[Relay Unit Be-84-a (Teletype Trunk)]
[From the U.S. Government Publishing Office, www.gpo.gov]
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WAR DEPARTMENT TECHNICAL MANUAL
RELAY UNIT
BE-84-A
(TELETYPE TRUNK)
WAR DEPARTMENT • 8 APRIL 194
NTSU LIBRARY
WAR DEPARTMENT TECHNICAL MANUAL
T M 11-343
RELAY UNIT
BE-84-A
WAR DEPARTMENT • 8 APRIL 1944
United States Government Printing Office Washington : 1944
For sale bv the Superintendent of Documents. U. S. Government Printing Office, Washington 25, D. C. - Price 15 cents
WAR DEPARTMENT, Washington 25, D. C., 8 April 1944. TM 11—343, Relay Unit BE—84—A, (Teletype Trunk), is published for the information and guidance of all concerned.
[A. G. 300.7 (3 Mar 44).]
By order of the Secretary of War:
G. C. MARSHALL, Chief of Staff. Official:
J. A. ULIO,
Major General,
The Adjutant General.
Distribution :
Distribution as prescribed in par. 9a FM 21-6; I Bn 11 (2) ; I G 11 (10)
I Bn 11: T/O & E 11-15, Sig Bn.
I C 11: T/O & E 11-97, Sig Co Opn; 11-18, Sig Co Wire Opn; 11-107, Sig Co Dep; 11-127 Sig Co Rep; 1 1-327 Sig Port Sv Co; 11-88-S, Sig Opn Co, Armd Sig Bn.
(For explanation of symbols see FM 21-6.)
II
CONTENTS
Section I. Description.
Paragraph Page
Purpose_____________________________________ 1 1
Application_________________________________ 2 1
Equipment arrangement_______________________ 3 1
Power_______________________________________ 4 3
Major components____________________________ 5 3
Method of supervision_______________________ 6 ✓ 4
Radio induction suppression_________________ 7 4
Operating range limitations_________________ 8 4
Dimensions and weights______________________ 9 4
II. Installation and Operation.
General_____________________________________ 10 5
Preparation for use and line-up procedure-_ 11 7
Operating instructions______________________ 12 8
Adjustments to maintain service_____________ 13 8
III. Functioning of Parts.
Transmission of signals_____________________ 14 9
Supervisory circuit operation_______________ 15 9
IV. Maintenance.
Servicing__________________________________ 16 12
Inspection and preparation for servicing_ 17 12
Adjustment of polar relays_________________ 18 12
Adjustment of relays A, B, C, and D________ 19 14
Replacing fuses and lamps__________________ 20 14
Procedure in case of relay unit failure__ 21 14
V. Supplementary Data.
Replaceable parts__________________________ 22 15
List of manufacturers______________________ 23 19
in
DESTRUCTION NOTICE
WHY—To prevent the enemy from using or salvaging this equipment for his benefit.
WHEN—When ordered by your commander.
HOW—1. Smash—Use sledges, axes, hand axes, pickaxes, hammers, crowbars, heavy tools, etc.
2. Cut—Use axes, hand axes, machetes, etc.
3. Burn-—Use gasoline, kerosene, oil, flame throwers, incendiary grenades, etc.
4. Explosives—Use firearms, grenades, TNT, etc.
5. Disposal—Bury in slit trenches, fox holes, other holes. Throw in streams. Scatter.
USE ANYTHING IMMEDIATELY AVAILABLE FOR DESTRUCTION OF THIS EQUIPMENT
WHAT—1. Smash—Cabinet, terminals, rheostat, key, switches, meter, rectifier, carrying case, relays, and all other electrical equipment.
2. Cut—All connecting cords and wires.
3. Burn—All wire, charts, circuit labels, instruction books, technical manuals.
4. Bury or scatter—Any or all of the above pieces after breaking.
DESTROY EVERYTHING
SAFETY NOTICE
IF IT BECOMES NECESSARY TO REMOVE THE UNIT FROM THE METAL CABINET, DISCONNECT THE POWER CORD FROM THE 115 VOLT A-C SUPPLY AND THE 115 VOLT D-C LEAD FROM KEY AND
LAMP UNIT TO SWITCHBOARD BD-100. CARE SHOULD BE EXERCISED TO AVOID TOUCHING TERMINALS WITH BARE HANDS WHILE TESTING. ALL TEST LEADS SHOULD BE INSULATED.
