US2429056A - Slide fence protection system for railroads - Google Patents

Description

Oct. 14, 1947.

w. v. GROBJEAN SLIDE FENCE PROTEGTIOXSYS TEM FOR RAILROADS 2 Sheets-Sheet 2 Filed Sept. 22, 1945 H15 ATTORNEY Patented Oct. 14, 1947 SLIDE FENCE PROTECTION SYSTEM RAILROADS FOR Wilbur Grosjean, Omaha, Nehru, assignor to The Union Switch and Signal Company, Swissvaile, Pa., a corporation of Pennsylvania Application September 22, 1945, Serial N0.=B17 ,9-7 7 8 Claims. (01. 246-.121)

Myinvention relates to slide fence protection systems for railroads, and more particularly to a system of circuits for use in connection with protection devices such as slide fences or slide detectors such as are .used along the right of way of railroads to detect slides, falling rock or other abnormal conditions.

The principal object of my inventionis the provision of an improved system of circuits suitable for controlling block signaling systems, including those for single track railroads, whereby the operation of a slide detector in any block section due to the encroachment of foreign objects upon the right of way conditions the signal which governs train movements'into the section to indicate stop, if it has been cleared, and also conditions the corresponding distant signal in the rear thereof to indicate caution, but without interrupting "the line circuits by which the signals are normally controlled.

A further object of my invention is the provision of improved means for retaining the-indications of the operation of the slide detector system until after the-obstruction which caused its operation has been removed and the detector circuits have been restored to their normal condition.

A further feature of my invention is the provision of manually operable .keys or push buttons at the locations of the signalsgoverning train movements into a block section containing one or more slide detectors, whereby the signal system may be restored to its normal condition by the crew of a train which has been stopped at asignal as a result of a temporary interruption. of the protection circuits or in the event an ObStXllC-r tion which caused the interruption has already been removed and theprotection circuit restored by the maintenance forces.

Another feature of my invention is the provision of means for transmitting indications of the operation of any slide detector in a block over the circuits ofthe protection system to a station at one end of the block, from which point a distinctive indication identifying the block is transmitted to the train dispatchers oflice.

I shall describe one form of apparatus embodying my invention and shall then point out .the

novel features thereof in claims.

Inthe accompanying drawings, Figs. 1A and 13, arranged side by side,show at the top a single line diagram of the track plan for a typical stretch of single track railway equipped with automatic block signalsfor governing traihc movements in both directions and having slidedetector fences at four extended locations within the stretch and identified by the reference characters ISF to 48F, respectively. The circuits directly below those of the track plan are theline circuits for a typical signaling system for controlling the signals shown in the track ,p'lan, While the group of circuits below these are the'line circuits by which the signal system is governed by the condition of the slide detector fences in accordance with my invention. The circuits in the lower portion are the, lighting circuits for the signals controlled jointly'by the two groups of line circuits above referred to.

The signaling system as shown herein is generally similar tothat disclosed in a'pending application for Letters Patent of the United States, Serial No. "501254, filed September 4, 1943, by Henry S. Young, for Railway trafiic controlling apparatus. Inthis system continuous track circuits are provided throughout the stretch for governingthe signals in accordance with traflic conditions, the tracks being divided into sections by insulated joints. Each track section is provided with a closed track-circuit identified by the reference character T with a numerical prefix identifying its location. Each track :circuit has a track battery B, and a normally energized track relay similarly identified, at its other end.

The track plan as shown embraces three sections of a single track block and includes three sets of opposing intermediate signals, comprising the signals II to 1-4 in Fig. 1A and the signals I 5 and 16 in Fig. 113, each of which is of the three-position color light type having three lamps G, "Y "and R for indicating proceed, :caution and stop, respectively, controlled by a polarized line relay bearing the designation HD with identifying prefix.

The plan also includes a short OS section 5T at one end of the block, which containsa track switch 5W connecting the single track stretch with a passing siding. Train movements into section :5T are governed by head block .signals subject to manual control, these comprising the entering signals ELA and -6LB and the leaving signals fiRAiand 'SRB. Each head block signal as shown is of the Searchlight type having a signal lamp adapted to display light of different colors by the operation of a polarized mechanism such as BLAG. V V

In order to simplify the various circuits shown herein, I have shown only the terminals of the local sources of current for energizing the relays, these beingidentified by the reference characters B and C, designating the positive or supply terminal and the negative or common return terminal, respectively. It is to be understood that each polarized signal relay HD or mechanism G operates its contacts to the left when the lefthand terminal of its winding is connected to the positive terminal B. thi being designated the normal position corresponding to the caution indication of the signal, the reverse or right-hand position corresponding to the proceed indication.

