Self-checking circuit arrangement for operation of a searchlight signal

The circuit arrangement of this invention includes a signal searchlight wherein the lamp is in an electrical series circuit with interlock contact switches. The switches interlock the display color lens such as yellow and green to control the electrical energization of the signal circuit. Logic control switching devices in a remote wayside control box supply signals through a cable to operate a bipolar device to selectively display the desired color.

BACKGROUND OF THE INVENTION 
The searchlight signal is generally a single lamp device located along the 
wayside of a railroad to provide information to the locomotive concerning 
current track operating conditions. The searchlight signals are generally 
a single lamp device in which the color of the signal light source is 
colored either red, green, or yellow by interposing colored lens in front 
of the single lamp. The devices are normally designed with the yellow and 
green lenses being held away from the light path by gravity and/or springs 
such that the device tends to fail in the red mode. The locomotive 
engineer interprets the red signal as a warning and normally would proceed 
to stop forward motion on such a track. The green signal is generally an 
all clear signal, and generally indicates no safety speed restrictions on 
that block of track. The yellow is a caution and its specific operating 
requirements may vary with different railways, but is usually indicated to 
proceed at some limited speed of operation of the train into the next 
section of track. It can be understood that a false energization or a 
sticking of the lens in the yellow or green positions could result in an 
error condition in which the vital mode of operation on the section of 
track would not be properly communicated to the on-board personnel. It is 
therefore highly desirable that in any failure mode the red signal be 
shown. 
One way in which the lens systems have been operated is through the use of 
a bipolar or double acting electric solenoid. Typically when the electric 
solenoid is activated by a current of a given polarity it will move the 
yellow lens in front of the light source, and when the solenoid is 
activated by a current of the reverse polarity the green lens will be 
moved into the path of the light source. With the solenoid deenergized the 
green and yellow lenses are withdrawn from the path of the light source 
and the red lens is positioned to give a red signal. At any time in which 
the operation of the signal light is in doubt it is desirable to show the 
most restrictive color, namely red, or no light signal whatsoever. If the 
light signal is not given, the locomotive engineer can then assume that 
the signal is not functioning properly and take appropriate action, such 
as would be usually done under the red or most restrictive condition. 
Mechanically interlocking the red, green, and yellow lenses helps to 
assure the correct operation of a given signal. Such signal lights have 
always been a concern in the railway industry, and it has been a practice 
to better indicate the correct signal by having switches mounted on each 
color lens, especially the yellow and green lenses. These switches are 
activated when the respective lens is either fully engaged or fully 
removed from the light source path. Prior art solutions to insure 
reliability and vitality of operation have been to run the contacts from 
the respective yellow and green lens switches down from the light mast via 
a cableway to the wayside control where such contacts have been used in a 
relaying system to check and verify the position of the respect yellow and 
green lenses. Such verification could then indicate whether a malfunction 
had occurred and appropriate circuitry at the wayside could provide for a 
back-up operating condition. Under such back-up position the circuitry 
would generally prevent lamp energization unless the proper lens carrier 
was in the proper position. The wiring arrangement generally used in the 
prior circuits would be eight wires going back to the wayside control from 
the signal, namely one pair from the yellow contacts, one pair from the 
green contacts, one pair from the light filament, and one pair for the 
bipolar solenoid operation. Such additional wiring, cabling, and the 
associated inter-connections can introduce other potential failure 
problems such as conductor to conductor shorts within the cable bundles. 
It is one of the objects of this invention to provide for vital operation 
of a multi-color searchlight while limiting the number of wires that must 
be run between the wayside signal control and the signal light device 
itself. In addition to achieving a vital searchlight operation, the 
circuits also reduce the number of conductors that must be run thereby 
improving the ease of installation and reducing the chances for large 
multiple conductors to cause the circuit to have shorts or cross 
connections. 
It is also one of the objects of this invention to provide for a direct and 
simple circuit that can be checked for vitality and that is compatible 
with existing searchlight mechanisms. 
