US3925704A

US3925704A - Lighting system with variable flashing rate

Info

Publication number: US3925704A
Application number: US517601A
Authority: US
Inventors: Donald L Camic
Original assignee: Hughey and Phillips Inc
Current assignee: Hughey and Phillips Inc
Priority date: 1974-10-24
Filing date: 1974-10-24
Publication date: 1975-12-09
Anticipated expiration: 1992-12-09

Abstract

A novel flashing light system for use on airport runways, or the like, is provided in which variable flashing rates for the lamps in the system are achieved with the use of an all-solid-state master timer. Particular circuits, including integrated digital count down circuits, which may be used to supply pulses to the lights in the system at selectable rates, are provided. In addition, the transient-sensitive semiconductor circuits which generate the control pulses are isolated from the lines which feed trigger pulses to the power supplies for the respective strobe lights, such isolation being accomplished by reed relays, optical couplers, or the like.

Description

Camic LIGHTING SYSTEM WITH VARIABLE FLASHING RATE Dec. 9, 1975 Primary Examiner.lames B. Mullins Attorney, Agent, or FirmBruce L. Birchard [75} Inventor: Donald L. Camic, Granada Hills,

Calif.

{'31 Assignee: Hughey and Phillips, Inc., Burbank, [57] ABSTRACT Calif. A novel flashing light system for use on airport runaw i [u] Flled' 1974 ways, or the like, is provided in which variable flashing [2 l] Appl, No.: 517,601 rates for the lamps in the system are achieved with the use of an all-solid-state master timer. Particular cir cuits, including integrated digital count down circuits [52] 3 5 which may be used to supply pulses to the lights in the l t C12 {40/82 system at selectable rates, are provided. In addition. 5/00 the transient-sensitive semiconductor circuits which g j 3 41 generate the control pulses are isolated from the lines g g}? 2 which feed trigger pulses to the power supplies for the 328/6 75 respective strobe lights, such isolation being accom References Cited plished by reed relays, optical couplers, or the like.

UNITED STATES PATENTS 17 Claims, 5 Drawing Figures $488,553 l/l97ll Grafton 4 4 4 i 4 v Y v i 4 i BIS/360 X l2 l2 l2 2 lO 7 1 J- l6 l6 l6 2O 2O 2 2o 2t f r l L 2 5- J I 2 4 O VAC, 4

US. Patent Dec. 9, 1975 Sheet 1 of 3 3,925,704

240 VAC IZOVAO US. Patent Dec. 9, 1975 Sheet 3 Of3 3,925,704

A. 2 2 c o m 9 m m x I m,

w .I .2 ML i \J 6 MR W QKB I M 4 $1. m 8 6 l m m a F w a B 1 5 +111 LIGHTING SYSTEM WITH VARIABLE FLASHING RATE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to lighting systems in which the lights of the system are flashed in sequence, for example, an airport runway lighting system.

2. Description of the Prior Art The Federal Aviation Agency of the United States Government (FAA) has long set certain specifications for the lighting of airport runways. This is particularly true at the threshold and the temiinus of the runway where a combination of steadily running and flashing lights is specified. The invention herein is particularly related to the flashing lights or strobe lights which are utilized in such applications (although this invention may be applied in other fields). The acronym REIL, which stands for runway end identifier light", has be come widely used in this field to designate any light involved in such systems. Various combinations of steady and flashing lights are specified by the FAA, the particular specification varying with the size and extent of use of the airport. In one configuration a set of REILS provides two flashing lights near the end of the runway, located in line with the runway threshold, 40 feet to each side of the runway edge lights. There is a series of steady lights aligned with each other and with the REILS at the threshold of the runway. In another application the FAA has designated the specifications for an omni-directional lead-in approach lighting system. Such a system consists of seven strobe lights located in the approach area of the runway. Five of these strobe lights are located on the extended runway center line starting 300 feet from the runway landing threshold and being placed at 300 foot intervals up to and including I500 feet in front of the runway threshold. The remaining two strobe lights are located on the sides of the runway landing threshold. The strobe lights flash in sequence toward the runway at a rate of, in one instance, once per second with the two strobe lights located at the sides of the runway landing threshold flashing simultaneously with each of the lead-in lights.

