BLOCK SIGNALING ADJUNCTS
Switch Detection and Locking 502
Switch Circuit Controllers 502
Line Break Circuit 503
Polarized Switch Repeater Circuit 503
Hand-Operated Switch Machine 503
Spring Switch Lock 503
Light-Out Protection 504
Power Off Relay 504
Hot Filament/Cold Filament Check 506
Double Filaments 506
Approach Lighting 509
Special Protective Devices 509
Slide Detection 509
Flood Detection 511
Fire Detection 511
Dragging Equipment Detection 512
Electric Switch Locking 513
Locking the Lever 513
Locking the Lock Rod 514
Wheel Thermo-Scanner Unit 519
Door and Cover 526
Reference Target and Sensor 526
Chart Recorder 527
Optional Arrangements 528
Several methods and devices are used to detect the positions of switch points and to lock them in position. Regardless of the method or device used, the object is safe operation of trains over switch points.
Switch Circuit Controllers
A switch circuit controller is a device which is commonly either a part of or used with a switch operating mechanism. It is operated by a rod connected to the switch. The controller is used to check whether the switch point is within a specified distance of the stock rail. Controllers are also used to check the positions of derails and other devices.
501 shows a GRS Model 7 switch circuit controller as it would be installed with
a hand- throw switch. When the handth row switch is operated, a rod connected
between the switch points and the crank on the switch circuit controller moves
the contacts within the controller, Figure 502, to affect the associated signal
The Model 7 switch circuit controller is available with either of two types of contact operation. The Model 7J has cam-and-roller operated contacts. With the switch normal, back contacts are held closed by spring pressure. When the switch points are moved toward reverse, cam action forces the back contacts open and the front contacts closed. Model 7J contacts can be adjusted to move in opposite directions as the switch points are moved. The Model 7K has push-pull contact operation, the contacts are forced into their closed or opened positions in response to the positions of the switch points. Model 7K contacts all move in the same direction when the switch points move.
Figure 501. GRS Model 7 switch circuit controller and Model 9B electric switch lock applied to a hand-throw switch.
- SWITCH STAND
The circuit in Figure 503 shows an application of a controller in automatic block signaling. This circuit detects the condition of the track between signal 1 and signal 2. This is accomplished by breaking the control wires through contacts on the track relays a’ and b’ and on the switch circuit controller. Whenever any of these contacts is open, signal 2 will indicate stop. Figures 504 and 505 show contact arrangement and wiring of line break circuits using Model 7K controllers.
Polarized Switch Repeater Circuit
The circuit shown in Figure 506 uses a Model 7J controller and switch repeater relays to indicate
position of the switch points. NWPR and RWPR are biased-neutral relays. They
will pick up only when current is flowing in the proper direction through their
coils, as indicated by the arrows.
Hand-Operated Switch Machine
Circuit controllers, in addition to a switch operating mechanism and a lock rod to lock the switch normal and reverse, are included in the GRS Model 9 hand-operated switch machine, Figures 507A and B. A Model 10 electric lock, which locks the hand- throw lever, may be added, as well as a target staff, high or low.
As shown in Figure 507B, the Model 9 has two built-in circuit controllers, one normal and one reverse, which check both switch position and locking. (The Model 9 is also available with a normal controller only). Contacts latch in “switch unlocked” position if the switch is accidentally trailed through when positioned normal.
Spring Switch Lock
A spring switch permits trains entering at the heel of a switch to pass through or “trail” the switch even though the switch is not positioned for such a move. A powerful spring, hydraulically buffered, keeps the points closed for facing point moves but allows them to be forced open by train wheels for trailing moves. The spring device is shown as “Mechanical Switchman” in Figure 508.
The GRS spring switch lock provides locking for facing point moves, yet unlocks automatically for trailing moves. Built-in circuit controllers check both locking and point position. A handthrow mechanism is also built in so that the lock can be operated manually, as well as automatically for a trailing move.
Operating the handthrow lever withdraws the locking plunger from the lock rod and throws the switch. During automatic unlocking, which occurs when the switch is trailed, the locking mechanism in the lock is operated by the initial deflection of the switch rail. This deflection occurs when a train trails the switch. The train wheel forces the open point towards the stock rail. This deflection is transformed into a movement of the crank and rods which withdraws the locking plunger from the lock rod, releasing the switch. Circuit controllers built into the lock mechanism operate contacts to control the signal aspects. Figure 509 shows a typical installation.
