US2904624A - Electrical signalling apparatus - Google Patents

Description

Sept. 15, 1959 J. T. NEISWINTER ELECTRICAL SIGNALLING APPARATUS 2 Sheets-Sheet 2 Filed June 8, 1955 n d 3W Pmm 2,904,524 I A ELECTRICAL SIGNALLING APPARATUS James T. Neiswinter, Garden City, N.Y.

Application June 8,1955, Serial No. 513,921

6 Claims. (Cl. 1784.1)

. 2 counting the pulses of the received code signal, means for registering those pulses of a code signal which are long pulses and means for performing an external function at the termination of the received code signal intended for that particular receiver is defined by the numher and positions of long pulses if any registered at said receiver. That is to say, each receiver further includes meansfor distinguishing those pulse codes intended for its operation, so that only those receivers in the circuit which are intended to perform a given function will respond to a code signal sent by the transmitter requiring the performance of that function. In order that the operator at the control sending station may be advised of the performance of the required function by the intended receiver, each receiver further includes means responsive to the actuation of its' controlled function for transmitting to the sender station an answer back signal for the transmission of electrical signals from'a control station to a remote station, means located at'the'remote station and responsive to such signals may be caused to selectively actuate a function switch or otherwise'etfectuate the performance of a selected function. T I 7 As is known, teletypewriter systems (also known as printer telegraph systems) are extensively used in the transmission of information telegraphically for the actuation of automatic printing equipmentat remote stations. Such systems operate upon pulse signals sent out on a telegraph line, for example, by a sending station to one or more remote stations, which signals are varied in suitable manner (e.g., by varying the number of pulses of a given type Within a code group) and in accordance with established codes so that different pulse trains are caused to actuate different elements of the automatic printing equipment. Basically, systems of this type such as are employed in the United States are single current, closed circuit systems in which a line joining the control station and remote receiving stations is normally closed energizing, at the sender location, an annunciator device. In order to insure that a receiver does not erroneously operate upon misinformation inadvertently received by it either from the sending station or asa result of disturbances in the circuit line, the receiver is additionally provided according to the invention with pulse measuring means for detecting the reception of a wrong pulse for effectively disabling the receiver until the reception of a correct signal.

' In a preferred form of the present invention, means are provided to cause the code signals developed by the sender station and employed at the receiver station effectivelyto blind or inactivate teletypewriter apparatus in the circuit, thereby to prevent false operation of the'tele- 3 typewriterin response to such code signals.

(Le, carrying current) and in which intelligence is conveyed by momentarily opening the line. Any'supplemental signalling system, therefore, which isto use such a line should be immune to interference from the teletypewriter information and, conversely, should not interfere with the normal operation of the latter.

In accordance with an illustrative form of the present invention, there is provided an electrical signalling system in which the signal comprises a plurality of pulses whose respective lengths are varied in accordance with predetermined codes so that intelligence may be conveyed. Specifically, for example, the system includes atransmitter or sender capable of sending pulse trains in accordance with a plurality of codes such that different kinds of information are represented by different pulse Additional objects and advantages of the present invention will become'apparentto those skilled in the art from a study of the following detailed description of the accompanying drawing, in which:

Figure l'illustrates, by a series of Waveforms, typical code'signals in accordance with the present invention;

Figure 2 is a block diagram showing a sender and receivenaccording to the present invention connected in a circuitwith a teletypewriter line; I

Figure 3 illustrates, by way of a block and schematic diagram, apparatus capable of producing and transmitting coded pulse signals in accordance with the invention; and i Figure 4 is a schematic diagram illustrating a pulse I code signal receiver in accordance with a specific form of trains. That is to say, all codes of the system may have an equal number of pulses (mar or space pulses), all of the pulses of a given code being of either one of two fixed durations. Thus intelligence may be conveyed via the pulse trains by varying the number and position of the longer of the two pulse durations. Further in accordance With the invention, the sender transmits the pulse information by periodically opening the teletypewriter line with which the apparatus is associated to produce space pulses, the intervals between the space pulses being marking pulses.

At one or more locations remote from the control or transmitter and the other receivers, comprises means for the'invention; and

Figure 4a is a schematic diagram illustrative of a power supply arrangement suitable for use in connection with the receiver of Figure 4.

' f DESCRIPTION oF TYPICAL CODE SIGNALS As pointed out briefly above, the code signal employed in accordance wtih thepresent invention consists of a fixed number of mark and space pulses. Since the nor mal 'co nditionof the teletypewriter line is a marking condition in which current is flowing, the pulses are produced by interrupting the current in the line periodically to produce spacing pulses. Thus, it will be understood that the code signal of the invention consists of alternate mark and space pulses. In accordance with a specific example to be'. described herein by Way of illustration, each code signal transmitted by the sender consists of four space signals or pulses with three intervening mark pulses, the interval between two successive space pulses on a line necessarily being a marking condition. The condition of the line before the code signal starts is a marking condition and the condition of the line after the code signal terminates will also be marking. Hence, the code signal will be understood as produced by interrupting the steady state marking condition of the line with the first space pulse of the code signal. The first space pulse is followed by a mark pulse, then the second space pulse, another mark pulse, the third space pulse, another mark pulse, the fourth space pulse, and finally, the steady state marking condition of the circuit.

Figure 1(a) illustrates a basic code signal in which the length of each of the space and mark pulses is by Way of example 60 milliseconds. As shown, the pulses are numbered, for convenience, consecutively from the beginning of the signal, so that the space pulses are pulses No. 1, N0. 3, No. 5 and No. 7, While the mark .pulses are pulses No. 2, No. 4 and No.6. Also in the interest of simplicity, the final marking condition of the line circuit at the endzof the code signal may be referred to as pulse No. 8.

As has been mentioned, it is necessary, for selective signalling purposes, that .each code signal be different from each other code signal. This difference between the signals for the purpose of adding intelligence -to the basic signal is obtained, in accordance with the invention, by making one or more of'the pulses of each code signal a long pulse (e.g., 400 milliseconds) instead of the basic short length of 60 milliseconds. The remaining waveforms of Figure 1 illustrate different examples of conveying intelligence via the basic code signal shown in Figure 1(a). In Figure 1(b), pulses No. 1 and No. 4 are shown as long pulses, while in Figure 1(c), pulses No. 1, No. 4 and No.6 are'long pulses.

Since, as explained, only two pulse lengths '(i.e., long'or short) are used in the code signal, the total number of combinations of pulses or a total number of codes is a function of the number of pulses in the code signal. Thus; with a total of 7 pulses, as illustrated, the number of combinations possible is 2 or 128. If only five pulses were used in the signal, the number of combinations would be 32, While if 11 pulses were used, for example, the number of combinations possible would be 2 or 2,048.