For different applications, the time lapse between the firing of the strobe lights in a sequence differs. Also, under differing weather conditions the rate of flashing may be varied to achieve optimum viewability by the pilot of an approaching aircraft. In the past, variations in the sequencing rate of successive strobe lights in the lighting system was difficult because the sequential flashing was achieved by electromechanical means. For example, in prior art master timers the sequencing of the strobe lights was achieved by means of cams and metal contacts activated thereby or by means of reed switches actuated by one or more motor-driven permanent magnets. The motor normally utilized was a synchronous motor and its speed was not adjustable to achieve a range of desired sequential flashing rates. Further, there was a normal degradation in the operation of the system with time as a result of the wearing of the moving parts, such as those in the synchronous motor. There were the usual additional problems caused by heat generated by the synchronous motor and its associated circuits.

None of the prior art known to applicant provides the flexibility, compactness and reliability which has been achieved by applicants invention.

Accordingly, it is a general object of the present invention to provide an improved lighting system with sequentially flashed lights.

It is a further object of the present invention to provide an airport runway approach lighting system capable of performing the desired functions involved in approach lighting in an improved and efficient manner.

It is a more specific object of the present invention to provide an airport runway approach lighting system and apparatus therefore having improved flexibility and reliability.

SUMMARY OF THE INVENTION In brief, apparatus in accordance with the present invention derives timing pulses from the power line (which for the purposes of this discussion will be considered to be operating at 60 Hz). The timing pulses at the 60 pulses per second rate are fed to one section of a hex inverter, a commonly available integrated circuit component. The output terminal of the inverter is fed to three additional circuit points. The first of these is the 1/60" position on a selector switch. The second of these points is an input terminal on a dual-D type flip flop which divides the pulse rate by two at one of its output terminals and by four at a second of its output terminals. The first of its output terminals is connected to the 1/30 position on a selector switch and the second output terminal is connected to the 1/15 position on that same selector switch. That selector switch permits the choice of a desired sequential flashing interval.

The third output path from the hex inverter section goes to a decade counter dividing circuit which divides the pulse rate by 30 and produces a reset pulse for the main decade counter. As a result the strobe light flashing sequence is commenced two times per second. As has been indicated, the control of the time interval between the firing of successive strobe lights in a sequence may be selected by a selector switch. The output of the selector switch is fed to the main decade counter which provides output pulses, in sequence, at each of its output terminals, the number of those output terminals corresponding to the number of lights to be flashed, plus one. Transistorized buffer amplifiers between the output terminals of the decade counter and a respective one of a group of reed relays corresponding in number to the number of strobe lights to be flashed, cause the reed relays to be activated sequentially and those reed relays couple AC or DC trigger pulses to the power supplies of the strobe lights in sequence, causing the strobe lights to be fired. By merely adjusting the selector switch, the time between successive flashes of the sequentially flashed strobe lights can be changed to meet the particular requirements in a given application. Circuits in the master timer automatically generate reset pulses which cause the entire cycle of sequential light energization to be repeated.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the present invention may be had from a consideration of the following detailed description, taken in conjunction with the accompanying drawings in which:

FIG. I is a block diagram showing a system in accordance with the present invention;

FIG. 2 (A & B) is a diagram, partially in schematic form and partially in block form, of one form of the master timer portion of the system of FIG. I.

3 FIG. 3 is a diagram, partially in schematic form and partially in block form, showing one form of trigger voltage coupling circuit; and

FIG. 4 is a diagram. partially in block form and partially in schematic form showing an additional circuit for coupling trigger voltages to lamps to be flashed.

DESCRIPTION OF THE PREFERRED EMBODIMENT 1n PK}. 1, a variable flash rate lighting system includes a plurality of Xenon flash lamp heads 12, each flash lamp head including a Xenon flash lamp, a stepup pulse transformer and a condenser discharge circuit coupled to the primary of the pulse transformer, all of which are not shown because they are well known in the art. The DC current for charging the condenser is provided through a conductor 18 from a combination control box and power supply 20. A conductor 16 provides a selected trigger pulse from each control box to its associated flash lamp head 12. Each control boxpower supply 20 includes a selector switch, not shown, which makes it possible to choose which of eight trigger pulses, for example, from master timer 14 is chosen to fire the flash lamp associated with a respective control box 20. As a result, the sequence of flashing of the respective lamps can be changed to provide any desired order. The respective conductors 16 may carry control pulses of 90 volt amplitude, for example, with the voltage applied to the Xenon lamps in the respective heads 12 approximating 30,000 volts. Operating voltage for each control box-power supply 20 is derived from a power line source, such as a 240 VAC power line, through terminals 21 and a pair of conductors represented by a cable 22 feeding each power supply 20. The master timer 14 supplies sequenced trigger pulses through a multiple-wire cable 24, a multiple-wire bus 25 and a plurality of

control pulse cables

26, 28, and 32 which are fed from the bus 25 out of a plurality of

junction boxes

34, 36, 38 and 40 and, in turn, feed respective ones of the control-box-power supplies 20. Operating power for the master timer 14 may be derived from a 120 volt or 240 volt AC line source through a power cable 42.