The signal line relays HD are controlled by the track relays TR over a two wire reversible line circuit system in which the direction of trafiic is established and the clearing of the head block signals is governed manually from the train dispatchers ofiice by means of a centralized trafhe control system by the operation of code controlled relays of the polar stick type, such as the trafilc direction relay BLFS and the signal control relay BLHS, shown in Fig. 1B.

A directional stick relay such as the relay HS is provided for each intermediate signal to control the polarity of the current supplied to the line relay for the next signal in the rear in accordance with the well known absolute-permissive scheme of operation.

The signal lamps for the intermediate signals are normally dark, but become lighted upon the approach of a train by the release of an approach relay AR which is included in the line circuit in series with the relay HD for the signal in the rear. As shown, the line circuit system is set up for trafiic movements from left to right with the contacts of the trafltlc relay BLFS and of the similar relay at the opposite end of the block in their left-hand positions, and with relay llHD energized in the normal direction, with relays ISHD, l5I-ID and GLHD energized in the reverse direction and with all of the approach relays AR energized.

The slide detector fences SF may be of any suitable type and are therefore shown only diagrammatically herein. These may be, for eX- ample, of the type shown in Letters Patent of the United States No. 2,187,518, issued January 16, 1940, to William C. McWhirter, for Circuit controllers. For an understanding of my invention, it will suffice to point out that each fence is divided into two sections held together under tension by heavy coil springs. A circuit controller such as the controller ICC for the slide detector fence ISF is mounted in a suitable housing located between the sections and. comprises a set of four contacts a, b, c and d which are normally held closed by a latch. Two trip rods for releasing the latch are attached to the adjacent sections of the fence, the arrangement being such that a lateral displacement of the wires of either section of the fence due to a slide, falling rocks, or the like, will trip the latch and open the four contacts.

A drop annunciator is also provided as explained in the patent by means of which a colored disc or plate is exposed to indicate in which of the two fence sections the displacement occurred. The contacts remain open even though the obstruction is removed, but after the fence has been restored to its normal condition the contacts may be latched closed manually by the maintainer, the operated drop annunciator being restored to its normal position at'the same time.

Contacts at and b of each circuit controller such as ICC are included in a stick circuit for a normally energized slide detector relay, such as the relay IZSD, I4SD or IBSD, located at one end of the block section within which the slide detector fence is located, and each such relay controls a repeating relay such as the relay D, I5SD or 6LSD, located at the other end of the block section, over contacts 0 and d of the fence circuit controller. Any displacement of either section of the fence which is suflicient to release the circuit controller latch and open its contacts therefore releases the relays SD at both ends of the block section. A contact 0 of each relay SD is included in the circuit for the lamp or mechanism for the adjacent signal governing traffic movements into the block section, which contact is operated to condition the signal to indicate stop when relay SD releases, Each relay SD also has pole changer contacts 6 and f in the signal line circuit as illustrated by relay i3SD, for example, by which the polarity of the current supplied to relay IEHD is changed from reverse to normal when relay I3SD releases, to condition the signal [5 which governs the movement of trafiic approaching the location of relay I3SD to indicate caution instead of proceed. A push button PB at each signal location and an auxiliary line relay Z, and back contacts 0 of the track relays provide means whereby the slide detector stick relays may be picked up following the removal of an obstruction and the resetting of the contacts of the circuit controller CC in their closed position.

Each repeating relay such as relay ISSD or I5SD controls the polarity of the current supplied to the slide detector repeating relay such as relay ISSD or IBLSD for the next section at the right, providing a system of cascade connected circuits by which the opening of any of the slide detector circuit controllers is indicated at the C. T. C. station at one end of the block either by the release of the neutral contacts of or by a reversal of the polar contacts of the slide detector repeating relay BLSD at that location. From this station the indication is transmitted to the dispatchers office to release an indication relay such as the relay llSDK to light a lamp E on the operators control panel. Usually this indication is transmitted to the ofiice over an intermittently available channel of the code type communication system, but for simplicity this is represented in the drawing by the equivalent direct wire circuit, such as would be used if the distance were relatively short.

