US2998545A

US2998545A - Navigation light changer having lamp current monitor

Info

Publication number: US2998545A
Application number: US737769A
Authority: US
Inventors: Smyth Henry Lyall Ross
Original assignee: National Research Council of Canada
Current assignee: National Research Council of Canada
Priority date: 1958-05-26
Filing date: 1958-05-26
Publication date: 1961-08-29
Anticipated expiration: 1978-08-29

Description

Allg- 1961 H. R. SMYTH 2,998,545

NAVIGATION LIGHT CHANGER HAVING LAMP CURRENT MONITOR Filed May 26, 1958 2 Sheets-Sheet 1 R3 R4 TR2 34 :l I3 R18 TRA TRB TRC TRD TRE RI? 22 23 RIG 22 l l l I Potential on i .TRD collectors of m ME 4/ I T|ME T 1 2 INVENTOR I 7 HENRY LYALL R055 SMYTH l 1 lumen output I i 1 1 P1 0651- A; 9 Z 2 l I AGENT Aug. 29, 1961 Filed May 26, 1958 H. L. R. SMYTH 2,998,545

NAVIGATION LIGHT CHANGER HAVING LAMP CURRENT MONITOR 2 Sheets-Sheet 2 I! al "Will M In lllifi 1 INVENTOR HENRY LYALL R055 SMYTH AGENT United States Patentf'O 2,998,545 NAVIGATION LIGHT CHANGER HAV'IN LAMP CURRENT MONITOR Henry Lyall Ross Smyth, Ottawa, Ontario, Canada, as-

signor to National Research Council, Ottawa, Ontario, Canada, a corporation of Canada Filed May 26, 1958, Ser. No. 737,769 4 Claims. (Cl. 315-89) earlier application Serial 664,605, filed June 10, 1957, I

for Automatic Lamp Changers, now Patent 2,892,966.

Navigational marker lights installed on buoys, particularly unattended buoy lights situated in remote locations serving inland waterway and coastal marine craft, are required to operate reliably for long periods of time without attention. Such lights desirably are fitted with automatic lamp replacement apparatus to provide continuity of service, and in some installations lamps are deliberately energized above their rated voltage in increase efiiicency, necessitating more frequent replacement. The number of inspections per year or per season which it has heretofore been found necessary to carry out in order to maintain a given standard of performance of the complete installation has incurred a costly upkeep charge. The maintenance problem is particularly aggravated when the marker lights are located in hazardous waters and at very distant sites.

The apparatus presently in use is characterized by complexity and bulk, involving motor-actuated switch devices and circuit breakers for interruptedly energizing a stepping motor magnet in response to an open lamp circuit condition. These devices have required frequent attention to the switching contacts.

Heretofore apparatus devised for and employed at unattended navigation marker lights for detecting a lamp failure has depended on change in the resistance of a lamp filament circuit, for example the change from usual opcrating resistance to substantially infinite resistance of a broken or burnt out filament. A defective lamp disables a detecting relay, whose contacts remain closed, thereby supplying battery to an electromagnetic stepping motor which is self-interrupting by means of a mechanical linkage to the detecting relay, and drives a turret loaded with lamps connected to switching segments until a good lamp is in circuit. The detecting relay and the self interrupting stepping relay have both proved to be sources of trouble, the interrupter contacts in particular being susceptible to sticking or failure, due to maladjustment.

Accordingly this invention is concerned to provide th combination of a periodic switching circuit which does not use moving contacts employing transistor devices for energizing a signal lamp at intervals, with motor-driven lamp-changing mechanism energizable under control of a monitor circuit responsive to lamp flashing to inhibit functioning of the mechanism unless the lamp fails to light in an energizing interval.

It is a further object to provide a simplified control for lamp changing mechanism wherein a transistor switching stage periodically energizes a solenoid winding whose armature is coupled with pawl and ratchet drive means to advance the mechanism in response to failure of a lamp to light with suflicient brightness.

Yet another object is the provision of low cost and efiicient monitor means for detecting the magnitude of a filament current in a flashing lamp and for controlling energization of simple and reliable solenoid powered paWl-and-ratchet driven lamp changing mechanism during the flash interval in response to detection of a current less than a predetermined magnitude.

