TELEPHONE RELAYS WIRE SPRING TYPE

e [Music] the parade of the relays and it's a long parade reaches back to the very beginning of telephone switching systems that have grown in size and complexity to make possible modern high-speed telephone Communications relays are the very heart of these switching systems and here are the latest members of the relay family the wire spring type but let's hear the story from a bell laboratory's engineer we have many interesting problems here at the Bell Laboratories some easy some not so easy and uh speaking of relays what would you do if you were asked the design of relays that would have twice the sensitivity and operate and release twice as fast as its predecessor the UR Rel that would have improve contact performance and where necessary operate twice as many contacts as former relays and then just to make the problem tough the relay must cost less to make than existing relays require very little maintenance and last for 40 years well that was a job we set out to do and we finally came up with this little fellow the wire spring relay we knew that a relay meeting these objectives was not only necessary for service but would result in tremendous overall Savings of course we didn't hit on The Wire spring relay right away at first we considered modifying other existing relays but it wasn't long before the thinking centered around this design here are a few of the early in which wire Springs were used look at old M24 we thought it might be the answer but we found that a sliding motion between various parts shortened its life many designs were studied and tested before we finally got what we wanted here is an AF for general purpose relay corresponding to the UR relay this is the AG or slow release relay serving the same functions as the Y relay and here is the AJ relay this relay is similar to the AF general purpose except that it is constructed to provide greater sensitivity and to operate heavier contact loads but let's take a close look at the relay it has several unique features for example the wire Springs to which are attached the movable contacts and the fixed or stationary contacts the fiber Cod here at the front which is attached to the ometer and actuates the movable contacts another feature of the relay is that the parts are held together with only a heavy spring clip it is much more simple in design there are just about a dozen separate parts the comparable U type has about 75 you probably remember seeing how U and Y type relays were adjusted after assembly it was necessary to adjust spring tension and follow and check each spring individually on The Wire spring relay very little adjustment is necessary the construction of the core plate makes Mass adjustment of the contacts a simple matter this all adds up to reduce costs but let's examine each part of the relay separately we'll begin with the core coil and core plate they are formed into an assembly during manufacturer at the Hawthorne plant of Western Electric the coil construction is similar to the one used in the U and Y relays in this operation the core plate is forced onto the core the core plate not only permits Mass adjustment of the contacts but serves to keep the core legs in alignment and provides the back stop for the ometry the coil terminals are brought out at the front as well as the back of the relay for convenience in making current flow tests now we come to the amateur it has non-magnetic stop discs like the UR relay the amateur and core line up in this manner and the magnetic field can be visualized like this the large core and the large pole face area serve to increase the useful magnetic flux this increases magnet sensitivity and pulling power it also reduces magnetic interference the ameter is hinged on a spring in a manner to reduce rebound which could cause false operation of contacts let's compare the rebound in a UR relay and a wire spring relay here in slow motion photography made with a high-speed camera we can see the rebound in a UR relay now the relay operates as it releases watch the amateure rebound after it strikes the back stop now let's watch the wire spring relay remember this armateur operates to the right which is opposite from the UR relay now it releases notice rebound has been reduced the molded mounting bracket serves as a base for supporting the parts of the relay it also insulates the relay from the mounting plate thus making mounting plate insulation unnecessary here's the fixed spring assembly it is made up of 12 heavy wires it has a plastic section at the rear and one in front in addition to holding the wires in place the front section has molded guide slots for the movable contact Springs the fixed wires may or may not have contacts on the ends but the full complement of 12 wires is always provided to support the front molded section and to provide a high and uniform tension of the fixed assembly against the core plate it also provides an index for counting the terminals at the back of the relay this will give you an idea of the small size of the contacts they are little blocks made of an inexpensive metal a thin layer of precious metal padium only 10,000 of an inch thick is welded on the left side the right side or both sides as needed for a particular contact Arrangement here the contact blocks are welded to the ends of the stationary wire assembly next let's talk about the movable contact Springs this particular assembly consists of 24 wires arranged in pairs molded into a single assembly each movable pair is associated with a single fixed contact and the combination is called a twin contact each wire carries a contact and is entirely independent from its mate the twin wire assemblies differ also in the number of wires and in their position the wires that are not needed for the particular Arrangement required are cut off close to the molded plastic section before the wires are molded into Combs they must be perfectly straight it took a lot of research and Manufacturing development to find a practical way to straighten wire for example it was found that pushing rather than pulling the wire gave the best results these tubes feed the wires to rotating dyes where the straightening is accomplished now the wire as straight as human Ingenuity can make it goes directly to the molding press here the wire assembly is molded into a continuous strip the assembly is then cut to length the Springs now have to be cleaned after which they are stacked in magazines ready for the next operation as you can see the