Electric Bells and All About Them Part 8

"It will be noticed that the strokes to represent a letter do not in any case exceed four, and that all the figures are represented by five strokes of varying length to each figure. Stops, and other marks of punctuation, are represented by six strokes, which are in their combination representations of two or three letters respectively, as shown below:--

Comma (,) by A A A or --- Full stop (.) " I I I "

Interrogation (?) " U D " -- Hyphen (-) " B A " -- Apostrophe (') " W G " ---- Inverted commas (") " A F " -- Parenthesis () " K K " ---- Semi-colon (;) " K Ch " ----- Surprise (!) " N Ch " ----- Colon (:) " I Ch " ----

"In sending signals to indicate stops, no regard must be had to the letters which they represent; these are only given as aids to memory, and are not to be represented separately on the bell. Bell signals must be given with a certain amount of regularity as to time; indeed, to carry on a conversation in this way it is necessary to be as punctilious in time as when playing a piece of music on a piano, if the signals are to be understood. The dots of the signal should therefore be represented in time by _one_, and the dashes by _two_, whilst the s.p.a.ces between words and figures where a stop does not intervene should be represented by a pause equal to that taken by a person counting _three_, the s.p.a.ce between a word and a stop being of the same duration. To make this more clear I give an example. The mistress signals to her coachman:--

G E T T H E -- - - 221 1 2 3 2 1111 1 3

C A R R I A G E -- - - - - -- 2121 12 121 121 11 12 221 1 3

R E A D Y - - - --- 121 1 12 211 2122

"The coachman replies:--

R E A D Y - - - --- 121 1 12 211 2122

"When the mistress is ready she signals:--

B R I N G T H E - - - -- - 2111 121 11 21 221 3 2 1111 1 3

C A R R I A G E -- - - - - -- 2121 12 121 121 11 12 221 1

"And the coachman replies with a single long ring to signify that he understands. It will be found convenient to have an answering signal from the receiving end of the line to each word separately. This must be sent in the pause after each word, and consists of the short signal E when the word is understood, or the double short signal I when the word is not understood. A negative reply to a question may be given by the signal for N -, and an affirmative by the signal for ae --; other abbreviations may be devised and used where desired. The code having been committed to memory, it will be quite easy to transpose the words and send messages in cypher when we wish to make a confidential communication; or the bells may be m.u.f.fled under a thick cloak, and thus, whilst the measured beats are heard by the person for whom the signal is intended, others outside the room will not be annoyed by them."

[Ill.u.s.tration: Fig. 65.]

-- 63. At -- 48, we noticed that a device known as a _Relay_ is a convenient, if not an essential mode of working continuous ringing bells. Here we will direct our attention to its structural arrangement, and to its adaptations. Let us suppose that we had to ring a bell at a considerable distance, so far indeed that a single battery would not energise the electro-magnets of an ordinary bell, sufficiently to produce a distinct ring. It is evident that if we could signal, ever so feebly, to an attendant at the other end of the line to make contact with another battery at the distant end of the line to _his_ bell, by means, say, of a key similar to that shown at Fig. 65, we should get a clear ring, since this second battery, being close to the bell, would send plenty of current to energise the bell's magnets. But this would require a person constantly in attendance. Now the _relay_ does this automatically; it _relays_ another battery in the circuit. The manner in which it effects this will be rendered clear, on examination of Fig. 66.

Here we have an armature A attached to a light spring, which can play between an insulated stop C, and a contact screw B. The play of this armature can be regulated to a nicety by turning the screws B or C.

