Relay Interlocking 902
Switch Machines 902
Methods of Control 905
Controls and Indications 906
Direct Wire Near Group Control 906
Direct Wire Remote Group Control 906
Remote Control Systems 908
Basic Circuits 908
A Typical Control Panel 908
Circuit Symbols 909
Switch Control 910
Clearing a Signal 910
OS Indication 913
Preconditioning - Its Prevention 913
Relay Interlocking and Switch Control 914
Signal Indication Locking 914
Approach Locking 914
Approach Locking, Time Release 915
Approach Locking, Track Release 916
Detector Locking 917
Switch Repeater and Correspondence Relays 917
Switch Control 917
Home Signal Controls 918
Approach Signal Controls 919
Entrance-Exit Interlocking 919
NX Knobs 920
Route Selection 921
NX Circuits 922
Circuit Symbols 928
NX Nomenclature 928
Route Initiation 928
Route Completion 928
Route Selecting Relay YR 931
Interlocking is employed to facilitate and safeguard the movement of trains at terminals, junction points, railroad grade crossings, and drawbridges. It is defined as: “An arrangement of signals and signal appliances so interconnected that their movements must succeed each other in proper sequence and for which interlocking rules are in effect. It may be operated manually or automatically.”
The first interlockings were mechanical. Then electric operation of switches and signals was introduced, retaining mechanical means of interlocking their operations. In present systems, relay circuits provide the interlocking. Figure 901 is a small, typical relay interlocking control machine.
When the operator of the interlocking is located within the locality of the interlocked switches and signals, controls are direct wire, and central energy sources are provided to operate the relays, signals, and electric switch machines. Energy sources are commonly batteries of storage cells, with provision for charging from commercially available power.
standby power sources, such as motor generator sets, are also provided.
When one - or sometimes several - locations are distant from the control center, remote control and indication systems are used, with switch machine and signal energy sources at the locations. There are many types of remote control systems, some using physical line circuits, some carrier, some microwave, and - relatively few - space radio.
Automatic interlockings require no operators. They are actuated by the presence of the trains on the controlling track circuits. A crossing at grade is a good example. Such an automatic interlocking usually operates so that the first train to arrive locks out opposing signals and then causes signals for its route to be cleared. Otherwise, the protective circuitry is basically the same as for an attended relay interlocking.
To understand the relay interlocking circuits to follow later, it will be necessary to explain the electrical control of the switch machine. We shall use the GRS Model 55G, Figure 902, as a typical example.
Figure 901. A typical relay interlocking control machine for use on a table oriesk.
electric switch machine such as may be used in a relay interlocking is actually
an electrically operated switch and lock movement that indicates its position.
It unlocks the switch, operates it to the called-for position, and locks the
switch in that position, and, at appropriate times in the operation, opens and
shunts indication circuits. Some machines, such as the GRS models 55F and H,
Figure 903, are dual control. That is, they are arranged so that trainmen can
operate the switch by hand, such as may be convenient when doing considerable
switching at a remote location.
The principal parts of an electric switch machine such as the Model 55G are motor, gearing, operating and locking members, pole-changer, point detector of the over-and-locked type, and lock and detector rod combinations to fit specified requirements.
The switch machine controller, Figure 904, mounted inside the machine, consists of an overload relay and two biased-neutral contactors. The magnetic structure of each biased-neutral contactor is such that it will operate only when current flows through its windings in a specified direction. This feature provides for two-wire polarized control of the switch machine, either over line or by means of local control relays. Operating energy to the switch machine is controlled through the heavy-duty contacts of the biased-neutral contactors.
The overload relay acts to de-energize the contactors if the motor draws excessive current,
example, if an obstruction jams the switch. Reversing the controller energy
automatically resets the overload relay to permit operating the machine in the
A typical wiring diagram for a Model 55G switch machine is shown in Figures 905a and b. Figure 905a shows the switch reverse and switch control relay WZR positioned to call for the switch to move toward normal. When contactor Cl picks up, contactor C2 is forced down by a mechanical interlock between the armatures of the two contactors. When the switch machine is over and locked normal, Figure 905b, motor control contact 7D-2C opens, cutting energy off Cl, and the contactor contacts center as shown. Motor control contact 8D-1C is
Figure 902. Model 55 G electric switch machine, with cover removed.
Figure 903. Typical installation of Model 55H electric switch machine.
[ TERMINAL FOR
10-VOLT D-C CONT ROL
- (GRS NO. 42760-233 OR. 2 FOR 24-VOLT D-C OPERATION)
Figure 904. Controller for Models 55G and 55H electric switch machines, shown with cover removed and for d-c operation and control.
Switch control operating circuit, operating toward nornial.
PLUG-IN TERMINAL 2
F — ASED-NEUTRAL CONTROLLER —
closed, ready to furnish an energy path to C2 when WZR is driven down to call
for the switch reverse.
