THE STEP BY STEP SWITCH 197 TYPE SELECTORS Part 2

e [Music] the step-by-step dial equipment used in hundreds of telephone offices throughout the country makes it possible for customers to dial their calls and have these calls completed accurately and quickly this is the result of years of research development careful manufacturer and installation once in service however continued reliability depends on the maintenance man and in the Bell System practices he finds the requirements and adjusting procedures that will ensure long switch life and proper operation in this film we will look at the 197 type switch used as a selector here it is in its special stand properly adjusted oil has been removed so the parts may be seen clearly at normal operating speed the action is so fast that in most cases it is difficult to see the effect that various adjustments have on its operation we will use high-speed photography taken with this fast a camera so that we may see in slow motion like this P ratchet thus raising the shaft One Step each time the Armature operates a device called the vertical dog which is tensioned by a spring engages each vertical tooth to hold the shaft while the vertical pole releases for the next step the vertical dog is the upper part of the double dog a close look at the vertical pole and Ratchet shows the action that is important for proper vertical stepping notice the clearance between the ratchet tooth and the vertical dog as the pole releases notice it bounce looking at the shaft from the other side we see that this bounce is caused when the vertical paw finger strikes the vertical paw guide some Paw bounce is always present but does not cause trouble so long as the switch is in proper adjustment now let's see what happens when various parts of the vertical stepping mechanism are not in adjustment the space between the vertical magnets and the vertical Armature can be varied by means of these adjusting nuts here the magnets are too low this may cause under stepping or overstepping if in this high-speed shot notice that the Armature sometimes fails to move the pole upward sufficiently to permit the vertical dog to support the shaft this failure is is due to the vertical magnets being too low now here the magnets still are too low but the adjustment has been changed slightly now the Paw actually flips the vertical shaft up sufficiently to cause overstepping in this case the magnets are too high the effect of this adjustment is shown in the next high-speed shot the Armature continues upward until the pole jams between the over throw stop and the flank of the tooth this results in excessive wear on the Paul bearing when the vertical magnet are too high the vertical stepping becomes sluggish and the switch may not meet pulsing requirements this can be readily seen when the improperly adjusted switch on the right is compared with the one in proper adjustment on the left the slow action of the switch on the right is due to the decreased amateur pull because the vertical magnets are too high the vertical Armature spring can be seen more clearly with the release Armature removed this spring restores the vertical Armature to normal when the vertical magnet releases in this high-speed picture we will see the under stepping that results from too much armateur spring tension the armateur and Paul do not complete their full upward stroke the vertical dog barely slides under the ratchet teeth this time it failed now watch the effect of too little tension on the armateur spring the vertical pole bounces up and down and hangs on the flank of the ratchet tooth this switch probably would not release proper clearance between the vertical pole finger and the vertical pole guide is important to proper switch operation this clearance is measured with the vertical pole just touching the ratchet tooth with too little clearance as in this case the vertical pole cannot properly engage the vertical ratchet it strikes the lifting surface of the tooth instead of sliding along the flank as it should this causes undue wear on the ratchet and pole and may result in under stepping on the other hand tooo much clearance affects the release of the switch as the shaft releases watch the pole bounce as each tooth strikes it this might very well cause a no release condition and certainly will result in excessive wear the mechanical parts of a switch must of course be properly adjusted equally important however are the relays that control the mechanical oper ation if these relays are not in adjustment a switch that is otherwise in perfect condition May Fail the a relay which responds to the dial pulses is an example in this high-speed picture we see a switch in perfect mechanical adjustment failing to step properly due to maladjustment of the a relay the pulsing test set is provided to ensure that the a relay and the vertical stepping mechanism will meet actual conditions encountered in service proper tensioning of the double dog spring is necessary to ensure that the dog will move quickly into the ratchet teeth it is also important that the double dog bearings shall not bind each ratchet tooth is notched these notches are made for the purpose of creating a bulge on the unders surface of each tooth in this high-speed shot we see the action of a properly adjusted vertical dog riding in the center of the notches this adjustment ensures that the Bulge will rest on the vertical dog this bulge provides clearance for the stationary dog during rotary cut in which we will see in a few moments the mark on the notch is caused by the inner edge of the vertical dog looking at the switch from the front we see the vertical dog whose action we have just seen and the stationary dog which supports the shaft during rotary