Figure 502A. GRS Model 7 switch circuit controller.
Figure 502B. GRS Model 7 switch circuit controller with cover open.
Rule 27 of the “Standard Code of Operating Rules,” Association of American Railroads, states: “A signal imperfectly displayed, or the absence of a signal at a place where a signal is usually shown, must be. regarded as the most restrictive indication that can be given by that signal, except that when the day indication is plainly seen, or when sufficient lights in a position or color position light signal are displayed to determine indication of the signal, it will govern.”
The Federal Railroad Administration “Rules, Standards, and Instructions for Railroad Signal Systems,” in Paragraph 236.25, states: “If an arm of a semaphore signal assumes a false restrictive position or if a lamp in a light signal fails the signal shall not display a less restrictive aspect than intended.”
with a two-arm signal displaying, for example, red over green, failure of the
lamp in the red signal unit, would leave a green aspect - an unacceptable
condition. Figure 510 shows a circuit that is designed to avoid an unintended
display of a less restrictive aspect. First, however, let us consider the
power-off function, also indicated in Figure 510.
Power Off Relay
Signal lamps are usually supplied a.c. from the secondary of a lighting transformer. Symbols are EBX, positive; and ENX, negative, E meaning “electric light.” Should the a.c. fall below a predetermined value, power off relay POR releases its armature transferring, through its Contacts, the energy supply from a.c. to d.c. from a standby battery. The d-c symbols are B for positive battery and N for negative battery.
— — YGP
Figure 503. Simplified circuit of 2-block, 3-indication signaling with polarized line circuit, showing typical application of switch circuit controller.
SIGNAL CONTROL LINE
Figure 504. Typical line break circuit and switch layout for Model 7K controller located on the normally open point side of the switch.
SIGNAL CONTROL LINE
Figure 505. Typical line break circuit and switch layout for Model 7K controller located on the normally closed point side of the switch.
SWITCH CIRCUIT CONTROLLER CONTACTS
Makes at end of movement. Breaks at end of
Breaks at beginning of movement.
NOTE: Arrows in relay symbols indicate the direction of current to pick up relays.
SWITCH NORMALLY CLOSED
Figure 506. Typical polarized switch repeater circuit for Model 7J controller, using biased-neutral relays.
Hot Filament/Cold Filament Check
In Figure 510, EBX is normally fed through a front contact of POR and the low resistance coil of light-out relay LOR, through the lamp in signal unit A, returning to ENX via another front contact on POR.
Obviously, the light-out relay must be capable of operation on either a.c. or d.c. The rectifier inserted in multiple with the low resistance winding of operation on either a.c. or d.c. The rectifier inserted in multiple with the low resistance winding sine wave and will flow through the upper coil of LOR, thus energizing the relay. During the other half of the sine wave, however, current will pass through the rectifier, and the induced current from LOR also circulates through the rectifier, keeping LOR front contacts closed.
When the lamp in signal unit A burns out, energy to LOR is cut off and it will open its front contacts and cut off energy to both signal units A and B. Thus A will be a dark signal and B will be red - a more restrictive indication than intended, but a safer one.
Now let us consider how this circuit functions when the a-c supply fails, and the POR drops and cuts off the a.c. to the signal lamps. Now positive energy from the battery flows through the lower, (high resistance) coil of LOR, through a back contact of POR, through the upper coil of LOR, through
filament of signal A lamp, and to negative through another back contact of POR.
Note that the signal lamps are not lighted unless AR is down - a train is
approaching. This is to conserve battery. With AR up, the circuit is checking
the continuity of the cold lamp filament. The resistance of the lower coil of
LOR is too high to permit enough current to flow to light the lamp. Now if the
lamp filament opens, the d.c. flowing in series through both coils of LOR is
cut off, and LOR drops, with results as already described.
With POR down and AR down, the lamp in signal A is lighted by d.c. through AR back, POR back, the top (low resistance) coil of LOR and back to negative d.c. through another back of POR. This is a hot filament check with a.c. off. Again, if signal A lamp filament opens, LOR drops, with results as already described.
Double filament lamps may be used in the signals. When the high wattage filament burns out, a lower wattage filament in the same lamp envelope displays a weak aspect. Thus, when a train comes within range of the signal, the engineman sees the weak aspect and may proceed as indicated. This eliminates a stop and enforcement of Rule 27. Trainmen are expected to report the weak aspect so the lamp bulb will be changed out.