By Way of contrast with the usual teletypewritercode signal wherein the length of each code signal or character is the same, it is t'o'be noted that the overall length of each code signal in accordance With the present invention depends upon the number of long pulses which it contains, so that the overall lengths of the various code signals are not the same.

Also 'with respect to the usual operation of a teletypewriter circuit, it is to'be noted that pulse No. 1 of the present code signal is in all cases a long pulse, so that it may serve to blind teletypewriters connected in the circuit. Since in accordance with the present invention the duration of the long pulse (viz. about 400 milliseconds) is adjusted to be an integral multiple of the length of a standard teletypewritercode signal, teletypewriters in the circuit with the receiver of the present invention are prevented from printing in response to the present code signal through the action of means in the receiver responsive to the first long pulse.

It may also be noted, as a practical matter, that'the number of long pulse measuring and storing circuitsrequired in the receivers may be reduced by limiting the number of long pulses in any code signal to a given maximum, such as 4, for example, including pulse No. 1 (which is always long in the use on teletypewriter c-ircuits,-as pointed out above). With a maximum of. four long pulses in any code signal having seven pulses in all, there is provided a total of 31 codes for a system.

By virtue ofthe disparity in length of the lon and short pulses of the present'code signal, and as W-illbe understood more fully hereinafter, there is little likelihood that any normal transmission distortion of the coded signal can produce, in any given case, erroneousrespons'e by the receiver for which the signal is intended or 'by'a'ny receiver for which the signal is not intended.

4 DESCRIPTION OF ILLUSTRATIVE CODE SIGNAL TRANSMITTING APPARATUS Figure 2 illustrates, by way of a block diagram, a pulse code signalling system of the present invention and arranged in a typical environment in circuit with a teletypewriter line. As will be noted from Figure 2, first and second teletypewriter stations indicated by the blocks 50 and 52 are serially connected via the leads '54 and 56. A pulse code signalling transmitter in accordance with the invention is represented by the block 58 and is connected in series with the.lead-56. Similarly connected in series with the teletypewriters 50 and 52 and the pulse code transmitter 58 is a pulse code receiver 60 which, as indicated by the blocks 61, 62 and 63 to which it is joined by the leads 64, 65 and 66, is adapted to control one or more of a plurality of external functions. One important usage of the system of the present invention in combination with a teletypewriter circuit is that of connecting and disconnecting teletypewriters .at remote .points. Thus, the blocks 61, 62 and 63 which bear the designations function No. 1, function No. 2, and function N maybe understood as representing a plurality of teletypewriters. By wayofex-ample, the con necting of the teletypewriters represented by the external function blocks may be on an individual basis, with an individual code for. each connection.

While any suitable forrnof pulse code transmitter capable of producing and transmitting signals of the type illustrated in Figure .1 may be employed in the system of the .present invention, Figure 3 illustrates diagrammatically an arrangement for performing'the transmitter function.

One form of pulse code transmitter mechanism suitable for use in-block 58 of Figure 2 is shown in Figure 3 in series with the 'teletypewriterline defined by the leads 54 and 56. Electric current for the teletypewrittenline "is provided for example .by the battery 68. Pulse code signals of lthe type described in connection with Figure 1 are produced by the apparatus of Figure 3 in the following manner: A shaft 69, adapted to be rotated by a constant speed electric motor 70 through the agency of an electromagnetic clutch 71 for example, carries a plurality of cams 72, 72a-and -72b formed of a suitable conductive'material. Also carried by the shaft 69 is a slip ring commutator '73 against which is urged, as by a spring 74, a brush'75, so that a circuit may be traced from the cams through the shaft and brush to the line .54. Each ofthe cams 72,"72a and 7217 has associated therewith a stationary contact member which is adapted to make contact only with the raised portions of cam periphery. A s'electe'd one of the'co-ntacts, indicated by reference numerals '77, 77a and 77b, may be connected to the teletypewriter line 56 through the agency of a selector switch member 78. Each cam, as shown, is provided with a number of cutout portions which do not make contact with the contact members '77, '77a and 7712, so that it willbe understood, that as the shaft 69 is rotated, carrying the'cams therewith, the circuit will be interrupted as the cutout portion of the cam, passes under the contact member associated with that cam. Thus, with each cam different fro'm each other cam of the group, a number of code signals equal to the number of cams may be produced by the transmitter.

It should further "be noted that each cam is provided with one cutout portion for each space pulse of the signal to be produced. 'In this fashiomby varying the respective arc'uate dimensions of the cutout portions of the cam, the long and short mark and space pulses described above can be produced by a cam.

Figure 3 further illustrates, in simplified form, means for causing'rotation of" the cams through 'a single revolutionwhereby to produce a pulse signal such asthose shown in" Figure l. "Specifically, the 'clutch71 is normally deenergized s'o'that the shaft'69 and its associated'ca'ms remainsta'tionary. Whena 'pushbutton' switch '79 is momentarily closed, a circuit is completed from a battery 80 through a relay winding 81, thereby moving down the contacts 82 and 83 associated with the winding 81. When the contact 82 closes in circuit with the terminal 84, current flows from a battery 85 through the elements 84 and 82 to the clutch 71, thereby energizing the clutch.

At this point, it may be noted that the shaft 69 also carries a detent cam member 86 which, when in the position shown in the drawing, holds a switch contact 87 away from a terminal 88 against the urging of a compression spring 89. As soon as the shaft 69 is rotated slightly after energization of the clutch 71, the detent 86 is moved away from the spring contact 87, thereby permitting it to complete a circuit through the terminal 88, a relay winding 90 and the relay winding 81. Thus, the relay members 82 and 83 are held down through the continuing energization of the winding 81 after the switch 79 has been released.

During the rotation of the cam, the line circuit'is broken by each cutout portion of the cam to produce a space pulse whose duration is determined by the arcuate dimension of that cutout portion. At the end of a complete rotation of the cam, the detent 86 again urges the member 87 out of contact with the terminal 88, so that the circuit from the battery 85 through the relay 81 is broken, thereby deenergizing the clutch 71 and causing a cessation of rotation of the shaft 69.

Note may also be made at this time of the additional circuitry of Figure 3. Connected in series with the line 56 is a relay winding 91 which, when energized, moves a contact member 92 away from a terminal 93. The relay winding 90, mentioned earlier, is adapted, when energized, to move a switch member 94 into contact with a terminal 95 which is connected to one electrode of a suitable lamp 96. The other electrode of the lamp 96 is connected to a terminal 97 adapted to be contacted by the relay member 83. The member 83 is, however, maintained out of the contact with the terminal 97 during the energization of the winding 81. It will, therefore, be appreciated that, during the production of the code signal by rotation of the cam, the lamp 96 is prevented from being energized by reason of the fact that its normal connection to ground through the contact member 83 and terminal 87 is maintained open. The lamp and its function will be described in greater detail hereinafter when its function as an answer back annunciator is discussed.