Other objects and features will become apparent in a careful reading of the following description of the invention and of practical means of carrying it into effect and by study of the accompanying drawings, in which,

FIGURE 1 is a schematic circuit diagram of a lamp flasher with lamp current monitor and changing mechanism operative according to the invention;

FIGURES 2 and 3 are graphs relating keying waveform, lumen output, and monitor responses of the apparatus of FIGURE 1;

FIGURE 4 is an elevation view, partly in cross-section, of a complete flashing light assembly showing a lam turret, Fresnel lens and control devices;

FIGURE 5 is an alternative corrective circuit for the monitor amplifier; and

FIGURE 6 is an enlarged cut-away elevation view of the mechanical drive for a lamp turret of FIGURE 1.

An economical and relatively low cost flasher system having daylight-responsive inhibiting means'to discontinue flashing when ambient light rises above a predetermined level is described and claimed in applicants copending application entitled Lamp Flasher With Daylight-Responsive Inhibiting Means, Unites States Serial No. 657,365, filed May 6, 1957, now Patent No. 2,891,195. The operation of the circuits and devices of an embodiment described in the related application, which is incorporated in FIGURE 1 of this application, is included here to assist in more fully comprehending the present invention. Briefly, a pair of transistors TR1 and TR2 preferably PNP junction type have their collectors and bases cross-connected by relatively large capacitance means C1 and C2; each base is shunted to its respective collector by individual shunt resistors, R3 and R4, .with individual resistors R2 and R5 in series with the collectors whereby with emitters positively polarized by a source of supply, as by bus 60 connected with supply positive lead 13, a multivibrator operation is achieved with one transistor switched to fully on state while the other is biassed o for a predetermined duration, and thereafter a reversal of states ensuing. The circuit is freely running as long as operating voltages are applied. By arranging that capacitor C2 is the smaller, the on time for TR2 is made to be a fraction of the recurrence period, the value of shunt resistor R4 being adjustable to control the flashes per minute switching rate.

The keying waveform appearing on the collector of TRZ may be examined by reference to FIGURE 2, wherein substantially full supply voltage potential appears as TR2 is duly biassed on during the interval F, and substantially negative supply potentil appears during the remainder of the recurrence period T. During the interval F no current flows in the low-valued coupling resistor R7 out of the base of relaying stage transistor TR3, hence this stage is switched off. There is therefore substantially negative supply potential at the collector end of the coupling resistor R9 which is also of low value hence stage TR4 is strongly biassed on. erably a relatively high current type of transistor whose emitter passes the total of all thebase currents of the switching stage comprising TRS, TR6 connected in parallel.

A group of lamps which may be four or any other convenient number, of which but the

lamps

12 and 12 are The latter is prefindicated in FIG. 1, have one terminal of their filaments connected to a common ground bus on the turret axle, and their individual other filament terminals connected to corresponding commutator segments spaced at equal angular intervals about the axis of rotation of the turret, only

segments

16 and 16 being indicated in the drawing.

In the position shown for the lamp turret a fixed wiper 15 completes the flashing circuit through lamps 12 by way of the emitter-collector paths of the switching stage, including the small test resistor R8 in series therewith, from the positive supply bus 13. Accordingly, as the keying stage is switched on during a fish interval F, as is graphically illustrated in FIG. 2, the lamp filament lights, and thereafter remains dark throughout the remainder of the recurrence period T.

During flash interval F, positive potential is applied from the collector bus 25 of the switching stage to a lead 29 which provides positive supply to the monitor amplifier group of transistors, TRA, TRB, TRC, TRD, and TRE. It will be observed that the potential of the lower end of resistor R8 will always be the potential of the bus 25 common to the collector electrodes of TRS and TR6. An additional conductor 58 is permanently connected to the upper end of resistor R8 and with the base of the transistor TRA of the monitor amplifier. Resistance R8 is chosen to be of such value that at the desired operating current through lamp 12, the voltage drop between its terminals is a small fraction of a volt; for example, when lamp 12 draws a current of 0.46 ampere from a nominal 6-volt supply, resistor R8 in one specific embodiment had a potential between its ends of 0.15 volt during a flash interval.