Figure 507B. Normal and reverse Circuit controllers are built into the Model 9 hand-operated switch machine.
Figure 507A. GRS Model 9 hand-operated switch machine.
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Figure 509. Typical spring switch lock installation.
Figure 508. Right-hand layout of spring switch lock, with right-hand point normally closed.
Figure 510. Typical circuit for light-out detection with SA-1 signals.
It is common practice on many railroads to have the signals lighted only when a train is approaching a signal which governs its movements. Approach lighting is done for two main reasons: (1) to conserve electrical energy when a signal indication is not necessary and (2) to convey signal indications more distinctively when a train approaches a location having many signals.
One of the simplest methods is to use an auxiliary relay at the battery end of, and in series with, a line controlled signal relay or mechanism.
Figure 511 shows a circuit with approach lighting relay 4AER in series with the signal control relay. Should a train occupy track circuit 2T or 3T, signal control relay 2HR would drop, opening its front contact and removing energy from approach
relay 4AER. When 4AER drops, closing its back contact, lamp energy is applied
to the signal.
Figure 512 shows a circuit with approach lighting relay 1AER in series with a GRS Type SA-1 searchlight signal. When a train arrives on track circuit 2T, the circuit through 1AER is opened at 2TR front, and the back contact of 1AER closes to apply energy to signal 1 lamp 1 E.
SPECIAL PROTECTIVE DEVICES
Slide detector fences, Figure 513, can warn of track obstruction from rock and landslides. They protect the traffic through cuts, at the bases of rocky slopes, and in tunnels.
_____ I [TR
Figure 511. Series line approach lighting relay in series with signal control relay.
Figure 512. Series line approach lighting relay in series with SA-1 signal mechanism.
are constructed and located according to local conditions in the slide area.
They are usually installed in sections up to about 400 feet long. The usual
practice is to use a five-foot, pole-suspended fence, mounted enough above the
ground level to allow smaller stones to pass under without operating the fence.
A Model 7 switch circuit controller, Figure 514, is mounted on a steel mast between each pair of fence sections. The fence sections are anchored at their outer ends and are loosely stapled to all intermediate fence posts to allow for lateral movement. When a slide occurs, the fence movement is transmitted to an operating pipe and trigger arrangement that unlatches a spring to operate the controller.
If the fence is located in automatic block territory, the controller may be included in the line circuit control. Outside automatic block territory, it may be used to control special slide warning signals.
Flood detection provides signal protection for high water conditions that may be weakening bridges, undermining fill, or otherwise creating hazards.
systems consist of a float-operated contactor installed in locations dictated
by experience. One such device, Figure 515, is so arranged that when the water
reaches a predetermined level the float will rise high enough to open the
contacts to put the associated signals to stop. Such devices are usually trip
contacts that, once operated, must be reset manually.
Fire detection, desirable in wooden trestles, wood- lined tunnels, snow sheds, etc.,usually consists of fusible wire in series with the signal circuit. This wire melts in the presence of fire, opening the signal circuit.
A circuit controller, spring loaded similarly to that shown in Figure 514, can also be used. A rope, made of some material that will part easily when exposed to flame, is used to keep the controller contacts closed. When fire parts the rope, the spring snaps the circuit controller contacts open, thus controlling appropriate signal circuits to indicate the hazardous condition.
Figure 513. Slide detector fence.
Dragging Equipment Detection
The GRS self-resetting dragging equipment detector, Figure 516, can check trains or individual cars moving either way over the tracks. It will reset itself after each operation.
The detector is used in places where dragging equipment would be especially detrimental to the movement of trains or to track devices such as switches, retarders, etc. Dragging equipment detectors are installed at the entrances to tunnels and at approaches to interlocking plants and classification yards.
dragging equipment detector consists of a shaft supported by bearings at either
end. Bearings are housed in compartments which are spring mounted on brackets
fastened to the ties. Six blades, adjustable for various rail heights, are
bolted to the shaft. A torsion bar extending through the shaft keeps the shaft
in position so that the blades remain vertical and will return to their
vertical position after having been deflected by dragging equipment.
The bearing compartment on one end of the detector houses a simple device for adjusting the torque as required. Thus the detector may be adjusted so that it will not open its contact when struck relatively light blows, for example by icicles hanging from the running gear.
A normally closed contact, housed in the opposite bearing compartment, is arranged so that it will open whenever the shaft is rotated 5 degrees or more in either direction.
