US1821114A - Alternating current signaling system - Google Patents

Description

Sept. 1, 1931. F. E. PERNO 1i' 1,821,114

ALTERNATING CURRENT SIGNALING SYS'IEI Sept. 1, 1931. F; E. PERNOT ALTERNATING CURRENT SIGNALING SYSTEM Filed Sept. 8, 1926 2 Sheets-Sheet 2' Z Z'IG H 4 5 1 4 5 M l 52 TI? 1 g Y 9:11--

W L 58 I l atented Sept. l,

FREDERICK EUGENE PERNOT, OF LONDON, ENGLAND ALTER-NAT'ING CURRENT SIGNALING SYSTEM Application filed September 8, 1926, Serial No. 134,138, and in Great Britain September 12, 1925.

The present invention has reference to those types of telegraph signaling systems wherein the signal elements are formed by trains of a ternations of an alternating current. The invention has for its principal object to secure a more rapid rate of signaling as well as the employment of desirable forms of signaling codes. The invention is applicable to those systems wherein alternating current is used for the transmission of a single series of messages or to those systems wherein several alternating currents or alternating currents in combination with direct current are used for the simultaneous transmission of a plurality of messages.

The principal feature of the present invention consists in the utilization of alternating currents of different intensity for the different elements of a signaling code.

In carrying the present invention into effect the alternating currents constituting the different elements of the signaling code may be of different intensity as transmitted and received or may be of different intensity only as received.

A practical embodiment of the latter alternative which constitutes a feature of the 'ivention consists in utilizing alternating currents of different frequencies for the different elements of the si naling code, the attenuation along the cable being different for the different frequencies and the currents as received consequently being of d i ft'erent intensity.

A. further feature of the invention is the provision of means whereby the alternating currents are made to actuate a receiving device in opposi e directions, one direction for dots and the other for dashes thus enabling the employment of the familiar type of code known as recorder or cable code.

British patent specifications 176,827; 178,- 873; and U. S. A. application No. 624,224 describe various methods of utilizing trains of alternating current as signal elements in multiplex transmission of signals. The common signaling code utilized in connection with uch systems is the Morse code, wherein the signal elements consist of dots and dashes, which, in alternating current systems are distinguished from each other by the difference in duration of the signal impulses comprised by the trains of alternations. Spaces between signal impulses commonly comprise a mere absence of alternating current, but in accordance With the present invention the different intensities of the alternating current differentiate between dots and dashes so that the spaces between such elements can be shortened or eliminated.

The use of the present invention obviates the need of producing dashes of a prolonged nature, as in the Morse code, and thus secures the advantage of the more concise form of code, cable code. Spaces between code elements in a single letter are not required, and a further gain in speed over Morse code operation is achieved by their elimination.

In operating cable code according to the presentinvention, spaces are represented by an alternating current of one intensity, dashes by an alternating current of another intensity, and dots by an alternating current of yet another intensity, any one of which may be Zero. For example, at the transmitting end of the system, an E. M. F. of volts applied to the system may be taken to represent spacing; anE. M. F. of zero may be taken to represent dashes, and an E. M. F. of may be taken to repre-' sent dots. At the receiving end of the system the alternating current may be rectified, and if the rectification be accomplished in accordance with a linear relation, then unidirectional currents of relative intensities 0 for dashes, 1 for spaces and 2 for dots will be produced and made available for actuating any usual type of receiving apparatus. If a bias equivalent to a negative unit of signal strength be given this relay or instrument, then the resultant actuating forces upon it under the above series of signal strengths will be; 1 for dashes, 0 for spaces, and +1 for dots; and these are the normal conditions pertaining to the cable code system of signals.

If the rectifying device at the receiving end operate in accordance With a square law, that is, the rectified output being proportional to the square of the alternating current being rectified, then, in order to produce the relative outputs, 0, 1 and 2 above mentioned, there should be employed at the transmitting end E. M. F.s of

1 2 ,VZ Whatever law rectification may follow, the transmitting E. M. F. can be regulated so as to produce the desired rectifier outputs under the different conditions. Convenient forms of rectifiers for this purpose are the usual forms of thermionic valve rectifiers and bolo neter bridge rectifiers, the latter beingdescribed in British Patent No. 218,- 3611.-

The transmitted alternating currents of different strengths may conveniently be produced by applying steady currents of dif ferentstrengths to the field of an alternating current generator through the use of a key and r-heostat or plurality of batteries, or by the employment of a key and rheostats in the connection between a steady alternating current source and the system to which the signals are to he delivered.