GENERAL DESCRIPTION OF PULSE CODE RECEIVER COMPONENTS In order to facilitate an understanding of the receiver of Figure 4, a detailed description of which is to follow, its various components will first be described in accordance with their functions.

As will be understood from the foregoing, the functions to be performed by the receiver may be enumerated generally as follows: first the counting of the pulses of a received code signal; second, registering those pulses of a code signal which are long pulses; third, causing an external function to be performed following the reception of a code signal intended for that receiver; and, finally, transmitting an answer back pulse to the transmitter after the performance of the external function has been completed.

The first operation, namely, the counting of pulses is performed by a series of relays designated LP1 and P2 through P7, inclusive. Relay LP1 is associated with a pulse measuring circuit of such character that the relay is operated only by a space pulse which is longer than some minimum value such as 200 milliseconds which is shorter than a long space pulse of a code signal of the type described in connection with Figure 1 but longer than a normal teletypewriter space signal. Operation of the relay LPl applies operating voltage to the other relays of the receiver. In the code signals of the present invention, the first space pulse of each signal is always long, so that the relay LP1 is in all cases operated thereby to activate '6 the other relays; It is important to note, however, that on the usual teletypewriter signals, no space pulse is in-. cluded of sufficient duration to operate the relay LP1, so that the receiver remains inoperative during the reception of teletypewriter signals.

After the operation of relay LP1, the relays designated P2 and P7 operate in sequence as the corresponding pulses are received from the line. Since the relays P2 and P7 are not associated with the pulse measuring circuit which causes relay LP2 to operate, relays P2 to P7 will operate regardless whether the corresponding pulse is long or short. An additional long pulse registering relay designated LP2 is provided in the receiver to register when the second pulse of a received code signal is of long duration. For the remaining pulses (i.e. pulses 3 through 7), only two long pulse measuring relays are provided, these relays being designated A and B. Where the number of long pulse measuring relays is thus limited in order to reduce the. number of relays in the receiver, the long pulse relays other than the relays LP1 and LP2 are so cross connected as to register only when a selected two of the five remaining pulses are long. Such a reduction in the number of long pulse relays correspondinglyreduces the number of external functions that a given receiver can control from 64 to 7. Where, for example, it is desired to control more than seven functions from a single receiver, the addition of one long pulse measuring relay makes possible the control of fifteen functions. (The code in which all pulses except No. 1 are short is not included when there is more than one receiver on a line.) Similarly, the addition of two external long pulse relays raises the control capabilities of the receiver to thirty-one functions, while the addition of three external long pulse relays provides for the control of sixty-four functions. Such external long pulse relays may be connected to the receiver via suitable terminals on the receiver terminal strip.

As mentioned, the receiver of the present invention is further provided with means for furnishing an answer back signal to the sender upon the performance of an external function in response to a code signal transmitted by the latter. The answer back signal, is, in fact, afforded by the momentary opening of the line through the action of the answer back relay AB.

The long pulse measuring relay LP1 is'controlled by one of four gas discharge tubes in the receiver, namely, the tube LS, which fires on a long space pulse to operate either the relay LP1 (if on the first pulse of the series) or one of the relays -A and B, depending upon which pulses these relays are cross-connected to measure. The time constant circuit associated with the tube LS prevents the tube from firing on a short space pulse or on teletypewriter signals.

While the tube LS fires, as explained, only on a long space pulse, the tube LM which is also a gas discharge device fires on a long mark pulse to operate one of the relays A and B depending upon which pulses these pulses are cross connected to time. The tube LM does not fire, however, prior in response to a short mark pulse.

A third gas discharge tube CLR fires upon the reception by the receiver of an extra long marking pulse whereby to operate a clearing relay CLR to clear all operated U-type relays (except for the relay HG, to be described) in the receiver. The final gas discharge tube in the receiver, namely, tube DAB (disconnect answer back) fires when an external function relay controlled by the receiver is released on a disconnect signal, thereby causing the relay AB to operate to send an answer back to the transmitter.

The remaining three U-type relays in the receiver perform the following functions: The relay WP (wrong pulse) operates whenever a long pulse is received which the relays A and B are not cross connected to register. Operation of the wrong pulse relay WP disables the receiver to prevent it from operating an external function. Thus, for example, if the proper pulses were received to operate the relays A and B in such manner that an external function would be performed and then an unwanted additional long pulse were received such as might occur under conditions of trouble, the relay WP would operate upon the unwanted pulse to prevent the receiver from performing external function on that particular code.

The clearing relay CLR normally operates to release all operated 'U-type relays of the receiver, except for the relay HG mentioned above, upon the reception of the long marking pulse which occurs at the end of a code signal (i.e., pulse No. 8). If one or more accidental space pulses should be received, however, the relays CLR operates upon the following extra long marking pulse which occurs to clear the receiver. The relay HG, which constitutes the sole exception to the U-type relay clearing action of the relay CLR, operates at the end of any connect code signal and is released by a disconnect signal. When operated, the relay HG serves to connect ground to a particular terminal of the receiver. This terminal may be employed for locking one or more external function relays in their operated positions. When a disconnect signal is received, the ground connection is broken and the external relays released. In the event that an external disconnecting arrangement is provided in a receiver, the relay HG is rendered unnecessary and should be made inoperative, as by removing its winding from the battery or other source of operating voltage.

In Figure 4a of the drawings, there is shown a small voltage supply, partially separated or isolated from the main voltage supply of the receiver, which is used for the timing circuits associated with the gas discharge tubes LS, LM and CLR. This voltage is designated in the drawing by a plus sign within a square in order to distinguish it from the main power supply which is indicated as a plus sign by itself. In the drawing, the voltage supply for the timing circuits is available at the terminal 100, while the voltage supply for the remaining circuits of the receiver is provided at the terminal 101. The reason for the use of an isolated power supply for the timing circuits is that it undergoes less voltage drop than does the main power supply as the relays of the receiver become operated.

DETAILED DESCRIPTION OF PULSE CODE RECEIVER As will be noted from Figure 4, the receiver includes several cold cathode tubes for-example, of the commercial type 443A. The grid-cathode path of such a tube requires an applied voltage in the range of 70 to 90 volts to cause conduction. The actual required voltage varies from tube to tube, but 'is ordinarily in the range indicated. Below the firing voltage for this path, there is no conduction at all. Above the firing voltage, conduction takes place, with the grid-cathode path having a sustaining voltage drop across it about 10 volts or so less than the firing voltage. This voltage drop is nearly the same regardless of how much current is flowing in the path. For'this reason, an external resistance must always be included in the grid circuit to prevent excessive current flow which would damage the tube, since the tube itself can ofier no more limiting back voltage to a high current than it can to a low current flow.

