US2522874A - Circuit failure indicator for receiving telegraphs - Google Patents

Description

CIRCUIT FAILURE INDICATOR FOR RECEIVING TELEGRAPHS @www i sept. 19, 195o Patented Sept. 19, 1950 2,522,8'ZiA CIRCUIT FAILURE INDICATQR FR RECEIVING TELEGRAPHS Alfred Kahn, Queens Village, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application January 4, 1946, Serial No. 639,088

11 Claims. l

This invention relates to an error indicator for a receiving telegraph. The principal purpose of the invention is to indicate conditions of signal reception, particularly when the communications channel fails to bring in the signal.

Various types of error indicating devices have been used inthe past, such as those which develop an error indication whenever the code signal itself becomes mutilated. For example, in U. S. Patent Re. 22,394, which was a reissue on November 23, 1943, of an original Patent 2,183,147, dated December l2, 1939, and granted to John B. Moore et al., the apparatus used was adapted to respond normally to code signals all of which were composed of a uniform number of marking elements and a uniform number of spacing elements. Whenever the number of marking elements as received for any individual code signal became abnormal. an error indication was produced. Such a system is more eiciently employed when the signals are multiplexed.

In multiplex printing telegraphy the code sig nals for a plurality of messages are continuously received and applied cyclically to the respective printers, each printer having a code translating device which operates to select a character to be printed.. The printing function must follow the receipt of the last code element in a character signal, Hence the time intervals allowed to different printers for performing their printing functions are staggered so that the code selecting mechanism of each printer may be prepared to translate the signals assigned to it without any spacing between the signals for diiierent printers.

With simplex operation, however, time must be allowed between successive character code combinations for the printer to operate, or else some sort of storage means must be provided which will permit of continuous reception of the code combinations and intermittent set-up of the char-l acter selections preceding the times required for mechanical functioning of the printer.

In my invention as herein disclosed I have provided a rotary distributor which comprises not only a sufcient number of segments for code signal translation, but also an additional number of segments which may be used for circuit condition indication. Such a distributor preferably has at least eight segments in the distributor ring, five of which are used for the conventional five-unit code and three of which are used for circuit condition indication. If the now well known sevemunit code is to be used, then seven segments will, oi'` course, be required for character selection plus three additional segments for circuit condition indication, a total of ten seg-v ments, as in the embodiment herein disclosed.

It is an object of my invention to provide auxiliary error detecting equipment which may be advantageously used for producing a warning signal whenever receiving conditions over a radio or other communications channel become inoperative.

It is another object of my invention to provide an indicator to be .used at a telegraph receiving station for calling attention to a communications channel failure.

Other objects and advantages of my invention will be made apparent in the detailed description to `follow. This description is accompanied by a drawing in which Fig. 1 shows a preferred arrangement of a rotary distributor to be used at a transmitting station for composing the character signals and for transmitting other pre-arranged signals to be be used for error indication at a receiving station,

and

Fig. 3 shows a plot of cathode voltages in a gaseous tube corresponding to successive charges to be impressed upon a certain condenser ina portion of the circuit shown in Fig. 2.

It should be stated in the outset that my invention iinds its greatest utility in detecting operational failures rather than in detecting occasional mutilations of the traflic signals. It is common practice when no traiiic is being handled to continuously transmit an idlentime signal in order to maintain contact and synchronism between a transmitting and a receiving station, particularly in single channel operation. The idle-time signal has the same characteristics as other character signals. That is, it is composed of three'marking elements and four spacing elements, provided the seven-unit code is used. characteristics of all other character combinations, failure to receive it during periods of trafiic inactivity will produce an error indication on the printer.

But such an'idle-time signal in my case is not necessarily applied to the distributor segments which are reserved for character code signals. The reason for this is that I preferably employ a distributor having supplemental segments to be used primarily for indicating circuit failure and for idle-time signals. By removing the idle-time It having the same signal from the portion of the distributor which is used to selectively operate a printer a considerable saving is made in wear and tear on the code translating mechanism of the printer. The advantage of this arrangement is, therefore, apparent, lparticularly on circuits where the ratio of inactive to active periods is high, but where Contact must be maintained between transmitting 4and receiving stations throughout a large part of the business day.

Another consideration which is apparent in the use of my invention is that no relay storage or other storage means are required for simplex operation of a printer. The distributor brush while passing over the supplemental segments allows time for mechanical functioning of the printer between code selecting operations.

