In figure 24 certain of the elements are evidently superfluous.

The circuit may be simplified to the form of Fig. NOTE: All sloping lines have hinderance of the variable written below; horizontal lines have negative of this hinder- ance. Xn Fig. In certain cases it is possible to greatly simplify the circuit by shifting the levels down. Suppose the function S6 0,3,6 is desired. The zero level then also becomes the 3rd level and the 6th level. Eliminating unnecessary elements the circuit of Fig. This device is especially useful if the a-numbers form an arithmetic progression, although it can sometimes be applied in other cases.

The functions n n Z 2 Xk and 12Xk t which were shown to require the Must 1 1 elements for a series-parallel realization have very simple circuits when developed in this manner. The function EXk is, of course, just the opposite. They will be recognized as the familiar circuit for con- trolling a light from n points.

It can be shown that for any given selection of a-numbers at least n of the elements will be super- fluous. It follows that any symmetric function of n variables can be realized with at most n elements. Equations from Given Operating Characteristics. In gen- eral, there is a certain set of independent variables A, B, C, There is also a set of dependent variables x, y, z It is required to find a network which gives for each possible comblination of values of the independent variables, the correct values for all the dependent variables.

The following principles give the general method of solu- tion. Additional dependent variables must be introduced for each added phase of operation of a sequential system. Thus if it is desired to construct a system which operates in three steps, two additional variables must be introduced to represent the beginning of the last two steps. These additional variables may represent contacts on a stepping switch or relays which lock in sequentially.

Other forms of relays which may be necessary will usually be obvious from the nature of the problem. The hinderance equations for each of the dependent variables should now be written down. These functions may involve any of the variables, dependent or independent, including the variable whose function is being determined as, for example, in a look in circuit. The conditions may be either conditions for operation or for non-operation.

Equations are written from operating characteristics according to Table II. To illustrate the use of this table sup- pose a relay A is to operate if x is operated and y or z is operated and x or w or z is not operated. It does not, of course, matter if the same conditions are put in the expression more than once--all super- fluous material will disappear in the final simplifi- cation.

The expressions for the various dependent variables should next be simplified as much as possible by means of the theorems on manipulation of these quan- tities. The switch or relay The switch or relay X X is not operated. Morgan's Theorem. The resulting circuit should now be drawn. Any necessary additions dictated by practical considerations such as current carrying ability, so- quence of contact operation, etc. It is possible to perform complex mathematical operations by means of relay circuits.

Numbers may be represented by the positions of relays or stepping switches, and interconnections between sets of relays can be made to represent various mathematical opera- tions. In fact, any operation that can be completely described to the required accuracy if numerical in a finite number of steps using the words "if'," "or," "and," etc.

The last two examples are illustrations of mathematical operations accomplished with relays. A Selective Circuit A relay A is to operate when any one, any three or when all four of the relays w, x, y, and z are operated.

It requires 20 ele- ments. A still fur- ther reduction may be made with the following device. First writes A - 14 0,2 This has the circuit of Fig.

What is required is the negative of this function. This is a planar net- work and we may apply the theorem on the dual of a net- work, thus obtaining the circuit shown in Fig. There are to be 5 push button switches available on the front of the lock. These will be labeled a, b, c, d, e. To operate the lock the buttons must be pressed in the following order - c, b, a and c simultaneously, d. When operated in this sequence the lock is to be unlocked, but if any button is pressed incorrectly an alarm U is to operate.

To relock the system a switch g must be operated. To release the alarm once it has started a switch h must be operated.

This being a sequential system either a stepping switch or additional sequential relays are required. Using sequential relays let them be denoted by w, x, y, and z corresponding respectively to the correct sequence of operating the push buttons. An additional time delay relay is also required due to the third step in the operation. Obviously, even in correct operation a and c cannot be pressed at ex- actly the same time, but if only one is pressed and held down the alarm should operate.

Therefore assume an auxiliary time delay relay v which will operate if either a or c alone is pressed at the end of step 2 and held down longer than time a the delay of the relay.

There are to be thirteen lights, marked 0, 1, Posi Akmal. Ali A. A short summary of this paper. Download Download PDF. Translate PDF. There is only one current operated element in the relay, no voltage coil etc. When normal current flows through this coil, the magnetic effect generated by the coil is not sufficient to move the moving element of the relay, as in this condition the restraining force is greater than deflecting force.

But when the current through the coil increased, the magnetic effect increases, and after certain level of current, the deflecting force generated by the magnetic effect of the coil, crosses the restraining force, as a result, the moving element starts moving to change the contact position in the relay. Although there are different types of over current relays but basic working principle of over current relay is more or less same for all. Instantaneous over current relay.

Definite time over current relay. Inverse time over current relay. Inverse time over current relay or simply inverse OC relay is again subdivided as inverse definite minimum time IDMT , very inverse time, extremely inverse time over current relay or OC relay. Instantaneous Over Current Relay Construction and working principle of instantaneous over current relay quite simple. A piece of iron is so fitted by hinge support and restraining spring in the relay, that when there is not sufficient current in the coil, the NO contacts remain open.

When current in the coil crosses a present value, the attractive force becomes sufficient to pull the iron piece towards the magnetic core and consequently the No contacts are closed. The preset value of current in the relay coil is referred as pick up setting current. This relay is referred as instantaneous over current relay, as ideally, the relay operates as soon as the current in the coil gets higher than pick up setting current.

So it eliminates the arching problem. The EMR conducts the entire load current without any loss. Thus, it eliminates the heat problem too. Related Post: Types of ICs. Classification of Integrated Circuits and Their Limitation.

A reed switch is made up of two metal blades made up of ferromagnetic material hermetically sealed in a glass tube which also supports the metal blades. The glass is filled with inert gas. When the coil is energized, the ferromagnetic metal blades attract each other and form a closed path. As there is no moving armature so there is no contact wear-out problem. The glass tube is also filled with inert gas which also prolongs its life. An electrothermal relay is made up of bimetallic made up of two metals having different thermal expansion coefficients strip.

When the current flow through the conductor, it produces heat. Due to which the temperature of the bimetallic strip rises and expands.

The metal having high thermal expansion coefficient expands more than the other metal. Thermal relays are usually used for electric motor protection. The polarized relay uses a permanent magnet with an electromagnet. The permanent magnet provides a fixed position for the armature. The electromagnetic coil changes the position of the armature about a fixed pivot.

The armature position depends on the polarity of the control input. Some relay having back EMF diodes does have polarity since the diode will bypass the coil if the connection is reversed. Your email address will not be published. Notify me of follow-up comments by email. Notify me of new posts by email. Electrical Technology 1 8 minutes read. Show More.

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