Ringing and Listening Keys

The general principles of the ringing key have already been referred to. Ringing keys are of two general types, one having horizontal springs and the other vertical. IMG:384091999325875926_fig266_t.gif.png:Illustration_ Fig. 266. Horizontal-Spring Listening and Ringing Key Fig. 266. Horizontal-Spring Listening and Ringing Key View full size illustration. Horizontal Spring Type. Various Bell operating companies have generally adhered to the horizontal spring type except in individual and four-party-line keys. The construction of a Western Electric Company horizontal spring key is shown in Fig. 266. In this particular key, as illustrated, there are two cam levers operating upon three sets of springs. The cam lever at the left operates the ordinary ringing and listening set of springs according to whether it is pushed one way or the other. In ringing on single-party lines the cam lever at the left is the one to be used; while on two-party lines the lever at the left serves to ring the first party and the ringing key at the right the second party. In order that the operator may have an indication as to which station on a two-party line she has called, a small target 1 carried on a lever 2 is provided. This target may display a black or a white field, according to which of its positions it occupies. The lever 2 is connected by the links 3 and 4 with the two key levers and the target is thus moved into one position or the other, according to which lever was last thrown into ringing position. It will be noticed that the springs are mounted horizontally and on edge. This on-edge feature has the advantage of permitting ready inspection of the contacts and of avoiding the liability of dust gathering between the contacts. As will be seen, at the lower end of each switch lever there is a roller of insulating material which serves as a wedge, when forced between the two long springs of any set, to force them apart and into engagement with their respective outer springs. IMG:384091999325875926_fig267_t.gif.png:Illustration_ Fig. 267. Vertical-Spring Listening and Ringing Key Fig. 267. Vertical-Spring Listening and Ringing Key View full size illustration. Vertical Spring Type. The other type of ringing and listening key employing vertical springs is almost universally used by the various independent manufacturing companies. A good example of this is shown in Fig. 267, which shows partly in elevation and partly in section a double key of the Monarch Company. The operation of this is obvious from its mode of construction. The right-hand set of springs of the right-hand key in this cut are the springs of the listening key, while the left-hand set of the right-hand key are those of the calling-plug ringing key. The left-hand set of the left-hand key may be those of a ring-back key on the answering plug, while the right-hand set of the left-hand key may be for any special purpose. It is obvious that these groups of springs may be grouped in different combinations or omitted in part, as required. This same general form of key is also manufactured by the Kellogg Company and the Dean Company, that of the Kellogg Company being illustrated in perspective, Fig. 268. The keys of this general type have the same advantages as those of the horizontal on-edge arrangement with respect to the gathering of dust, and while perhaps the contacts are not so readily get-at-able for inspection, yet they have the advantage of being somewhat more simple, and of taking up le horizontal space on the key shelf. IMG:384091999325875926_fig268_t.gif.png:Illustration_ Fig. 268. Vertical Listening and Ringing Key Fig. 268. Vertical Listening and Ringing Key View full size illustration. IMG:384091999325875926_fig269_t.gif.png:Illustration_ Fig. 269. Four-Party Listening and Ringing Key Fig. 269. Four-Party Listening and Ringing Key View full size illustration. Party-Line Ringing Keys. For party-line ringing the key matter becomes somewhat more complicated. Usually the arrangement is such that in connection with each calling plug there are a number of keys, each arranged with respect to the circuits of the plug so as to send out the proper combination and direction of current, if the polarity system is used; or the proper frequency of current if the harmonic system is used; or the proper number of impulses if the step-by-step or broken-line system is used. The number of different kinds of arrangements and combinations is legion, and we will here illustrate only an example of a four-party line ringing key adapted for harmonic ringing. A Kellogg party-line listening and ringing key is shown in Fig. 269. In this, besides the regular listening key, are shown four push-button keys, each adapted, when depre ed, to break the connection back of the key, and at the same time connect the proper calling generator with the calling plug. Self-Indicating Keys. A complication that has given a good deal of trouble in the matter of party-line ringing is due to the fact that it is sometimes nece ary to ring a second or a third time on a party-line connection, because the party called may not respond the first time. The operator is not always able to remember which one of the four keys a ociated with the plug connected with the desired party she has pre ed on the first occasion and, therefore, when it becomes nece ary to ring again, she may ring the wrong party. This is provided for in a very ingenious way in the key shown in Fig. 269, by making the arrangement such that after a given key has been depre ed to its full extent in ringing, and then released, it does not come quite back to its normal position but remains slightly depre ed. This always serves as an indication to the operator, therefore, as to which key she depre ed last, and in the case of a re-ring, she merely pre es the key that is already down a little way. On the next call if she is required to pre another one of the four keys, the one which remained down a slight distance on the last call will be released and the one that is fully depre ed will be the one that remains down as an indication. Such keys, where the key that was last used leaves an indication to that effect, are called indicating ringing keys. In other forms the indication is given by causing the key lever to move a little target which remains exposed until some other key in the same set is moved. The key shown in Fig. 266 is an example of this type. **NOTE** The matter of automatic ringing and other special forms of ringing will be referred to and discu ed at their proper places in this work, but at this point they are not pertinent as they are not employed in simple switchboards.