IV
Section I
DESCRIPTION
1. Purpose
Relay Unit BE-84-A (Teletype Trunk), in combination with teletypewriter Switchboard BD-100 provides a means of establishing connections with a commercial teletypewriter exchange (TWX) in the continental United States. Relay Unit BE-84-A in operation with teletypewriter Switchboard BD-100 is shown in figure 1.
2. Application
The relay unit is located with the teletypewriter switchboard, and is designed primarily for use on Bell System line conductors. Relay Unit BE-84-A provides one circuit to a TWX switchboard. More than one relay unit may be used with a teletypewriter switchboard if required by the traffic load. An application schematic diagram, indicating the equipments involved in an over-all circuit between a teletypewriter switchboard and a TWX switchboard, is shown in figure 2.
3. Equipment Arrangement
The equipment is arranged as a portable unit and assembled in a compact metal cabinet, with the terminals, a rheostat, a key, switches, and a meter exposed on the top panel. The unit contains a built-in selenium-disk rectifier for supplying line voltage. A durable wooden carrying case equipped with shockproofing material serves as protection during transit. A key and lamp unit, supplied with wires for connecting to terminals in Switchboard BD-100 (fig. 5), is attached to Switchboard BD-100 during service periods. The key and lamp unit is permanently connected to Relay Unit BE-84-A by an 8-foot cord. Relay Unit BE-84-A, in its
carrying case, is shown in figure 3. It is supplied with a 10-foot cord for connecting to the a-c supply. The demountable polar relays are held in place by shockproof felt pads. (See fig. 5.)
4. Power
The 75-volt rectifier which supplies line battery requires 115-volt, 50-60 cycle alternating current to operate. This a-c power may be obtained from a commercial source or a gasoline engine-driven alternator. Approximately 60 watts from the a-c supply are required. The milliammeter associated with the bias measuring circuit is normally connected in series with a resistor across the d-c side of the rectifier to indicate the rectifier’s output voltage. Power for the supervisory relays and the loop circuit of the relay unit is obtained from the 115-volt rectifier used with Switchboard BD-100. This power requirement is substantially the same as a station line circuit in the teletypewriter switchboard.
5. Major Components
The relay unit contains a polar relay telegraph repeater for the repetition of communication signals between the line facility and the teletypewriter switchboard; neutral supervisory relays and power relays; a bias measuring circuit used to adjust the current in the bias winding of the receiving relay; a rectifier for supplying direct current for the line conductors and bias winding of the receiving relay; a key and lamp unit for controlling the supervisory features of the relay unit. Also, apparatus is furnished so that service to the central office may be arranged on a 1-wire or 2-wire basis. In the case of 2-wire operation, one of the line conductors and
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Figure 1. Relay Unit BE—84—A in operation with. Switchboard BD—100.
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TRUNKS TO DISTANT POINTS
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Figure 2. Application schematic diagram.
LINE-UP INSTRUCTION
PLATES SEE FIG. 6 OPERATING INSTRUCTION PLATE SEE FIG. 7 i
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Figure 3. Relay Unit BE—84—A in carrying case.
3
its associated terminating apparatus serves to neutralize the effects of ground potentials, 25-cycle power induction, and other forms of interference. With 1-wire operation, a 60-cycle filter is used in the signal line to reduce interference from power lines of this frequency.
6. Method of Supervision
The method of supervision is known as open-line supervision. Current flows only while a call is in progress. With this form of supervision, the TWX switchboard operator calls by sending 20-cycle ringing current; the teletypewriter printer switchboard operator calls, recalls, and disconnects by using the TWX key in the key and lamp unit. When the TWX key is turned to ON, the normal marking current flows in the line; when it is OFF, no line current flows.
7. Radio Induction Suppression
The contacts of the polar relays and the a-c power cord are equipped with filters. Bypass condensers are connected to the line terminals of the relay
unit. This apparatus is provided to reduce interference to radio receiving equipment.