Figure 517 shows one way to circuit the detector at the entrance to an interlocking plant. Dragging equipment detector relay DEDR in the tower
Figure 514. Spring-loaded circuit controller and trigger arrangement to detect motion of slide detector fence.
Figure 515. Flood detector.
normally fed by a multiple circuit through a front contact of track relay 1TR
and the normally closed contact of the dragging equipment detector. Unless
there is a train on track circuit iT, relay DEDR cannot be dropped by pushing
the detector blades. This circuiting keeps vandals from putting signal 2 to
When a train with dragging equipment moves toward signal 2, 1TR will be down. As soon as the dragging parts hit the blades, the detector contact opens. Current is cut off from relay DEDR, and it opens its front contacts and closes its back contacts. Current is cut off from DEDPR, and it opens its front contacts, thus putting signal 2 to stop.
The buzzer and the indication lamp in the tower are fed current through the back contact of DEDR. To reset DEDR, the towerman simply presses the reset pushbutton.
ELECTRIC SWITCH LOCKING
Federal Railroad Administration Rule 236.314 states, in part, “Electric lock shall be provided for each hand-operated switch or derail within inter-
limits, except where train movements are made at not exceeding 20 miles per
hour.” An electric switch lock provides a means of interlocking a manually
operated switch with the signal cirCu its so that the switch cannot be operated
unless traffic conditions permit, or unless an emergency release (normally
sealed) is operated.
Locking the Lever
The GRS Model 10 electric switch lock, Figures 518 and 519, locks the handthrow lever of most ground- throw switch stands, and hand-operated switch machines.
The lock is operated by depressing the latch and removing the switch padlock. This action puts associated signals to stop. If traffic conditions permit, the lock coils are energized, and an indication lamp, visible through a window in the cover, lights. The lamp indicates to the trainman that the mechanism is unlocked. The pedal can now be depressed and the handthrow lever of the switch stand operated to move the switch points.
interlocked emergency release is provided on the lock to be used if the switch
must be unlocked when the normal circuit does not respond. The emergency
release can be sealed.
The typical circuit in Figure 520A is arranged for remote control of the Model 10 electric switch lock. Release of the lock for a move from the siding
Figure 516. GRS self-resetting dragging equipment detector.
Figure 518. GRS Model 10 electric switch lock, shown with cover closed.
0 ED PR
Figure 517. Simplified circuit for dragging equipment detector.
•1 — TI
GRS Model 10 electric switch lock, shown with cover open.
onto the main line is accomplished as follows:
mechanically operated contacts 2, 3, and 4 in the lock mechanism are operated when the trainman’s padlock is removed from the switch stand, Figure 520B. Contact 4b opens the circuit to lever normal switch repeater relay LNWPR, which drops, opening the line wire circuits to signal control HD relays controlling approach signals 2 and 5. Back contacts on LNWPR close circuits from the HD wires through westward and eastward traffic relays WFR and EFR to common. If traffic conditions permit, the remote operator, upon being notified, energizes switch lock control relay WLZR by line wire control, Figure 520G. Front contacts of WFR, EFR, and WLZR now establish a circuit through the lock magnet coil to release the lock.
Figure 5200 shows release of the switch lock for a move onto the siding. Note that these circuits are showing a series overlay track circuit for detecting the presence of a train on the main at the switch location. Overlay circuits, discussed further in Section 400 under “High Frequency Track Circuits,” require no insulated joints. In the series overlay, shown here, the presence of a train on the circuit picks up the track relay, designated OTR.
With a train standing in the track section, which energizes track relay OTR, and with WLZR energized by the remote operator, energy is fed through
front contact on OTR, front contact on WLZR, and mechanically operated contact
3F to the lock magnet coil. In this case the front contacts on WFR and EFR are
bypassed, as the train has automatically established its block protection.
The typical circuit in Figure 521A is arranged for automatic control of the Model 10 electric switch lock. For a move onto the mainline, the trainman, as with manual control, removes the padlock, Figure 521B, opening the mechanically operated contacts and dropping LNWPR. If there were no trains approaching either signal 2 or 5, WFR and EFR traffic relays would pick up and energize the lock magnet coil through mechanically operated contact 3F. We show WFR de-energized, indicating that a train is approaching, and time element relay TER is running time. This circuit prevents the trainman from getting a release until enough time has elapsed to permit any approaching train to obey the stop signal. Figure 521C shows TER time run out and the lock released.