stepping the Bulge creates a clearance between the vertical ratchet tooth and the stationary dog this clearance allows the vertical tooth to slide over the stationary dog but the purpose of this bulge can be destroyed by improper adjustment of the vertical dog in this case the vertical dog is too low the shaft will catch on the stationary dog and fail to cut in in this case the vertical dog has been adjusted too high the dog barely slides under the vertical tooth occasionally under stepping results for the tension on the double dog spring also is important too little tension may cause under stepping if there were too much tension the switch would seem to perform correctly but the dog and shaft would wear excessively due to the unnecessary pressure if the vertical dog is adjusted out too far the shaft May overstep this overstepping is due to the fact that the tip of the dog do does not press against the flank of the next tooth on each vertical step as it should when properly adjusted here the dog fails to support the shaft all together and the switch under steps if the vertical dog is in too far it has the effect of displacing the rotary dog and moving it out so it will not function properly during rotary stepping all of the things we've seen have an important bearing on vertical stepping and no one adjustment can be made without considering its effect on other related adjustments now let's look at the Rotary stepping mechanism it is difficult to see so the rotary stepping has been photographed on another switch that has been cut off at this line seen here from the top the rotary magnets operate the rotary Armature on the end of the Armature is a rotary pole which is guided into the proper rotary tooth by the rotary pole guide the shaft is prevented from returning to normal by the rotary dog the rotary dog is the lower part of the double dog proper rotary pole action is essential for satisfactory switch performance notice that the pole guide is adjusted so the rotary pole strikes the flank of each tooth notice the slight flexing of the front stop as it stops the forward motion of the rotary pole also note the action of the rotary dog the backward movement of the ratchet at the end of each rotary step indicates proper magnet adjustment as in the case of vertical stepping the position of the rotary magnets has a marked effect on rotary operation this switch has insufficient armateur travel we will see what happens with high-speed photography the rotary pole barely rotates the shaft enough to allow the rotary dog to engage under stepping often results notice that the pole never reaches the front stop now let's see the effect of too much Armature air gap notice how the pole slams against the front stop this is because the Armature no longer strikes the rotary magnet cores you may also have noticed that the rotary pole action is sluggish compared to the properly adjusted switch on the left this decrease in operating speed can be clearly seen this may cause the switch to fail to meet its operating requirements let's look again for a moment at the action of the rotary pole and rotary dog when the switch is properly adjusted the pole rotates the shaft sufficiently to allow positive action by the rotary dog but there is no excess rotary motion or overthrow this is extremely important to proper wiper action on the bank terminals this switch is just completing its vertical stepping and will then cut in the wipers move from side to side on the terminal but do not leave it or touch the next terminal this so-call scrubbing action of the wipers on the terminals helps to ensure good contact here the front stop has been adjusted so there is too much clearance notice that the pole no longer strikes the front stop and checking the rotary dog shows considerable overthrow and now watch the effect of overthrow on the wiper action this view through the bank shows the action very clearly each time the wipers momentarily leave a terminal or touch the next terminal there is a chance for circuit failure of course if there is not enough front stop clearance the pole jams against the front stop and finally may cause breakage or we may have under stepping if the ratchet does not rotate far enough for the rotary dog to engage the rotary back stop determines the position of the armateur and Paul in their released position this is properly adjusted notice the position of the Paw in relation to the ratchet teeth here the back stop has been adjusted to give too much back stop clearance the effect is much the same as too much Armature travel since it widens the gap between the rotary magnets and the rotary Armature the action is sluggish if there is too little back stop clearance the pole may not clear the rotary teeth this causes unnecessary wear and may prevent release of the switch this switch has been given too much armateur spring tension this condition slows down the stepping cycle and slams The Amateur against the back stop causing excessive bounce and wear the adjustment of the rotary pole in relation to the rotary ratchet teeth is important to proper operation and long switch life this adjustment is accomplished by means of the rotary pole guide the pole should strike the flank of the tooth and then slide forward until it strikes the radial face the Paul must meet the tooth squarely to prevent unnecessary wear this is clearly shown in the Bell System practices this pole is properly adjusted as the pole guide is turned counterclockwise note that the pole strikes further out on the flank of the tooth in fact as the guide moves further out the pole may not clear the rotary teeth thus preventing release let's start again with the pole properly adjusted as the pole guide is turned clockwise the pole strikes the