The present invention will be more read ily understood by reference to the followingdescription and figures, wherein Fig. I shows an alternating current transmitting system for the production of differenteamplitude currents.

Fig. II shows an alternative transmitting system for the same purpose.

F ig. III shows a receiving system for interpreting the different-amplitude alternating current signals as cable code.

In Figure I, at 1 is the armature of an alternating current generator, the armature delivering its output over leads 2 to whatever transmission circuit is to be utilized. The alternating current output is controlled to form signals by the current in the field winding 3, the field current being controlled by the signaling keys 4 and 4. The signaling keys 4 and 4' are shown as the armatu Tfis of relays, controlled by magnets 5 and 5", operating from any source in the usual manner wherein the depression of one key (4) corresponds to a dot and the other (4) corresponds to a dash. For a space both keysrest against their respective back sto s 6 and 6 under the influence of springs S and One terminal of source 9 is joined to back stop 6 of the dash key by lead 11, and the other terminal of source 9 is joined by lead 12 to the back stop 6 of the dot key and by leads 13 and 14 to the front stop 7 of the dash key. Lead 15 joins the front stop 7 of the dot key to the lever 4 of the dash key. ltesistances 10 and 10 are joined to dot and dash keys 4 and 4 respectively, and

and 50 volts.

the other ends of the resistances are joined by lead 19, from which goes lead 16 to one terminal of the field 3. The other terminal of the field is joined by leads 14 and 17 to the front stop '7 of the dash key. Condenser 18 is oined across the field 3 in order to aid in shaping the signal current in held 3 as well as to prevent sparking at the relay contacts.

Vvhen dash key 4 is drawn against its front stop 7', then battery or source 9 terminating in back stop 6 is disconnected, and no current can flow to alternator field 3. Hence the alternator output is ero for a. dash. When both keys rest against their back stops for a space, then the alternator field 3 is shunted by resistance 10 and source 9 supplies current to the shunted field through resistance 10, producing, for example, 02 ampere in field 3 and a correspending armature voltage of 20 volts. When dot key 4 is depressed, resistances 10 and 10 are joined in parallel and in series with field 3, and the current in field 3 is thus greater than in the previous case of a space. Say, for example, that the field current for a dot is 0.3 ampere and that the corresponding alternating electromotivc force produced in the armature is volts. By suitably choosing the values of resistances 10 and 10, the field current can be given any desired values for dots and spaces, for

If E=voltage of source 9 X=resistance of dash rheostat 10 Y resistance of dot rheostat 1O I=desired dot current in field J=desired space current in field R resistance of field then X (E R[) /J and ()ther arrangements of keys and rheostats could be used, but the advantage of the ar rangeinent shown in Figure I is that, under the three conditions of dashes, spaces and dots, the two resistances 10 and 10 are always included in parallel across the field circuit, so that the time-constant effective during any change of current from one value to another is always constant, thus leading to uniformity in the shapes of the I."

In this figure delivered from the secondary winding23 of a transformer 24. For cable code op eration, dot key 34 and dash 34 are operated by respective magnets 36 and 36, against the spring controls 35 and 35, in the ordinary manner, between respective back stops 33 and 33 and respective front stops 32 and 32. The primary winding of transformer 24 contains two portions 25 and 26. The junction between the two portions is joined by lead 28 to the front stop 32 of the dot key 34. The other terminal of portion 26 is joined by lead 27 to the back stop 33 of dash key 34', and the other terminal of portion 25 is oined by lead 29 to one terminal of the alternating current source 20. The other terminal of the alternating current source is joined to the dot key 34 by lead 30, and the dash key 34 is joined by lead 31 to the back stop 33 of the dot key.