Referring rst to Figure l, I show therein the arrangement of the distributor ring required at a transmitting station whereby the present invention may be practiced. At the transmitter I employ a solidl distributor ring II and a segmented ring I2 comprising ten active segments numbered I to I'v inclusive. These rings are shown in developed form. Intervening between the segments are insulation segments which are of suflicient width to avoid short-circuiting between `active segments when the brush `passes over them. The rotor of vthe distributor has mounted thereon two interconnected brushes I3. Of the ten active segments, the first seven, that is, segments l to I inclusive, are connected to individual contacts of a keying device, preferably one conventionally controlled'by a perforated tape. These segments may be normally active only during times when messages are transmitted, being ineffective at other times. The remaining segments 8, 9 and I0 are utilized primarily for idle time signals and for circuit failure indication functions. In order to generate signals for such purposes segments 8 and IU are connected permanently to the negative terminal of a direct current source while segment 9v is connected to the positive terminal of said source. A neutral center-tap on the same source will be understood to be grounded.

The solid ring II collects the signals as composed by the tape keying device and applies them conventionally for keying the carrier wave of a radio transmitter.

Referring n'ow to Fig. 2, I show a radio receiving unit I 4 having on its input side an antenna circuit including an lantenna I5 anda ground connection. On the output side of the unit I4 I show preferably a polar relay I6, the tongue I'I of which is arranged to swing between two conta'ctsv I8. and I9 having different potentials alpplied thereto. As shown in the drawing contact I8` is negative with respect to ground while contact I9'is grounded. The source usually employed is one in` which an intermediate point thereof is grounded.

They relay tongue Il is connected to the solid ring 2'0 in a receiving distributor. Associated with' this ring is a segmented ring 2| having segments Il to IIIv inclusive corresponding to those of' the transmitter distributor. In other words, segments I to 'I inclusive are those required for character code signal reception and translation in. order to control a receiving printer. These segments are connected respectively to different selecting units in the printer. Segments 8, 9 and IUare those which correspond with the pre-arranged idle-time and circuit condition indicating portion of the signals as will be described below.

Under normal operation of the receiving relay I6, and during the reception of traic signals, either minus or ground potential will be applied to the respective segments I to I inclusive in accordance with the composition of each code signal. Translation of the code signals is accomplished conventionally and need not be described herein. The operation of relay I6 while the brush 22 traverses segments 8, 9 and I0 will be such that normally segments 8 and I0 receive negative pulses while segment 9 receives a relatively positive pulse, say, of ground potential.

The circuit arrangement of Fig. 2 includes two discharge tubesl 23.1and 24 which are connected as in a' conventional trigger circuit arrangement. That is to say, the anode in tube 23 is coupled across a capacitor 2'5 to the grid in tube 24. The anode in tube 24.l is coupled through a resistor 26 tothe grid in tube 23. The anodes in the two tubes are connected to a positive terminal of ya suitable direct current supply source through resistors 21. The cathode in tube 23 is connected.

to ground through a resistor 28. The grid in tube 23 is connected through a resistor 29 to a tap on a potentiometer 3U, this potentiometer being connected between ground and a direct current source terminal more negative than ground, here indicated by a minus sign The cathode in tube 24 is directly grounded and the grid in this tube is connectedto ground through a resistor 3 I.

The grid in tube 23 is normally held sufficiently negative by adjustment of the tap on potentiometer 3U so that a positive pulse above the threshold bias must be applied to this grid in order to drive the tube conductive. Otherwise, for conductivity, the cathode in this tube must be driven more negative by a negative pulse from segment 9 in the distributor ring, such a pulse being impressed across a resistor 32. Since normally the pulses applied to segments 8 and I0 are negative and the pulses applied to segment 9 are at ground potential tube 23 remains non-conductive until a false signal is received over these segments. In such cases'tube 23 will become conductive and this condition will result in the blocking of tube 24 due to the toggle action in this pair of tubes. Such toggle action may be reversed after a predetermined time interval which results from the time constant characteristics of the circuit, particularly as determined by the chosen values of the capacitor 25 in relation to resistors 26, 2'! and 3 I.

