Telephone Relays U and Y Type (Part 2)

[Music] la there are more than 15 million reays in the Bell System they are welld designed and wellmade together with adjustment procedures developed to secure the best performance reays are durable reliable ready to do a good job provided we adjust them properly when they're in trouble over at the Bell Laboratories an engineer is going to show us how U and Y type relays are better than the other flat type relays let's look at a u relay that is properly adjusted first we'll examine the Armature bounce with the help of highspeed Photography we'll do this twice so the first time watch the Armature the Armature operates now we'll release the relay see it bounce against the adjusting nut now this time watch The Springs see them vibrate this spring vibration is always present but it will not cause trouble if the relay is properly adjusted if you look closely you will see that there is no false contact operation it's the result of changes in Armature design and careful proportioning of the stationary and movable Springs this Improvement was necessary to meet the more exacting requirements of the newer switching systems and now just a word about the Y type relay which was developed to provide slow release characteristics from outward appearances it doesn't look very different from the U type this drawing show shows the difference in the magnetic circuits notice the two stop discs welded on the Armature of the UR relay these discs are non-magnetic and introduce an air gap thus permitting the relay to release promptly however on the Y relay the discs are omitted to make it a slow release relay instead a raised surface is stamped into the Armature this is known as embossing and serves a very important purpose in the mass production of Y relays the angle with which the Armature meets the pole piece varies between relays in this exaggerated view you will notice however that the Armature rests against the pole piece with a onepoint contact due to the embossment this provides greater uniformity in the release time of Y type relays to increase the release time and provide some degree of variation for various circuit conditions copper or aluminum sleeves of different thicknesses are placed over the core of the relay the thicker the sleeve the longer the release time some people find it hard to believe that there is actually much difference in release time between a fast release and slow release relay in this high-speed shot let's compare the u relay on the left with the slow release y relay on the right notice there isn't much difference in the operate time but now watch them release as current is removed from both windings at the same instant the Y relay remains in his operated position for some time after the UR relay has released but remember the Fast Tax camera has slowed the action 200 times the requirements for adjusting relays properly are right here in the Bell System practices they are developed to secure good performance with the least headaches for the maintenance m and that's something any central office man would be glad to talk about that's right occasionally a relay fails when it does the best medicine is a careful job of adjusting all adjustment procedures are right here in the Bell System practices unless we follow them the value of careful relay design and manufacture can be lost I'm not going to try to cover all of these requirements but I would like to show you some of the things that cause many of our relay troubles the first thing I'll show you with this movie projector is dust and lint on relay Springs this can happen in a central office when the covers are left off it's what we call manmade trouble relay cover should be removed only when absolutely necessary and replaced as soon as possible here's a drawing from the practices showing one of the adjustments that is important to prevent contact chatter there must be proper clearance between the ends of the spring studs and the adjacent Springs to check the spring stud clearance the number 510c test lamp is a very helpful tool to magnify and illuminate these Close Quarters here's a relay properly adjusted except that there is insufficient stud Gap at this point when a relay does not have enough stud Gap this is what happens watch the spring action as the Armature bounces see the contact open well here is the same relay with proper stud Gap the contact chatter has been removed contact chatter may cause circuit troubles and is sure to result in excessive contact erosion at the contacts carry current this drawing shows one arrangement of a typical spring pile up on a u relay Springs A and D press against the spring stut which rests against the Armature and provides what is called Armature back tension this tension must be at or above the specified limit for it is one of the things that affects Armature bounce but here's another important thing the tension of the spring pilps must be balanced within specified limits or we would have a misalignment of the Armature like this such a relay would be unbalanced would not meet requirements or perform properly and while we are talking about Armature back tension the use of the 70 type gram gauge certainly deserves consideration but it must be used properly or an incorrect reading results place the read flat against the Armature at a point even with and behind the adjusting nut the re must lie in the same plane as the Armature now rotate the gauge making sure the re remains flat when the Armature just leaves the adjusting nut the gauge will show the tension if a pushing motion like this is used the reading will be wrong another important requirement of relay adjustment is contact make commonly called follow this relay is properly adjusted as it operates watch the deflection of the moving Springs after their contacts made against the stationary or spool head Springs this is an indication of contact follow proper follow creates adequate pressure contact follow also provides an allowance for contact and spring stud wear before failures result let's look at this break makes spring combination that is not properly adjusted note that the lower contact of the bifurcated spring makes before the upper contact breaks the same contact bunching happens as the relay releases this may cause FY circuit operation now here is the way the contact should operate The Brak contacts open before the make contacts close no discussion about relay adjustment is complete without a word about contact erosion watch The Arc that occurs on the top contact of this relay when it releases this will cause severe contact erosion that may result in contact locking or loss of adjustment due to loss of contact metal or its transfer from one contact to another here are some examples these are silver contct s see the large buildups they may snag in the holes of their mating contacts and fail to open these are Palladium contacts that did lock eroded contacts