When dash key 34 is depressed for a dash, the circuit of alternator 2O terminates at the idle front stop 32 of the dash key, and hence no electromotive force is impressed upon the primary winding of transformer 24, and hence no alternating current is produded in the secondary winding and the transmission circuit. hen both keys rest against their back stops for a space then the electromotive force of source is impressed across both portions and 26 of the primary transformer winding in series, resulting, say, in the production of 20 volts in the secondary winding 23. When the dot key is depressed for a dot, then the electromotive force of source 20 is impressed across portion 25 alone of the primary winding of transformer 24, resulting in a greater secondary electromotive force, say volts, than in the case of a space. It is obvious that any desired ratio between space voltage and dot voltage can be produced at the terminals 21 and 22 of the transmission circuit, for in accordance with the ordinary law governing transformers space E. M. F. turns in winding portions (25) dot E. M.F. sum of turns in winding portions (25) and (26) Connections to dash key 34 are made through the back stop 33 of the dot key 34 in order to prevent, in the event of error, a wrongful connection between the terminals of the primary windings 25 and 26.

If it is desired to carry the invention into effect by way of transmitting signals of different frequency as previously set forth, either different alternations for the different-frequency signal elements can be utilized, there being a separate alternator for each frequency, or alternatively a single generating source such as a valve oscillator may be employed and its output frequency varied for the different signal elements by changing the capacity and/or inductance associated in the oscillating circuit, as is well known in the art. Nevertheless, whichever method 38 of a transformer. Secondary 39 of ni e.

transformer connects through battery 40 to grid 41 and filament 42 of a three-electrode valve, the battery 40 being used to cause the valve to act as a rectifier, as is well known in the art. At 43 is the valve plate or anode connecting through battery 45 and leads 47 and 48 to the moving coil 54 of an ordinary cable relay and to the filament 42. In the filament circuit is battery 44 for lighting the filament. An adjustable resistance 49 shunts the relay coil 54 (enabling the deflections of the latter to be controlled) and a condenser 46 is also shunted across the relay coil for the purpose of absorbing ripples produced in the anode current by the rectification of the alternating current (or E. M. F.) impressed upon the grid. A battery 51 in series with resistance connects by leads 52 and 53 across the relay coil and its shunt.

Now suppose that the valve rectification proceeds according to a square law. The signal strengths at the grid will then be adjusted so as to be,'say, S volts for dots,

volts for spaces, and 0 volts for dashes. In the anode circuit unidirectional currents of respective mean values of 2a+b, a+b and b will be produced; 2a, a, and 0 being the respective rectified portions whilst Z) is the steady value of anode current when 0 alternating E. M. F. is impressed upon the grid. Now, if E=E. M. F. of battery 51 and R be the resistance of rheostat 50, and if R be adjusteduntil the relation E /R=w+b be fulfilled, then when the plate or anode current is (1+?) for spaces there will be no current flow through shunt 49 and relay coil 54. The relay coil will thus stand in its neutral position for spaces, as is customary in ordinary direct-current cable code working. When the anode currents falls to b for a dash, a current of a will be produced in relay coil 54, and when the anode current rises to 2a+b for a dot, then the current in the relay coil will be +a, and the required conditions for a directionally responsive operating relay 54 for cable code reception are established. The deflections of the relay coil 54 may then be utilized in any well known 7 ZLU ma ne fo the u t er hand ng o t e signals, for instance as shown, by causing tongue 55 ca ied by e ay o l to play between contact butts 56 and 57, thus cause ng bette 9, onnected to t gue by lead 58 to actuate magnet 62 or 6.3 through lead or v6.1 according to whether contact is established at butt 5 6.or 57 according as the signal is a dot or a dash, the latter in turn depending upon the strength of the arriving alternating current signal.

I t b no that ba tery 51 an resistance ,50 serveto establish neutralizing effect or bias in the receiving circuit equal to :the anode current during spaces. This bias could be secured, less advantageously, however, by mechanical action on the relay coil, as by twisting the suspension fibres, or it might also be produced in the relay coil by causing a current to flow through an auxiliary winding, but the result in any case remains the same.

In actual practice, the valve rectification does not proceed exactly according to a square law, so that the received signal strengths are adjusted by trial (either at the transmitting end of the system or by the transformer 38, 39, or equivalently) until in the anode circuit the space current is equal to the mean of the dot and dash currents. The bias current from battery 51 is then adjusted to suit the resulting space current.

If, instead of a valve rectifier, a bolometer bridge as described in British Patent No. 218,361 be utilized, .then separate biasing means need not be provided as described. The ohmic balance in the bridge would be established to suit the heater element tempcrature produced by the alternating spac-. ing current, thus leaving the associated relay in a neutral position for spaces. The zero alternating current of dashes and the increased alternating current of dots would produce imbalances in opposite directions, thus causing the associated relay to operate in conformity with cable code signals.