The signal system is shOWn in the drawings as set up for traffic movements from right to left, the code controlled relay fiLFS and a similar relay at the opposite end of the block having been 0perated to close their left-hand contacts. Relay Ill-ID, for signal ll, occupies its energized position as shown and a connection to terminals B and C at contacts a and b of relay l IHD energizes relay ISHD in the reverse direction over line wires -2l and 22, to condition signal l3 to indicate proceed. A connection to terminals B and C over the pole changer contacts 6 and f of relay ISSD, contacts a and b of relay I3HD and wires 23 and 24 energizes relay IEHD reverse to condition signal 15 to indicate proceed, and a similar circuit controlled by relays 158D and I5HD over wires 25 and 26 energizes relay GLHD reverse. When switch 5W is locked normal a switch indication relay ENWP is energized and if the code controlled relay BLHS is reversed by the central office operator, the mechanism BLAG is energized to condition signal 6LA to indicate caution or proceed over a, circuit including the neutral and polar contacts of relay ELHD and having a connection to terminals B and C over contacts a and b of relay GLHHS, contact of the slide detector relay ELSD and contact b of the track relay TR. When switch 5W is locked reverse, a switch indication relay SRWP is energized in place of relay SNWP and the'mechanism BLBG is energized to cause signal 6LB to indicate caution or proceed in place of signal GLA.

I shall now briefly describe the operations resulting from a train movement through the stretch from right to leftwith the protection system in its normal inactive condition. When the train enters section 5T, signal BLA or GLB is restored to stop by the release of relay STR.

When the train enters section 6LT, relays BLHD and [EAR are released by the shunting of the track relay GLTR, and lamp G of the signal l5 ahead of the train becomes lighted over the circuit including back contact a of relay |5AR and front contacts 0 of relays 'ISSD and I5HD. As the train advances into section IGT these conditions aremaintained by the release of relay ISTR and in addition therdirectional stick relay 15S is energized over a connection to terminal B at the back contact d of relay IBTRand front contact (1 of relay I'5HD.

When the train enters section I 5T, relays ISHD, ISAR and |3AR are released by the shunting of the track relay IETR. Lamp G of the signal l3 ahead of the train becomes lighted, due to the release of relay I3AR, lamp G of signal I5 is extinguished and lamp R for that signal is lighted due to the releas of relay I5HD, and lamp R of the opposing signal I6 is lighted due to the release of, relay l-GAR. These conditions are maintained by the release of relay MTR as the train enters section MT and when the train vacatessection IBT relay IG'IR picks up and relays fiLHD and l EAR become energized by current of normal polarity over a connection to terminals B and C at contacts b and a of relay [58,

which rela is held energized over a stick circuit comprising a connection to terminal B at back contact d of relay l5HD. The energization of relay IGAR causes signal l6 to become dark, and the energization of relay GLHS allows signal BLA or GLB to be manually controlled to indicate caution to permit a following train to enter the block.

Similar conditions prevail with respect to signals l3, l4 and I5 as the train advances through sections ,I3T and HT, and when the train vacates section I 4T, relay I SS is in its energized position allowing relay I5HD to become energized in the normal direction, releasing relay I58 and conditioning signal I5 to indicate caution and reversing the polarity of the current supplied to relay GLHD to allow signal GLA or 6LB to indicate proceed.

I shall now assume that a displacement of the slide protection fence [SF occurs While the system is set up for traflic movements from right to left as above described, resulting in the opening of the contacts of the circuit controller ICC to disconnect terminals B and C from line Wires 2! and 28 and to open the circuit over line wires 29 and 30 so that relays IZSD, l2Z and I3SD release. The dropping of contact 0 of relay I3SD extinguishes lamp G and lights lamp R of signal l3, provided relay |3AR has been released by a train approaching that signal, and the dropping of contacts e and of relay |3SD changes the polar- 6. ity of the current'su'pplied over line wires .23 and 24. to operate relay |5HD to from reverse to normal which extinguishes lamp G and lights lamp Y'of signal 1:5, provided relay IEAR is released, so that the approaching train will receive successive caution and stop signal indications at signals l5 and I3, assuming of course it has not already passed these signals before the displacement of fence I SF occurs.