Other point detector contacts, Figures 906a-c, detect the position of the switch points through the point detector rods. They are also operated by the lock rods to check whether the switch is properly locked. Figure 906a shows how normal switch correspondence relay NWCR is energized when the switch is over and locked normal. As soon as the switch machine starts to move from its over and locked position, Figure 906b, contacts 5C-6C and 7C-8C open, and shunt contact 6C-7C is established. Thus, as shown by the blue path, NWCR is not only de-energized, but a shunt is established to prevent either NWCR or RWCR from picking up.
When the switch is over and locked reverse, Figure 906c, reverse switch correspondence relay RWCR is energized.
Methods of Control
The two-way communication - controls and indications - between the individual lever relay interlocking control panel or the NX control panel and the track circuits, signals, switches, and other
on the railroad, is either by direct wire (unit wire) or by any of several wire
conserving remote control code systems.
The fundamental purpose or object of a code system is to do the same work over two line wires that is done over several line wires in a unit-wire system. In a code system, the circuits between the
Figure 906a. Switch repeater relay Circuit, switch over and locked normal.
Figure 905b. Switch control circuit, over and locked normal.
Figure 906b. Switch repeater relay circuit, switch unlocked and moving toward reverse.
Switch repeater relay circuit, switch over and locked reverse.
control office and field are not organized on the “normally closed” circuit princple. This principle applies only to the circuits relied upon for safety, such as the switch and signal control circuits, approach locking, etc. These circuits are the same for a code-type system as for the unit-wire type. The code part of the system, however, is entirely open circuit, as failures of the code apparatus do not affect safety. The code communication circuits are used to transmit controls and indications with the minimum of apparatus and line wires and as reliably as can be done with an open-circuit scheme.
a more detailed description of the principles of coding, see the section on
centralized traffic control.
Figure 907 illustrates diagrammatically the interrelation between the various systems. It is intended to emphasize the importance of a thorough understanding of the relay interlocking principles and circuiting surrounding the wayside functions, as these are common to the various systems. It will be noted from Figure 907 that starting from a control machine of the individual lever (IL) type, we can proceed through the control office indication and control circuits via direct wire to the field functions or through office indication and control circuits via direct wire to field indication and control circuits to the field functions or through the control office end of a remote control system via physical line, carrier, or microwave, to the field end of the system. In each case, we come to the relay interlocking of the field functions. Likewise, starting from an entrance-exit (NX) type control office facility and proceeding through the network circuits one can then, by any one of the three before mentioned communication means, again arrive at the same relay interlocking of the field functions.
Controls and Indications
When a control machine operator sets up a route in an interlocking, he turns a knob or manipulates levers to send out controls to operate a switch machine, signal or other devices in the interlocking plant. When the device has operated to the position called for, an indication is transmitted back to the control machine to tell the operator that the device has responded properly to his control.
Direct Wire Near Group Control
A near group, Figure 908, is controlled over direct wires from the control machine to the control relays. This system requires a relatively large number of line wires. When the distance between the control machine and the control relays becomes great enough, it is no longer economical to use direct wire control.
Direct Wire Remote Group Control
With remote group direct wire control, Figure 909, the controls and indications are carried through relays in the control office to relays in the wayside case. These relays in turn control relays which operate the switches and signals. Many of these controls and indications run over the same line wires. This method of control has its limitations, again from the cost of line wire, as the distance from the control office to the field location increases.
Figure 907. Interrelation of systems.
Figure 908. Direct wire near group control.
These systems for transmission of controls and indications are economical of line wire. Through the use of coding relays (or solid state electronics in the more modern systems) they send out controls and receive indications on line wires - usually one pair.
These remote control systems are further described in Section 1000, “Centralized Traffic Control”. Centralized traffic control is actually a series of relay interlocking, all on a common remote control system.
An explanation of direct wire, near group control of a relay interlocking, controlled from an individual lever (IL) type of control panel, is presented in the circuits on the following pages. A layout consisting of a single power-operated turnout with a full complement of signals has been selected.
A Typical Control Panel
We have chosen the type of control panel shown in Figure 910 because it permits a clearer, simpler explanation of the basic relay interlocking circuits. Relay interlockings are also controlled via keyboards and video monitors, such as the Traffic Master II described under centralized traffic control, but the basic relay interlocking circuits remain the same.
The track diagram in the upper portion of the panel represents the track layout (shown in more
above the panel). We are controlling the junction of a non-signaled branch line
with a single- track main line equipped with absolute permissive block
signaling. In accordance with interlocking practice, signals 1L are located at
the clearance point between the main and branch lines, and signal iRis located
in advance of the switch points. These signals govern train movements in
accordance with the route set up and the condition of the block ahead.
