US2231397A - Error detector for telegraph printers - Google Patents

Description

Feb 11, .J. A. SPENCER ERROR DETECTOR FOR TELEGRAPH PRINTERS Filed March 50, 1958 2 Sheets-Sheet l INVENTOR. JAMES/1. SPENCER ATTORNEY.

Rab. J. A. SPENCER 9 31397 ERROR DETECTOR FOR TELEGRAPH PRINTERS Filed March 50. 193B 2 Sheets-Sheet 2 mg I -n mu 3 Z 4;

INVENTOR. 73 67 JAMES A. SPENCER ATTORNEY.

Patented Feb. 11, 1941 UNITED STATES I canon nr'rao'ron roa TELEGRAPH PRINTERS James A. Spencer, Teaneck, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application March 30, 1938, Serial No. 198,809

. 14 Claims.

This invention relates to error detectors and has particularly to do with means associated with a printing telegraph receiving apparatus for detecting errors of transmission of code signals, also for detecting the occurrence of fading conditions when telegraph code signals are transmitted over a radio channel.

This application is a continuation in part of my co-pending application, Serial No. 147,398, filed June 10, 1937, which issued April 11, 1939 as Patent No. 2,153,737.

It is an object of my invention to provide means for detectinginstances of mutilation of code signals and to provide means for controlling a teletypewriter in such manner as to prevent the printing of characters in response to mutilated signals. It is a further object of my invention to provide a system for causing an error designating character to be printed in place of an intelligence bearing character in response to either the reception of a mutilated signal or otherwise in response to a fading condition on a radio channel.

While the principles involved in carrying out my invention are largely common to the parent application and to this continuation case, I have herein shown a specific embodiment of the invention which has been found particularly useful due to its adaptability to printing telegraph receivers of a conventional type. v

As in the parent application, so also in this case, I prefer to make use of a signalling code having equal intervals for each character and having preferably seven or eight time intervals allotted to each code signal so that a fixed number of marking time intervals may always be present in each code signal.

A code signalling system in which the signals are of equal length and possess a fixed ratio other than 1 to 1 between the number of marking and spacing units thereof has been disclosed in U. S. Patent No. 2,183,147, granted Dec. 12, 1939 to John B. Moore and Richard E. Mathes.

A telegraph printer adapted to be actuated by code signals of uniform length and having as many as seven or eight time elements in each code signal would require, of course, an equal number of selector bars. As explained in the application of Moore, et al. above referred to, it is desirable that a fixed number of selector bars be actuated in making the selection of any charactor to be printed. If a shift key, is employed, then seven units in the code signal would be suflicient. If no shift key is employed, then eight units would be required for differently characterizing each code signal for ordinary communications purposes. My invention has particularly to do with a novel means for counting the number of marking impulses in each code signal so that if the fixed number of such impulses is three, them the reception of any code signal having more or 5 less than three marking impulses would be efiective upon the error detecting device of my invention so as to enable the receiving printer to print an error indicating character in place of the intended character. 10

I have found that an electrical circuit arrangement for carrying out the objects of my invention. is preferable to a purely mechanical structure which might be designed for obtaining similar results. If the marking impulses are mechanil5 cally counted, it is true that it is possible to detect the errors which may occur in transmission, but an objection to the use of mechanical means lies in the problems of maintenance of such a system as well as problems of maintaining a suitable 20 printing speed. My invention is free from these objections because it operates on the bwis of current differentials resulting from the completion of a definite number of circuits, each completion being upon reception of a. marking impulse. The 25 error detector, therefore, operates under the control of the received signal.

My invention will now be described in more detail, reference being made to the accompanying drawings in which Figure 1 shows a. fragmentary plan view of a series of contact springs associated with the selector bars of a conventional printing telegraph instrument;

Fig. 2 shows a front elevation of the contact 3 springs, the selector bars, and associated apparatus for use in error detection; and

Fig. 3 shows schematically an end view elevation of the contact springs, the code selector bars, a pull bar and lever mechanism connecting with a 40 type bar of the printer, which type bar may be used for error detection and may be restrained from making a stroke by means of an electromagnet in response to the reception of a correct code signal. 45

In the description to follow, like parts are given, like reference numerals in the several figures. Although the invention is herein illustrated by only one embodiment, the several figures are presented for more clearly showing the structural 50 details fromdifferent points of view.