In addition, the dropping of the pole changer contacts b and d of relay I3SD changes the polarity of the current supplied over line wires 33 and 34 to relay ISSD from normal to reverse so that this relay thereupon operates its polar contacts h and 9 from left to right to eflfect a similar change in the polarity of the current supe plied over its front contacts b and d and line wires '31 and 38 to relay GLSD. The polar contact h of relay BLSD thereupon opens, transmitting an indication to the ofiice to release relay I4SDK and thereby causing lamp E to be lighted to indicate to the operator that the controller contacts of one of the slide protection fences lSF-ESF in the block has been opened.

Similar conditions prevail if the displacement of fence ZSF or 38F occurs, in which case relays MSD, I 4Z and I5SD release. The dropping of contact 0 of relay ISSD conditions signal l5 to'indicate stop, the dropping of contacts e and 7 of relay I'BSD changes the polarity of the current supplied to line wires 25 and 26 reverse to normal to condition signal ELA or GLB to indicate caution instead of proceed. If the polar contacts h and :i of relay I 5SD occupy their normal position as shown, the dropping of contacts b and d of relay I5SD reverses relay 6LSD thereby releasing relay l-GSDK to light lamp E. If a displacement of fence 48F occurs, relays BSD, IBZ and BLSD release and the opening of contact 0 of relay GLSD in the signal mechanism circuits holds signals GLA and GLB at stop and the opening of contact b of relay GLSD releases relay l-4SDK to light lamp E.

Returning now to a consideration of the efiect of the displacement of the fence ISF, it will be evident that if the trouble is not corrected by the maintenance forces before a train reaches signal I 3 the train will be stopped at that signal. After obtaining authorization from the dispatcher, the train will continue through section l2-|3 at slow speed. In the event the trouble is corrected and the contacts of controller ICC are latched closed while the train occupies section I3T but before it enters section I2T a circuit is completed from terminal B at back contact 9 of relay |3SD to terminal C of the source at that location over back contact 0 of the track relay I3TR, the line wires 29 and 30 and back contact b of relay I 2SD through the winding of the slow release relay I2Z, which relay assumes its energized position closing its contact a to complete a pick-up circuit for relay I'2SD over wires 27 and 28. If the trouble is corrected after the train enters section IZT, relay IZSD is picked up directly over back contact a of the track relay IZTR. In either case relay IZSD will assume its energized position and as soon as the train vacates section I31,- relay |3SD will become energized over the circuit including front contacts I) and d of relay I2SD,' line wires 29 and 30 and front contact 0 of relay I3TR.

In the event the trouble is not corrected while the block section I2-l3 is occupied by the train but is corrected subsequently, the next following train will be stopped at signal I3. The train crew will 'then operate the push button I3PB at that location, therebycompleting a circuit for relay NZ to reenergize relays IZSD and 'I3SD as above described, whereupon the indication displayed by signal it will change from stop to caution or proceed and the train may resume its movement through the block. It will be noted that a stick circuit is provided for relay I3SD including its own front contact a which serves to prevent its release due to the opening of front contact of relay I3TR.

The protection system may also be restored to normal in the manner just described in the event relay IZSD is released due to any temporary interruption of its stick circuit not due to the operation of the controller ICC, the system being self-restoring if the duration of the interruption is less than the release period of relay I2Z. In each instance when relay I2SD becomes energized, relay ISSD is reenergized and the polar contacts of relays lESD and GLSD assume their normal positions, whereby the indication relay l-4SDK is released and lamp E on the operators control panel is extinguished.

With traffic movements from right to left set up as above described, the opening of the contacts of either of the circuit controllers 2 CC or 300 due to the displacement of oneof the slide protection fences ZSF or 35F in block section l3l5 or the opening of those of controller 400 due to the displacement of the fence 4S1 places the system in a condition corresponding to that described, and its restoration to normal may be effected by similar operations as will be obvious from a consideration of the drawings.

In signaling systems of the reversible line circuit type as shown herein, the line circuit system is used not only to govern the signals but also to control trafiic direction indicating and locking apparatus at the control office and to govern the operation of electric switch locks which are provided for the protection of outlying hand throw switches, as is explained in the Young application hereinbefore referred to. Inasmuch as the operation of the protection system of my invention does not interrupt the continuity of the reversible line circuit system, these additional functions of the system are in no way interfered with, as will be readily apparent. Furthermore, the operation of the directional stick relays S as required to effect the clearing of the signals for a following train is not interfered with by the operation of the protection system, as would be the case if the line relays I-ID were released by the detector relays SD or if the contacts of the controllers CC were included in the signal line circuits.