These two screws are both borne by a double bent arm (of metal) affixed to the pillar D. This pillar is separated from the rest of the frame by an insulating collar or washer of ebonite, so that no current can pa.s.s from E to D, unless the armature be pulled down so as to make contact with the contact screw B. Just under the armature, stands the electro-magnet G, which when energised can and does pull down the armature A. It will be readily understood that if we connect the wires from the electro-magnet G, to the wires proceeding from the battery and push (or other form of contact) at the distant station, the electro-magnet, being wound with a large quant.i.ty of fine wire, will become sufficiently magnetized to pull the armature down through the small s.p.a.ce intervening between C and B; so that if the screws D and E are connected respectively to the free terminals of a battery and bell coupled together at the nearer station, this second battery will be thrown into circuit with the bell, and cause it to ring as well and as exactly as if the most skilful and most trustworthy a.s.sistant were in communication with the distant signaller. Every tap, every release of the contact, (be it push, key, or switch) made at the distant end, will be faithfully reproduced at the nearer end, by the motion of the armature A. For this reason we may use a comparatively weak battery to work the relay, which in its turn brings a more powerful and _local_ battery into play, for doing whatever work is required. In cases where a number of calls are required to be made simultaneously from one centre, as in the case of calling a.s.sistance from several fire engine stations at once, a relay is fixed at each station, each connected with its own local battery and bell. The current from the sending station pa.s.ses direct through all the relays, connecting all the local batteries and bells at the same time. This is perhaps the best way of ringing any number of bells from one push or contact, at a distant point. Ordinary trembling bells, unless fitted with an appropriate contrivance, cannot well be rung if connected up in _series_. This is owing to the fact that the clappers of the bells do not all break or make contact at the same time, so that intermittent ringing and interruptions take place. With single stroke bells, this is not the case, as the pulling down of the armature does not break the contact.

[Ill.u.s.tration: Fig. 66.]

[Ill.u.s.tration: Fig. 67.]

[Ill.u.s.tration: Fig. 68.]

-- 64. We now have to consider those contrivances by means of which it is possible for an attendant to know when a single bell is actuated by a number of pushes in different rooms, etc., from whence the signal emanates. These contrivances are known as _indicators_. Indicators may be conveniently divided into 3 cla.s.ses, viz.:--1st, indicators with _mechanical_ replacements; 2nd, those with electrical replacements; and 3rdly, those which are self replacing. Of the former cla.s.s we may mention two typical forms, namely, the ordinary "fall back" indicator, and the drop indicator. All indicators depend in their action on the sudden magnetisation of an electro-magnet by the same current that works the electric bell at the time the call is sent. To understand the way in which this may be effected, let the reader turn to the ill.u.s.tration of the Relay (Fig. 66), and let him suppose that the pillar D, with its accompanying rectangle B C, were removed, leaving only the electro-magnet G, with its frame and armature A. If this armature holds up a light tablet or card, on which is marked the number of the room, it is evident that any downward motion of the armature, such as would occur if the electro-magnet were energised by a current pa.s.sing around it, would let the tablet fall, so as to become visible through a hole cut in the frame containing this contrivance. It is also equally evident that the card or tablet would require replacing by hand, after having once fallen, to render it capable of again notifying a call. Fig. 67 shows the working parts of one of these "drop" indicators, as sent out by Messrs. Binsw.a.n.ger. In another modification, known as Thorpe's "Semaph.o.r.e Indicator," we have a most ingenious application of the same principle in a very compact form. In this (Fig. 68), the electro-magnet is placed directly behind a disc-shaped iron armature, on which is painted or marked the number of the room etc. (in this case 4); this armature is attached by a springy shank to the drop bar, shown to the left of the electro-magnet. In front of the armature is a light metal disc, also pivoted on the drop bar. This engages in a catch above, when pushed up so as to cover the number. When pushed up, the spring of the armature retains it in its place so that the number is hidden. When the current pa.s.ses around the electro-magnet, the armature is pulled toward it, and thus frees the covering disc, which therefore falls, and displays the number. The ordinary form of "fall back" indicator (a misnomer, by the way, since the indicator falls forwards) is well ill.u.s.trated at Fig 69. Here we have an ordinary electro-magnet A, with its wires _w_ _w'_ standing over an armature B attached to a spring C, which bears on its lower extremity, a toothed projection which serves to hold up the short arm of the bent lever D, which supports the number plate E. When the electro-magnet A is energised by the current, it pulls up the armature B, which releases the detent D from the tooth C; the number plate therefore falls forwards, as shown by the dotted lines, and shows itself at the aperture E', which is in front of the indicator frame. To replace the number out of sight, the attendant pushes back the plate E, till it again engages the bent lever D in the tooth C. This replacement of the number plate, which the attendant in charge is obliged to perform, gives rise to confusion, if through carelessness it is not effected at once, as two or more numbers may be left showing at one time. For this reason, indicators which require no extraneous a.s.sistance to replace them, are preferred by many. Indicators with electrical replacements meet in part the necessities of the case. This form of indicator consists usually of a permanent bar magnet pivoted near its centre, so that it can hang vertically between the two poles of an electro-magnet placed at its lower extremity. The upper extremity carries the number plate, which shows through the aperture in the frame.