Home signals 1L and 1R have two arms each, that is there are two separate Type SA-1 signals mounted on each signal mast. Signal 1LA on the main line governs traffic to the left over the switch normal. Signal 1LB on the branch line governs traffic to the left over the switch reverse. Signal iRA, top arm, governs traffic to the right over the switch normal, and signal 1RB, bottom arm, governs traffic to the right over the switch reverse onto the non-signaled branch line. Single arm automatic signals 15 and 44 act as mainline approach signals to the plant and signal 01 as the approach signal from the branch line. The home signals normally display red (stop) aspects, and the approach signals display yellow (approach) aspects.
Three approach lights AE on the panel indicate when their respective approaches are occupied by a train (a single-stroke gong or other audible signal is also provided to indicate that a train has arrived on the approach). Track light TE indicates track circuit 2T (at the switch) is occupied.
Switch lever 2 has two positions, normal (N) and reverse (R). This lever is used to control the
Figure 909. Direct wire remote group control.
15T B B 1LT 2T
LGE (SIGNAL CLEAR) — LE (LOCK)—
RGE (SIGNAL CLEAR)
— SIGNAL LEVER
i— SWITCH LEVER L_WE (SWITCH CORRESPONDENCE)
Figure 910. Relay interlocking control panel and track layout.
machine. When in the vertical or normal (N) position, it calls for the switch
machine to line up a route straight through on the main line. When in the
horizontal or reverse (R) position, it calls for the switch machine to line up
a route for the branch line. Switch lever contacts NC (Figure 912) are closed
from normal (N) to center position (C). Switch lever contacts RC are closed
from reverse (R) to center (C). Contacts N and R are closed only when the lever
is in the normal or reverse position.
Lock light LE, located in the barrel of the switch lever, indicates the switch is locked and out of the operator’s control. Correspondence light WE, located below the switch lever, indicates when the switch machine is not in correspondence with the switch lever.
Signal lever 1 has three positions, right, left and stop. When positioned to the left (L), it initiates a control to clear either signal 1 LA or 1 LB for traffic movement to the left. When positioned to the right (R), it initiates a control to clear signal 1 RA or 1 RB for traffic movement to the right. In the vertical position, all signals are at stop. Signal-clear lights RGE and LGE indicate when signals are cleared for a traffic movement to the right or left.
The relays, signal mechanisms, and switch machine referred to in the following circuit description all operate on direct current supplied by battery. The diagram in Figure 911 shows the symbols used to identify the positive (BL), negative (NL), and common (CL) of split battery.
Indication and signal lamps are usually supplied energy from the secondary of a transformer. The diagram in Figure 911 shows the symbols which identify the taps on a transformer secondary.
The colored lines in the following figures show the parts of the circuits which are being discussed.
When a train approaches the interlocking plant, the track relays drop and in turn drop approach
1RT BB 44T p R 45T
Figure 911. Power supply symbols.
AR, Figure 912, closing its back contact to complete the circuit from EB
through lamp AE to
Detection of a train on the approach is usually arranged so that the control machine operator has time to clear the home and, in turn, the approach signal before the engineman has to make a brake application.
Lock indication relay LKR, slow release to bridge the crossover of correspondence relay CWZR, indicates when it is possible to operate the switch machine. Magnetic-stick relay CWZR checks that the switch lever, if it is to be effective in controlling the switch, must be in position to correspond with the position of the switch machine, and agreeing with the position of magnetic-stick switch control relay WZR.
Figure 912 shows the circuit which was energized to move the switch normal for a main line move. With the switch lever in the N position, positive of split battery, BL, is applied to the LKR, CWZR, and WZR relays in series to common, CL, of the split battery. A front contact of lock relay L is inserted in the circuit to prevent changing the position of the WZR relay when the locking in the field is in effect, such as when a signal has been cleared.
To reverse a switch, Figure 913, the operator moves the switch lever to the R position. Negative NL of split battery applied through the RC contact on the lever drops magnetic-stick relays CWZR and
to call for the switch machine to operate to the reverse position for a move
onto the branch line.
If the operator leaves the switch lever in the center position, part way between N and R, Figure 914, both sides of split battery, NL and BL, are applied through lever contacts NC and RC to hold LKR relay energized. Lock indication light LE, controlled over a back contact of the LKR relay, cannot be lit. Correspondence light WE will be lit, indicating that the position of the switch lever does not correspond with the position of the switch machine. The WE lamp is controlled over a back contact of either NWCR or RWCR, the normal or reverse switch correspondence relays, and switch lever contacts normal or reverse.
Clearing A Signal
Signal control relays LGZR and RGZR, for clearing signals to the left or right are biased-neutral relays. They will pick up only when voltage of the proper polarity is applied to their windings. LGZR and RGZR repeat the left or right position of the signal lever only if the switch lever is in correspondence with the CWZR relay. This check of correspondence between the switch lever and relay CWZR, known as the route-check feature, ensures that a signal cannot be cleared over an unintended route if the CWZR relay, and consequently the WZR relay, since they operate in series, do not follow the position of the switch lever.
The circuit in Figure 915 shows the condition that exists when signal lever 4 has been positioned
Figure 912. Relay interlocking control and indication circuits, switch control.