SUMMARY OF INVENTION 
This invention provides for a simple circuit which uses the electrical 
contacts that are mechanically interlocked with the yellow and green 
lenses in a single light source searchlight to provide vital logic to 
control the current to the light source. The circuit uses the connection 
of the green and yellow interlocking contacts in a series arrangement with 
the light source to provide a vital operating circuit which requires four 
or less electrical conductors between the actual signal and the wayside 
control.

PRESENTLY PREFERRED EMBODIMENTS 
Further understanding of the invention can be gained with reference to the 
presently preferred embodiments shown in FIGS. 1 through 4. In these 
figures certain switching devices have been shown in a circular 
representation having R, Y, or G referenced letters within the circle. 
These switching devices can be manually operated switches, relay contacts, 
solid state devices or other switching devices which provide a closure 
when the respective color condition is desired. The letter within the 
circular switching device indicates R for red, Y for yellow, G for green, 
or specified combinations of these desired color conditions where more 
than one reference letter is shown. The switching devices may be any 
device or control including computer logic which acts as a contact closure 
function. 
Referring now specifically to FIG. 1 there is shown a searchlight signal 
lamp 1 which for purposes of this drawing is shown as being a filament 
type lamp. Associated with the lamp but not shown are green, yellow, and 
red lenses which are mechanically arranged so as to selectively position 
the respective color in front of the light source so that the searchlight 
signal will appear to be either yellow, green, or red. The lens carriers 
are moved to a yellow or green position by operation of the bipolar lens 
operating solenoid 4. When a voltage of a positive polarity is placed on 
the solenoid, in the direction shown by +=Y, the directional current 
within the solenoid will move the yellow lens into a display position. 
Conversely when a voltage with a positive polarity is placed on the side 
of the solenoid 4 indicated by +=G, the oppositely directed current within 
the solenoid will move the lens carrier to a display the green color 
position. Interlocked to the lens carriers, in this embodiment mechanical 
interlocking is contemplated, are two interlocking switches 2 and 3. As 
shown in FIG. 1 when neither yellow nor green lenses are positioned the 
transfer contacts associated with switches 2 and 3 are in the down 
position indicating that neither yellow nor green lenses are in the light 
display path of the filament of lamp 1. It is assumed that when both 
yellow and green lenses are in the down position, the red lens is 
mechanically interlocked to be in the direct light path of the searchlight 
1. If solenoid 4 is activated by a voltage having a positive polarity on 
the side indicated +=Y then the solenoid would operate to move the 
respective yellow carrier in front of the lamp 1 and simultaneously move 
transfer contact from switch 2 to the up or (Y) yellow position. 
Conversely if an opposite polarity voltage is applied to solenoid 4 such 
that the +=G side of the solenoid is now made positive, the solenoid 4 
would operate to move the green lens carrier in front of the lamp 1 and 
simultaneously interlock switch 3 would move the respective transfer 
contact up to the (G) green position. This mechanical interlocking of 
switches 2 and 3 to the colored lenses is known from the prior art. As can 
be seen, the necessary current path through the solenoid 4 is controlled 
by operation of the wayside located control elements. 
A fail-over relay 8 has one of its input terminals B connected to a source 
of positive voltage such as the plus terminal of a battery, and the other 
of the fail-safe relays terminals N connected to a negative or common 
voltage ground source. The fail-over relay 8 is used at the wayside 
position and indicates either an operating mode or a non-operating mode. 
This device can also be achieved using solid state or computer logic, but 
is shown in the presently preferred embodiment as a fail-over 
electromechanical vital relay device. In the system a vital fail-over 
relay is used which is picked-up if the system operation is in the proper 
mode, but which drops out if the safety factors built into the electronic 
or logic control system indicate that the system no longer has proper 
control of the searchlight signal. In such case when the fail-over relay 
drops out the red indication light if possible must be shown, but no 
failure of the lens control shall result in a yellow or green indication. 