This bar magnet is made a trifle heavier at the upper end, so that it must rest against either the one or other pole of the electro-magnet below. If the _north_ pole of the bar magnet rests against the _right_ hand pole of the electro-magnet when the number does not show, we can cause the bar magnet to cross over to the other pole, and display the number by sending a current through the electro-magnet in such a direction as to make its right hand pole a north pole, and its left hand a south pole. This is because the two north poles will repel each other, while the south will attract the north. On being once tilted over, the bar magnet cannot return to its former position, until the person who used the bell sends a current in the opposite direction (which he can do by means of a reversing switch), when the poles of the electro-magnet being reversed, the bar magnet will be pulled back into its original position. Indicators of this cla.s.s, owing to the fact that their replacement depends on the _polarity_ of the bar magnet, are also known as "polarised indicators."

[Ill.u.s.tration: Fig. 69.]

-- 65. For general efficiency and trustworthiness, the _pendulum indicator_; as shown at Fig. 70, is unsurpa.s.sed. It consists of an electro-magnet with prolongation at the free end on which is delicately pivoted a soft iron armature. From the centre of this armature hangs, pendulum fas.h.i.+on, a light bra.s.s rod carrying a vane of fluted silver gla.s.s, or a card with a number on it, as may be found most convenient.

This vane or card hangs just before the aperture in the indicator frame.

Stops are usually placed on each side of the pendulum rod to limit the swing. When the electro-magnet is magnetised by the pa.s.sage of the current, the armature is pulled suddenly on one side, and then the pendulum swings backwards and forwards in front of the aperture for some minutes before it comes to rest. When fitted with silver fluted gla.s.s, the motion of the vane is clearly visible even in badly lighted places.

As the pendulum, after performing several oscillations, comes to rest by itself in front of the aperture, this indicator requires no setting.

Messrs. Binsw.a.n.ger fit these indicators with double core magnets, and have a patented adjustment for regulating the duration of the swings of the pendulum, which may be made to swing for two or three minutes when the circuit is completed by pressing the push; it then returns to its normal position, thus saving the servant the trouble of replacing the "drop."

[Ill.u.s.tration: Fig. 70.]

Messrs. Gent, of Leicester, have also patented a device in connection with this form of indicator, which we give in the patentee's own words:--"The objection so frequently urged against the use of Electric Bells, that the servants cannot be depended upon to perform the operation of replacing the signals, cannot any longer apply, for the pendulum signals require no attention whatever. It consists of an electro-magnet having forks standing up in which [V] openings are made. An armature of soft iron, with a piece of thin steel projecting at each end lies suspended at the bottom of the [V] opening, a bra.s.s stem carrying the signal card is screwed into the armature, the action being, that when a current is allowed to pa.s.s through the electro-magnet the armature with the pendulum is drawn towards it and held there until the current ceases to pa.s.s, when it instantly looses its hold of the armature, which swings away and continues to oscillate for two or three minutes, so that if the servant happens to be out of the way, it may be seen on her return which pendulum has been set in motion. The Pendulum Indicator we have recently patented is entirely self-contained. The magnet has its projecting poles riveted into the bra.s.s base which carries the flag. The flag is constructed as Fig. 70, but swings in closed bearings, which prevents its jerking out of its place, and enables us to send it out in position ready for use. It will be seen this _patented_ improvement makes all screws and plates as formerly used for securing the parts unnecessary.