CLI’- 1?- rLL
FIELD - 4
CONTROL OFFICE 2 AE—TE
CONTROL OFFICE 2 AE-TE- — BL
I SIG. LEVER
I ______ _____ SW. LEVER ______ _____ ISIG. LEVER
Figure 913. Relay interlocking control and indication circuits, switch reverse.
—s--—— EN LGE
Figure 914. Relay interlocking control and indication circuits, switch lever in center position.
CONTROL OFFICE 2 AE-TE-’ LKR BL
NL ROE LGE SIG. LEVER
EB •I.Iru R
EB • tJ 2
—s-— EN LGE
Figure 915. Relay interlocking control and indication circuits, signal 1 R cleared.
the right to clear signal 1R over the switch reverse for a branch-line move.
Positive BL of split battery is applied through R contact of the signal lever,
R contact of the switch lever and back contact R of CWZR to check the switch
lever in the reverse position. Relay RGZR picks up and is then stuck up through
a circuit which bypasses the switch lever and CWZR contacts, thus preventing
putting signal 1R to stop by unintentional operation of the switch lever.
When signal 1R has cleared, right red signal repeater relay RRPR drops closing its back contact, Figure 915, to apply EB to right signal clear indication lamp RGE. Lock indication lamp LE, controlled over a back contact on LKR, is lighted to indicate that the switch cannot now be moved unless the signal is first put to stop.
When atrain has accepted the clearsignal, itmoves into the interlocking plant. When it has just passed the home signal it arrives on the OS track, dropping track relay 2TR, Figure 916. Lamp energy is thus applied to light lamp TE indicating that a train is on the switch track circuit.
the train passes the home signal, the signal goes to red, and right red signal
repeater relay RRPR picks up, opening the circuit to lamp
Preconditioning - Its Prevention
With preconditioning, the levers on the control machine can be lined up for a following move, so that when the first train clears the home signal the new route is immediately set up. Figure 917 shows a circuit arranged to prevent preconditioning of the switch control when the locking in the field is in effect. The circuit is organized in such a manner that if the position of the switch lever is changed when the LKR relay is de-energized, due to the L relay being down, the WZR and CWZR relays will not assume the new position called for by the switch lever when locking becomes released and the L relay picks up to close the circuit in the field.
As shown in Figure 917, the L relay contact will be open when the signal is clear. This causes LKR to close its back contacts. CWZR, a magnetic-stick relay, remains in its last-operated position. When
Figure 916. Relay interlocking control and indication circuits, train passing signal 1R.
CONTROL OFFICE 2 AE-TE
Ł8 -G——— EN
train leaves the interlocking, L relay picks up, but with the circuit from BL
through switch lever contact NC still open at the contacts on LKR, a change in
switch machine position cannot be effected. The circuit therefore ensures that
the switch lever must be returned to the reverse position to correspond with
the position of the CWZR relay and thus the switch machine. After this correspondence
is established and the LKR relay picked up, the switch lever can be moved to N
and the CWZR and WZR relays will follow.
Relay Interlocking and Switch Control
Having the WZR and GZR relays for the control of the switch and signals, the next consideration is to develop a system of relay interlocking that will protect the power switch machine (1) against operation when a home signal is displaying a proceed aspect for a route over it, (2) against operation for a predetermined time after a home signal has been put to stop with a train occupying the approach section and, (3) against operation under a train.
Signal indication Locking
Signal indication locking is that part of the locking that prevents changing the position of the switch points when a home signal is clear.
signal repeater relays 1RRP and 1LRP, Figure 918, detect the clearing of a home
signal, as they are energized over contacts in the home signals that are closed
only when these signals are displaying a stop indication. Energy for the
circuits of the AS relays is taken over front contacts of the RP relays, thus
relays 1R-AS or iL-AS will be deenergized when their respective signals are
clear. Front contacts of the AS relays are included in the control of lock
relay L, which, when down, locks the switch by opening the pickup circuit of
the LS relay.
Approach locking is that part of the locking that protects against changing the route in advance of a train which has accepted an approach signal displaying a proceed aspect permitting it to approach the plant at a speed too high to be brought to a stop short of a home signal.
Approach relays iRA, 1LAA and 1LBA, Figure 919, detect the presence of a train on any one of the three approaches to the plant. The circuits of the approach relays are taken over front contacts of the track relays of the section between the home signal and the approach signal as well as the relay for the track circuit in the rear of the approach signal.
The direct pickup of the AS relays is taken over front contacts of the A relays, thus an AS relay will
E B ——-—- - $— EN
E B -s—-— EN
Figure 917. Relay interlocking control and indication circuits, preventing preconditioning.