With an operative lamp properly positioned in circuit, and appropriate operating voltages applied to

conductors

13, 14, the potential of conductor 58 during the flash interval will fall by a fraction of 21 volt below that of the emitter of TRA, whereby the emitter-to-collector path of this transistor is caused to be conducting. Accordingly, the state of the individual transistors TRA to TRD inclusive is determined by the direct resistance coupling between the collector of a preceding stage with the base of the following stage, whereby TRA and TRC are biassed "On while TRB and TRD are biassed Off. The potential of the base of TRE is substantially that of its emitter, due to zero voltage drop across R16, whereby base current is substantially zero and TRE is biassed fully Oir. It will therefore be apparent that no current can flow in the winding of lamp changer solenoid 20 through the final stage TRE of the monitor amplifier so that the turret remains unmoved. At the end of each flash period the potential of conductor 29 fall substantially to zero as TRS and TR6 are biassed 01?, so that during rest periods the entire monitor amplifier is disabled.

Should lamp 12 fail, as for instance in the event of disintegration of the filament for any reason, or if the resistance of the entire lamp circuit including contact resistances, should rise appreciably, the voltage drop across test resistor R8 during a flash interval will be less than a predetermined amount, or even zero. If the bias applied to the base of TRA under such conditions fails to make TRA sufi'iciently conducting to cause TRB to be biassed off, armature 21 of electromagnet 20 will be pulled down due to current flow therein via the emitter-collector path of TRE, against the force of restoring spring 30. As a result ratchet wheel 23 is thereby caused to move under action of pawl 22 by one tooth distance. At the termination of the interval armature 21 is restored to its rest position, and the pawl is retracted ready to re-engage the ratchet as described, when the potential of conductor 29 falls to zero.

Referring to FIG. 6, it will be seen that turret body 32 is coupled to pinion 24 on the shaft of ratchet 23 for mechanical drive thereby so that in each succeeding interval as TRS and TR6 are switched On, the group of lamps is advanced by an increment of angular displacement, eventually bringing another segment and lamp into the circuit, as for example segment 16 and lamp 12. With the restoration of flashing by substitution of a new andoperative lamp as load for the switching stage TRS and TR6, the output of stage. TRB of the monitor amplifier is again inhibited and electromagnet 20 ceases to be energized so long as lamp 12' remains operative.

While the interposition of any resistance load in series between a constant voltage supply such as a battery and the filament of a lamp is generally to be avoided in the interests of efliciency, it is entirely satisfactory in the embodiments of the present invention since test resistance R8 may be made so small as to leave substantially full supply voltage to be applied across the lamp itself. In general apart from considerations of cost of battery supply and of the monitor system, the wattage load of the monitor amplifier group of transistors, the flash brilliance of a lamp in the circuit, and the ratio of useful lamp watts to all other dissipative loads, will be proportioned to satisfy the requirements of a given installation. The test resistance R8 may be made to be less than one percent of the filament resistance of an energized lamp, with appropriately high gain being provided in the monitor amplifier stage. In one actual circuit foundto be suitable, R8 had a voltage drop across its terminals during the flash interval of 0.15 volt while 6.10 volts drop was measured across the lamp filament, when operated from a nominal 6 volt supply battery having open circuit voltage, fresh, of 6.8 volts. The loss of intensity of light output of the lamp due to test resistor R8 as compared with output at the same supply voltage without R8 was observed to be slight. In this installation, during a flash interval, the ratio between watts dissipated in the lamp load and the watts taken by all other dissipative loads including TRA and TRC and the resistor R8, was as 2.93 watts to 91 milliwatts, indicating an efliciency of approximately 97%. The improvement over the prior art represented by this figure may be appreciated by considering that in the monitor circuits heretofore devised employing series or shunt electromagnetic relay detectors associated with a lamp circuit the efficiency figure has been of the order of The monitoring function described above may be realized at relatively low cost, and the resistor R8 may take any suitable form. A preferred form comprises a short length of resistance wire such as Advance, #18 B. & S. gauge, having 0.182 ohm per foot.

The reliability of a monitor device according to the invention has been found to be superior to any prior art device known to applicant, attributable for the most part to absence of moving contacts in the system, and providing that only the turret segments and axle are friction contacts, which operate at extremely low duty cycles.