I shall now assume that the operator reverses the traflic direction to clear the signals which govern movements from right to left through the block. This may be accomplished when the block is vacant by reversing the traffic relayfiLFS and also a similar relay at the left-hand end of the block to release relay i iI-ID, thereby releasing relays ISHD, ISHD and ELI-ID successively, the release of relay l5I-ID completing a circuit for relay IBHD over wires 25 and 26 and the right-hand contacts a and b of relay ELFS, this circuit also including a contact e of an approach lockin relay ELAS which is energized when signals SLA and 6L3 are at stop, contacts a and b of a pole changer relay tPtPC controlled by signal ERA and a front contact a of relay 5TB. Relay iBHD is thereby energized in the normal or reverse direction to efiect the successive energization of relays ED and IZHD and the various approach relays AR also become energized. In view of the symmetry of the circuits, it will be evident that the operations resulting from train movements from left to right through the stretch when the protection system is in its normal inactive condition will be similar to those already described, and consequently these will be understood without further description. The control of the signals for the left to right direction by the detector relays SD is also similar to that already described, and likewise the restoration of the protection system by the track relays. For left to right movements, the relays IZSD etc. may be reenergized by the operation of a push button such as I2PB at the same location, as is obvious.

Although I have herein shown and described but one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In a protection system for railroads, a stretch of railway track, a protection device adjacent said stretch, a track circuit for said stretch having a normally energized track relay, a circuit controller having contacts arranged to be manually closed and to open when the protection device is displaced from a normal position, a signal at each end of the stretch for governing trafiic movements into the stretch, line circuits for clearing each signal including front contacts of said track relay, a normally energized detector relay adjacent one of said signals, a repeating relay adjacent the other signal controlled over front contacts of said detector relay, a pick-up circuit for the detector relay including a back contact of said track relay and said circuit controller contacts, a stick circuit for the detector relay including its own front contact and said circuit controller contacts, and means responsive to the release of the detector relay and of its repeating relay for causing the display of stop indications by said signals irrespective of the condition of said line circuits.

2. In a protection system for railroads, a stretch of railway track, a protection device adjacent said stretch, a track circuit in said stretch having a normally energized track relay, a circuit controller having contacts arranged to be manually closed and to open in the event the protection device is displaced from a normal position, a signal for governing trafiic movements into the stretch, a line circuit including front contacts of said track relay for clearing the signal, a normally energized detector relay, a pick-up circuit for the detector relay including a normally open manually operable contact adjacent the signal and said circuit controller contacts, a stick circuit for the detector relay including its own front contact and said circuit controller contacts, and means responsive to the release of the detector relay for causing the display of a stop indication by said signal without interrupting said line circuit.

3. In a protection system for railroads, a stretch of railway track, a protection device adjacent said stretch, a track circuit in said stretch having a normally energized track relay, a circuit controller having contacts arranged to be manually closed and to open in the event the protection device is displaced from a normal position, a signal at each end of the stretch for governing traffic .movements into the stretch, line circuits for clearing each signal including front contacts of said track relay, a normally energized detector relay and a slow release relay-adjacent one of the signals, a repeating relay adjacent the other signal controlledover apair of line wires by front contacts ofsai'ddetector relay, a pick-up circuit for saiddetector relay including a normally open manually operable contact adjacent thereto, a second pick-up circuit for said detector relay including a front contact of said slow release relay, and a stick circuit for said detector relay including its own front contact, all of said relay circuits including said circuit controller contacts, an energizing circuit for said slow release relay including a normally open manually operable contact at the location of said repeating relay, a back contact of said repeating relay, said line wires and a back contact of said detector relay, and means responsive to the release of said detector relay and of its repeating relay for causing the display of a stop indication by said signals irrespective of the condition of said line circuits.