IT RR ILT
IPT RR 447 P4
immediately pick up after a home signal is put to stop if the approach is
occupied. For example, when home signal 1R was clear 1RRP was deenergized, thus
dropping 1R-AS. Also, RGZR was up, dropping lock relay L and locking the
switch. If an approaching train occupies track 14T, the circuit to IR-A is
opened by track relay 14T. Thus 1R-AS cannot now be picked up by putting signal
1 R to stop and picking up 1 RRP. With 1 R-AS down, the circuit to lock relay L is open, and the switch cannot be operated - it is approach locked. It will be noted that relay 1 L-AS has two approaches in it direct pickup circuit, 1LAA on the main line and 1LBA on the branch line. Contacts of switch-repeater relays NWC and RWC shunt one or the other out of the circuit, depending on the route set up.
Approach Locking, Time Release
When a train is occupying the approach to a signal that is manually put to stop, Figure 920, time-element relay TE will be energized over a back contact of AS. After the time expires for which the
is set, it will close its front contact to energize the AS relay, Figure 921,
and AS back opens the circuit to TE.
The AAR Signal Manual, Part 28, concerning time releases, says, in part:
1. The minimum releasing time should be more than the maximum braking time encountered when a full service application of the brakes is made for the purpose of stopping a train of minimum braking power just before it reaches the home signal.
2. In territory where two-block indication governs, the basis for setting the time releases must be the time required to move the distance between the approach signal and the signal locked, plus 1500 ft. at a speed of 30 miles per hour (44 ft. per second).
3. The minimum release time setting of time releases must be greater than the maximum time required for any train to stop with a full service application of the brakes before reaching a point where a stop is required.
Figure 918. ReLay interlocking locking and switch control circuits showing signal indication locking.
IRJ BB 441 R,R
IL -R P YGLA-YG
ILB-A 01 01*
ILA-A IR 44 45
The release time setting should be equal to or greater than the time required
fora train to travel the distance between the approach signal and the point
where a stop is required, plus a distance factor to provide additional time, at
a speed not to exceed 30 mph. (See AAR Manual for specific examples.)
Assuming that approach signal 15 is located 9000 ft. in the rear of signal 1R, the time setting for
1RTE would be 9000 ft. plus 1500 ft. or 10,500 ft. divided by 44 ft. per second, equaling 238 seconds or about four minutes.
Where one time release handles two or more approaches, as does 1LTE, the setting must be for the longest time encountered.
To check that time-element relays return to normal after each operation, their back-checking contacts are included in lock relay circuits.
Approach Locking, Track Release
To permit the route to be changed for a following train that has entered onto the approach before
first train has cleared the plant, a track release on AS is provided. This
circuit, Figure 922, is over a back contact of detector track repeater relay
2TP and a back contact of the track relay for the next track section that the
train will enter in the route. This is known as a two-track release. The
purpose of the second track in this circuit is to guard against the possiblity
of energizing the AS relay in the advance of an oncoming train if the detector
track should be momentarily dropped, such as might happen if track forces were
working on the track and a bar accidentally shunted the track.
It will be noted that there is a difference in the track-releasing portions of the two AS circuits. This is because in the case of 1RAS, the second track in the route may be either 1RT or O1T depending on the route set up, thus these tracks are selected into the circuit over contacts of switch repeater relays NWC or RWC. In the case of iL-AS, the second track in the route is always 1LT so no selection is
IfT SB ILT RR 21 A
Figure 919. Relay interlocking locking and switch control circuits showing approach locking.
IS T B_B I LT
IRr RB 44T RR 45T
Detector locking is that part of the locking, Figure 922, that protects against moving the switch under a train. It is accomplished by including front contacts of detector track repeater relay 2TP in the circuits of the L and LS relays.
Switch Repeater and Correspondence Relays
Switch-point repeater and correspondence relays NWC and RWC, Figure 922, are biased- neutral relays. Their control circuit is pole changed over the point-detector contacts in the switch machine and is energized only when the switch points are locked in the full normal or full reverse position. With the points normal, control wire WP is positive with respect to wire NWP. This polarity is reversed when the points are in the reverse position. To enforce correspondence between the position of the switch and the route called for, a contact of the WZR relay is included in the circuit which, when in the normal position, connects the NWC relay and when reverse connects the RWC relay. See also Figures 906a-c.
Switch control is accomplished through a polar controller in the machine, operated over wires NW and RW, Figure 923. When the position of relay WZR is changed from normal to reverse, the NWC relay will drop, closing the circuit to pick up relay LS, providing relays 2TP and L are both up. (The LS relay permits the machine to complete its stroke after the L relay drops.)
When the machine locks up in the reverse position, in correspondence with relay WZR, relay RWC will pick up to remove energy from relay LS. The dropping of relay LS disconnects battery from the switch machine and shunts its control wires to protect against false operation from crosses. See also Figures 905a and b.
14T P P
rf7k In - P P LI B ,‘ LI
ILB-A 01 OIA
ILA-A ‘R 44 45
Figure 920. Approach locking circuit shown at instant 1 RTE front contact closes.
RWC NW L
contacts of relays RGZR and LGZR are included in the control of relay L to
de-energize this relay when an attempt is made to clear a signal. This is to
permit including a back contact of the L relay in the signal-control circuits
to check that the locking is in force before a signal can be cleared.