For a movement onto the siding, the OTR would be up, and a circuit completed through mechanically operated contact 3F to energize the lock magnet coil.
Locking the Lock Rod
The GRS Model 9B electric switch lock, Figure 522, locks the lock rod on a switch. It may be used to lock the lock rod in one position only, or, when equipped with a double adjustable lock rod, it may be used to lock the lock rod in both the normal and reverse positions. The lock may also be used to lock any device which can be locked with a lock rod - derails, tunnel doors, etc.
The lock consists essentially of a locking plunger, Figure 523, that can be raised or lowered by a hand crank, and an electromagnet which lifts a locking key from a notch in a locking dog. The movement of the hand crank is normally blocked by the electrically actuated locking key so the trainman cannot raise the plunger out of the lock rod if the lock coils are not energized.
Figure 524A shows a typical switch lock control circuit with emergency release and normally de-energized approach relays. The broken lines indicate additional circuiting for optional supervisory control. The circled letters “N” and “B” under “Crank-operated Contacts” are symbols used to indicate contact operation. The N contact is closed only when the switch lock hand crank is
TRANSCEIVER TO RAILS
2 - 5H0
Figure 520A. Circuit for remote control of Model 10 electric switch lock in APB territory, shown with no train on the siding or on the main.
2 — 5HD
Figure 520B. Circuit for remote control of Model 10 electric switch lock in APB territory - train on siding, padlock removed from lock.
Figure 520D. Circuit for remote control of Model 10 electric switch lock in APB territory - train on main occupying series overlay circuit at switch. With padlock removed lock is released as soon as WLZR is energized.
-I, —, I
Figure 520C. Circuit for control of Model 10 electric switch lock in APB territory - WLZR energized by remote control, lock released, switch can be thrown.
Figure 521A. Circuit for automatic control of Model 10 electric switch lock in APB territory. Train on siding, westbound train approaching signal 5.
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Figure 521B. Circuit for automatic control of Model 10 electric switch lock in APB territory. Train on siding, padlock removed, westbound train approaching signal 5. Time element relay TER started.
SSRAS OVERLAy iTO RAILS
TRANSCEIVE ____ J ‘\.r4J’
Figure 521C. Circuit for automatic control of Model 10 electric switch lock in APB territory. Time element relay TER has run its time and lock is released. The westbound train on the main has come to a stop in approach to ;1
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Figure 522. The Model 9B electric switch lock dwarf model is less than two feet high; the high model is 43.5 inches high.
its normal, locked position. The B contact is closed only when the hand crank
is in its preliminary unlock position.
Release of the lock for a move onto the main line is accomplished as follows: when the trainman makes a preliminary movement of the crank handle, Figure 524B, contact N is opened, breaking the signal control circuits by de-energizing normal switch repeater relay NWPR. No train is approaching, and westward and eastward approach relays WAR and EAR are energized through back contacts of NWPR. (With supervisory control, the operator is required to energize switch lock control relay WLZR by line wire control). Front contacts on WAR and EAR now establish a circuit to the coil of the switch lock.
For a movement onto the siding, Figure 524C, overlay track relay OTR is picked up, its front contact closing a circuit to the lock magnet coil.
Figure 525A shows a typical switch lock circuit with time release and normally de-energized approach relays. Broken lines show additional circuits for optional remote supervisory control. As shown in Figure 5258, preliminary movement of the crank handle will open the signal controls through contact N, dropping NWPR. With no train approaching, WAR and EAR will pick up, closing the lock coil circuit through their front contacts. With supervisory control, WLZR must also be energized by a control from the operator. (Positive would not be connected to the heel of WAR, but would connect only to the heel of WLZR, as shown in the broken line circuit). If a train is approaching, one of the approach relays will not pick up. Thus a circuit through time element relay TER and contact B on the crank will be completed. When time has run out, a front contact on TER will energize the lock coil. Track release for a movement onto the siding is accomplished the same as for the circuit shown in Figure 524B.
WHEEL THERMO-SCANNER UNIT
An overheated journal (hot box) on a railway car axle indicates faulty bearing operation. If not corrected, bearing and journal failure can result, possibly leading to derailment.
The GRS Wheel Thermo-Scanner Unit, Figure 526, detects overheated journals, thus permitting timely corrective action. Installed at trackside, the unit optically examines the heat (infrared) radiation from each wheel of passing trains. Operation
Operating parts of Model 9B electric switch lock.
is effective over the range of train speeds from 5 to 85 mph. Since the journal is concealed by the bearing and journal box, the unit focusses on the wheel hub, Figure 527. The temperature of the hub, which absorbs heat from the directly adjacent journal, accurately indicates journal tern peratu re.