Telegraph typewriters adapted to print characters in response to five-unit code signals have been in general use for sometime. When, however, it was discovered that a seven-, or eightunit code had certain advantaga for purposes of error detection, it became necessary to increase the number of code selector bars from five to'at,

mounted in ways 3 so that they may be actuated by a slight longitudinal movement in response to the code signals. The various cuts or notches 5 in the code bars are so arranged that when the code bars are adjusted in response to a code signal all seven of the notches 5 are opposed to one particular pull bar, or type selector I for selecting the same and for actuating a type bar 9.

Now, according to my invention, thereis provided a series of contact springs and I3 disposed in pairs, each pair being associated with one of the code bars I respectively. The contact springs are preferably mounted in a holder I5 of insulating material and may be clamped together in the usual manner for a spring pile-up." Considering each pair of contact springs the spring II is relatively stiff, while the spring I3 is relatively flexible and is provided with a rearwardly extending portion carrying an insulator II. A certain spring tension causes the spring I3 and its insulator ll to be urged against a shoulder I9 on the code bar to be disclosed in this continuation application.- Furthermore, I have found that certain modifications of the error detecting circuit arrangement are desirable and they will, therefore, now be described.

Connected with each of the contact springs I3 is a resistor 2|. The several resistors 2| are of like value and all are fed with energy from any suitable current source, the positive terminal of which is here shown connected to a common conductor 23. The companion contacts II are connected in parallel to a common conductor 25 leading to a relay 21 which is serially connected through the windings of two further relays 29 and 3|. The ground connection beyond the relay 3| may be considered the same as the negative terminal of the source.

The relays 21, 29 and 3| are biased by springs 33 whose tensions are suitably adjusted for causing each of the relays to respond to currents of different amplitude. The adjustments of these spring tensions are, therefore, made suitable for causing relay 21 to operate on a current strength equal to the current passed through one or more of the resistors 2|. Relay 29 is adjusted to operate on a current strength equal to the total current passed through exactly three of the resistors 2|. Relay 3| is adjusted to operate only on a current strength equal to the total current passed by at least to of the resistors 2|.

It will be remembered that in carrying out my invention I preferably utilize seven-unit code signals in which every signal is characterized by the presence of exactly three marking impulses. The relays 21, 29 and 3| are provided with circuit arrangements through their associated contact springs for operating a magnet 35 whose armature 75 31 is pivoted at 39. A lever member 4| which supports the armature 31 normally holds the armature away from the core-piece of the magnet 35 under tension of a spring 43. A push rod 45 is connected at one end to the lever arm 4| and is supported at the other end by a bracket 43 having slot 49 opposite the pull bar 1e so that no matter what combination of marking and spacing elements may be set up on the code bars there is always an open space at 49 for the pull bar I. to drop into, provided it is not restrained from so doing by the actuation of the magnet 35 and the forward movement of the push rod 45. It will, therefore, be seen that for normal reception of intelligence-bearing telegraph signals the magnet 35 should be energized each time a character is to be printed. When, however, a code signal becomes mutilated, or even if it drops out due ,to fading, it is required that the magnet 35 shall not be energized and that the error designating type bar 90 shall be actuated. The circuit for controlling the magnet 35 will now be described.

The positive terminal of a direct current source leads through a resistor 5| to the winding of the magnet 35 and thence to the movable contacts of relays 21 and 3|. The back contact of relay 21 is grounded as is the negative side of the operating source. The front contact of relay 29 isalso grounded. The back contact of relay 3| is connected to the movable contact of relay 29. If desired, a capacitor 53 may be connected in shunt with the winding of the magnet 35 for reducing contact sparking at the relays.

When unmutilated signals are received, namely, signals uniformly bearing three marking impulses, the current flowing through the conductor 25 which is derived from the source through three of the resistors 2| in parallel is just sufficient to actuate relays 21 and 29 but is insulllcient to actuate relay 3|. Under this condition an energizing current for magnet 35 will flow through the tongue and back contact of relay 3|, the tongue and front contact of relay 29 and thence to ground. If, however, the signal is mutilated so that only one or two marking impulses are received, then fewer than three pairs of contacts ||I3 will be closed and the current flow through less than three of the resistors 2| will be insuflicient to actuate either of the relays 29, 3|.