Springs are as yet entirely straight but they won't be for long because in the first press the contact ends of the wires are formed into a shape resembling the letter z now the contacts are welded on the precious metal is in tape form and just enough for the contact is welded on and cut it takes about a Penny's worth of the precious metal for reach twin contact in a 10,000 line office this amounts to several th000 for contacts alone next the spring assembly goes through a series of forming operations the last one of which puts a Bend into the wires to obtain the desired spring tension this tension need never be adjusted since it gives a contact pressure that is stable throughout the life of the relay however in former relays such as the U type contact pressure is affected by stud and contact wear and adjustment of the individual Springs is necessary from time to time to provide proper contact performance the wire spring relay has been designed so that slide between surfaces is practically eliminated this together with fewer wearing surfaces and the pre-tension Springs add up to a marked improvement in the adjustment life of the relay another new design feature is the punched fiber card which is supported by the amateure on one side and the balancing spring on the other a side view shows the balancing spring more clearly the pre-tension and the balancing spring causes the card to hold the amateure against the back stop and to hold these make contacts open operating the relay very slowly you can observe how the Armature pulls the card with it allowing the movable contacts on the left to meet with their mating fixed contacts let's see it again and this time watch the break context note that as the Cod follows the ameter it pushes the brake contact s away from the fixed contacts the pre-tension in the Twin wires always tends to hold these movable contacts against their meeting fixed contacts when released the balancing spring forces the card to return to its unoperated position having the card near the contacts has several advantages one of them being the redu of spring vibration here is a slow motion picture of a UR relay watch the spring vibration the wire spring relay has less spring vibration less spring vibration means less possibility of contact chatter this means less contact erosion and more positive circuit operation let's take a closer look at some of the cards that are available to provide various contact Arrangements contacts actuated by a card with straight edges like this move together but without any guaranteed make or break sequence again we'll operate the relay very slowly this card causes some contacts as indicated by the arrows to operate earlier or later than others the arrangement is called an early brake make transfer the brake contacts are made to open before the make contacts close here is an early make brake transfer or continuity watch the top set of contacts the make contacts close before the brake contacts open the make contacts have now closed now the brake contacts start to open this is a preliminary make if you will watch the set of contacts in the middle you'll see that they make earlier than any of the others these various contact combinations require one of three specified amateur travels in The Wire spring relay amatur travel is determined by the dimension of the core plate the three travels available are short intermediate and long thus adjustment for reter travel has been eliminated in the wi spring relay well to make a long story short we think the wire spring relay will live up to the objectives we set out to meet we think these little fellas are good for a billion operations let me show you something here they are undergoing an accelerator test a billion operations how much is that well these relays are operating 20 times a second that's over 1,700,000 times a day a year and a half from now these relays will have operated a billion times that's about the maximum number of times any relay will be required to operate yes let's close the door among the relay's many advantages is the almost complete elimination of magnetic interference magnetic interference is the effect the magnetic field of a relay has on adjacent relays here is a trunk unit using U and Y relays now even though their design provided a marked improvement over former relays their magnetic effect on adjacent relays was such that special procedures had to be observed during adjustment and Equipment had to be arranged with proper spacing between relays notice that this trunk unit is mounted on three plates to provide space between certain relays so that their magnetic fields will not cause interference now here is the same trunk unit using wire spring relays the equipment can be mounted more compactly and only two plates are needed because the design of the wi spring relay reduces magnetic interference to almost nothing another significant Advantage is the relay speed of operation on this simple demonstration board we have connected a u and an AF relay in parallel when we close the circuit this Center lamp will light the bulb on the right will light through the contacts of the wire spring relay thereby indicating the operate time of the relay the bulb on the left will light through the contacts of the u relay the instant it operates with the help of slow motion photography we can demonstrate that the wire spring relay is about twice as fast as the UR relay when both are operating under the same load conditions when we talk of speed we mean milliseconds time intervals to too brief for the eye to evaluate see how much faster the wi spring relay is this greater speed means that less common control equipment will be needed resulting in substantial savings another another important consideration this Relay can operate more contacts sometimes one wire spring relay will do where two relays we used before but there's another new feature we haven't even mentioned it's a transparent plastic dust cover this cover not only keeps dust from the contacts it also protects the delicate contact Springs from injury now what does all this mean well for one thing it means that engineering of switching circuits will be simplified fewer relays per line it means a more economical arrangement of equipment less space required for the same sized office it means less maintenance per line when you add it all up it means faster service better service more customer satisfaction we expect a lot from this little fellow he's the very heart of modern highspeed telephone service [Music]