The trigger circuit, comprising tubes 23 and 24 and associated circuit components, is utilized to operate a conventional pulse counting circuit arrangement which includes diode rectifier units 38`and 39 and time constant circuit consisting of a resistor 36 in series with a capacitor 31, these two elements being connected between the anode in tube 24 andthe junction between the anode of the diode 38 and the cathode of' diode 39. The cathode of diode 38 is connected to ground through a resistor 33. The anode in diode 39 is connected to ground through a, resistor 4I, this resistor being shunted by a capacitor 40.

In order to detect not less than a predetermined number of circuit failures in a given time interval and toprovide non-detection of isolated cases of erroneous signal reception the counting circuit is arranged'to ignite a gas lled tube 42. This tube. hasits cathode connected to the junction between the anode of the diode 39 and one electrode of capacitor 4U. The anode in tube 42 is connected through the winding of a relay 43 and through normally closed contacts 4l and 48 of this relay to a positive potential source indicated by the plus sign In shunt with the contacts 41 and 48 is a manually operable switch 49. The grid in the gas filled tube 42 is connected through a resistor 44 to a tap on a potentiometer 45, this potentiometer being connected between ground and the negative terminal of a source whose positive terminal is grounded.

Relay 43 is also provided with contacts 53 and I `which are arranged to close before contacts 41 and 48 open. Contacts 5l) and 5l when closed complete a circuit from the positive source terminal through a resistor 53 and through these contacts to an indicator lamp 52 one terminal of which is grounded.

Circuit operation Under normal conditions tube 23 will be cut 01T and tube 24 will be conductive. This state will exist so long as segments 8 and I3 continue to apply negative potential to the grid of tube 23 and so long as segment 9 continues to impress ground potential on the cathode of tube 23.

If, however, the received error indicating pulses vary from their correct arrangement such as by the polarity of any one or more of the applied voltages being reversed, then the trigger circuit will be actuated in such manner that tube 23 becomes conductive and tube 24 is cut off. If this condition continues for a period of time determined by the tube electrode potentials and the time constant of the trigger circuit components, principally condenser 25 and resistor 3|, then a voltage will be developed across the resistor 36 and condenser 31 such as to place a substantial charge on condenser 40, thus producing a voltage drop in resistor 4I and driving the cathode in the gas filled tube 42 more negative. The time constant of the trigger circuit including components 25 and 21 is so chosen that this circuit is not restored to its normal condition of stability in a time shorter than that required to send the three error indicating pulses, nor longer than that required to send the next group oi signaling elements. Thus one and only one operation of the trigger circuit is possible during one revolution of the face-plate brushes 22.

At the moment when tube 24 is made non-conductive a positive pulse is coupled through condenser 31 to the interconnected anode and cathode elements of the diode tubes 38 and 39. The positive pulse is shorted to ground by diode 38 whose cathode is connected to ground through a resistor 33. The negative pulse produced by the return of the trigger circuit to normal will pass through the diode 39 and cause an increment of charge to appear across the terminals of condenser 43. Resistor 4i will discharge the condenser at a fixed rate. If the charge increment is repetitive for each distributor cycle, then after a fixed number of error cycles comes in, say, three, the net charge on condenser 4l) will be such as to effectively drive the cathode in tube 42 negative with respect to the potential of its grid, so as to ignite this gaseous tube. By adjusting the grid bias as by means of the adjustable tap on the potentiometer 45 the magnitude of the charge ini crement on condenser 40 and on the cathode of tube 42 may be made operative after any reasonable required number of signals has been received in error. If the device has been set to operate on three errors and two are received in succession but not the third, then condenser 4B will discharge so that if another error is received on the next distributor cycle then tube 42` will not fire. However, should another error occur immediately then tube 42 will fire.

Fig. 3 explains the possible sequence of operations due to successive applications of charge potentials to the condenser 40. The ring voltage applied negatively to the cathode in tube 42 with respect to the Voltage in its grid is represented by the line f. The charging potentials which drive the cathode more and more negative` are represented by steep front slopes in the sawtooth wave. Negative peaks of this wave are shown at points a, b, c, d and e. The longer slopes interconnecting the wave fronts represent discharges of the condenser 4|] through. resistor 4 l. If. circuit failures occur during two successive cycles of the distributor but not a third then the condenser will discharge as along the dotted line g in the graph of Fig. 3. quire two successive cyclic periods of circuit failure to bring the charging voltage on the condenser 46 to the point where the gas filled tube 42 would be ignited. This is shown at point e of the saw-tooth wave.