The dropping out of one or two marking impulses in a seven-unit code signal. therefore, results in a de-energization of the magnet 35, since its actuating circuit is broken by the release of relay 29 and also by the pulling up of the armature of relay 21. Hence, there is no ground connection for a return circuit from the magnet 35. Under this condition the push rod 45 assumes a withdrawn position with respect to the pull bar 12. The pull bar I; is, therefore, permitted to drop into the notches 49 of the seven code bars and actuation of the error symbol type bar is effected. This type bar may also be actuated by de-energization of the magnet 35 when a static impulse is superimposed upon the transmitted signal, thereby increasing the number of marking impulses in the code signal to four or more. Under these conditions the excess current supplied through four or more of the resistors 2| and through contacts which are closed between the springs II and I3 for different code bars will sponse to a marking impulse have been moved into position for opening up an alignment of notches 5 opposite one of the pull bars I, this selected pull bar is permitted to drop into the code bar notches under the tension of a spring 51. Immediately the printing ball 59 is raised and its associated printing bail roller 6| is also pushed up into the notches 63 inback of each pull bar I. As the selected pull bar drops into the notches of the code bar I the printing ball 59 engages with a shoulder 65 on the pull bar. Hence the pull bar I is lifted and swings the type bar actuator 61 upwardly about the pivot center 69. Thetype bar 9 swings on the pivot center 'II and is caused to make a. stroke against the paper by the upward movement of the pin 13 which is supported at the end of the actuating bar 61. All of the pull bars 1 are substantially alike and function in the same manner. There is just one fundamental difference, however, between the selection of the error designating type bar 9e and the selection of any other type bar. The difference resides in the manner inwhich the error designating pull bar 1e is controlled compared with the normal control of the other pull bars by direct selection of the code bars I. In the case of the error pull bar 1e there is always an open alignment of notches 49 in the code bars I. But when proper intelligence-bearing signals are received the magnet 35restrains the pull bar 1e from entering the'notches 49. When an error occurs, the withdrawal of the push rod 45 enables the pull bar I; to enter the notches 49, thus providing a selection of the error designating type bar for printing an error designating symbol.

Under certain conditions as in testing the operability of the telegraph circuits and radio channels, it is useful to employ the relay 21 for showing the occurrence -of mutilated signals of the kind where one or two of the marking impulses are dropped out. Itis apparent that when only the relay '2! is actuated and relays 29 and 3| are not actuated, then no closed circuit through the magnet 35 is obtainable. This condition occurs when the received code signal consists of one or two marking impulses only. In order to differentiate, therefore, between signal mutilations of this type and a complete absence of signals the switch 55 must be closed so that the magnet 35 will be energized if no signals are received. Of course, under this condition there would be no operation of the error designating type bar.

It is quite'generally desired, however, that in the operation of a radio communications circuit a monitoring idle-time signal shall be periodically repeated so that in case such a monitoring signal should not be received, notice will be given at the receiving station of abnormalities or fading conditionsin the telegraph circuit or in the radio channel. In order to provide for differentiating between a proper spacing signal as transmitted from the point of origin of a communication and complete fading of the signal at the receiver, it is required that the circuit through the tongue of relay 21 be opened as by opening the switch 95. Under these conditions although the error detecting circuit through the resistors 2| includes. the serially connected windings of the relays 21, 29 and 2|, nevertheless only the relays 29 and ii are effective to control the magnet because the switch I5 is opened.

It will be seen that the reception of an unmutilated-code signal constituted by threemark ing impulses and four spacing impulses results in the actuation of relay 29 while relay 9| remains unactuated. Magnet 35 is energized as before stated. However, if neither or both of the relays 29 and 3| are actuated then the circuit through magnet 35 is opened and the printing of an error designating symbol results.