When the relay 8 is picked-up into position b, the plus voltage is then 
fed to a voltage regulator 5 which may have functions of voltage 
stabilization, voltage boost or regulation, and surge protection. If a red 
light indication is desired only the red switching device 12 is closed and 
devices 14, 13, and 11 remain open circuited. In such a case current flows 
through regulator 5 and through switching device 12 to conductor 16 in the 
cable. Inside the signal device conductor 16 is attached to the interlock 
switch 2 through the transfer contact associated with the yellow lens 
being in the non-displayed condition (as shown). Current can then flow 
through the transfer bar of switch 2 through the filament of lamp 1 to the 
interlock switch 3 via the transfer bar associated with the non-display of 
the green lens (down as shown) to wire 19. While wire 19 feeds one end of 
solenoid 4 it can be seen that the solenoid does not operate to move 
either of the lenses because a complete current path cannot be 
established, since switching elements 11 and 14 remain open circuited. A 
completed current path for the searchlight filament continues from wire 19 
through conductor 15 in the cable to the negative terminal on relay 8 via 
the lower movable contact which is in the b position. In this manner a 
current path is established to light the filament of lamp 1 when the 
desired red lens is in the display position. If either the yellow or green 
lens are stuck in a display position such as due to mechanical failure the 
current is interrupted by respective interlock switches 2 or 3 to result 
in no color light being displayed. 
When the yellow signal display is desired, switch device 11 is closed while 
switch devices 12, 13, and 14 remain open. Again the fail-over relay 8 is 
in the B position so the positive voltage at the B terminal of relay 8 
passes through the regulator 5 to feed both switch device 11 and conductor 
18. Switch device 11 provides positive voltage to conductor 17 which feeds 
into the signal box and the +=Y terminal on the solenoid 4. A return 
current path from the opposite end of solenoid 4 is provided by means of 
electrical conductor 15 which feeds through the b positioned lower contact 
on relay 8 to the N or negative terminal of the battery. This current path 
via conductors 17 and 15 provide operating current such that the bipolar 
solenoid 4 causes the yellow lens carrier to be moved in front of the 
light source thereby causing the interlocking switch 2 to be moved upward 
to the yellow display, (Y) position. At that time the current being 
supplied via conductor 17 is also provided with a path through switch 2 in 
its upward or yellow displayed (Y) position through the filament of lamp 1 
and then via switch 3, in its down or non-green position, to wire 19. The 
completed lamp filament circuit similarly follows back through the cable 
via conductor 15. Similarly, if erroneously the yellow lens is down or the 
green lens is up in a display position, respective interlock switch 2 or 3 
interrupts the current path to the filament of lamp 1. 
When it is desired that the green lens be displayed in front of the 
filament lamp switch devices 14 and 13 are caused to close and switch 
devices 11 and 12 remain open circuited. Relay 8 is in its b position 
indicating that the wayside logic and control systems desire the signal 
light to function. 
When it is desired to operate the green display mode the current path to 
solenoid 4 is from the negative voltage terminal 6 through switch device 
14 which is now closed to conductor 17 to the signal housing which contain 
bipolar solenoid 4. The current returns via conductor 15 to the wayside 
control box where relay 8 is in position b and return path is provided to 
the neutral or ground via the lower movable contact. Such a current path 
provides a polarity through bipolar solenoid 4 such that a solenoid side 
marked +=G is positive, and the solenoid motor causes the lens carriers to 
move the green lens into a (G) display position in front of lamp 1. When 
the green lens is in front of the lamp, switch 3 which is mechanically 
connected to the lens is moved to its upper or (G) position and a filament 
current to lamp 1 is provided via fail-over relay input terminal B to 
regulator 5, to conductor 18 in the cable, via interlocking switch 3 which 
is in its (G) position or up position, to the filament in lamp 1, then 
through switch 2 which is in a non-display of yellow position (down), and 
then via conductor 16 to the wayside control box. Switch device 13 is now 
closed providing a path from cable conductor 16 to the relay 8 which is 
now connected via the lower movable contact in the b position to the 
neutral (N) terminal on the relays. Should the green lens move from the 
display green position the filament current is interrupted by switch 3. 
Should the yellow lens be erroneously moved into position the switch 2 
terminates the current to filament in lamp 1. 