4. In a protection system for railroads, a stretch of railway track, a protection device adjacent said stretch. a track circuit in said stretch having a normally energized track relay, a circuit controller having contacts arranged to be manually closed and to open in the event the protection device is displaced from a normal position, a signal at each end of the stretch for governing trafilc movements into the stretch, line circuits for clearing each signal including front contacts of said track relay, a normally energized detector relay adjacent one of the signals, a repeating rela adjacent the other signal controlled by front contacts of said detector relay, a manually operable key adjacent each signal, a pick-up circuit for said detector relay including said circuit controller contacts and contacts closed in response to the operation of either of said keys, a stick circuit for said detector relay including its own front contact and said circuit controller contacts, and means responsive to the release of said detector relay and of its repeating relay for causing the display of a stop indication irrespective of the condition of said line circuits.

5. In combination with a stretch of railway track divided into block sections, signals at the ends of said sections for governing traffic movements through the stretch, a system of cascade connected polarized line circuits extending through said stretch for controlling said signals to cause the display of caution or proceed indications in accordance with the polarity of the current supplied thereto, a protection device ad- J'acent the tracks of one section of said stretch, a circuit controller having contacts arranged to be manually closed and to open in the event the protection device is displaced from a normal position, a detector relay and a normally open manually operable contact adjacent the signal governing trafiic movementsinto said one section, pick-up and stick circuits for the detector relay including said manually operable contact and a front contact of the detector relay, respectively, both of said circuits including said circuit controller contacts, means including contacts of the detector relay in a local circuit for the adjacent signal for causing the display of a stop indication thereby without interrupting the line circuit for such signal in response to the release of said detector relay, and means including other contacts of said detector relay for governing the polarity of the current supplied to the line circuit for the next signal in the rear thereof to condition such signal to display a caution indication in response to the release'of said-detector relay.

6.. In a protection system for. railroads, a stretch of, railway track, a protection device adjacent said stretch, a track circuit for said stretch having a normally energized track relay, a circuit controller havingicontacts arranged to be manually closed and to open when the protection device is displaced from a normal position, a signal for governing trafiic movements into the stretch, a control circuit for clearing the signal including front contacts of said track relay, a normally energized detector relay, a slow release relay, ick-up and stick circuits for the detector relay including a front contact of the slow release relay and of said detector relay, respectively, both of said circuits including said circuit controller contacts, a repeating relay adjacent said signal, a circuit for said slow release relay including back contacts of said detector relay, of the repeating relay and of the track relay, a circuit for the repeating relay including front contacts of said detector relay and also including a front contact of the track relay bridged by a front contact of said repeating relay, and means controlled by said repeating relay when released for causing the display of a stop indication by said signal irrespective of the condition of said control circuit.

7. In a protection system for railroads, a stretch of railway track, a protection device adjacent said stretch, a track circuit for said stretch having a normally energized track relay, a circuit controller having contacts arranged to be manually closed and to open when the protection device is displaced from a normal position, a normally energized detector relay controlled by said contacts, a first signal for governing traiiic movements into said stretch, a second signal for governing traific approaching said first signal, a line relay controlled over front contacts of said track relay for controlling said firstsignal, a directional stick relay, a pick-up circuit for said stick relay including a front contact of said line relay and a contact closed by an approaching train. a stick circuit for said stick relay including a back contact of said line relay, means controlled by the directional stick relay when energized for conditioning the second signal to indicate caution, means controlled by the line relay and the detector relay for conditioning the second signal to indicate proceed when both said relays are energized and to indicate caution when only said line relay is energized. and means controlled by said detector relay when released for conditioning said first signal to indicate stop irrespective of the condition of said line relay.

8. In combination with a stretch of railway track divided into block sections, signals at the ends of said sections for governing trafiic movements through the stretch, a protection device in each section, a circuit controller for each device having contacts which open when the device is displaced from a normal position, a normally energized detector relay for each section controlled by the circuit controller for the device in such section, means responsive to the release of each such relay for causing the display of a stop indication by the signal which governs trafiic movements into such section, an indication relay controlled by one of said detector relays in accordance with the character of the current supplied thereto, indication means at a control office controlled by said indication relay, and means for controll ng said detector relays in cascade by governing the character of the current supplied to 11 one or more of such relays whereby said indica- REFERENCES CITED tion relay is actuated to one position when an of The following references are of record in the the detector relays are energized and to another fil of this patent: position in response to the release of any one of said relays a 5 UNITED STATES PATENTS Number Name Date WILBUR V. GROSJEAN. 2,232,379 Field Feb. 18, 1941

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