The heart of the lighting system according to this invention is in the master timer 14 which eliminates the inflexible and relatively unreliable electromechanical sequencing systems of the prior art. The details of the master timer 14 are set forth in FIG. 2 (A & B). In FIG. 2 (A & B), operating AC power for the master timer 14 is supplied through a pair of

terminals

44 and 46. For example, this may be 120 volts AC. That power is supplied through a power transformer 48 which has a pair of secondary windings 50 and 52. The AC voltage appearing across the secondary 50 is rectified in conventional fashion to provide an output voltage approximating 120 volts DC at a pair of

terminals

54 and 56. The output voltage appearing across the secondary 52 is rectified in conventional fashion and provides the positive operating voltage appearing at a terminal 60. A terminal 58 is at ground potential with respect to the terminal 60 and the terminal 54. The AC voltage appearing at a terminal 62 is coupled through a diode 64 into a first inverter section of a hex inverter 66. The hex inverter 66 is an integrated circuit having six inverters on a single chip. The effect of diode 64 is to pass only the positive half of the sine have voltage supplied to it. as a result of which tuning pulses at 60 pulses per second are supplied to the first 111\L1'1tl section in hex inverter 66. The output signal from the first section of inverter 66 appears at a terminal 68. That signal appearing at the terminal 68 is coupled to three other points in the circuit of master timer 14. First, the output signal appearing at the terminal 68 is fed through a conductor 70 and a conductor 72 to a first terminal 74 of a selector switch 76, that selector switch 76 permitting a selection of the time between sequential flashes of the successive strobe lights in the approach lighting system. Output signals from the selector switch 76 appear on an output line 78. The time between successive pulses on the output line 78 when a switching arm 80 is in contact with the terminal 74 is 1/60 of a second. Output signals from the terminal 68 are also fed through the conductor 70 and a conductor 82 to a terminal 84 of an integrated circuit 86 known in the trade as a dual D" type of flip flop. At an output terminal 88 of dual D flip flop 86, output pulses are produced at a pulse rate which is onehalf of the pulse rate of the signal applied to the terminal 84. That is, pulses appear at the terminal 88 every l/30 of a second. Those pulses at l/30 of a second pulse rate are fed from the output terminal 88 to a second terminal 90 of the selector switch 76. The pulses appearing at the output terminal 88 are also fed to a terminal 92 of a second flip flop section 94 in the dual D flip flop 86. As a result of the flip flop action of the second section 94, output pulses appear at an output terminal 96 at a separation of l/l5 of a second. Those pulses at 1/15 of a second spacing are fed from the output terminal 96 to a third terminal 98 of the selector switch 76.

The third path for output pulses from the first section of the hex inverter 66 is from the output terminal 68 through a conductor 100 to a terminal 102 of a decade counter 104 which divides the number of pulses per second appearing at output terminal 68 by a factor of ten and produces an output pulse train at a rate of six pulses per second at a terminal 106 of the decade counter 104. The pulses at six pulses per second are fed from the output terminal 106 to an input terminal 108 of a second decade counter 110, the function of which is to divide its input pulse rate by three, thus producing an output pulse two times per second at an output terminal 112. The output pulse from the output terminal 112 is fed through a conductor 114 to an input terminal 116 of a positive NAND gate 118. Similarly, a pulse is taken from an output terminal 120 of the decade counter 104 and fed to an input terminal 122 of the NAND gate 118. Output pulses from the NAND gate 118 are taken from a terminal 124 and fed by way of a conductor 126 to an input terminal 128 of a second portion of hex inverter 66 at an output terminal 130 of which a reset pulse is derived and fed via a conductor 132, a conductor 134 and a conductor 136 to a pair of

reset terminals

138 and 140 on the dual D type flip flop integrated circuit 86. That same reset pulse from the output terminal 130 is supplied by the conductor 134 to a reset terminal 141 of a flip flop 142. It should be noted that the divide by 30 circuit made up of the decade counters 104 and 110 resets itself by reason of an output pulse taken from an output terminal 144 on the decade counter 110, that output pulse being fed by way of a conductor 146 to a reset terminal 148 on the decade counter 110 and a reset terminal 150 on the de cade counter 104.