Whilst the present invention has been described in detail with reference to cable code signals, it is obvious that the inven-. tion is not limited thereto in its application. It is applicable to any signal code involving three or more current conditions in the system (cable code as a special case involving three conditions), and the invention is deemed to extend to such general application.

Claims:

1. In an alternating current signaling system, a generator or generators of alternating currents supplying said system and automatic means for varying the excitation of the generator or enerators independently of the frequency df the alternating current generated thereby, and receiving devices operated in different directions by the alternatinsert-i4 ing current impulses of different intensity, which respond'at a distant station to the varying intensity of the successive waves or parts of waves of the alternating current.

2. In an alternating current signaling syss tern, an alternator supplying signal energy to .the system, a transformer including pr1- mary and secondary windings, the secondary winding being connected to the transmission line of the system, said primary winds ing including a plurality of taps connected to different numbers of turns and make and break apparatus selectively connecting the alternator to predetermined taps of the primary winding whereby to produce signal impulses of varying intensity in the line.

3. In an alternating current signaling system, an alternating current generator, means for definitely varying the field current thereof to produce signal impulses of three different intensities in the armature circuit thereof, a receiving apparatus associated with the armature circuit and including a thermionic valve for rectifying the signal impulses, a moving coil relay connected with the rectifier and operating a recorder in response to definite signal impulses, and means for imposing on said coil a biasing current equal to the anode current of the rectifier increased by the strength of an intermediate signal impulse, whereby to render the coil directionally responsive to said other impulses.

.4, In an alternating current signaling system, a source of alternating current of substantially uniform intensity, means for systematically varying the intensity of the alternating current to produce signal impulses and a receiving apparatus operatively associated with said system, and including a relay having an element movable in opposite directions in response to the signal impulses of different intensities.

5. In an alternating current signaling system, a source of alternating current of substantially uniform intensity, means for systematically varying the intensity of the alternating current independently of the time period of said current to produce desired signal impulses and a receiving apparatus operatively associated with said system and including means for rectifying the signal impulses and a relay including movable coil rota-table in opposite directions in response to signal impulses of different intensities.

6. An alternating current signaling system comprising a source of alternating current of substantially uniform intensity, means for systematically varying the intensity of the alternating current to produce desired signal impulses, and a receiving station operatively associated with said system and including a thermionic rectifier for the signal impulses, recording apparatus including a moving coil relay connected to the rectifier, and means for biasing the moving coil of the relay to render the same directionally responsive to signal impulses of different intensity.

7. In an alternating current signaling system utilizing variations in current in tensity to produce desired signal impulses of a plurality of different values, the method of rendering a moving coil recording apparatus connected in said system directionally responsive to the signal impulses of varying intensity comprising rectifying the signal impulses by means of a thermionic valve, delivering the rectified impulses to said moving coil recording apparatus, and simultaneously supplying the said coil with a biasing current of opposite polarity and of a value equal to the normal anode current of the valve increased by the current value of an intermediate signal impulse.

8.111 an alternating current signaling system, utilizing variations in current intensity for producing signal impulses, a transmitting circuit including aplurality of impedance elements and switching means for varying the circuit connections of said elements while maintaining all of said elements in the circuit whereby to maintain the time constant effective during changes in current intensities substantially constant.

9. In an alternating current signaling system, utilizing variations in current intensity for producing signal impulses, the method of maintaining the time constant effective during any change of current value substantially uniform comprising connecting a plurality of impedance elements in the transmitting circuit and varying the relative effective values of said elements by changing the circuit connections thereof in a manner to produce currents of desired values while maintaining all of said elements in the circuit for all values of current in excess of a predetermined minimum.

10. An alternating current signaling system comprising a source of alternating current of substantially uniform intensity,

means for varying the intensity of said current in time periods independent of the time period of the alternating current to produce signal impulses, a receiving apparatus operatively associated with the system and including a rectifier for the signal impulses, a direct current recording apparatus operatively associated with the rectifier and including a moving coil relay and a biasing current traversing said coil and functioning to cause the same to rotate in opposite directions in response to currents of different intensities.

11. In an alternating current system employing signal current impulses of three different intensities, a receiving apparatus for said signal impulses including a thermionic valve, a movable coil relay associated with FREDERICK EUGENE PERNOT.

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