When tube 42 becomes conductive relay 43 operates and closes its contacts 5u and 5| for lighting the indicator lamp 52. Preferably-relay 43 is of the quick-acting, slow-release type so that the lamp 52 will remain lit for an appreciable time to give the necessary error indication. If the switch 49 is left open then relay 43 will operate to open the anode circuit of tube 42 by breaking the contacts 41 and 43. This permits the counter circuit to again become effective upon repetition of the error signals. If, however, it is desired that the lamp 52 shall remain lit indenitely to effect detection of only the first cyclic -period of circuit failure, then switch 49v will be closed manually and tube 42 will remain conductive until the attendant opens the switch 49.

Tube 42 when it conducts, rapidly discharges condenser 45 so that the entire circuitis quickly conditioned to detect and indicate succeeding errors.

It will, of course, be understood that in carrying out my invention the number of segments to be included in the distributor rings l2 and `2| may be varied -according to circumstances and according to the particular requirements of any printing telegraph system in which this device is tc be employed. i

It will also be understood by those skilled in the art that when my invention is applied to a synchronous simplex telegraph system synchronizing means of any well known type may be adopted for holding the receiving distributor in correct phase relation to the transmitting dis` tributor. I have not shown any synchronizing means as an essentialpart of my invention, but call attention to the fact that where the'8th,` 9th and 10th segments of my distributor are used for idle-time signals, these same signals must be relied upon for controlling the operation of the phase corrector during times when no message traflic is being transmitted. Only in the case of complete failure to receive any signals would phase correction fail of accomplishment.

Various modifications will, ofcourse, suggest themselves to those skilled in the art. Such modifications may be employed without departing from the spirit and scope of the invention.

I claim: Y

1. A system for indicating circuit failures in a telegraph channel comprising a receiving distributor having segments for the translation` of message code signals and other segments for theu After that it would retranslation of idle-time signals, electronic-means coupled to said other segments and arranged to be activated by said idle-time signals when incorrectly received and unaffected by said idletime signals Whenl correctly received, and indicating means subject to control by said electronic means to provide an indication upon repetition of failure to receive said idle-time signals or uponreception thereof in mutilated form during a predetermined time interval.

2. A system for indicating circuit failures in a telegraph channel comprising a receiving distributor having segments for the translation of message code signals and other segments for the translation of idle-time signals, an electronic trigger circuit normally biased to maintain a firstcondition of stability and means coupled to said other segments for producing a second condition of stability of said trigger circuit during a predetermined time interval in response to failure to receive said idle-time signals or from reception thereof in mutilated form, and means subject to control by said trigger circuit for making an indication of circuit failure whenever said second condition of stability is repeatedly produced during said pre-determined time interval.

3; Avsystem for indicating circuit failures in a telegraph channel comprising a receiving distributor having segments for the translation of message code signals and other segments for the translation of idle-time signals, and electronic trigger circuit normally biased to maintain a rst condition of stability and means coupled to said other segments for producing a second condition of stability of said trigger circuit during a predetermined time interval, said means operating uponv failure to receive said idle-time signals or fromireception thereof in mutilated form, and means for making an indication of circuit failure Whenever said second condition of stability is repeatedly produced during a time interval commensurate with a predetermined number of cycles of said distributor.

4. Monitoring apparatus for use in code signal reception comprising distributor means for allocating message code signals to a translator therefor and for differently allocating idle-time signals, electronicmeans having two conditions of. stability, means for maintaining the first of said conditions so long as the idle-time signals are correctly received, and means responsive to failure to correctly receive an idle-time signal during any single cycle of said distributor means forv inducing the second of said conditions, a gaseous tube having its discharge path connected in circuit with a device for storing energy pulses whichI arise during transitions from the second to'thei'lrst of said conditions of stability in said electronicmeans, said tube having a control electrode connected-in an input circuit by which it is triggered into conductivity in response to the upbuilding of said energy pulses to a critical value', a relay in circuit with the discharge path of said gaseous tube' and indicator means operable bysaid relay during the conductive state of said gaseous tube.

Apparatus according to claim 4 and including a rectifier stage interposed between said electronic means and said device for storing energy pulses.`

6. Apparatus according to claim 4 and including rneans for draining the pulse energy out of said-storing device at a rate such that said criticaltriggering value is reached only after the persistence of idle-time signal failures for a predetermined number of cycles of said distributor means.