require maintenance if they're not too bad the buildups can be removed with a 527a tool the proper blade must be used with care so as not to remove useful metal here are the silver contacts we saw a moment ago after treating with a 527a tool when the contacts are too far gone new contacts will be welded on with the contact Welding Tool and in all cases the relay must then be checked for adjustment of course contact protection networks like these 181 types help to reduce contact erosion and troubles here are some 184 types these networks a condenser and resistance in series help to reduce the momentary voltage surge that occurs when the relay contacts open the effect of contact protection can be shown very clearly on an oscilloscope scope this is an electrical picture of the arc resulting when contacts do not have protection this line at 0 volts shows the voltage across the contacts before they open at this point the contacts open note the high voltage Peaks arcing of as much as 3 amp occurs during this period and continues until the voltage drops now here is a picture of an identical circuit with protection the line shows zero volts until the contacts open in this case however notice how the protection Network reduces the voltage surge so that no arcing occurs but the secret of good relay performance is proper adjustment understanding the importance of following the procedures in our practices is basic if we are going to avoid relay Troubles of course the Bell Laboratories Engineers are always looking for improvements take the problem of stud Weare yes stud Weare results after millions of operations at the relay as the stud wears down contact follow becomes less contact pressure decreases and eventually we have contact chatter and failures we have improved this condition by a new stud material of synthetic Rubber and graphite that reduces wear now Hing pin wear is a condition that may cause trouble on relays that operate 100 million times or more during a normal relay lifetime about 15% of the relays in the average office work this hard here is one that shows what I mean notice the movement of the Armature due to the hinge pin holes becoming enlarged the Armature drops down and rubs on the spool head this may have a serious effect on the operate and Rel waste time but new relays we've overcome this by substituting a spring hinge however we have kept the advantage of the overlap between the Armature and endol here's a condition that sometimes develops on the fast operating utype relay these stop discs on the Armature finally penetrate it into the core this FX contact follow and increases release time we've been able to practically eliminate this condition by using a different metal for the Stop discs on hardworking relays for relays that develop this condition in service we have a plastic separator that slips over the core speaking of separators here's one developed for another purpose I'm going to show you two y relays they're the same in every respect except that the one on the left is new the one on the right's been in service for a long time they are both operated watch them release the relay on the right is too slow it has developed what we call aging of iron parts and eventually may not release at all its magnetic properties have changed this condition has been corrected in present relays by using hydrogen anal iron during manufacturer however however when the condition occurs in the older relays that are already in service it can be corrected with a magnetic separator theel system practices explain how this should be done and here is an interesting little gadget called a motion limiting washer it was developed to prevent the breaking of coil leads the reason for this breakage had us puzzled for some time but this is the main cause notice the slight movement between the winding and the core this vibration occurring mostly on Fast operating new relays sometimes causes the coil leads to break from repeated bending however this washer is now slipped over the core during manufacturer and sealed to the front end of the coil thus reducing coil vibration and now one more thing I know you've all seen the instructions in the practices about magnetic interference between relays here are eight U relays mounted around a y relay as you might find them in any office when adjusting a relay to meet circuit and timing conditions the adjustment may be critically affected by magnetic interference from adjacent relays that are operated this may be hard to believe so uh let's run a test this 35 type test set will give us the current reading on this Center Y type relay now here we have a timing set that we will use later it is designed to show the actual operate and release time first let's get readings of the release current values I'll operate the center relay notice that the adjacent relays are not operated I'm not showing the operate values because magnetic interference has a greater effect on the release there it's released now watch the center scale the release current value is about 7 Ms let's put this down so we won't forget it now I'll energize the center relay and relays 2 and eight directly above and below the center relay what's the release current value again on the center scale 10 and 210 MS now I'll operate the center relay and all adjacent relays this time the reading will be on the top scale it is 20 MS note the increase in current values due to Magnetic interference from the adjacent relays now let's use the timing test set to see the effect of magnetic interference on release time each microampere on the scale is 1 millisecond so a full scale reading would be 100 milliseconds the first test will be with all adjacent relays unoperated the center relay will release as I throw this key release time is 72 milliseconds now all operate relays 2 and 8 the release time is 54 milliseconds now let's see what happens when all adjacent relays are energized the release time is now 32 milliseconds in most circuits relays operate as a team therefore timing is extremely important and yet as you can see release current values and release time are very definitely affected by adjacent energized relays the same thing would happen in very de if other combinations of adjacent relays were energized this is very important to know for it may mean that a relay you think you have properly adjusted will not at all times meet the circuit requirements the circuit requirement tables on the circuit drawings are prepared so that satisfactory operation and release of relays is ensured provided the instructions in the Bell System practices are carefully followed that's the story all right but actually only a small percentage of the relays in an office ever develop trouble and have to be adjusted so long as they keep on working leave them alone because tinkering can cause a lot of relay trouble but when they do need adjusting remember do the job right according to the book [Music]