If a positive voltage of 100 volts or more is connected to the plate of the tube, the firing of the grid-cathode path will also fire the plate-cathode path. Once the platecathode path conducts, the grid loses all control of it and, in order to stop the conduction of this path, it is necessary to remove the plate voltage, at least momentarily, to de-ionize the tube and cause it to become non-conducting or extinguished. Since the plate-cathode path will fire directly if about .180 volts or more is applied directly across it, it is necessary in "all circuits where the grid voltage alone is desired to control the tube to keep the plate voltage, including momentary surge voltages, below this value to prevent unwanted firing of the platecathode path.

The foregoing information regarding the theory of cold cathode operation has been afforded in the interests of completeness of description. The circuitry and operation of the receiver of Figure 4 will now be described in detail in connection with the several component portions of the receiver described generally in the preceding section.

Long space pulse timer The long space pulse timer comprises tube LS, capacitor C1, and resistors R1, R2 and R3. Resistors R1 and R2 are of low value and are provided to limit the current that flows into or out of the capacitor C1 when it is discharged by the operation of the relay L or by the firing ofthe grid-cathode path of the tube LS.

While relay L is operated to marking, a ground is applied through the resistor R2 to the capacitor C1, hold' ing it at or near ground potential. When relay L operates to its spacing contacts 4 and 5 on a space pulse received from the line, the positive battery connected through resistor R3 starts charging capacitor C1 to a positive voltage. In about 200 milliseconds, the voltage on capacitor C1 reaches a value sufiicient to fire the gridcathode path of tube LS. Thus, if the space pulse is 200 milliseconds or more in length, the tube LS will fire, while if the space pulse is less than this amount, the relay L will re-operate to its marking contacts 1 and 2, discharging capacitor C1 before the voltage on the capacitor has reached a value high enough to fire the tube LS. On selector code signals of the present invention, the long pulses of 400 milliseconds will, therefore, fire the tube LS, while the short pulses of 60 milliseconds will not fire it. It is also to be noted that the space pulses of normal teletypewriter signals (viz. 132 milliseconds maximum) will not fire the tube LS. Thus, on teletypewriter signals, no action will take place in the receiver except for the operation and release of the relay L.

The first pulse of each code signal is a long pulse and, therefore, on pulse No. 1 of a code, the tube LS will fire in its grid-cathode path. Since positive battery is connected through the windingof the relay LP1 to the plate of the tube LS, the plate-cathode path of the tube will also conduct and relay LP1 will lock operate it. To summarize, it has been seen that, on pulse No. l of a code signal, relay LP1 will be operated, while on normal teletypewriter signals it will not be operated.

Long mark pulse timer The long mark pulse timer comprises the tube LM, the capacitor C2 and the resistors R4, R5 and R6.

While the relay L is operated to marking, positive battery is connected through resistor R4 to capacitor C2, charging the latter to a positive value which depends upon the length of time during which the relay L is on its marking contact. During the idle condition of the receiver and of the line circuit, the voltage on capacitor C2 reaches a'value 'suflicient to fire the grid-cathode path of tube LM. During the idle condition, however, when relay LP1 is not operating, no positive voltage is connected to the resistor R21 associated with the relay LP2 and, therefore, no positive voltage is connected to the plateof the tube LM and the plate-cathode path of this tube is not fired. Since during the idle condition of the receiver and the line circuit, the amount of current flowing in the grid-cathode path of the tube LM is quite small by virtue of the high resistance of resistor R4, such current has no detrimental eifect upon the life of the tube.

'During the reception of a space pulse, the relay L is operated to its spacing contacts 4 and 5, so that capacitor C2 is grounded and no timing action takes place in the long mark tinier. When the relay L re-operates to its marking contacts 1 and 2, by reason of the beginning of a mark pulse on the line, the ground is removed from capacitor C2 and it starts to charge to a positive voltage. If the mark pulse being received is less than 200 milliseconds long, the tube LM will not fire. If the pulse is more than 200 milliseconds long, the tube LM will fire and operate the relay that is connected to its plate circuit at the time of the particular pulse. Thus, it is seen that the tube LM will fire on a long mark pulse of a code signal of the present invention but will not fire on a short pulse.

CLR timing circuit The CLR (clear) timing circuit comprises the tube CLR, capacitor C3 and resistors R10, R11 and R12. This timing circuit also times mark pulses but, because of the higher resistance and capacity involved in its timing network, a longer mark pulse is required to fire the tube CLR than is required to fire the tube LM. The length of mark pulse required to fire the tube CLR is approximately 700 milliseconds, compared to the 200 millisecond pulse required to fire the tube LM. Therefore, on a normal long mark pulse of a code signal (i.e., 400 milliseconds), tube CLR will not fire. In the case of one or more break signals on a line which might operate relay LP1 and the other relays of the receiver, the tube CLR will be fired on the first marking condition of 700 milliseconds or more that occurs after the one or more of the break signals. The firing of tube CLR operates a relay bearing the same designation (CLR) to restore the re ceiver to its normal idle condition. This particular aspect of the present invention will be described in greater detail hereinafter.

Counting circuit There are, as has been stated, seven pulses in the code signal of the present invention, so that it is necessary to have an indication in the receiver of which pulse of the seven is being received at any particular time during a signal period. This is accomplished by the counting circuit comprising the seven relays LP1, P2 through P7 inclusive. While the relay LP1 operates only when the first pulse of a code is a long one, the relays P2 through P7 operate to count either short or long pulses. numbered 2 through 7.

- In the idle condition of the receiver and with the line marking, the following conditions exist: the neon pilot lamp 103 connected to contact '1 of the relay L is lighted. When this lamp is lighted, it is an indication that power is connected to the receiver and that the line is closed. The lamp 103 also follows signals on the line, as Will be understood. By reason of the fact that, in the idle condition of the receiver, the relay L is operated to its marking contact 1 and 2, the capacitor C1 of the timing circuit associated with tube LS is grounded. Capacitors C2 and C3 of the timing circuit associated with tube LM and CLR are charged to a positive voltage which fires the grid-cathode paths in these tubes causing them to conduct a few microamperes of current. With the relay LP1 unoperated, however, no voltage is connected to the plates of these tubes so that their plate-cathode paths remain non-conducting. By reason of the fact that the relay LP1 supplies battery voltage to the winding of all of the other U-type relays except for the relay HG, these also remain unoperated, since the relay LP1 it isel-f unoperated. Thus, in the idle condition of the receiver, the relay L can follow teletypewriter signals on the line but no action can occur in the receiver other than the charging of the capacitor C1 to values insufficient to fire the tube LS when the relay L is spacing, followed by the discharging of this capacitor by the operation of relay L to mar-king period.