tooth closer to the notch finally the pole strikes the edge of the tooth or misses it all together causing paw damage shaft wear or under stepping here are some rotary PS that show the results of poor rotary guide adjustment and misalignment with the radial face of the teeth note the worn bearings these Paws actually failed in service the rotary ratchet also suffers when the pole is not adjusted properly here we see the normal pin which is attached to the shaft the normal pin determines the position of the shaft shaft and Ratchet in their rotary normal position careful adjustment of this pin will ensure that the rotary paw will properly Engage The Tooth on the first rotary step the stationary dog supports the shaft during rotary operation although we have mentioned the purpose of the stationary dog before let's look at the clearance that must be observed if the switch is to operate properly adjusted correctly the stationary dog just clears the front edge of the vertical ratchet and rides freely toward the front of the slot too far to the front the dog rubs against the vertical teeth and interferes with stepping too far to the back the dog will will barely support the shaft on the first rotary step we will step the shaft up one step at a time now watch the cut in if the stationary dog is too high the vertical tooth climbs over the stationary dog causing undue wear or the switch may not cut in at all too low the shaft drops when it cuts in and here we see what may happen to the wiper action improper adjustment of the wipers as well as the stationary dog may cause snagging which soon wears the bank insulators these are the principal functions of the rotary stepping mechanism these together with the vertical stepping operations provide the means whereby a call is Advanced through the central office equipment a release mechanism is provided so the switch May release promptly when the customer is through with his call this is accomplished by means of a release magnet release Armature and release Armature pin when the calling party disconnects the Armature pin will strike the double dog thus releasing the rotary ratchet the shaft rotates supported by the stationary dog when the stationary dog enters the slot in the vertical ratchet the shaft drops to Vertical normal let's repeat the release operation but this time watch the action of the release link this link will engage the lug on the double dog as the release Armature operates this link holds the double dog away from the ratchet teeth thus ensuring complete release of the switch if this release link is adjusted too far in as in this case it will not drop over the double dog lug here the link is too far out a poor service condition may result as shown here by high-speed photography this switch is just starting its rotary stepping due to poor adjustment the release link will drop over the double dog during stepping the switch will return to Rotary normal as it does here or a double connection may result the release Armature pin must also be adjusted if the switch is to work properly too far out as shown here the pin does not push the double dog in far enough to let the release link drop over the log if the pin is too far in the Double Dog Log is pushed against the back of the release link causing unnecessary wear the vertical off-normal spring assembly opens and closes electrical circuits for rotary stepping and release it consists of the contact Springs the studs and the vertical ofnormal lever the upper part of which is called the ofnormal finger when the shaft Rises the vertical ofnormal lever releases the Springs which close electrical circuits as the shaft drops it depresses the vertical offn normal finger and the Spring contact open the stud Gap must be adjusted properly this shows proper adjustment here the stud Gap is too great the offn normal finger may bounce up and hit the normal pin during release in this high-speed picture watch the off-normal finger bounce up it was snagged by the normal finger during rotary release the stud Gap can be controlled by adjusting the vertical offn normal Springs be sure however when the switch is on the 10th step of the first level to have clearance between the off-normal finger and the normal pin clamp the cam Springs are used to place busy tone on the customer's line if the switch rotates to the 11th step on first selectors they also remove dial tone therefore they must be adjusted to not operate on the 10th step as we see here but so they will operate on the 11th step there are many other important adjustments that have not been mentioned mentioned in this film these together with the many that have been covered all play a vital part in making the step-by-step selector a properly operating piece of equipment that will give long and trouble-free service to do a good job a job that results in good service the maintenance man first makes sure that he has found the source of the trouble it may be the character of the pulse received it may be a matter of mechanical adjustment it may require cleaning or lubrication so the maintenance man takes the necessary steps to see that the trouble is cleared at its source many troubles can be cleared by making adjustments that compensate for but do not remove the source at best this is a temporary method and soon the switch can no longer meet marginal conditions in the Bell System practices are the adjustments that will enable us to realize the full benefits of careful engineering and manufacturer as is true of any complex Precision piece of equipment one adjustment affects another therefore a partial job may cause more trouble than it prevents the maintenance man's answer to this is a complete and careful job whenever adjustment becomes necessary [Music]