As has been indicated, the selector switch 76 deter mines the sequential interval for the strobe lights in the system When the switch arm 80 is in contact with the terminal 74, as shown, pulses at the rate of 60 pulses per second are fed through the conductor 78 to an input terminal 152 of the decade counter 139. Output pulses in sequence, occur at a plurality of

output terminals

154, 156, 158, 160, 162, 164, 166, 168 and 170. The output pulses appearing at the first eight of those terminals (being eight sequential pulses spaced by U60 of a second) are fed to buffer transistors as will be described hereinafter. For purposes of clarity, only four of the eight buffer transistors and subsequent circuits are shown in FIG. 2. The buffer circuits and the circuits which follow are identical in configuration. This limitation in number to four buffer transistors and circuits following those transistors corresponds to the limitation in FIG. 1 of the number of strobe lights and power supplies to four, although the actual system contemplated herein was designed for eight strobe lights. it should be understood that the circuits following the

output terminals

158, 160, 162 and 164 are identical with the circuits shown following the

output terminals

154, 156, 168 and 170.

The output pulse from the terminal 154 is fed through a current limiting resistor 172 to the base of a buffer transistor 174 the collector of which is connected to one terminal 176 of a coil 178 in a reed relay 180. A second terminal 182 of the coil 178 in the reed relay 180 is connected to a positive voltage bus 184. Similarly, the output terminal 156 is coupled through a current limiting resistor 186 to the base of a buffer transistor 188 the collector of which is connected to a terminal 190 on a coil 192 of a second reed relay 194. A remaining terminal 196 of the coil 192 is connected to the positive voltage bus 184. The terminal 166 is coupled through a current limiting resistor 198 to the base of a transistor 200, the collector of which is cou pled to a terminal 202 of a coil 204 in a reed relay 206. A remaining terminal 208 of the coil 204 is coupled to the positive voltage bus 184. The output terminal 168 is coupled through a current limiting resistor 210 to the base of a buffer transistor 212 the collector of which is connected to a terminal 214 on a coil 216 of a reed relay 218. A remaining terminal 220 of the coil 216 is coupled to the positive voltage bus 184. The output pulses appearing at the terminals 154-168 are positive in polarity and as each of these pulses is provided, in sequence, to its associated buffer transistor, for exam--

ple transistors

174, 188, 200 and 212, each of these transistors saturates momentarily and, as a result, the collector of each of the transistors is brought to within a few hundred millivolts of ground potential with the result that current flows, in sequence, through the successive reed relay coils 178, 192, 204 and 216, for example. When that current flow occurs in the relay coils the

respective contacts

222, 224, 226 and 228, for example, close momentarily permitting current from a trigger voltage line 230 to flow, in sequence, for the period of the closure to a plurality of

pulse output terminals

232, 234, 236 and 238.

The ninth pulse from the decade counter 139 is taken from the output terminal 170 and coupled through a connector 240 to an input terminal 242 on the flip flop 142. The appearance of the ninth pulse from the decadc counter 138 at the input terminal 242 causes the flip flop 142 to produce, at an output terminal 244, a positive voltage which is coupled through a connector 245 to an input terminal 247 on the decade counter 139. That positive voltage at the terminal 247 stops or inhibits the counting by decade counter 138 until it til reset pulse arrives at the terminal 137 of counter 139. As has been indicated, the reset pulse also resets the flip flop 142 and the dual flip flop 86. A plurality of

diodes

246, 248, 250 and 252 prevent voltage transients from appearing on the low voltage bus 184 as a result of the closure of the trigger-pulsecarrying contacts in the reed relays.

An indicator, such as an LED 254 may be connected to each of a plurality of

terminals

256, 258, 260 and 262 and the corresponding terminals of any remaining strobe light triggering circuits in the system to indicate that each of the strobe light power supplies is receiving a trigger pulse from the master timer 14.