,When the first pulse of a code in accordance with the invention is received, relay L operates to space long enough for the tube LS to fire and to operate the relay LP1, associated therewith. I Relay locks operated through the resistor R13 to ground, which safn locking contacts also remove battery from the plate of the tube LS, extinguishing this tube. The operation of the relay LP1 (armature B5 to contact B4) connects positive battery from the terminal through associated resistors to certain terminals of relays P4 through P7, LPZ, A, B, WP and CLR to permit energization of such windings by conditionally applying ground to other associated winding terminals of these relays.

At the beginning of pulse No. 2, relay L returns to marking. The ground now applied to contact 1 of relay L is connected through an armature and contact on the relays CLR, P7, P5 and P3 to the junction of the windings of relays P2 and P3. Since relay P2 now has battery connected to its winding (from terminal B1 of now operated relay LP1), it will be operated by the ground. The operation of relay P2 of the counting circuit thus registers the beginning of pulse No. 2 of the code signal.

It is important to note that the closing of relay P2 closes the blinding contacts B4 and B5. These blinding contacts shunt the contacts 107 and 109 on the teletypewriter line relay associated with the receiver in the circuit and connected to the terminals 8 and 9. This action establishes a marking condition in the teletypewriter printing magnet 111.

It should also be noted at this point that, insofar as the blinding feature of the present invention is concerned, the armature and contact of the line relay of the teletypewriter remain thus shunted (and inactivated) for the remainder of the reception of the ocde signal and, in fact, until after the performance of the external function and answer back signal have been completed, or until the receiver circuits are otherwise returned to their idle condition. By virtue of the novel blinding action of the present invention on the associated teletypewriter apparatus, such apparatus is prevented from responding falsely to the code signal intended for the receiver.

At the beginning of pulse No. 3, the relay L operates to its spacing contacts, thus removing the ground that had been applied through contact 1 to the junction of the windings of relays P2 and P3. Relay P3, which during pulse No. 2, had been held unoperated by the ground on each side of its winding, is thus rendered operative. The operation of relay P3 registers the beginning of pulse No. 3 of the code signal.

I At the beginning of pulse No. 4, relay L operates to its marking contact. Ground applied to contact 1 is now connected through armatures and contacts on the relays CLR, P7 and P5 and operated relay P3 to the junction of the windings of relays P4 and PS. This causes the operation of the relay P4 to register the start of pulse At the beginning of pulse No. 5, relay L releases to remove the ground at the junction of the windings of relays P4 and P5 which causes the operation of relay P5 to count the fifth pulse.

. At the beginning of pulse No. 6, relay L operatesto mark in order to apply ground through armature and contact of relays CLR, P7, and operated relays P5 and P3 to the junction of the windings of relays P6 and P7. This operates the relay P6 to count pulse No. 6. l

At the beginning of pulse No. 7, relay L operates to space to remove the above ground, thereby causing the operation of relay P7.

To summarize the above actions, it has been seen that the occurrence of pulse 1 of a code signal (which is always a long pulse) caused the tube LS to fire and to operate the relay LP1. The operation of relay LP1 connected battery to the windings or relays P2 to P7 of the count ing circuit. At the beginning of pulse 2, relay P2 operated; at the beginning of pulse 3, relay P3 operated, and thus continuing to the operation of relay P7 at the beginning of pulse No. 7. It will be noted that, since the operation of each of the relays P2 through P7 occurred at the beginning of the corresponding pulse, the operation,

ofthose. relays occurs regardless of the length of that pulse.

Operation of long pulse relay LP2 The common disconnect code for all receivers in accordance with the invention is a code in which pulse No. 2 is long (so that the code may be designated as code No. 2). The fact that pulse No. 1 is also long should be understood from the foregoing explanation of the code signal. It is necessary, therefore, that each receiver be provided with a relay for registering whenever pulse No. 2 of a received code is a long pulse, since thisaction will. always be required by the disconnect code, even though the other codes involved with other receivers do not have pulse N0. 2 as along pulse.

When relay L armature returns to its marking contact at the beginning of pulse 2, the capacitors C2 and C3 begin charging. If pulse No. 2 is a long pulse, the tube LM will be fired. At this time in the counting circuit only relays LPI and P2 are operated, so that the plate of tube LM 'will be connected to the winding of relays LP2 and the firing of tube LM will cause the operation of relay LE2. Relay LP2 will lock operated to ground, and the operation of its locking contacts will remove posi tive battery from the plate of tube LM, thus causing that tube to be extinguished.

The operation of relay LPZ will, therefore, register and store in the receiver the information that pulse No. 2 of the code was a long pulse. This information is used at the end or" the code signal to aid in determining which of the internal functions (to be described) is to be performed.

Operation of relays A and B In order for a receiver to be able to respond. properly to all of the code combinations possible with six variable, codepulses, it would be necessary to provide a relay of the long pulse measuring and storing variety for association with each of pulses 3 through 7, in the same manner that relays LPl and LPZ are associated with the, first and second pulses. The provision of such five additional long pulse measuring relays (for pulses 3 through 7) would render it possible for the receiver to respond to a total of 64c0des, which, for the majority of applications, of selective signalling on teletypewriter circuits, may wellbe. su-. perfiuous. The receiver of Figure 4, therefore, is de signed-so that it is capable of registering only the occurrence of 2 of the pulses (pulses 3 through 7') as long pulses. This registering action is performed'by the relays A and B which are cross connected to be associated with 2 predetermined pulses of the code signal. When the relays A and Bare cross connected, for. association with the pulses 3 and 4, for example, those relaysmay be considered as relays LP3 and LP4 for that particular cross connection. On anotherreceiver, the relays A and B may be cross connected for association with the pulses 5 and 6, in which event the relays A and B would then be considered as designated LPS and LP6.

It is further to .be noted that the armatures .and contacts of relays P2 through P7 of the counting circuit are. arranged so that, during pulse No. 2, whenrelay P2 is operated, the plateof tube LM is connected to the. wind. ingot relay LPZ. Ifpuise No. 2 is a long pulse, tube LM will be fired during the pulse to cause the. operation of relay LP2. Tube LS will not fire during this .pu-lse, since .it is arranged to time only space pulses.

During pulse No. 3, when relays P2 and P 3-are 0p-v erated, the plate of tube LS is connected to. terminal 33 of the receiver (designated P3). If it is desired to. registerthe occurrence of pulse 3 when it is along pulse, either the winding of relay A-orthe winding of relay B is cross connected to the terminal 33. When pulse, 3 does occur as a long pulse, therefore, tube LS will fire to operate the relay connected to terminal 33.