As can be seen in the circuit of FIG. 1 the interlocking contacts 2 and 3 
associated with respective yellow and green lenses are wired into the 
logic circuitry such as to provide that the red display can light only if 
both of the contacts are down or in their non-display yellow, non-display 
green positions. Also the signal can only light yellow if the yellow 
contact is up and similarly the green only if the green contact is up. In 
each case the fail-over relay contact when energized pass battery through 
a regulating device, through which ever control switch devices are closed, 
and if the lens carrier is in the correct position, through the check 
contacts of switches 2 and 3 to the lamp filament. Note that when the 
fail-over relay 8 drops it provides lamp voltage which is of the opposite 
polarity to that normally used through the red check contacts to the lamp. 
In each case, this applies positive voltage to the green position of the 
lens control solenoid, so that no possible short within the cable can make 
the lens carrier operated by solenoid 4 to shift to yellow; since there is 
no higher positive voltage in the system that could erroneously reach the 
Y terminal of solenoid 4. 
If FIG. 1 four control wires are used in the cable and four switch devices 
are also used. In all cables it is anticipated that an additional ground 
wire for shielding purposes may be used. If the fail-over relay 8 drops it 
applies battery directly to the red interlock contacts and to the lamp, 
but of reverse polarity so that plus voltage is applied to the green 
control end of the solenoid. Thus no cable short can make the yellow end 
more positive, so the mechanism cannot shift to a yellow display position. 
If the cable wires 17 and 18 are shorted, the solenoid can shift to green 
but in so doing opens the path through the green interlock contact switch 
3 to the lamp filament. Thus the solenoid 4 can be tied into the lamp 
voltages without any possibility of lighting other than the red in the 
event of the fail-over relay dropping. 
Referring now to FIG. 2 shows a second presently preferred embodiment which 
assumes a supply system where there is no power supply available other 
than the main battery. A pole changing operation for the solenoid is 
generally provided by control switch devices 20, 23, 24, and 25, while 
switch devices 21, 22 and 26 generally provide logic for the lamp 1. A 
total of seven switch devices are used, and only three conductors 27, 28, 
and 29 are required to be in the cable between the signal and the wayside 
control unit. In normal operation each color command can only operate the 
lamp if the lens carrier of the respective color is in the correct 
position. And, as in FIG. 1, a dropped fail-over relay 9 makes a cable 
short unable to operate the solenoid in the yellow direction and unable to 
light the lamp in the false green. 
In normal operation if a red signal light is required the fail-over relay 9 
is picked-up and positive battery voltage is fed from the B terminal of 
the relay 9 to the regulator 5 through the closed red (R) switch device 22 
via conductor 28 in the cable to the signal unit. Within the signal unit 
positive voltage is supplied to the interlock yellow switch 2 which is in 
the non-yellow display position (down) through the filament in lamp 1 
through switch 3 which is in the non-green display position (down) to wire 
30. Wire 30 connects to a return path via cable conductor 27 to the 
wayside unit and via switching device 26 which is now closed to the b 
position of the lower switch contact on the relay 9 to the neutral 
terminal. Similar to the previous circuit the solenoid 4 cannot operate as 
a completed current path does not exist due to switch devices 20, 23, 24, 
25 being in an open position. 
When a yellow display is required and fail-over relay 9 has been picked-up 
plus voltage from the B terminal of the relay 9 is fed through the voltage 
regulator 5 through switch device 20 through the cable via conductor 29 to 
the +=Y side of the solenoid 4 and a return path from the solenoid 4 is 
available through the cable by conductor 27 to the wayside unit. From the 
wayside unit conductor 27 is provided with a return current path by (Y) 
switch device 25 which is now closed and connected through the b position 
contact on the lower switch to the N terminal of the fail-over relay 9. 
This current path causes the bipolar solenoid 4 to move the respective 
yellow lens carrier to a yellow display (Y) position causing switch 2 to 
move upward to (Y), the yellow display position. A positive voltage being 
available at the upper yellow transfer contact (Y) of switch 2, a current 
path through lamp filament via switch 2, lamp filament of lamp 1, and 
switch 3 which is in its down or non-green displayed position to wire 30. 
Filament current returns via conductor 27 in a cable similar to that 
current path used by solenoid 4. 