Home Signal Controls
Home signal controls check the proper alignment and locking of the switches in the route, the opposing home signal at stop and the condition of the block to the next signal in advance.
Referring to Figure 924, let us assume that signal iRA is to be cleared to the right over the switch normal. Placing the control lever in the right position picks up relay RGZR, which drops relay L, closing the circuit from 1 RA signal coil over a back contact of RWC to check that the switch is not reverse, a front contact of 2TP, a front contact of iL-AS to check that opposing signals are at stop, back contacts of relays L and LS to check that energy is removed from the switch machine, front
of relay NWC checking that the switch points are over and locked normal in
correspondence with the switch control, front contacts of the track relays of
the section between the plant and signal 45, then to battery over front
contacts of 45YGP, clear repeater of signal 45. Some railroads also include a
back contact of the time element relay in this signal control network to check
that the TE is in its fully de-energized position.
With 45YGP up, the polarity on the circuit is such that iRA will display a green aspect. With 45YGP down, indicating that signal 45 is displaying a stop aspect, its directional stick relay, 45S, must be up to apply a polarity such that signal iRA will display a yellow aspect.
It will be noted that had the switch been reverse, RWC up and NWC down, a local circuit incI ud ing the plant selections would have been closed to the coil of signal 1RB over a front contact of 1LBA to check the condition otthe branch line to the extent that it is track circuited.
ILB A 01 OIA
Figure 921. Approach locking circuit shown with 1 RAS energized, 1 RTE check contact closed.
2 14T R_R 15T B_B 1LT RR
15T 8.8 1LT
RWC NWC LS
Figure 922. Relay interlocking locking and switch control circuits showing approach locking with track relase.
control of the left signals is similar to that just described for the right
signals except that both left signals receive polar energy from the signal in
Approach Signal Controls
Approach signal controls, Figure 924, are taken over front contacts of all track relays between them and the opposing home signals. A front contact of the opposing AS is included to ensure that opposing signals are at stop. The circuits are then pole changed on the home signal YGP relays to cause the approach signals to display approach (yellow) aspects when the home signals are at stop and proceed (green) aspects when the home signals are clear.
When the opposing AS relay or the track relay within the plant is down for a route that does not conflict with an approach signal, it is shunted out of its circuit by front contacts of the NWC or RWC relays, as shown in the controls of signals 01 and
circuits discussed and shown here are typical for a small plant and become more
complex as the plant increases in size with more functions to be controlled,
but the fundamental principles involved remain the same.
In this section, we are describing NX as applied with a control panel such as shown in Figure 925. Please note, however, that the NX principle of operation is equally applicable to the Traffic Master II, color video control system, as described in Section 1000 “Centralized Traffic Control.”
The basic idea behind NX was that a route has has an entrance and an exit. The term NX was coined by the General Railway Signal Company from the first syllables of the words eN-trance-
1RT BB 44T RR 45T
ILB-A 0’ OIA
I1’ R ILT
As shown, the control panel track diagram has an NX knob at every possible
entrance and exit. Each NX knob represents an interlocking signal on the
An NX knob is used for two purposes, as the entrance to the route or as the exit of the route, depending on whether it is the first knob manipulated or the second. When used to select the exit, an NX knob is manipulated in the push mode only.
When used for the entrance, an NX knob can be manipulated in four ways. Each manipulation has a distinct purpose, thus:
1. PUSHED - When the route is lined up by first pushing the knob at the entrance and then pushing the knob at the exit, the passage of the first train over the route restores everything to normal. Thus this manipulation provides automatic route restoration.
the route has been lined up by pushing the knobs at the entrance and the exit,
and the operator decides to cancel the route, he may do so by pulling the knob
at the entrance. If the train is not already on the approach track, he can
immediately line up another route for it; otherwise he must allow a
predetermined time to elapse before trying to line up another route. (Some
signal systems require a release time whenever a cleared signal is manually put
3. PUSHED AND TURNED LEFT - When the route is lined up by pushing the knob at the entrance and turning it left, the route is held for a succession of trains. The signal is given for high- or medium-speed moves and repeatedly clears after each train leaves the block. Everything is restored to normal manually by pulling the knob at the entrance, except that route locking of switches remains in effect as required by ordinary inter-
: I ,L 01 T
• BA IR nc
iRT 88 441’ R..R
Figure 923. Relay interlocking locking and switch control circuits.
151 B.B ILl RR ...FI A R
IRT B..6 441 R1R
practice, and is so indicated on the panel.
4. TURNED RIGHT - When the route is lined up by turning the knob at the entrance to the right, the route is again held for a succession of trains, and the signal is given for low- speed moves only. This signal may or may not be track-circuit controlled, depending on railroad practice. Everything is restored to normal manually by pulling the knob at the entrance, except that route locking of switches remains in effect.