The idle-time signal which was hereinbefore mentioned should, of course, be one which contains three marking impulses, but which is a specific signal not otherwise used for the transmission of intelligence. So long as either intelligence signals or idle-time signals are received, the errordesignating type bar is re.- strained from operation. If, however, either a mutilated signal is received or if no signal is received, then the synchronous actuation of the printer will be such as to cause the error-designating symbol to be typed.

The principles and method of operation of my invention are not restricted to the use of any particular telegraph typewriter structure. It is well known that a number of different embodiments of telegraph printers are operable by'mcans of type selectors under control of difierent forms of code element responsive devices. Some of these telegraph typewriter-embodiments operate on the start-stop principle while others are adapted to operate in response to the reception of synchronous multiplex signals. My invention is, therefore, adaptable to any of these difierent embodiments of telegraph typewriters including those which possess type bars as well as those which operate with type wheels.

Several jpractical advantages result from the improvements herein shown as compared with the original embodiment of my invention which was described and shown in the parent application aforementioned. Among these advantages it may be mentioned that by employing contacts H and I3 which are directly controllable by the code bars of the printing telegraph instrument not only are electrical failures detected by the operation of the error type bar, but mechanical failures of the printing telegraph apparatus itself may also be detected.

Another advantage resides in the provision for distinguishing between space signals and fading. When a space signal is transmitted as between words and sentences, three of the code bars I are selected for obstructing all of the pull bars 1 from entering any of the notches 5, with the exception of the error designating pull bar 1e. This pull bar 1e, however, is normally obstructed by the actuation of the magnet 35. But when fading occurs, the magnet 35 is lie-energized, and the pull bar 1e becomes operative, provided the switch 55 is left open.

Still another advantage of the improvements herein shown and described over the arrangement of the parent application is that of simplicity of construction. In the improved embodiment it is no longer required that the contacts ll-l3 shall be controlled by independent relays in response to the reception of the various marking impulses of each code signal.

Varlous modifications of my invention may suggest themselves to those skilled in the art upon a review of the disclosure as herein given. .However, the scope ofpthe invention itself is to be understood as having all the breadth that is permitted by the claims. 1

I claim:

1. An error detecting device for a telegraph printer comprising a plurality of contact elements arranged in pairs, each pair being closeable by the operation of an appropriate code-bar in said p'rinter,.means responsive to'the movement of a prescribed number of said code-bars into selecting positions for printing a character, and means operable by the closure or a number of said contact pairs other than said prescribed number within a time interval allotted to the decoding of a single multi-element code signal for indicating a mutilation of said signal.

2. An error detecting device for a telegraph printer comprising a plurality of parallel-circuited resistors, a relaylsystem operable in series with a selected number of said resistors, means directly operable by the code bars of said printer for energizing said relay system through selected ones of said resistors, and means variably controlled by said relay system ior.indicating a departure from a prescribed number of code bar operations within a time interval allotted to the de-coding of a single multi-element code signal.

3. A device for detecting telegraph signal mutilations comprising a telegraph printer responsive to un-mutilated equal-length code signals, an error-designating type-bar in said printer, a plurality of code bars permutationally selectable upon reception of marking impulses in each code signal, a variably resistive circuit arrangement including contacts mechanically closeable by said code bars, and means operable through said circuit for causing the error-designating type bar to be actuated whenever the number or received marking impulses differs from the number prescribed for an un-mutilated code signal.

4. A device according to claim 3 and having further means operable through said circuit for causing the error-designating type-bar to be actuated upon the occurrence of a code-signal transmission with respect to which all the marking impulses have faded out.

5. In combination with a telegraph typewriter having code-selector bars, pull-bars and type bars mutually cooperative in response to uniformlength code signals for transcribing intelligence,

an error-designating type bar, an error pull-bar for said error type bar, said error pull-bar being mechanically independent of said code bars, a magnet having means controlled by its armature for blocking the error pull-bar, and means responsive to the reception of an un-mutilated code signal for actuating said magnet thereby to prevent the operation of said error pull-bar and error-designating type bar.

6. In combination with a telegraph typewriter having code-selector bars, pull-bars and type bars mutually cooperative in response to uniformlength code signals for transcribing intelligence, an error-designating type bar, an error pull-bar for said error type bar, said error pull-bar being mechanically independent of said code bars, a magnet having means controlled by its armature for blocking the error pull bar, and means operative in the event'oi fading of any or all of the transmitted marking impulses appropriate to one of said code signals for disabling said magnet thereby to unblock the error pull-bar and thus to enable the error-designating type-bar to operate.