During pulse No. 4, when relays P2; P3 and P4'are operated, the plate of tube LM is connected to terminal 34 -015 the receiver (designated P4). If it is desired to 1'2 register the occurrence of pulse 4 when it is a longpulse, either the winding of relay A or B is connected. to: this terminal. Whenpulse 4 does occur as a long pulse, tube LM will fire tooperate the relay connectedsto terminal 34;

The same circuitry is applicable to the use of terminals 35, 36. and 37 (designated in the drawing as P5, P6 and P7). When it is desired to register the occurrence of any of, these pulses when it is a long pulse, the winding of either A or B is connected to. the terminal.. When the particular pulse is long, the firing of either tube LM o1. LS, whichever is involved, will, then operate the relay connected to the terminal. It will be appreciated, that only two of the 5 terminals, 33 through 37, can be so connected, in view of the fact that only two relays (A and B) are provided in addition to'the long pulse measuring relay LP2 for measuring longpulses after the first space pulse.

In accordance with the present invention, the operation of relay WP (wrong pulse) in. any code signal received by the apparatus of Figure 4 prevents the receiver from performing an external function of that code. The normal use of the relay WP is to connect it torthe unused pulse terminals of the receiver (such as the terminals 33. through 37, depending upon which of these are not con nected to the relays A and B). Thus, for example, if the relays A and Bare connected to terminals 33'and 34, to register the occurrence of pulses 3 and 4 as long pulses, relay, WP would then be connected to the remaining terminals 35, 36 and 37. This prevents overlapping operation in areceiver on codes in which the third pulse (code No. 3) or the third andfifth pulses. (code 35) are long pulses, for example, when the receiver is arranged to receive codes based only on long pulses No. 3 and No. 4' (i.e., the relays A and B connected to the terminals 33 and 34). Without the use of relay,WP in this case, there would be no difierence in the receiver between the. reception of code No. 3 and of code .No. 35, the receiver operating the same on code 35 or code No. 3. With the, relay WP connected to the terminal 35, the reception of code 35 will cause the operation of relay WP andno. external function will be performed. The reception of code No. 3 would, however, operate this particular receiver as planned'to performan eX-ternal function.

Fan circuit of the relays B, A, and LPZ As shown in Figure 4, the'armatures and contacts of the relays LP2, A, and B, are connected from right to left in what is commonly called-a fan circuit. The fan circuit begins at relay B (armature T5). Contacts T4 and T6 of this relay fan out to relay A (armature T5 and.

B2). Contacts T4, T6, B1 and- B3 of relay A fan out to armatures T5, T8, B3, and B2 of relay LP2. Thus, there are 8 contacts associated with these armatures. The. contacts appear on terminals 22 to 29' of the receiver for connection to external function circuits such as relay windings.

At the end of each code signal, a ground is connected momentarily to the armature T2 of relay WP. If relay- WP is unoperated, ground will be connected through to relay B (armature T5). This ground can be made to appear on any one of the 8 terminals associated with the 8 fan contacts on relay LP2 by operating certain relays of the three. Thus, when all three relays are operated, a ground on relay B (armature T5) will appear on the terminal 22. When only the relays A and.B are. operated, the above-mentioned ground will appear on terminal 23. With relays LPZ and B operated on, ground will appear on the terminal 24, and so on.

Since the relays LP2, A and B can indicate the recepa tion of a total of only 3 long pulses, the number of combinations possible with. these relays is 2(3) or,8. Since the combination in which all three of. the relays A, B, and LP2 remain unoperatedjis' not normally used, and, since the combination in which only the relay LPZ. is operated is used for the common disconnect signal, six

pulses No. 2 and 13 combinations are available for use in controlling functions external to the receiver. Additional relays can be added to the fan circuit by providing them externally. Thus, the 8 terminals 22 through 29 can be connected to 8 armatures of an external relay and the 16 contacts associated with these armatures used to control external functions. The winding of this external relay can be connected to one of the unused terminals such as 35 (if terminals 33 and 34 are used for the relays A and B). With the combination in which all four relays are unoperated, not used, and the combination in which only the relay LP2 is operated, used for the common disconnect signals, 14 combinations would be available for external use. The addition of 3 external relays to extend the fan circuit would result in 63 combinations available for external use. (The disconnect signal not included in these.)

An example of an external function relay is illustrated by the relay 115 (designated F1) connected to the terminal 24.

During the description of the code signal of the invention, it was explained that a code consist of 7 pulses,

after which the line is returned to its marking condition referred to as pulse No. 8. It will be understood, therefore, that the start of pulse No. 8 operates the relay L to its marking condition. The ground thus applied to its contact 1 is now, under the condition of relay P7 being operated, connected to relay WP (armature T2) and to the winding of the relay HG. The relay HG will be operated by this ground. It should be noted thatthe operation of relay HG requires only the operation of the entire count circuit and the final operation of relay L to marking on pulse No. 8. Thus, the relay HG will be operated by any code signal regardless of its combination of long and short pulses, with the one exception of the disconnect code. This latter code will release the relay HG if it is in an operated condition.

Operation external function relay The ground connected to relay WP (armature T2) at the start of pulse No. 8 of the code signal will be con- .nected to relay B (armature T) if the relay WP is unoperated and will not be so connected if the relay B is operated.

Assuming that the code 24 has been received (i.e., 4 being long pulses), the relays LP2 and B will have been operated during the reception of pulses 2 and 4 of the code and the relays A and WP will not have been operated. The ground applied to relay B (armature T5) will therefore be connected through to terminal 24 of the receiver where it will operate the external function relay 115 shown as an example.

If, on the other hand, the code 234 had been received, ( pulses 2, 3 and 4 being long pulses) the relays LP2, A and B would all have been operated at this time and the ground would have been connected to terminal 22 to operate an external relay which might be connected to that terminal.

Effect of operation of relay WP If the code 45 (i.e., pulses 4 and 5 being long pulses) had been received, the relays B and WP would have been operated during the reception of the code signal. The operation of the relay WP would then have prevented the ground from being applied to relay B (armature T5) and no operation of an external relay would have resulted.

"Holding ground provided by relay HG When the internal disconnect feature of the receiver is used, each external relay which is operated will lock operated to the ground connected to the terminal HG by the operation of relay HG. Since the relay HG operates on any connect code signal, this ground Will be available for an external relay to lock operate it to it.

An examination of the fan circuit on the lower armai4 tures of relays B, A, and LP2 will indicate how the ground applied to relay B (armature T5) at the start of pulse N0. 8 of the code signal can be fanned out to any one of the terminals 22 to 28 by the proper combination of operative and unoperative relays. The designations on the terminals indicate the relays which must be operated to cause the ground to appear on each partciular terminal.