7. Monitoring apparatus for use with telegraph circuits comprising a receiving distributor having segments reserved for message signals and further segments reserved for pre-arranged signals, an electronic trigger circuit normally biased to maintain a first condition of equilibrium, means to couple said trigger circuit to said further segments to shift said trigger circuit to a second condition of equilibrium upon failure to receive said prearranged signals, means responsive to said shift of equilibrium to store an increment of electric energy for a pre-determined time interval, and means responsive to said stored electric energy to indicate a repeated failure to receive said pre-arranged signals during said time interval.

8. Monitoring apparatus for use with telegraph circuits comprising a receiving distributor having segments reserved for message signals and further segments reserved for pre-arranged signals, an electronic trigger circuit normally biased to maintain a rst condition of equilibrium, means to couple said trigger circuit to said further segments to shift said trigger circuit to a second condition of equilibrium upon failure to receive said pre-arranged signals, the time constants of said trigger circuit having values at which the time at which the trigger circuit is restored to said first condition of equilibrium lies between the time required for transmission of said pre-arranged signals and said message signals, means responsive to said shift of equilibrium to store an increment of electric `energy for a pre-determined time interval, and means responsive to said stored electric energy to indicate a repeated failureV to receive said prearranged signals during said time interval.

9. Monitoring apparatus for use with telegraph circuits comprising a receiving distributor having segments reserved for message signals and further segments reserved forpre-arranged signals, an electronic trigger circuit normally biased to maintain a first state of equilibrium, means to couple said trigger circuit to said further segments to shift said trigger circuit to a second state of equilibrium upon failure to receive said pre-arranged signals, a capacitor coupled tosaid trigger circuit to store an increment of electric energy therein responsive to said shift of equilibrium, a resistor shunting said capacitor to discharge the sam-e after a pre-determined time interval, and electron discharge means coupled to said capacitor to initiate an electron discharge in response to said stored energy to indicate'a repeated failure to receive said pre-arranged signals during said time interval.

10. Monitoring apparatus for use with telegraph circuits comprising a receiving distributor having segments reserved for message signals'and further segments reserved for pre-arranged signals, an electronic trigger circuit normally biased to maintain a stable state of equilibrium, means to couple said trigger circuit to said further segments to shift said trigger circuit to an unstable state of equilibrium upon failure to receive said pre-arranged signals, the time constants of said trigger circuit having values at which said trigger circuit is returned to said stable state of equilibrium before the next succeeding reception of said pre-arranged signals, a capacitor, a pair of rectifier devices coupling said capacitor to said trigger circuit, saidA devices being poled to discharge positive pulses and translate negative pulses to charge said capacitor with an incremental charge in response to said return of equilibrium and means responsive to the charge on said capacitor to indicate a repeated failure to receive said pre-arranged signals.

11. Monitoring apparatus for use with telegraph circuits comprising Aa receiving distributor having segments reserved for message signals and further segments reserved for pre-arranged signals, an electronic trigger circuit normally biased to maintain a rst condition of equilibrium, means to couple said trigger circuit to said further segments to shift said trigger circuit to a second condition of equilibrium upon failure to receive said pre-arranged signals, said trigger circuit having time constant of values at which the trigger circuit is returned to said first condition of equilibrium to be in readiness for the succeeding transmission, a capacitor, rectifier elements coupling said capacitor to said trigger circuit to place an incremental charge on said capacitor upon each return to said first condition of equilibrium in response to each failure to receive said pre-arranged signals, a resistor coupled to said capacitor to discharge the same ata predetermined rate, a circuit including a grid controlled gaseous discharge tube coupled to said capacitor, and adapted to be triggered into conductivity at a predetermined charge on said capacitor, a utilization device in circuit with the discharge path of said discharge tube whereby said utilization device is actuated upon triggering into conductivity of said discharge tube in response to the upbuilding of the charge on said capacitor, :and means to vary the potential at which said discharge tube is triggered to vary the circuit failure repetition rate at which said utilization device is actuated.

ALFRED KAHN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,689,294 Potts Oct. 30, 1928 1,861,553 Shanck June '7, 1932 2,343,240 Molins Mar. '7, 1944 2,351,014 Connery Jlme 13, 1944 FOREIGN PATENTS Number Country Date 221,341 Germany Apr. 28, 1910 OTHER REFERENCES Bell Laboratories Record, Dec. 1943, Telegraph-Transmission Set, by W. T. Rea, 178--69A.

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