8. Operating Range Limitations
Operating range is determined by the telephone company. This is controlled largely by the type of line facility available in any particular area. Normally the operating range will be 20-25 miles. Under ideal conditions the operating range may extend to 80 miles.
9. Dimensions and Weights
The dimensions and weights of the relay unit and carrying case are as follows:
Component Length (in.) Height (in.) Depth (in.) Weight (lbs.)
Relay unit __ 24% 28 10 13% 11% 16 87 45
Carrying case
Total weight.
132
4
Section II
INSTALLATION AND OPERATION
10. General
a. Communicate with the telephone company to determine whether the line conductors and the TWX switchboard terminating equipment are available. The line connections should be made in the TWX central office prior to lining up the relay
unit for service, since the lineup procedure requires cooperation with the TWX central office test board attendant.
b. To determine the connections to be made by cords and wires, refer to figures 4 and 5. The connections established to the relay unit are the line
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Figure 5. Apparatus compartment door open.
LINE-UP INSTRUCTIONS FOR RELAY UNIT BE-84-A WITH SWITCHBOARD BO-IOO
I . REMOVE UNIT FROM CARRYING CASE. ARRANGE UNIT FOR ONE OR TWO-WIRE OPERATION PER INSTRUCTIONS OF LOCAL TELEPHONE COMPANY. FOR ONE-WIRE OPERATION .CONNECT LINE WIRE TO TERM INAL 'Ll" ANO STRAP TERMINAL 'A“ TO V AND TERMINAL “j" TO "K0. FOR TWO WIRE OPERATION, CONNECT SIGNAL LINE TO TERMINAL'Ll" AND NEUTRALIZING LINE TO TERMINAL *L2“ AND STRAP TERMINAL "j“ TO *H"
2 . MOUNT LAMP AND KEY UNIT OF RELAY UNIT BE-84-A ON UPPER LEFT SIDE OF SWITCHBOARD, USING SCREWS PROVIDED IN POCKET OF CARRYING CASE. CONNECT THE RED, BLACK AND GREEN WIRES TO THE BATTERY*', ” GND" AND "LINE I " TERMINALS, RESPECTIVELY, OF SWITCHBOARD . CONNECT OPERATOR'S PRINTER TO STATION LINE SELECTED. ADJUST LINE RHEOSTAT IN SWITCHBOARD BD- 100 TO GIVE 30 MILLIAMPERES AS INDICATED BY SWITCHBOARD METER AND ADJUST "LO" RELAY FOR ZERO BIAS.
3 .TURN "ADJ BIAS'RHEOSTAT IN RELAY UNIT BE-84-A TO*HIGH'POSITl ON AND SET "LINE RES* AT *300* OHMS. CONNECT POWER CORD TO 115 VOLTS A.C 5O-6O~. TURN "TWX" KEY IN KEY AND LAMP UNIT TO *ON* POSITION WHICH CALLS CENTRAL OFFICE AND TURN "ADJ VOLTS*' SWITCH SO THAT METER READS 75 V (RED LINE).
4 WHEN CENTRAL OFFICE ANSWERS (INDICATED BY METER VIBRATION) TYPE-"THIS IS ARMY SWBD. CALLING TEST-BOARD". WHEN TESTBOARD ANSWERS (INDICATED BY METER VIBRATION) TYPE-’THIS IS ARMY SWBD. SEND REPEAT SPACE SIGNALS FOR A LINE UP"
5 DEPRESS'REC BIAS' KEY AND TURN 'ADJ BIAS** RHEOSTAT SO THAT METER VIBRATES ON ZERO. ALSO ADJUST ’Ll "RELAY IN SWBD. BD-IOO ON SAME REPEAT SPACE SIGNALS. ASK TESTBOARD FOR VALUE OF'LINE RES" AND IF NOT *300"OHMS LINE UP AGAIN ON REPEAT SPACE SIGNALS. CHECK TRANSMISSION AND SUPERVISION IN BOTH DIRECTIONS WITH TESTBOARD.
Figure 6.
Facsimile of lineup instruction plates.