Operation of relays CLR and AB The operation of relay P7 connects the plate circuit of tube LM to the winding of relay CLR. Thus, about 200 milliseconds after pulse No. 8 starts, tube LM fires to operate the relay CLR. The operation of relay CLR (armature B2 to contact B1) connects the winding of relay AB through the fan circuit to the terminals 22 to 28 to which the ground from relay L (contact 1) has just been applied to operate an external relay. If an external relay connectedto the particular terminal has just been operated, there will now be ground on this terminal by reason of the operation of the locking contacts of the external relay. The combination of this external ground on the terminal and the battery on the winding of relay AB which is connected by the operation of the relay P7 causes the operation of the relay AB. Operation of the relay AB opens the line circuit to send an answer back signal. It will, therefore, be appreciated that an answer back signal is produced only if an external relay connected to the particular ter-minal has been operated, as indicated electrically by the presence of ground on that terminal as a result of the operation of the locking contact of the external relay.

Reference may now be made again to Figure 3. As stated during the description of the transmitter apparatus, shown in that figure, the end of pulse No. 7 was marked by the return of the detent cam 86 to urge the switch member 87 out of contact with the terminal 88, thereby breaking the circuit through the winding 90. The relay 90, however, is of the type which delays on opening, the amount of such delay being variable as indicated by the arrow 90'. At the end of pulse 7, the line is returned to its marking condition (as explained) so that current through the relay winding 91 in series with the line 56 energizes the relay 91 to move the armature 92 away from the contact terminal 93. With the relay armature 83 in electrical contact with the contact member 97 (by reason of the de-energization of the relay winding 81 after the opening of the switch 87), a circuit may be traced from ground through the armature 83, contact 97, and the lamp 96 through the still closed relay members 94 and 95 up to the contact 93. The opening of the line circuit by the receiver as an answer back signal in the manner described above deenergizes the relay winding 91 for the duration of the answer back signal, so that the armature 92 makes contact with the terminal 93, thereby completing a circuit from the battery 119 through the annunciator lamp 96, causing the lamp to fire and provide a signal to the operator to the eifect that the code signal has been received by the intended receiver and the external function performed thereby, and, in fact, with the external function relay lock operated.

Clearing of receiver at end of code signal The operation of the relay CLR (armature T2 to contact T1) removes battery from the winding of the relay LP1. The release of this relay will be delayed approximately milliseconds by the capacitor C8. When the relay LP1 does release, however, battery is removed from all other U-type relays except for the relay HG, causing their release. The release of the relay AB at this time terminates the answer back signal being sent back to the sending station.

The connection of battery to the winding of relay P2 by the operation of the clearing relay CLR, plus the delaying effect of capacitor C9 causes therelay P2 to 15 :release after the relay AB has released. This maintains the blinding action of the relay P2 contact applied .to the associated teletypewriter printing magnet 111 until the answer-back signal is completed, thus preventing this signal from producing a false printing response by the teletypewriter.

Internal disconnect feature using relay HG Upon the reception of the disconnect code (i.e., pulse No. 2 being long) only the relay L1 2 of .the fan circuit is operated. The ground applied to the relay B (armature T5) at the beginning of pulse No. 8 will, therefore, be connected to terminal .28. If the internal disconnect feature involving the relay HG is used, terminal 28 will be connected to terminal 30. This will, in turn, .connect the above-mentioned ground to the battery side of the winding of relay HG, causing this relay to release. The release of relay HG removes the ground from terminal .HG of the receiver. Any external relays which are locked operated to this ground will therefore be released.

External disconnect feature If it is desired to usethe external disconnect feature, the strap between terminal 28 and 30 is omitted and terminal 28 is connected to the external disconnecting circuit. In this case, the relay HG is not used and .its battery supply may be openedto prevent its operation.

During the time relay HG is operated, its armature T2 applies ground to one side of capacitor C4. While this ground is applied, the voltage on-this capacitor will be about 50 volts, by virtue of the ground on one side and the approximate 50 volts applied by the potentiometer comprised of resistors R7 and R9 on the other side. If no external relay on a particular receiver isoperated at the time when its relay HG is released, nochange in voltage will occur on the capacitor C4, since it .willstill be connected to ground through the resistor R8. f-If, on the other hand, an external relay had been locked'operated to the ground on terminal HG, the removal of this ground by the release of relay HG would leave the positive battery applied through the winding-of theexternal relay connected momentarily through the holding contacts of the relay to the normally grounded sideof capacitor C4. This would raise the voltage on that side of capacitor C4 from zero to at least 120 volts. The voltage on the other side of capacitor C4 would -momentarily increase by about the same amount (i.e., a change from about 'SOvolts positive to about 170 volts positive). This voltage is suificient to fire the tube DAB (disconnect answer-back) to cause the operation of the relay AB. The operation of relay AB opens .the line circuit to start an answer-back signal and also operate the relay CLR, operation of the latter serving to clear the receiver and terminate the answer-back signal.

It should be noted that, unless an operated external relay associated with a receiver is released by the disconnect signal, no answer-back signal is sent. Therefore, if a remote teletypewriter had been connected to the circuit andthen, as by reason of a power or equipment failure at that point, had become disconnected during the transmission of a message,.the sending of a disconnect signal would produce no answer-back signal. An operator receiving no answer-back signal to a disconnect code at a time when he was under the'impression that 'there'had'been a distant teletypewriter connected would be put on notice to check immediately with the remote point to ascertain whether the message-had been satisfactorily received.

Clearing of-receiver after linehits If one, two or three accidental or otherwise long space of the one'or more space pulses will, in about 700 milliresult. :If :four accidental long space pulses in ,q

seconds, cause the tubes CLRztO fire and clear the selcctQr receiver .so that no false operation of the rficeiver ca; successionare received, all relaysof the counting ci pit will be operated, just as on ;a code signal. If the relay WP is operated by one of the accidental pulses or if the proper combination of relays LP 2 A and B is not operated, no false operation of the receiver can result. The accide l c nc .of ou pa e p se in q ick succession on a circuit is quite improbable and the probability of false operation on line hits or other trouble conditions is made even more remote when the additionaL requirements are added that the four such pulses must not operate relay WP and must operate the relay 1,132., A and B in only certain combinations for a particular receiver.

From the foregoing, those skilled in the art will recognize that, in accordance with the present invention, .there is provided anew and improved selective signalling system of the pulse code variety, capable of use inconjunction with existing.teletypewritercircuits but incapable of interfering with the latter and immune to interference therefrom.