It will be seen at once that this is simplicity itself, and has nothing about it which may by any possibility be put out of order, either by warping or shrinking of the case or carelessness of attendants."

[Ill.u.s.tration: Fig. 71.]

There is only one point that needs further notice with regard to these pendulum indicators, and that is, that since the rapid break and make contact of the ringing bell interferes somewhat with the proper action of the indicator magnet, it is always advisable to work the indicator by means of a relay (fixed in the same frame) and a _local_ battery. This is shown in Fig. 71, where a second pair of wires attached to C and C, to the extreme right of the indicator frame, are brought from the same battery to work the indicator and contained relay. It is not advisable, however, with the pendulum indicator, to use the same battery for the indicator; the relay should throw a local battery into the indicator circuit. In Fig. 71 six pushes are shown to the left of the indicator frame. These, of course, are supposed to be in as many different rooms.

[Ill.u.s.tration: Fig. 72.]

We close this chapter with an engraving of a very compact and neat form of drop indicator devised by Messrs. Gent, and called by them a "Tripolar Indicator." It consists, as the name implies, of a single magnet, having one end of the iron core as one pole, the other end extending on each side like a [V], forming, as it were, three poles.

Though but one bobbin is used, the effect is very powerful. There are no springs or other complications, so that the arrangement is adapted for s.h.i.+p use, as are also those represented at Figs. 67 and 68. Pendulum and fall-back indicators, as well as polarised indicators, owing to the delicacy of the adjustments, are unfitted for use on board s.h.i.+p, or in the cabs of lifts, where the sudden jolts and jerks are sure to move the indicators, and falsify the indications. The tripolar indicator is ill.u.s.trated at Fig. 72.

CHAPTER V.

ON WIRING, CONNECTING UP, AND LOCALISING FAULTS.

-- 66. However good may be the bells, indicators, batteries, etc., used in an electric bell installation, if the _wiring_ be in any wise faulty, the system will surely be continually breaking down, and giving rise to dissatisfaction. It is therefore of the highest importance that the workman, if he value his good name, should pay the greatest attention to ensure that this part of his work be well and thoroughly done. This is all the more necessary, since while the bells, batteries, relays, pushes, etc., are easily got at for examination and repair, the wires, when once laid, are not so easily examined, and it entails a great deal of trouble to pull up floor boards, to remove skirtings etc., in order to be able to overhaul and replace defective wires or joints. The first consideration of course, is the kind and size of wire fitted to carry the current for indoor and outdoor work. Now this must evidently depend on three points. 1st, The amount of current (in amperes) required to ring the bell. 2nd, The battery power it is intended to employ. 3rd, The distance to which the lines are to be carried. From practical experience I have found that it is just possible to ring a 2-1/2" bell with 1/2 an ampere of current. Let us consider what this would allow us to use, in the way of batteries and wire, to ring such a bell. The electro-motive force of a single Leclanche cell is, as we have seen at -- 38, about 16 volt, and the internal resistance of the quart size, about 11 ohm. No. 20 gauge copper wire has a resistance of about 12 ohm to the pound, and in a pound (of the cotton covered wire) there are about 60 yards. Supposing we were to use 60 yards of this wire, we should have a wire resistance of 12 ohm, an internal resistance of 11 ohm, and a bell resistance of about 01 of an ohm, altogether about 24 ohms. Since the E.M.F. of the cell is 16 volt, we must divide this by the total resistance to get the amount of current pa.s.sing. That is to say:--

Ohms. Volts. Amperes.