TL5002I
or lines to the TWX central office and the power connection to a 115-volt, 50-60-cycle a-c supply. Also, local line, battery and ground connections are made from the key and lamp unit to Switchboard BD 100.
11. Preparation for Use and Lineup Procedure
The following lineup procedure is summarized on instruction plates attached to the relay unit. (A facsimile of these plates is shown in figure 6.)
a. Remove the relay unit from, and place it on the top of, the carrying case. As directed by the local telephone company, arrange the unit for 1-wire or 2-wire operation according to operating instructions. Refer to figure 4 for connections for 1-wire and 2-wire operation.
(1) For 1-wire operation. Connect signal line to terminal L2. Strap terminals A and B together,
and J and K together. (Do not strap terminals J and H.)
(2) For 2-wire operation. Connect signal line to terminal LI and neutralizing line to terminal L2. Strap terminals J and H together. (Do not strap terminals A and B or J and K.)
b. Mount the key and lamp unit on upper left side of switchboard, using the screws found in pocket of carrying case. (See fig. 3.) Connect the red wire to the negative battery terminal,—BATTERY black wire to GND, and green wire to a LINE terminal in switchboard. Connect the operator’s teletypewriter to the station line termination selected. Adjust the line rheostat in Switchboard BD—100 to give 30 milliamperes, as indicated by the swithboard meter, and adjust relay Lo for zero bias, using the switchboard-bias measuring circuit.
c. Turn the ADJ BIAS knob in Relay Unit BE— 84-A to the HIGH position. Set LINE RES knob
7
to 300. Connect the power cord to a source of 115-volt, 50-60-cycle alternating current. Turn TWX knob in key and lamp unit to ON, which calls central office, and turn ADJ VOLTS knob so that meter reads 75 V (red line).
d. When central office answers (indicated by meter vibration), type: THIS IS ARMY SWBD CALLING TESTBOARD. When testboard answers (indicated by meter vibration), type: THIS IS ARMY SWBD. SEND REPEAT SPACE SIGNALS FOR LINEUP.
Note. With the ADJ BIAS knob in the HIGH position and the LINE RES knob at 300, signals can be transmitted to the TWX central office, even though signals cannot be received from the central office until the bias of the receiving relay has been adjusted.
e. Depress REC BIAS button and turn ADJ BIAS knob so that meter vibrates on zero. Then adjust relay Li in Switchboard BD-100 on same repeat space signals.
f. Ask testboard for value of LINE RES and if not 300 ohms readjust to the value given and line up again on repeat space signals. Check transmission and supervision in both directions with testboard.
Note. A current greater than 30 milliamperes in the loop line to Switchboard BD-100 tends to introduce marking bias and a current less than 30 milliamperes tends to introduce spacing bias. This current may be changed slightly on instructions of testboard attendant at TWX central office.
12. Operating Instructions
Operating instruction plates are attached to the relay unit and the key and lamp unit. A facsimile of the operating instruction plate is shown in figure 7.
a. TO CALL, OR ANSWER A CALL. Operate TWX key to ON and connect operator’s teletypewriter to line in Switchboard BD-100 in normal manner.
b. TO RECALL. Operate TWX key momentarily (2 seconds) to OFF.
c. TO DISCONNECT. Operate TWX key to OFF. Disconnect line on Switchboard BD-100 in normal manner.
• d. TO SEND BREAK SIGNAL. Operate the printer break key for about 3 seconds.
Note. A break signal in either direction over a TWX connection will light the associated line lamp in the teletypewriter switchboard. If a connection has been set up through the teletypewriter switchboard to a station, it should not be taken down until it has been determined that both parties wish to discontinue the connection.
OPERATING INSTRUCTIONS
I. TO CALL OR TO ANSWER A CALL — OPERATE "TWX" KEY TO "ON" POSITION.
2. TO RECALL — OPERATE "TWX" KEY MOMENTARILY (2 SECONDS) TO "OFF" POSITION.
3. TO DISCONNECT ---- OPERATE "TWX"
KEY TO"OFF " POSITION.
4. TO SEND BREAK SIGNAL — OPERATE PRINTER BREAK KEY FOR ABOUT 3 SECONDS.
TL5OO22
Figure 7. O perating instruction plate for key and lamp unit.