Each NX knob can be provided with all four manipulations, or only as many as are required for the purpose. The operator is able to line up routes with characteristics that suit the demands of traffic. If a succession of trains is to use the same route, he pushes and turns the knob at the entrance and holds the route. If each train requires a new route, he pushes the knobs at the entrance and exit and allows the train to restore everything to normal.
The following sequence of figures shows how an NX panel, Figure 926a, is manipulated and how the various conditions are indicated to the operator.
Figure 926b. The operator wants to route a train to enter at signal 46 and exit at 52. He presses the NX knob at signal 46 symbol, corresponding with the point where the train will enter the route. The light in signal 46 symbol flashes green, and yellow lights flash at all available exit points.
Figure 926c. Next the operator presses the NX knob at signal 52, corresponding with the point where the train will leave the route. With entrance and exit points thus established, lights indicate the route, and lock lights go on for the switches in the route. If any switch in the route is not already properly positioned, the system lines it up. The switch position indicating lights flash while the switch is in transit, go steady when the switch is over and locked.
Figure 924. Relay interlocking signal control circuits.
926d. When all the switches are lined and locked, the signal symbol is lighted
steady green to show that the signal is clear.
Figure 926e. As the train travels over the route the yellow lights change to red. The green light in signal 46 symbol has gone out, indicating that the signal has gone to stop.
Figure 926f. As the train clears part of the route, the corresponding diagram lights go out, and switches 47 and 49 are released. This is indicated by their lock lights going out. These switches are now available for another route. When the train clears the route, the panel returns to its normal, dark condition, without requiring any action from the operator.
Figure 926g. If the operator wished to hold one
train at signal 50, he would press the knobs at 42
and 50. Then he could, for example, set up a route
for a second train by pressing knobs at 52 and 44. Figure 926h. The normal route from 52 to 44
is as shown.
926i. Here we show a route from 54 to 46 occupied. Now when the operator calls
for a route from 52 to 44, he simply presses 52 then 44, same as before. The NX
automatic route selection sets up the available alternate route over switch
45. In large, actual installations, there are sometimes several alternate routes. They are selected automatically in the order of preference as established by the circuit planning.
Figure 926j. Any of the switches can be operated manually, if they are not locked in a route lineup, by operating the proper test key. Here we show crossover 51 operated to normal and switch 47 to reverse.
Figure 928 shows simplified circuits for the very basic track layout shown therein. We have chosen to show a “Points-o-Lite” type of NX, as
Figure 925. An NX control console - some NX track layouts are much more complex than this.
_______ SWITCH ______ REVERSE LIGHTS;0]
Figure 926a. NX control panel, with elements identified.
Figure 926b 923
F LA S I-U N);0]
Figure 926d 924
NWZ Switch control RR Reverse relay
XR Exit relay
operation of entrance knob
Clears signal after route completed Calls for route over switch normal
relay Positions switch normal
Calls for route over switch reverse Positions switch reverse
Repeats track relay Indicates available exit points when NX knob at entrance is pressed Completes route when NX knob at exit is pressed, starts corn pietion network functioning
is relatively simple, yet has all the NX circuit fundamentals. In general, it
operates the same as the “Line-o-Lite” arrangement already described. The principal
difference is that the panel lights are points of light instead of bars of
We are describing the NX in terms of a direct wire system. NX, like relay interlocking, is also used with wire-saving remote control and coding systems, as shown in Figure 907.
Before following the sequence of circuit events, note the contact positions of the NX knob, shown in a box in Figure 928a. For circuit drawing purposes, the knob is shown inverted; that is, it is represented as moving upward when pressed, rather than downward, as in the actual case.
The interlocking circuits shown in the preceding sections were drawn with ‘drop line” circuit symbols, as shown in the top line of Figure 927. Shown below the drop line circuit is a comparable “straight line” circuit. This kind of circuit representation is also used in signaling practice and is used in the following NX simplified circuits.
STRAIGHT LINE __________ CIRCUIT SYMBOLS
Route selecting relay Selects route to be
followed by completion
EB Light energy
FEB Flashing light energy
Figure 928a shows the circuits energized when the operator presses knob 2NX to set up a route for a train to enter at signal 2. The sequence of operation is as follows:
1. Signal lever repeater relay 2GLP is energized through the NX knob push contact and the back of relay 2EX. Note that once 2GLP is up, it is held energized through the NX knob slide contact, the detector track, and its own front contact. Thus a GLP will stay up until its track is occupied or until the operator pulls the NX knob as, for example, if he should decide to manually cancel the entrance call. With 2GLP up, flashing light bus energy FEB is applied to the signal 2 clear panel lamp, as shown in the box labelled “Signal 2 Clear Light.”
2. Exit relays 4EX and 5EX, at the possible exit points, are picked up through 2GLP front and the backs of their respective lever repeater relays, 4GLP and 5GLP (thus checking that knobs 4NX and 5NX have not been pressed). The circuits to the EX relays also check that switch 8 is not being called by going through back contacts of 8NR and 8RR, relays that are used to call switch 8 normal or reverse. If there were more switches in the route, their NR and RR relay contacts would also be checked. Likewise, if there were more exit choices, their EX relays would be picked up.