A chart record is made of scanner output for each train. The recorder can be located in the wayside housing at the scanner installation, or it can be remotely located in an attended office. Scanner
Figure 524A. Typical switch-lock control circuit with emergency release and normally de-energized approach relays. Broken lines show optional remote supervisory control.
Figure 524B. Typical switch-lock control circuit with emergency release and normally de-energized approach relays. Shown with crank handle in preliminary release position.
SERIES OVERLAY TRACK CIRCUIT TRANSCEIVER
Figure 524C. Typical switch-lock control circuit with emergency release and normally de-energized approach relays. Eastbound train on main about to take siding.
I — _____
SERIES OVERLAY TRACK CIRCUIT TRANSCEIVER
Figure 525A. Typical switch-lock control circuit with time release and normally dc-energized approach relays. Broken lines show optional remote supervisory control.
SERIES OVERLAY TRACK CIRCUIT TRANSCEIVER
Figure 525B. Typical switch-lock control circuit with time release and normally de-energized approach relays. Shown with crank handle in preliminary release position.
SERIES OVERLAY TRACK CIRCUIT TRANSCEIVER
} TO RAILS
Figure 527. Radiation from hub area directly adjacent to journal is sensed by scanner.
to the recorder may be transmitted over a three-wire line for distances up to
five miles. For longer distances a carrier system such as GRS Data-Tran® is
The location for a Wheel Thermo-Scanner installation is selected so that journal temperatures will be representative of normal conditions. Typically this is on a section of tangent track which trains pass over after they have been running at road speeds for 10 miles or more, and where extended train braking will not have occurred on the approach.
528 shows a typical layout for a bidirectional installation. Scanners, blowers,
and wheel detectors are tie-mounted, simplifying iristallation.
Two scanners are used, one adjacent to each rail, directly opposite each other. These operate simultaneously to check wheels on both sides of the same axle.
Magnetic wheel detectors WD3 and WD4 are located about 45 feet from the scanners, exact distance depending on train speeds. These detectors identify direction of train approach. They also turn on the system, which includes opening a protective door on the scanner and starting the recorder so that the system is ready when the train reaches the scan point.
Magnetic wheel detectors WD1 and WD2 are directly adjacent to the scan point. They detect the presence of a wheel in immediate proximity to the scanner and, after a brief delay to allow for approximately 3-1/2 inches of wheel travel to the scan point, cause an optical shutter in the scanners to open momentarily.
For single-direction operation, detector pair WD3/WD1 or WD4/WD2 would be omitted.
Blowers, turned on when the scanner doors are open, pressurize scanners to prevent infiltration of dust and snow. Air discharged from the scanners also helps to clear snow from the line of sight to the car wheels.
The scanner, Figure 529, has a cast aluminum case and cover, a door mechanism, an external sensor for ambient temperature, a reference target for self-calibration, and a radiometer with associated optics. Environmental heaters are also included.
Door and Cover
To permit entry of infrared radiation, an opening with a door is provided in the cover of the scanner. The door is normally closed. When an approaching train is detected, a rotary solenoid linkage opens the door. The door remains open as long as wheel detections occur at intervals not exceeding 14 seconds. When an interval in excess of 14 seconds occurs, indicating that the train has departed, a spring and counterweight close the door.
controlled resistance heaters on the door and cover prevent snow and ice from
interfering with operation. A heater also keeps a mirror (part of the optical
system) in the bottom of the case free of snow and moisture.
Refrrence Target and Sensor
A normal journal operates at a temperature close to the local ambient temperature. Thus the temperature at which a journal is considered hot must be referenced to the ambient temperature.
The Wheel Thermo-Scanner Unit adjusts automatically to compensate for ambient variations. A reference target is mounted on the underside of the door so as to be in the field of view of the infrared detector (discussed later) when the door
Figure 529. Simplified cross sectional diagram of scanner.
DETECTOR DIRECTION 2-I
115 AC POWER
INFORMATION TO REMOTE RECORDER OR SIGNAL
Basic arrangement, bidirectional Wheel
Thermo-Scanner Unit installation.
closed. The target is a resistance heater element which is energized to raise
its temperature. A thermistor bridge, with one bridge element on the reference
target and another bridge element exposed to outside temperature in an external
sensor, detects the temperature differential between target and ambient.