In some applications it may be desirable to replace the reed relays with electronic circuits for coupling pulses out of the master timer 14 to the strobe lamp ignition circuits to be controlled. FIG. 3 represents one such circuit including a variation. In FIG. 3, output signals from

terminals

154, 156, 166 and 168 of decade counter 139 pass to opto-

isolators

270, 272, 274 and 276, and any additional opto-isolators required for the numbers of trigger pulses generated, in this case eight. As the trigger pulses excite the light-emitting

diode portions

278, 280, 282 and 284 of the opto-isolators output pulses appear on

connectors

286, 288, 290 and 292, respectively because of the lightto-electrical energy conversion by

elements

294, 296, 298 and 300 of the isolators. isolator 276 differs from

isolators

270, 272 and 274 in that it incorporates a triac section including element 300 and has an AC potential applied to the triac section through conductor 302. As a result isolator 276 puts out an AC pulse on connector 292 as contrasted with the DC pulses appearing on

conductors

286, 288 and 290.

in FIG. 4 an additional method for achieving AC pulse output with electrical isolation from the decade counter 139 is shown.

Pulse transformers

310, 312, 314 and 316 apply pulses from counter 139, as amplified by

drivers

174, 188, 200 and 212, to

triacs

318, 320, 322 and 324, respectively, which results in the gating of AC pulses from terminal 326 to

output terminals

232, 234, 236 and 238, respectively. These pulses are available as trigger pulses for the lamp ignition circuits in lamp heads 12.

Although there has been described hereinbefore a particular circuit for a lighting system with variable flashing rate in accordance with this invention for the purpose of illustrating in a manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications. variations or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention as defined in the appended claims.

What is claimed is:

1. A lighting system with variable flashing rate, said system including;

at least one strobe light,

a trigge rable ignition circuit coupled to said strobe light: and

a master timer coupled to said ignition circuit, said timer including:

a trigger-control-signal input tenninal adapted for the application of a trigger control signal thereto; at least one trigger-signal-output terminal;

a first source of pulses at a rate corresponding to the frequency of a master source;

a second source of pulses at l/rr of the rate of pulses from said first pulse source;

a third source of pulses at Van of the rate of pulses from said first pulse source;

selector switch means having an output terminal and having a plurality of fixed contacts connected, respectively, to said first source of pulses, said second source of pulses and said third source of pulses and having a switch arm movable, selectively, to each of said fixed contacts for providing, at the output terminal of said selector switch, pulses at a rate corresponding to the rate of the pulses at the fixed contact to which the switch arm is selectively moved;

a first decade counter having input and output terminals, one of said input terminals being coupled to said output terminal of said selector switch to receive pulses therefrom at a rate selected by the positioning of said switch arm with respect to said fixed contacts, said output terminals of said first decade counter having thereon, in sequence, pulses spaced in time according to the position of said switch arm in said selector switch; and

switching means coupled to said output terminals of said first decade counter and responsive to the sequential pulses therefrom to produce at said at least one trigger-signaboutput terminal trigger-signals, in sequence.

2. Apparatus according to claim 1 in which said switching means includes a plurality of transistors each driving a respective reed relay.

3. Apparatus according to claim 1 which includes, in addition, means for resetting said first decade counter at the conclusion of a predetermined number of counts thereby.

4. Apparatus according to claim 3 in which said predetermined number of counts is eight.

5. Apparatus according to claim 1 in which said means for providing pulses at U11 and /zn of the line rate includes a dual D flip flop.

6. Apparatus according to claim 3 in which said means for resetting said first decade counter includes means for dividing said line pulse rate by 30.

7. Apparatus according to claim 6 in which said means for dividing said line pulse rate by includes at least one additional decade counter.

8. Apparatus according to claim 3 which includes, in addition, means for inhibiting the counting of the first decade counter beyond a predetermined count, said inhibiting means being coupled between an output terminal and an inhibiting terminal of said first decade counter.

9. Apparatus according to claim 8 in which said inhibiting means includes a flip flop.

8 10. Apparatus according to claim 9 in which said inhibiting means is coupled to said means for resetting said first decade counter.

ll. Apparatus according to claim 1 in which said master source is the local power line.