13. Adjustments to Maintain Service The only adjustment required to maintain service is that of the rectifier voltage output in the case of an abnormal change in the a-c voltage supply after the initial lineup. The a-c voltage may vary plus and minus five volts without an appreciable effect on performance. Occasionally, and when abnormal a-c voltage changes occur while a TWX connection is up and no signals are being transmitted in either direction, check the reading of the meter and turn ADJ VOLTS knob as required to provide a meter reading of 75 V (red line). If a lineup check is desired, place a TWX call in the regular way and ask the operator for TESTBOARD.
8
Section III
FUNCTIONING OF PARTS
14. Transmission of Signals
Figure 8 shows an over-all transmission schematic diagram. The method of transmission (communication signaling on the line facility), is type B polar-ential, which is a d-c grounded-return system. This form of transmission requires no service adjustments to compensate for changes in the electrical characteristics of the line conductors caused by resistance-leakage or for grounded capacity variations resulting from wet and dry line conditions. Transmission is polar from the relay unit to the central office; differential from the central office to the relay unit. Sending relays SI and S2 apply negative 75 volts to the line for mark and positive 75 volts for space. Thus, reversal in line current occurs when signals are sent from the relay unit because at the TWX central office the line terminates in ground at contact M of relay S via the line winding of the receiving relay and certain supervisory relays. At the central office, the sending relay applies ground for mark and positive 130 volts for space. When transmission is from the TWX central office, line current does not reverse and space current is approximately 2y2 times mark current. This space current flows as a result of approximately 205 volts ( + 130 volts at TWX office and “75 volts at relay unit) being applied to the line. The bias current of the receiving relay in the relay unit is always in a marking direction, and is approximately the average of mark and space currents sent from the central office. Thus the net effect on the armature of the receiving relay in the relay unit is polar. On installation the marking line current is adjusted between 20 and 30 milliamperes. The loop circuit connected to Switchboard BD-100 is a balanced (neutral) one adjusted for a current of 30 milliamperes. The receiving relay in the relay unit supplies ground to
the loop for marking and negative 115 volts for spacing.
15. Supervisory Circuit Operation
Refer to functional schematic diagram (fig. 9), and detail circuit schematic diagram. (See fig. 10.)
a. INWARD CALL. An inward call is a call from the TWX switchboard to the printer switchboard. The TWX operator connects a cord to the line jack of the TWX trunk and throws a ringing key lever which sends 20-cycle ringing current over the signal line. Relay D in the relay unit responds to this ringing current and in turn operates relay B. Relay B removes ground from the M contact of receiving relay R, which opens the loop to the switchboard, releasing relay Li, which in turn releases the signal relay. The release of the signal relay causes the switchboard associated LINE lamp to light. Subsequent ringing on the part of the TWX operator is ineffective because relay B is locked operated through the OFF contacts in the TWX key. The teletypewriter switchboard operator turns the TWX key in the key and lamp unit to ON and answers the call in the regular manner through the line termination in Switchboard BD-100. The turning of this TWX key lights the associated guard lamp, releases relay B, and supplies ground to operate relay A. The guard lamp remains lit as long as Relay Unit BE-84-A is energized. Relay A energizes the relay unit rectifier, which supplies marking negative potential at contact M of relay SI. During the marking condition the positive side of the rectifier is grounded at contact M of relay S2. Relay A also supplies ground to operate relay C, which removes the ringing relay D from the line and connects the signal line (also the neutralizing
9
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Figure 8. Over-all transmission schematic diagram.
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Figure 9. Functional schematic diagram.
line if set is arranged lor 2-wire operation) to the line windings of the receiving relay R, thereby closing the transmission path.
b. OUTWARD CALL. An outward call is a call from the teletypewriter switchboard to the TWX switchboard. The teletypewriter switchboard operator connects the teletypewriter in the normal manner to the TWX trunk line and turns the T’WX key to ON, which operates relays A and C. As described in a above, this operation closes the a-c supply circuit to the relay unit rectifier and connects the line to the winding of relay R. The normal line current causes certain supervisory relays at the TWX office termination to light the LINE lamp, and the TWX operator answers, after connecting a cord to the LINE jack.
c. SUPERVISORY SIGNALS. (1) A recall signal to flash the TWX operator occurs when the teletypewriter switchboard operator turns the TWX key to OFF position for about 2 seconds. While the key is in OFF position the normal line current is removed, because relays A and C are released. When the key is again turned to ON the line battery is reapplied due to relays A and C reoperating. At this time the TWX operator receives a flashing supervisory lamp which is acted upon in a prescribed manner.