7. Incomblnation with a telegraph typewriter having code-selector bars, pull-bars and type bars mutually cooperative in response to uniformlength code signals for transcribing intelligence, an error-designating type bar, an error pull-bar for said error type bar. said error pull-bar being mechanically independent or said code bars, a magnet having means controlled by its armature for blocking the error pull-bar, and means operative upon receipt of a signal which is mutilated by the introduction therein oi spurious marking impulses for rendering said magnet inactive, thereby to unblock the error pull-bar and thus to enable the error-designating type-bar to operate.

8. In a printing telegraph receiving system, a

. printer having de-coding'members movable from non-selecting to selecting positions in response to the reception of marking elements of a signal, and character-printing devices selectively actuable in accordance with the permutational ad- Justment of said de-coding members to selecting positions, a plurality of pairs of contacts each pair being closeable by the movement of an appropriate one .0! said de-coding members to a selecting position, a resistor in circuit wth each contact pair respectively, an error-detecting relay system operable by closure of any of said contact pairs, the manner of operation of said system being dependent upon the number of said resistors which are connected in parallel by said contact closure, a magnet under control oi said errordetecting relay system, means for printing an error-symbol, and mechanism cooperating with said magnet in response to the reception of a single un-mutilated signal, when characterized as such by said relay system, for preventing the operation of said error-symbol printing means.

9. A device in accordance with claim 8 and having means operable in response to the reception 01 a mutilated signal also in the event of fading of a transmitted code signal for enabling the error-symbol printing means to operate.

10. In a printing telegraph receiving system, a printer having character selecting means responsive to a hired normal number of marking elements of a uniform-length code signal, means for detecting instances of mutilation and instances of fading of the code signals, said means comprising a relay operable by said character selecting means upon receipt of at least the normal number of marking impulses in a single one of said code signals, a second relay operable by said character selecting means only upon receipt of a superfluous marking impulse in said code signal, and means responsive to the simultaneous operation of both said relays and responsive also upon failure of both said relays to operate at the expected time of reception of a code signal for causing an error-designating character to be printed.

11. In the operation of a telegraph printer having a plurality of code selector members each movable to a selecting position in response to the reception of a marking element of an equal length code signal, the method of indicating a discrepancy between the transmission and reception over a communications channel of an unrepeated one of said signals, which comprises utilizing the movements of said code selector members to condition a sensing device for controlling the amplitude of an electric current, and causing an excess or deficiency in said amplitude with respect to a normal value to produce an indication of said discrepancy.

12. In the operation 01' a telegraph printer having a code selector member for each element of an equal length signal to be de-coded, and having type members including an error-designating type member, the method of actuating said errordesgnating type member in response to the reception of an unrepeated one of said signals and in lieu of an intended actuation of one of the other type selectors, which comprises permitting one of said code signals to be mutilated by the addition of a spurious impulse or by nullifying the receiving response to a transmitted marking element, causing said code selector members to cooperate in controlling the amplitude of an electric current, and causing said error-designating type selector to be actuated in response to a departure of said current from a normal value.

13. A telegraph printer having code selector bars and type bars, in combination with a plurality of circuit closing devices each individually controlled by the actuation of an appropriate code selector bar, means variably operable in accordance with the number of circuit closures by said devices for differentiating between the reception of un-mutilated and mutilated code signals, and an error indicating device operable by said difierentiating means upon reception of a mutilated signal for conditioning a particular one of said type bars to be actuated.

14, A telegraph printer comprising a plurality of code selector bars,.means for setting said selector bars in positions corresponding to the marking and spacing elements of a received code signal, a plurality of type bars any one of which is selectable by an appropriate permutational setting of said code selector bars, an error designating type bar, and means conditioned by said code selector bars upon reception of a mutilated signal for causing the error designating type bar to be actuated, the last said means including a plurality of circuit closing devices each device being operable under control of an appropriate code selector bar, and including marginal relays variably operable in accordance with the number of said devices which are operated.

JAMES A. SPENCER.

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