When it is desired to display a green signal using the circuit arrangement 
shown in FIG. 2 and fail-over relay 9 is in the up position, positive 
voltage is supplied through regulator 5 through switch device 23 to 
conductor 27 in the cable. Conductor 27 feeds the signal unit supplying 
positive voltage to the +=G terminal of the bipolar solenoid 4. A return 
path is provided from the solenoid 4 via conductor 29 in the cable to the 
wayside control unit. Switch device 24 which is now closed provides a path 
to the neutral or negative side of the battery via lower switch of the 
fail-over relay 9 which is in the up, b position, which causes the lens 
carriers to move the green lens into a display position, and transfer 
switch 3 to the upper or G position. The filament current is provided via 
switch device 21, conductor 28 in the cable, interlocking switch 2 which 
is in the down or non-yellow display position, switch 3 which is upward or 
in the green display (G) position, and the cable conductor 29 providing 
the return path similarly as that used by the solenoid current through 
switch device 24 to the neutral or negative terminal of the fail-over 
relay 9 which is in the up or b position. 
As can be seen from the circuit of FIG. 2 the circuit arrangement controls 
the signal device such that red can light only if both of the interlocking 
contacts are down, i.e., in their non-display yellow and green positions, 
and can only light yellow if the yellow interlock contact is up and can 
only light green if the green interlock contact is up. When the fail-over 
relay 9 of FIG. 2 drops it provides lamp voltage which is of the reverse 
polarity to that normally used through the red check contacts, switches 2 
and 3 in the down position, to the lamp. In each case this supplies 
positive voltage to the green position of the lens control solenoid 4 so 
that no possible short within the cable can make the lens carrier shift to 
yellow. A dropped fail-over relay 9 makes a cable short unable to operate 
the solenoid 4 in the yellow direction, and unable to light the lamp 
filament 2 in a false green. 
Referring now to FIG. 3 there is shown a third embodiment which provides 
additional features over the embodiments of FIGS. 1 and 2. Because lamp 
solenoid supplies are separate, regulator 5 may be used in order to 
provide ramp-up voltage or a reduced voltage for cold filament checking. 
This could not be done in the circuit of FIGS. 1 and 2, which use the same 
voltage supply for both lamp and solenoid operation because the reduced 
voltage of the lamp supply in the cold test position would not be 
sufficient to operate the solenoid 4. Two separate power supplies are used 
in addition to the battery. These may be available for other function in 
the wayside equipment. This embodiment uses five switch devices 31 through 
35 and requires the use of four conductors 36, 37, 38, and 39 in the cable 
that connects the signal light unit to the wayside control unit. Terminal 
6 has a negative voltage supply connected to the terminal while terminal 7 
has a positive voltage power supply connected thereto. The two remaining 
terminals of the fail-over relay 10 are respectively connected to the B or 
battery terminal and the N or neutral terminal. Switch device 31 is a 
device that creates a closed circuit between its respective terminals when 
either a yellow or a green display is desired. 
If a red display is desired from the circuit in FIG. 3 and the fail-over 
relay 10 is picked-up, voltage is provided from the B terminal of the 
fail-over relay 10 to the regulator 5, then to switch device 32 which is 
in a closed state. Switch device 32 feeds conductor 38 in the cable which 
provides voltage to the remotely located signal. The filament of lamp 1 is 
fed via interlocking switch contacts on switches 2 and 3 which are both in 
the down position because neither green nor yellow are displayed. The 
return path for the current from the lamp filament from interlocking 
switch 3 is via wire 40 to conductor 37 in the cable which feeds the 
wayside unit and the neutral terminal on fail-over relay 10 via the second 
switch which is in the b or up position. Bipolar solenoid 4 operates 
neither lens carrier, as a completed current path does not exist. If 
yellow display is wanted the lens carrier is moved to the yellow position 
by positive voltage from the fail-over relay 10 which is in the up 
position b being fed from terminal 7 through the respective b contact to 
the switch device 34 which is closed because a yellow lens display is 
desired. Device 34 feeds a positive signal voltage to conductor 36 in the 
cable which feeds directly to the +=Y terminal of the solenoid 4 causing 
the solenoid to move the yellow lens into position in front of the lamp 1 
and causing switch 2 to go to its upper position (Y) or a display yellow 
position. A return path for the current from solenoid 4 is provided 
through wire 40 to cable conductor 37 and from 37 to the neutral terminal 
on fail-over relay 10. 