(2) A disconnect signal occurs when the TWX key is turned to OFF. As described in (1) above, this removes the normal line current, and, since the TWX key is not turned to ON again, the TWX operator receives a steadily lighted supervisory lamp.
(3) A communication break signal to interrupt the sending station occurs when the printer break key is held depressed. During this interval the send relays operate to their S contacts, and send a spacing transmission signal.
d. BIAS MEASURING CIRCUIT. When the REC BIAS button is depressed, the milliammeter (100 0 100) is removed from the normal connection on the output of the rectifier, and is connected to an unbalanced bridge circuit in a leak circuit from the armature of the receiving relay. This circuit provides a means of adjusting the bias winding current of the receiving relay on repeat space characters from the TWX centra] office, thus providing unbiased signal reception. The measuring circuit is designed so that the meter needle vibrates at 0 as an average, when the bias current is correctly adjusted. After this adjustment, unbiased signals will be transmitted to the receiving relay Li in the teletypewriter switchboard.
Figure 10. Schematic circuit diagram. (See back of manual.)
11
Section IV
MAINTENANCE
16. Servicing
The necessary maintenance tools will be found in Tool Equipment TE-50.
17. Inspection and Preparation for
Servicing
Turn the unit cover so it rests on its back, and remove screws holding bottom panel. (See fig. 11.) A circuit label showing wiring of apparatus will be found on the inside of the bottom panel. When the relay unit is resting on its back, the position of the apparatus corresponds to that in the circuit label. (See fig. 12 at back of manual.) The rectifier may be taken out of the cabinet by removing the four round-head screws on the top of the panel.
18. Adjustment of Polar Relays
a. GENERAL. The location of the polar relays is shown in figure 5. Relay Test Set 1—193—A or the relay test circuits of Telegraph Terminal CF-2-A (Carrier) or Telegraph Terminal CF-2-B (Carrier), if available, can be used to test relays SI and S2 (255A). Polar lelay test panels such as used by telephone companies can be used to test all polar relays in Relay Unit BE-84-A. The adjusting procedure described below is a mechanical method which will not result in adjustments as accurate as can be obtained by the use of the above means, but may be used in the field in an emergency. Reconditioning and adjustment by a telephone company is recommended for relays with pitted contacts, or poorly aligned armatures or winding spools. No attempt should be made to adjust the polar
relays while they are in their normal operating position.
b. ADJUSTING PROCEDURE. (1) Loosen the knurled tension nuts (255A, D-163119A) or polepieceholdingscrews (209FG, D-163120FC) which clamp the pole-pieces, and turn pole-pieces as far away from the armature as possible.
(2) With an adjusting key (tommy tool) turn the screw contacts a few turns away from the armature.
(3) Clean contacts with carbon tetrachloride; then burnish contacts with contact burnisher. Insert a wedge-shaped stick (orange stick) between flexible contact springs while burnishing the armature contacts. Do not use any type of file.
(4) Remove all dirt (especially magnetic particles) from the face of the pole-pieces by contacting the pole faces lightly with a piece of friction tape.
(5) Check the alignment of the armature. It should be substantially in the center of the windingspool slot. All assembly screws and nuts should be tight. Contacts should line up so that the point of contact for a screw contact is wholly within the boundary of the opposite armature contact.
(6) With pole-pieces and the screw contacts away from armature as in b (1) and (2) above, adjust the armature to have a total contact travel of 0.004 inch in the following manner: Turn each screw contact until there is a clearance of 0.002 inch between it and the corresponding armature contact. Use thickness gauges if available.
(7) Turn the pole-pieces toward the armature until there is a clearance of approximately bie inch, or slightly less. Clamp the pole-pieces to just permit turning.
12
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