12. Apparatus according to claim 1 in which said switching means includes opto-isolators.

13. Apparatus according to claim 1 in which said switching means includes at least one triac.

14. Apparatus according to claim 1 in which said trigger signals are AC pulses.

15. Apparatus according to claim 1 in which said trigger signals are DC pulses.

16. Apparatus according to claim 1 in which n equals two.

17. A lighting system with variable flashing rate, said system including:

at least one strobe light;

a triggerable ignition circuit coupled to said strobe light; and

a master timer coupled to said ignition circuit, said timer including;

a trigger-control-signal input terminal adapted for the application of a trigger control signal thereto;

at least one trigger-signal-output terminal;

a second source of pulses at l/n of the rate of pulses from said first pulse source;

selector switch means having an output terminal and having a plurality of fixed contacts connected, respectively, to said first source of pulses and said second source of pulses having a switch arm mov able, selectively, to each of said fixed contacts for providing, at the output terminal of said selector switch, pulses at a rate corresponding to the rate of the pulses at the fixed Contact to which the switch arm is selectively moved;

a first decade counter having input and output termi nals, one of said input terminals being coupled to said output terminal of said selector switch to receive pulses therefrom at a rate selected by the positioning of said switch arm with respect to said fixed contacts, said output terminals of said first decade counter having thereon, in sequence, pulses spaced in time according to the position of said switch arm in said selector switch; and

switching means coupled to said output terminals of said first decade counter and responsive to the sequential pulses therefrom to produce at said at least one trigger-signal-output terminal trigger-signals, in sequence.

Claims

1. A lighting system with variable flashing rate, said system including: at least one strobe light; a triggerable ignition circuit coupled to said strobe light: and a master timer coupled to said ignition circuit, said timer including: a trigger-control-signal input terminal adapted for the application of a trigger control signal thereto; at least one trigger-signal-output terminal; a first source of pulses at a rate corresponding to the frequency of a master source; a second source of pulses at 1/n of the rate of pulses from said first pulse source; a third source of pulses at 1/2 n of the rate of pulses from said first pulse source; selector switch means having an output terminal and having a plurality of fixed contacts connected, respectively, to said first source of pulses, said second source of pulses and said third source of pulses and having a switch arm movable, selectively, to each of said fixed contacts for providing, at the output terminal of said selector switch, pulses at a rate corresponding to the rate of the pulses at the fixed contact to which the switch arm is selectively moved; a first decade counter having input and output terminals, one of said input terminals being coupled to said output terminal of said selector switch to receive pulses therefrom at a rate selected by the positioning of said switch arm with respect to said fixed contacts, said output terminals of said first decade counter having thereon, in sequence, pulses spaced in time according to the position of said switch arm in said selector switch; and switching means coupled to said output terminals of said first decade counter and responsive to the sequential pulses therefrom to produce at said at least one trigger-signal-output terminal trigger-signals, in sequence.

5. Apparatus according to claim 1 in which said means for providing pulses at 1/n and 1/2 n of the line rate includes a dual D flip flop.

7. Apparatus according to claim 6 in which said means for dividing said line pulse rate by 30 includes at least one additional decade counter.

10. Apparatus according to claim 9 in which said inhibiting means is coupled to said means for resetting said first decade counter.

11. Apparatus according to claim 1 in which said master source is the local power line.

14. Apparatus according to claim 1 in which said trigger signals are AC pulses.

15. Apparatus according to claim 1 in which said trigger signals are DC pulses.

16. Apparatus according to claim 1 in which n equals two.

17. A lighting system with variable flashing rate, said system including: at least one strobe light; a triggerable ignition circuit coupled to said strobe light; and a master timer coupled to said ignition circuit, said timer including; a trigger-control-signal input terminal adapted for the application of a trigger control signal thereto; at least one trigger-signal-output terminal; a first source of pulses at a rate corresponding to the frequency of a master source; a second source of pulses at 1/n of the rate of pulses from said first pulse source; selector switch means having an output terminal and having a plurality of fixed contacts connected, respectively, to said first source of pulses and said second source of pulses having a switch arm movable, selectively, to each of said fixed contacts for providing, at the output terminal of said selector switch, pulses at a rate corresponding to the rate of the pulses at the fixed contact to which the switch arm is selectively moved; a first decade counter having input and output terminals, one of said input terminals being coupled to said output terminal of said selector switch to receive pulses therefrom at a rate selected by the positioning of said switch arm with respect to said fixed contacts, said output terminals of said first decade counter having thereon, in sequence, pulses spaced in time according to the position of said switch arm in said selector switch; and switching means coupled to said output terminals of said first decade counter and responsive to the sequential pulses therefrom to produce at said at least one trigger-signal-output terminal trigger-signals, in sequence.