Having thus described my invention, whatl claim as new and, desire to secure by Letters Patent is:

1. .A.p ulse codereceiver foroperationin an electrical signalling system of .the' type including signal transmitting apparatus for producing and sendingover a tele- ;typewriter channel a code signal made up of a fixed number of rnarkandspace pulses Whichareof either oneof two .fixed,,different durations, the first pulse of such signal being ,a long pulse whose duration bears such a predeterminedrelation to the length of a teletypewriter codesignaL-that said first pulse produces a non-print spacing condition in a teletypewriter receptive of said code signal for theduration of .said first pulse, said receiver being adapted for connection to such teletype- Writer channel, said receiver comprising: means for counting the pulses of such signal, means connected to such channel and responsive to the termination of, the firstlong pulse of such code signal for energizing said counting circuit such that said counting circuit may count suc cessive pulses of such signal; a pair of terminals in said receiver adapted for connection to a teletypewriterequipment-ass ociated with such channel; and means in said countingcircuit associated with said terminals and energized concurrently withsaid counting circuitforinactivating such teletypewriter equipment for aperiodbeginning with the termination of said first long pulseland continuing until at least the termination ofthe last ,pulse of said received code signal.

2. The invention as defined by claim 1 which further comprises pulse measuring means for registering those pulses of the received signal which are of aselected one of such two diflerent durations, means operated by said pulse measuring means for performing a selected external functiondetermined by the number and position of pulses in such signal which are of said selected duration; means responsive to a termination of such pulse signal'for connecting an answer-back. circuitto said external function,

said answer-back circuit having means for producing an ofspace and mark pulses, which pulses areeither of-first or second durations and in which intelligence is conveyed by the position in the code of pulses of the first duration, said receiver being adapted to control an external function in response to such signal and comprising: a first pulse measuring means for receiving and recognizing a code signal by the length of the first pulse thereof; counting means comprising N counting circuits for counting the successive pulses of a received code signal consecutively; said pulse measuring means being operatively connected to said counting means for activating said counting means upon receipt of a code signal whose first pulse is of the appropriate duration; at least one but less than Nl additional pulse measuring means for recognizing received pulses of such first duration, said additional pulse measuring means being operatively connected to selected ones of said counting circuits to register the occurrence of a received pulse of said first duration in the positions in said signal corresponding to the counting circuits to which said pulse measuring means are respectively connected; means responsive to said additional pulse measuring means for performing an external function in accordance with the information of the received pulses; and wrong pulse detecting means for inactivating such external function performing means upon the receipt of a pulse of said first duration in a position in such signal not corresponding to the positions of pulses to whose counting circuits said additional pulse measuring means are connected.

4. A pulse code receiver adapted to receive from a sending station a signal made up of a fixed number N of space and mark pulses, which pulses are either of first or second durations and in which intelligence is conveyed by the position in the code of pulses of the first duration, said receiver being adapted to control an external func tion in response to such signal and comprising: a first pulse measuring means for receiving and recognizing a code signal by the length of the first pulse thereof; counting means comprising N counting circuits for counting the successive pulses of a received code signal consecutively; said pulse measuring means being operatively connected to said counting means for activating said counting means upon receipt of a code signal whose first pulse is of the appropriate duration; at least one but less than N1 additional pulse measuring means for recognizing received pulses of such first duration, said additional pulse measuring means being operatively connected to selected ones of said counting circuits to register the occurrence of a received pulse of said first duration in the positions in said signal corresponding to the counting circuits to which said pulse measuring means are respectively connected; means responsive to said additional pulse measuring means for performing an external function in accordance with the information of the received pulses; and wrong pulse detecting means for inactivating such external function performing means upon the receipt of a pulse of said first duration in a position in such signal not corresponding to the positions of pulses to whose counting circuits said additional pulse measuring means are connected, said wrong pulse detecting means comprising: a circuit connected to a counting circuit which has one of said additional pulse measuring means associated therewith, said circuit being operable in response to said pulse measuring means.

5. A function-performing pulse code receiver adapted to receive from a sending station a signal made up of a fixed number N of space and mark pulses which are either of first or second durations and in which a functionstopping signal is conveyed by a code which includes at least one pulse of such first duration in certain portion in such signal, said receiver comprising: a first pulse measuring means for receiving and recognizing a code signal by the length of the first pulse thereof; counting means for comprising N counting circuits for counting the successive pulses of a received code signal consecutively; additional pulse measuring means operatively connected to said counting means for registering the occurrence of a pulse of said first duration in said certain position; external function terminals in said receiver adapted for connection to an external equipment for activating such equipment; means responsive to said additional pulse-measuring means and connected to said terminals for disconnecting said such external equipment upon the receipt of such function-stopping signal and at the termination thereof; answer back means actuated by said counting circuit at the termination of the code signal and responsive to the electrical condition existing at said terminals for furnishing to such sending station an answer signal upon the completion of an external function; and means responsive to the electrical condition existing at said terminals during the final pulse of such signal for rendering said answer back means operative only when an equipment had been connected to said terminals at that time.

6. A function-performing pulse code receiver adapted to receive from a sending station a signal made up of a fixed number N of space and mark pulses which are either of first or second durations and in which a disconnect signal is conveyed by a code which includes at least one pulse of such first duration in certain portion in such signal, said receiver comprising: a first pulse measuring means for receiving and recognizing a code signal by the length of the first pulse thereof; counting means for comprising N counting circuits for counting the successive pulses of a received code signal consecutively; additional pulse measuring means operatively connected to said counting means for registering the occurrence of a pulse of said first duration in said certain position; external function terminals in said receiver adapted for connection to an external equipment for activating such equipment; means responsive to said additional pulsemeasuring means and connected to said terminals for disconnecting said such external equipment upon the receipt of such disconnect signal and at the termination thereof; answer back means actuated by said counting circuit at the termination of the code signal and responsive to the electrical condition existing at said terminals for furnishing to such sending station an answer signal upon the completion of an external function; and means responsive to the electrical condition existing at said terminals during the final pulse of such signal for rendering said answer back means operative only when an equipment had been connected to said terminals at that time; said means comprising a capacitive storage device operatively connected with said terminals for storing energy available at said terminals in the presence of a connected equipment.

References Cited in the file of this patent UNITED STATES PATENTS 2,229,249 Lewis Jan. 21, 1941 2,399,734 Hailes May 7, 1946 2,534,387 Thomas Dec. 19, 1950 2,534,388 Shenk Dec. 19, 1950 2,623,939 Derr Dec. 30, 1952 2,652,446 Oberman Sept. 15, 1953 2,675,537 Cahill Apr. 13, 1954 2,679,034 Albrighton May 18, 1954 2,690,548 Joel Sept. 28, 1954 2,752,414 Przysiecki June 26, 1956

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