A characteristic of filamentary incandescent lamps is that the waveform of lumen output with time (FIG. 3) does not coincide with the keying waveform (FIG. 2) due to the finite time or delay interval AF required for the filament to heat up to a light-emitting temperature. The delay interval is reducible by choice of a lamp with a filament of relatively small mass, but cannot be made zero. However the energization of electromagnet 20 will inherently be prevented as soon as the lamp current begins to flow, coincident with the application of the positive voltage keying wave to the stages TRA, TRB, TRC, TRD, and TRE. To safeguard the system against any possibility of an initial current spike flowing in winding 20, the wave may be deliberately delayed by an interval of at least the length AF.

A circuit for delaying application of positive potential to the monitor amplifier is shown in Figure 5 wherein stage TRD is shown having a delay capacitor C4 connected from the positive bus to the base. Charging current through the capacitor flowing inresistors R19 and R15 to negative supply effectively biasses the stage off until the capacitor has reached a degree of charge.

A practical embodiment of the invention is described with reference to FIGURES 4 and 6. A lamp turret 32 having a capacity of four lamps has its axle journalled in a frame comprising the upward extension of a casting 33 having a gear train housing closed by cover plate 55 and a back bearing plate 36-. The lamp turret assembly is supported with the frame base 37 secured to a thick disc cap 40, as by screws or other suitable fastening means, thereby securing a strap 38 to the assembly. Stud bolt means 39 passed through the ends of the strap are threadedly engaged in holes tapped into the main lamp base 10. A Fresnel type lens 11 is carried upon a sturdy metal base ring 50 having a series of captive bolts 51 spaced about the circumference, the base seating on bevelled face 49 of the lower housing. Suitable resilient sealing gasket means are provided to prevent dust and moisture from gaining entry when the bolts 51 are tightened down upon the slotted ears 52. For convenience the upper lens assembly is made to pivot upon the lower housing, hinging on pin 56 which is received in the hole 57 of the base shoulder provided.

Base may be supported in any suitable manner upon a buoy, tower, mast or other vertically extended structure, negative supply lead 14 from the battery being grounded to frame and positive lead 13 into the bore preferably through a sealing gland received in the side of the base.

A daylight-sensing photocell 34 is housed on the side of the back gear train plate 55 and is preferably shielded from direct lamp illumination as by a blackened sheet metal rectangular structure 35 built around it. The cell receives ambient illumination incident upon it as is transmitted inwards through the lens 11. When the resistance of the cell decreases sufiiciently as a result of ambient illumination, current flows from the positive supply lead 13 (see FIG. 1) through the Winding of relay M, drawing armature 59 away from contact 58 and thereby deenergizing the buss 60. It will be seen that whenever the intensity of ambient light on cell 34 remains low, buss 60 remains at positive potential to energize motor supply buss 29 and lamp supply wiper 15 in parallel via switching transistors TR5, TR6. The disabling relay M is supported on the amplifier chassis 43 which depends from the lid 40 and is hermetically enclosed in the cup 41, shown in cut-away section. O-rin'g seals are provided between the upper flaring part of can 41 and the bevelled face of lid 40, between which parts pressure is maintained when assembled, by suitable bolt means (not shown). Light flash monitor cell 17 which may be employed as an alternative control to the input of TRA as in applicants Patent 2,892,966, supported adjacent the base of the operating lamp, indicated in FIGURE 6 as lamp 12, is preferably set at an angle of 45 degrees with the vertical and facing upwardly towards the filament, so

as not to obstruct light which is radiated substantially uniformly through the equatorial plane of the lens. A sheet metal tab supporting structure 28 is suitably affixed upon the upper part of the casting 33. The series of lamps are detachably supported in any convenient manner upon the turret block 32, the support herein being indicated as pairs of screw heads 54, under which the lamp sockets are received and against which they are pressed outwardly by spring tension of the base contact.

Lamp energizing circuit leads are taken from the switching circuit by way of

binding posts

47, 48, the latter being grounded to the frame and the former being insulated and connected to suitable wiper means 15 (not shown) for contacting segments located on the turret on which the lamp filament leads terminate.

A solenoid stepping motor of conventional type is shown in FIGURE 6, operating ratchet wheel 23 by means of a pawl spring 22, wherein the turret 32 is driven by means of the gear train comprising gear 46, pinion 45,

gear 44-, and pinion 24. At each energization of wthe sole{ noid 20, the armature 21 pulls down and advances pawl 23 by one tooth distance. A lesser or a greater number of gears and other gear ratios may be used depending on the particular application in which the lamp is used. In the present instance, where the flashing rate is approxi mately 12 flashes per minute, a new lamp may be restored into the circuit in less than half a minute.