24) 160 (066,

or about 2/3 of an ampere; just a little over what is absolutely necessary to ring the bell. Now this would allow nothing for the deterioration in the battery, and the increased resistance in the pushes, joints, etc. We may safely say, therefore, that no copper wire, of less diameter than No. 18 gauge (48/1000 of an inch diameter) should be used in wiring up house bells, except only in very short circuits of two or three yards, with one single bell in circuit; and as the difference in price between No. 18 and No. 20 is very trifling, I should strongly recommend the bell-fitter to adhere to No. 18, as his smallest standard size. It would also be well to so proportion the size and arrangement of the batteries and wires, that, at the time of setting up, a current of at least one ampere should flow through the entire circuit. This will allow margin for the weakening of the battery, which takes place after it has been for some months in use. As a guide as to what resistance a given length of copper wire introduces into any circuit in which it may be employed, I subjoin the following table of the Birmingham wire gauge, diameter in 1,000ths of an inch, yards per lb., and resistance in ohms per lb. or 100 yards, of the wires which the fitter is likely to be called upon to employ:--

------------------------------------------------------------ Table of Resistance and lengths per lbs.

& 100 yards of cotton covered copper wires.

------------------------------------------------------------ Birmingham Diameter in Yards Ohms. Ohms. per Wire Gauge. 1000th of per lb. per lb. 100 yards.

an inch. ------------+-------------+----------+----------+----------- No. 12 100 9 00342 00038 14 80 15 00850 00094 16 62 24 02239 00249 18 48 41 06900 00766 20 41 59 12100 01333 22 32 109 31000 03444 ------------------------------------------------------------

-- 67. Whatever gauge wire be selected, it must be carefully insulated, to avoid all chance contact with nails, staples, metal pipes or other wires. The best insulation for wires employed indoors is gutta-percha, surrounded with a coating of cotton wound over it, except only in cases when the atmosphere is excessively dry. In these, as the gutta-percha is apt to crack, india-rubber as the inner coating is preferable. If No.

18 wire be used, the thickness of the entire insulating coating should be thick enough to bring it up to No. 10 gauge, say a little over 1/10th inch in diameter. There is one point that will be found very important in practice, and that is to have the cotton covering on the wires _leading_ to the bells of a different colour from that on the _return_ wires; in other words, the wires starting from the zinc poles of the battery to the bells, indicators, relays, etc., should be of a different colour from that leading from the carbon poles to the bells, etc.

Attention to this apparently trifling matter, will save an infinite amount of trouble in connecting up, repairing, or adding on fresh branch circuits. For outdoor work, wire of the same gauge (No. 18) may generally be used, but it must be covered to the thickness of 1/10" with pure gutta-percha, and over this must be wound tape served with Stockholm tar. Wires of this description, either with or without the tarred tape covering, may be obtained from all the leading electricians'

sundriesmen. Many firms use copper wire _tinned_ previous to being insulated. This tinning serves two good purposes, 1st, the copper wire does not verdigris so easily; 2ndly, it is more easily soldered. On the other hand, a tinned wire is always a little harder, and presents a little higher resistance. Whenever wires are to be joined together, the ends to be joined must be carefully divested of their covering for a length of about three inches, the copper carefully cleaned by sc.r.a.ping and sand-papering, twisted tightly and evenly together, as shown in Fig. 73 A, and soldered with ordinary soft solder (without spirits), and a little resin or composite candle as a flux. A heavy plumber's soldering iron, or even a tinman's bit, is not well adapted for this purpose, and the blowpipe is even worse, as the great heat melts and spoils the gutta-percha covering. The best form of bit, is one made out of a stout piece of round copper wire 1/4" thick with a nick filed in its upper surface for the wire to lie in (see Fig. 73 B). This may be fastened into a wooden handle, and when required heated over the flame of a spirit lamp. When the soldering has been neatly effected, the waste ends _a_ and _b_ of the wire should be cut off flush. The wire must then be carefully covered with warm Prout's elastic or softened gutta-percha, heated and kneaded round the wire with the fingers (moistened so as not to stick) until the joint is of the same size as the rest of the covered wire. As a further precaution, the joints should be wrapped with a layer of tarred tape. Let me strongly dissuade the fitter from ever being contented with a simply twisted joint. Although this may and does act while the surfaces are still clean, yet the copper soon oxidises, and a poor non-conducting joint is the final result.