By referring to the box in Figure 928a labelled “Typical Exit Light Circuit,” you will see how with the EX relays picked up, flashing light bus energy FEB is applied through exit lamps EXE to EN, the flashing bus “negative” (a.c. is used for lamps). Thus panel lamps 4XE and 5XE are flashed when their EX relays are up and XR’s down.
In Figure 928b, the operator has released knob 2NX and pressed knob 5NX. Relay 5XR picks up through 5EX front. This turns off flashing light 5EXE - see box labelled “Exit Light Circuit.” Note that an EX relay up makes the point a possible exit. If 5EX were down, pressing knob 5NX would pick up 5GLP, thus making 5 an entrance point. Once
Comparison of drop line and straight line Circuit symbols.
GLP Signal lever relay
GZ Signal clearing relay
Switch control relay
TP Track repeater relay EX Exit relay
Figure 928. Simplified NX “Points-o-Lite” circuit, shown with none of the NX knobs operated.
up, 5XR is stuck up through its own front and the 5EX pickup circuit.
With 5XR up, switch 8 reverse relay 8RR picks up, which drops 4EX, thus turning off exit light 4EXE. The pickup of 8RR calls for switch 8 to be operated to its reverse position. This is shown in Figure 928c. Operation of the RW2, NW2, and LP relays has already been covered in Figure 923, with the minor differences that Figure 923 shows only one WZR for a switch instead of separate WZR’s for each position, NWZR and RWZR. Also, Figure 923 uses the lock relay contacts directly instead of a lock relay repeater, LP.
The circuit for switch position indicating lamps NE and RE is shown in the box in Figure 928b labelled Typical Switch Light Circuit.” As soon as 8RR picks up - and assuming the switch machine is in its normal position - flashing bus energy FEB is applied to switch reverse lamp RE through the back of switch correspondence relay RWC (for operation of RWC and NWC, see Figure 923). When the switch machine is over and locked reverse, RWC picks up, shifting lamp RE to the steady light
EB, Figure 928d. Thus RE flashes while the switch is in transit and shows a
steady light when the switch is over and locked.
Figure 928d shows the circuits energized when the switch is positioned and the signal is clear. Signal control relay 2GZ picks up as soon as 8RWZ is up. Relay 2GZ calls for signal 2 to clear - subject to the field interlocking circuits. RE is lighted steady, GE remains flashing, and 5EXE is out (see circuits in boxes).
When a train accepts the signal and occupies track circuit 10, relays 2GLP, 5EX, 5XR, 8RR, and 2GZ will be de-energized. All panel lights will be extinguished, except the 1OTE.
When the train leaves the interlocking, the circuits will restore to the condition shown in Figure 928.
The “Points-o-Lite” panel lamps can display either of two colors. Thus, with additional circuiting (which we have omitted for simplicity) more information can be displayed to the control panel operator.
EX SR J
TE TP GE
V FEB EN—S I • EB EN —EE ‘ • FEB
TYPICAL EXIT LIGHT CIRCUIT TRACK LIGHT CIRCUIT TYPICAL SIGNAL CLEAR LIGHT
TYPICAL EXIT LIGHT CIRCUIT — FOR 45E AND 5XE
EX KR TE TP
- FEE EN—G I • EB
TRACK LIGHT CIRCUIT
‘ 2GLP I
EN— ‘‘ ‘ • FEBI SIGNAL 2 CLEAR LIGHT
Figure 928a. Simplified NX “Points-O-Lite” circuit. Knob 2NX pressed.
TRACK LIGHT CIRCUIT
Figure 928b. Simplified NX “Points-O-Lite” circuit. Knob 5NX pressed. *See Eigure 928c.
TYPICAL EXIT UGH
Figure 928c. Simplified NX switch control circuit, with 8RR and 8RWZ picked up. *See preceding circuit.
Figure 928d. Simplified NX “Points-0-Lite” circuit, with 2GZ picked up.
Route Selecting Relay YR
Entering at 2 and exiting at 5, we did not make use of the YR relay. To see how YR functions to select the correct route to be followed by the route completion network, consider a route with its entrance at 4 and its exit at 2. The sequence would then be:
1. Press knob 4NX
2. 4GLP up
4. 2EX up
Press knob 2NX
6. 2XR up
7. 8NR up through 8YR front
Entering at 5 and exiting at 4, the sequence
1. Press knob 5NX
2. 5GLP up
3. 2EX up
4. Press knob 2NX
5. 2XR up
6. 8RR up through 8YR back
EXE EX XR I YE TP GE EB I
EN FEB 1EN I • EB • FEB I
TYPICAL EXIT LIGHT CIRCUIT TRACK LIGHT CIRCUIT TYPICAL SIGNAL CLEAR LIGHT