When a yellow display is required, positive voltage is fed from the relay 
terminal 7 through the contact in the up position, through switch devices 
34 and wire 36 to the (Y) terminal of the solenoid 4, returning via wires 
40 and 37, through the relay contacts to N, thereby moving the lens 
carrier to the yellow position. Battery voltage is fed via the battery 
terminal on the fail-over relay 10 which is in the up b position to 
regulator 5, to switch device 31. Switch device 31, which is closed 
because a yellow or green display is desired, provides voltage to 
conductor 39 in the cable. Cable 39 feeds the signal unit and supplies 
voltage to the interlocking switch 2 which is in the Y position having 
been moved there by solenoid 4. Current through the filament of lamp 1 
returns via interlock switch 3 which is in the down position since green 
is not displayed, wire 40 and returned via conductor 37 in the cable to 
the neutral or negative terminal on the fail-over relay 10 which is in the 
up or b position. 
When a green signal is desired the circuit shown in FIG. 3 causes the green 
lens carrier to be moved into position in front of lamp 1 by supplying a 
negative voltage via terminal 6 on fail-over relay 10 through switch 
device 35 to conductor 36 in the cable. Conductor 36 feeds the remotely 
positioned signal control having bipolar solenoid 4. Polarity in this 
direction causes solenoid 4 to move the green lens carrier into a display 
position (G) causing switch 3 to move to its upper or green (G) display 
position. The return path for current from the solenoid 4 is via wire 40 
to cable 37, and then to the neutral on the fail-over relay 10. Filament 
current is provided from the B terminal on the fail-over relay 10 via 
voltage regulator 5 through switch device 31, which is now closed since a 
green (G) display is desired, through cable conductor 39 to switch 3 which 
is in the up or (G) position indicating a green display. Current from the 
switch 3 feeds filament of lamp 1 and returns via switch 2 which is in the 
down position, non-display yellow, and cable 38, through switch device 33, 
and to the N or neutral on the fail-over relay 10. 
As with the previous circuits the arrangement provides that when the 
fail-over relay drops, lamp voltage which is of the opposite polarity to 
that normally used through the lamp 1 when the display is red, is directed 
to the not displayed green contact of 3, the lamp filament 1, and the not 
displayed yellow contact of 2. In each case this applies a positive 
voltage to the display green side of the lens control solenoid so that no 
possible short within the cable can make the lens carrier shift to yellow. 
The filament is only energized by the yellow switch devices when the 
interlocking switch 2 is in the up or yellow position and the green 
interlocking switch 3 is in the down or not display green position. 
Conversely, the circuit is only activated by the green switch devices when 
the green interlocking switch 3 is in the up position and the yellow 
interlocking switch 2 is in the down or not display yellow position. As in 
the other circuit versions when the fail-over relay 10 drops it provides 
lamp voltage which is of the opposite polarity to that normally used 
through the interlock contacts to the lamp. In each case this applies 
positive voltage to the green display side of the lens control solenoid 4 
so that no possible short within the cable can make the carriers shift to 
yellow. 
A further embodiment is shown in FIG. 4 which is a partial schematic of a 
circuit similar to that shown in FIG. 3. The cable and the signal circuits 
are identical to that of FIG. 3 and save a relay contact on the fail-over 
relay 10 and use only a single additional voltage source. Power is 
supplied before the voltage regulator 5 to the wire 41 which leads to the 
line side of switch device 34. This provides in essence a source of 
positive voltage when the fail-over relay 10 is picked-up or in the b 
position. The operation of the switching devices 31 through 35 are 
identical as that explained in relation to FIG. 3. 
Although I have shown and described several forms of circuit apparatus 
which embody my present invention for a self-checking searchlight signal 
arrangement, it is understood that various changes and modifications may 
be made within the scope of the appended claims without departing from the 
spirit and scope of my invention. While functional switching devices have 
been discussed in this specification, other functional equivalents such as 
programs, microprocessors, solid state devices, and vital relays may be 
used within the scope of these claims.