"That'll do" will not do for electric bell-fitting.

[Ill.u.s.tration: Fig. 73.]

-- 68. Whenever possible, the wiring of a house, etc., for bell work, should be done as soon as the walls are up and the roof is on. The shortest and straightest convenient route from bell to battery, etc., should always be chosen where practicable to facilitate drawing the wire through and to avoid the loss of current which the resistance of long lengths of wire inevitably entails. The wires should be run in light zinc tubes nailed to the wall.

In joining up several lengths of tubing, the end of one piece of tube should be opened out _considerably_ of a trumpet shape for the other piece to slip in; and the end of this latter should also be _slightly_ opened out, so as not to catch in the covering of any wire drawn through it. The greatest care must be exercised in drawing the wires through the tubes or otherwise, that the covering be not abraded, or else leakage at this point may take place. In cases where tubes already exist, as in replacing old crank bells by the electric bells, the new wires can be drawn through the tubes, by tying the ends of the new wire to the old wire, and carefully pulling this out, when it brings the new wire with it. Or if the tubes are already empty, some straight stout wire may be run through the tubes, to which the new wires may be attached, and then drawn through, using, of course, every possible precaution to avoid the abrasion of the insulating covering of the wire, which would surely entail leakage and loss of current. All the old fittings, cranks, levers, etc., must be removed, and the holes left, carefully filled with dowels or plaster. In those cases where it is quite impossible to lay the wires in zinc or wooden tubes (as in putting up wires in furnished rooms already papered, etc.), the wires may be run along the walls, and suspended by staples driven in the least noticeable places; but in no case should the two wires (go and return) lie under the same staple, for fear of a short circuit. It must be borne in mind that each complete circuit will require at least two wires, viz., the one leading from the battery to the bell, and the other back from the bell to the battery; and these until connection is made between them by means of the "contact" (pull, push, or key) must be perfectly insulated from each other. In these cases, as far as possible, the wires should be laid in slots cut in the joists under the floor boards, or, better still, as tending to weaken the joists less, small holes may be bored in the joists and the wires pa.s.sed through them; or again, the wires may be led along the skirting board, along the side of the doorpost, etc., and when the sight of the wires is objectionable, covered with a light ornamental wood casing. When the wires have been laid and the position of the "pushes," etc., decided upon, the _blocks_ to which these are to be fastened must be bedded in the plaster. These blocks may be either square or circular pieces of elm, about 3 inches across, and 1 inch thick, bevelled off smaller above, so as to be easily and firmly set in the plaster. They may be fastened to the brickwork by two or three brads, at such a height to lie level with the finished plaster. There must of course be a hole in the centre of the block, through which the wires can pa.s.s to the push. When the block has been fixed in place, the zinc tube, if it does not come quite up to the block, should have its orifice stopped with a little paper, to prevent any plaster, etc., getting into the tube. A little care in setting the block will avoid the necessity of this makes.h.i.+ft. A long nail or screw driven into the block will serve to mark its place, and save time in hunting for it after the plastering has been done. When the blocks have been put in their places, and the plastering, papering, etc., done, the wires are drawn through the bottom hole of the push (after the lid or cover has been taken off), Fig. 74, and a very small piece of the covering of the wire having been removed from each wire, and brightened by sand papering, one piece is pa.s.sed round the shank of the screw connected with the lower spring, shown to the _right_ in Fig. 74, and the other round the shank of the screw connected to the upper spring, shown to the _left_ in the Fig. The screws must be loosened to enable the operator to pa.s.s the wire under their heads. The screws must then be tightened up to clench the wire quite firmly. In doing this, we must guard against three things.