The invention extends also to motor means other than the solenoid-actuated pawl-and-ratchet stepping motor shown. The latter is preferred as completely avoiding any moving contacts, but it is to be understood as entirely an equivalent to employ a brush type D.C. powered rotary electric motor, whose shaft is linked in driving relation to turret 32 by means of a suitable gear train.

Where the number of lamps carried by the turret is small, a spring motor of only such capacity as would suffice to rotate the turret only a few revolutions and powered adequately for at least one revolution may be employed, in conjunction with a solenoid actuated brake, stop, or dog to release the stop when a new lamp is to be substitued. Such spring motors and controls are believed to be well understood and suitable devices for driving a turret may take many forms.

The invention extends moreover to devices wherein the lamp energization is intermittent but the length of a flash may be several hours or even days, provided that the means controlling the motor operation is itself powered in common with the lamp energizing circuit, so that the motor is ineffective to drive the lamp changer mechanism except in periods when the lamp is supplied with energizing current.

While the invention has been particularly described with reference to a small type of lamp used in navigational marker lights, it is applicable to a wide range of installations and extends to all signal and illuminating devices as are required to operate reliably in steady or flashing lightt generating service, on fixed installations or in vehicles such as automobiles, boats and aircraft.

I claim:

1. In a signal device having a drive mechanism for a lamp carrier to position lamps and lamp circuit terminals for connecting a positioned lamp with an intermittent supply of electric current, the improvement comprising a lamp current test resistor connected in series with said circuit producing a test voltage across the resistor proportional to lamp current, said resistor having a resistance value of from about 0.01 to about 0.08 times the resistance of said lamp circuit when a lamp is. operating an electromagnetic driving motor for operating said mechanism and having a winding, and a drive control for said driving motor connecting said supply to said winding, said control comprising the emitter-to-collector path of a transistor having a base electrode determining the conduction state of said path, a direct-coupled voltage amplifier fed from said supply and having an input and delivering its output to said base electrode, and means appliying said test voltage to said amplifier input whereby to block said emitter-to-collector path when said test voltage exceeds a predetermined value and to energize said motor winding by current through said path when said test voltage is less than said value.

2. The device of claim 1 wherein said test resistor is permanently connected between said supply and a terminal of said lamp circuit and said terminal is separably connected with the filament of a positioned lamp moved by said carrier, and said amplifier comprises a plurality of resistance coupled transistor stages in cascade having said terminal connected permanently with the base electrode of the first stage to bias said base according to the potential difference across said resistor, and wherein each stage is fed from said supply in parallel with said emittear-collector path.

3. The device of claim 2 wherein said driving motor means and said drive mechanism comprise a solenoid having an armature, a pawl carried by the armature, a

ratchet wheel engaged by said pawl, and coupled with said lamp carrier to effect a predetermined movement of said carrier upon energization from said supply, said movement being a fraction of the totalvcarrier movement required to replace a subsequent lamp in operating position.

4. In a signal device of the type comprising a carrier for a plurality of lamps moveable to position lamps sucoessively in operating position and including contact means for connecting a positioned lamp in series with a lamp energizing circuit, a solenoid drive motor for advancing said carrier, and an intermittent source of electric current for supplying said circuit and said solenoid to cause said lamp to light during a flashing period and to tend to move said carrier concurrently with said flash, the improvement which comprises control means responsive to failure of a positioned lamp efiective to cause said motor to advance said carrier until a correctly functioning lamp is in position and thereafter to hold said carrier stationary so long as said lampfunctions correctly, said control comprising a direct coupled transistor voltage amplifier including an output switching stage having a base bias circuit wherein the emitter-collector path of said stage is in series with said solenoid and said source, a voltage divider circuit comprising a two-terminal fixed resistance element connected in series with the positioned lamp in said lamp energizing circuit, the ratio of said fixed resistance to the resistance of a heated lamp filament lying in the range from about 0.01 to about 0.08, and means connecting the terminals of said fixed resistance element to apply the potential difierence therebetween as input to said amplifier, whereby to bias said base for flow of current in said path to energize said solenoid when said potential difference is less than a given value and to hold said solenoid de-energized when said difierence exceeds said value.

References Cited in the file of this patent UNITED STATES PATENTS