Associated circuits, reacting to the differential, control heating energy to
the reference target so that it is maintained at an elevated temperature. This
is typically 80°F. above ambient, a representative threshold for excessive
The radiometer is enclosed to keep out foreign material, and is fitted with a window which permits entry of radiation. The window faces at a downward angle to guard against collection of dust and dirt on it. Infrared energy, entering the case through the open door, is reflected upward into the radiometer by a mirror in the bottom of the case.
Inside the radiometer a parabolic mirror and a flat mirror cooperate to focus energy on the infrared detector, a crystal approximately one millimeter (1/25-inch) square. A microscopic metallic film on the detector reflects visible light away from the detector but passes infrared. The detector is photoconductive, i.e., its resistance changes when exposed to radiation. The amount of change in a fixed time interval depends on the intensity of the radiation, hence indicates the temperature of the radiation source.
The optical path in the radiometer is normally blocked by a shutter which prevents stray radiation from reaching the detector. Immediately after a wheel passes over the wheel detector adjacent to the scanner, the shutter opens for a few milliseconds, just as the hub of the wheel is in the optical field of view. The geometry of the scanner installation adjacent to the rail, the focusing of the optical system, and the action of the shutter confine the source of the radiation to an area approximately one-half inch square on the hub of the wheel.
During the shutter-open interval, the detector “sees” and reacts to the infrared radiation from the hub. If the hub is cool, there is little change. If the hub is hot, there is appreciable change. Associated electronic circuitry senses the level of change and produces an output pulse, the amplitude of which indicates hub temperature.
In the absence of trains the Thermo-Scanner is on standby, and the door is closed. Once a minute during standby periods the radiometer shutter
Heated stylus chart recorder for Wheel Thermo-Scanner Unit with digital time
and date printer (in front of chart).
opens momentarily, and the detector views the reference target. The reference target represent a synthetic wheel hub whose temperature is at the threshold of acceptability. If the scanner output for this known input has drifted from the value required, sensitivity is automatically adjusted to compensate. Should the required adjustment be outside the available range, the system reports this fact to indicate need for corrective action.
The chart recorder, Figure 530, is of the heated stylus type. It provides four recording channels, two analog traces (stylus deflection proportional to input) and two ‘event” traces (uniform stylus deflection while input is present). An accessory permits printing time of day and numerical day of year along the edge of the chart.
Figure 531 shows the appearance of a typical recorder chart. The groups of small pulses on the analog channels are gating pulses derived from
wheel detector adjacent to the scanner. These are adjusted to produce
deflections of about 2.5 mm. For cool journals, the amplitude of the gating
pulses exceeds that of the thermal pulses so the latter are masked by the
One gating pulse appears for each wheel. The chart record for a typical four-axle car consists of two closely spaced deflections (leading truck), a relatively long space (car body), and two more closely spaced deflections (trailing truck). Six- axle cars and locomotives have similarly recognizable signatures.
Warm journals produce deflections perceptibly above the gating pulse. Hot journals produce deflection beyond the 10-mm scale line, the chart threshold for unacceptable journal temperature. If a hot journal is indicated, its position in the train is clearly identified by the wheel count at which it occurred.
• It a train passing the scanner location should be braking heavily for some reason, wheel tern peratures in general might be above normal. Recorder deflections could thus be consistently above gating-pulse height. Under these conditions an unacceptably high journal temperature may be detected by comparing deflections for opposite ends of the same axle. If the differential exceeds the threshold deflection level, a hot journal is indicated.
a verification of correct calibration, the chart recorder continues to run for
a brief time, after a train departs and the cover of the scanner closes. During
this interval the shutter opens momentarily to expose the detector to the
reference target. The output pulse from the scanner, recorded on the chart
after the last wheel of the train, verifies scanner calibration.
An automatic hot wheel detector may be included in the system. This detects scanner outputs which exceed a preset maximum. Detection actuates a relay which may be used to control a wayside signal or indicator informing the train crew of the condition, or to actuate an office alarm and to produce a record in the event channel of the train chart as indicated in Figure 531.
Automatic monitoring of scanner output for alarm action may be expanded to include comparison of opposite ends of the same axle, with alarm output if either excessive temperatures or excessive differentials are detected.
Figure 531. Typical appearance of a wheel thermal scan chart and information recorded.