U.S. patent number 3,792,309 [Application Number 05/285,091] was granted by the patent office on 1974-02-12 for strobe light intensity control.
This patent grant is currently assigned to Multi Electric Mfg. Inc.. Invention is credited to Clement J. McDonald.
United States Patent |
3,792,309 |
McDonald |
February 12, 1974 |
STROBE LIGHT INTENSITY CONTROL
Abstract
A strobe light circuit in which the light intensity of the
strobe lamp is varied by adding or removing selected flash
capacitors in circuit with the lamp to increase or decrease surge
current through the lamp. The circuit connection between each of
the flash capacitors and the strobe lamp is controlled by a
double-pole, double-throw relay with a normally open relay contact
in series with the flash capacitor to enable it to charge and
discharge and a normally closed contact across the flash capacitor
to discharge it when it is not being used to provide a portion of
the surge current. Both contacts are connected at the low side of
the power line to minimize electrical arcing and are mechanically
linked together such that the conducting set of contacts always
breaks contact before the nonconducting set of contacts closes.
Intensity control switches are provided to energize the relay coils
for the selected capacitors. One flash capacitor is always
connected across the strobe lamp to maintain a minimum light
intensity, and this capacitor is discharged through a normally
closed relay contact when power for the entire circuit is
interrupted.
Inventors: |
McDonald; Clement J. (River
Forest, IL) |
Assignee: |
Multi Electric Mfg. Inc.
(Chicago, IL)
|
Family
ID: |
23092702 |
Appl.
No.: |
05/285,091 |
Filed: |
August 30, 1972 |
Current U.S.
Class: |
315/200A;
315/241S; 315/362; 315/240; 315/245 |
Current CPC
Class: |
H05B
41/34 (20130101) |
Current International
Class: |
H05B
41/30 (20060101); H05B 41/34 (20060101); H03b
041/00 () |
Field of
Search: |
;315/2A,240,241S,362,245 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Saalbach; Herman Karl
Assistant Examiner: Mullins; James B.
Attorney, Agent or Firm: Hofgren, Wegner, Allen, Stellman
& McCord
Claims
I claim:
1. In a strobe light circuit having a source of power, a strobe
lamp connected across said source of power, and means for
repetitively firing said lamp, said lamp flashing when fired with a
light intensity directly related to the magnitude of surge current
therethrough, intensity control means for varying the light
intensity of said lamp, comprising:
capacitor means connected with the source of power and said lamp
for providing at least a portion of said surge current; and
switching means including
first switch means connected in series with the capacitor means
across the lamp and source of power switchable between
non-conductive and conductive states, said first switch means when
in its conductive state providing a charging path from the power
supply to charge the capacitor and also providing a discharge path
from the capacitor to the lamp when the lamp is fired to provide a
portion of said surge current thereto, said first switch means when
in its nonconductive state removing said charging and discharging
paths to prevent the capacitor from applying a portion of said
surge current to the lamp;
second switch menas connected across said capacitor means and
switchable between non-conductive and conductive states, to enable
said capacitor to charge from said source of power when in the
non-conductive state and to dissipate any charge on said capacitor
when in the conductive state, said second switch means being
normally in a state opposite to that of said first switch means;
and
means for actuating said switch means between states, the
conductive one of said first and second switch means switching to
its non-conductive state prior to the non-conductive one of said
first and second switch means switching to its conductive
state.
2. The light intensity control means of claim 1, including means
providing a switch signal for said switch means.
3. The light intensity control means of claim 2, in which both of
said switch means are controlled by relay coil means connected with
said switch signal providing means.
4. The light intensity control of claim 3, in which said relay coil
means comprises a single relay coil for controlling both of said
switch means.
5. The light intensity control means of claim 1, in which said
first and second switch means comprise mechanical switch contacts,
none of the contacts of either of said switch means being common to
the contacts of the other of said switch means.
6. The light intensity control means of claim 1, in which said
capacitor means comprises a plurality of capacitors connected in
parallel with each other, and said switching means comprises a
corresponding plurality of pairs of first and second switches
connected with said plurality of capacitors, respectively, each of
said plurality of pairs of first and second switches selectively
controlling the connection between said lamp and the capacitor to
which it is connected, whereby the light intensity of said lamp may
be selectively varied.
7. The light intensity control means of claim 1, in which said
power source has a low voltage terminal at a reference potential
and a high voltage terminal at other than said reference potential,
and said first switch means is connected between said low voltage
terminal and one side of said capacitor means.
8. The light intensity control means of claim 7, in which said
second switch means is connected at one side thereof to the
junction between the capacitor and the first switch means and
connected at the other side thereof through an impedance means to
the other side of the capacitor, both said other side of the
capacitor and said impedance means being connected to the high
voltage terminal of said source of power.
9. The light intensity control of claim 1 including a bleeder
resistor in series with said second switch means for dissipating
any charge on said capacitor when said second switch means is in
its conductive state.
Description
BACKGROUND OF THE INVENTION
This invention relates to a strobe light circuit and in particular
to a strobe light circuit for use as part of a landing field
approach lighting system in which the light intensity must be
varied with changes in atmospheric visibility.
Airports are required to provide approach lighting systems to
indicate to landing aircraft both which runway of a plurality of
runways is to be used and the direction from which the runway is to
be approached. These approach lighting systems comprise a plurality
of strobe lamps located at the end of the runways which flash in
sequence starting at the outermost unit from the runway and
progressing inwardly toward the runway threshold. The entire
sequence may be repeated twice a second.
The FAA requires the strobe lamp circuits or flasher units to be
designed for different intensity levels with a simple control such
as a switch to effect the changeover from one intensity level to
another. Flasher units commonly utilize gaseous discharge or strobe
lamps triggered at a selected frequency, the surge current through
the lamps being supplied by discharge current from selected ones of
a plurality of flasher capacitors. The light intensity with which
the lamp flashes is directly related to the total available surge
current which, in turn, is directly related to the total
capacitance connected across the lamp. By adding and removing flash
capacitors the intensity may be increased and decreased,
respectively.
The FAA further specifies that all intensity step changing of the
flashers is to be done with the system operating but if necessary,
power to all of the flasher units may be interrupted for a period
not to exceed two seconds during intensity step changeover. This
2-second shutdown period is at variance with the general
requirement that all intensity step changing of the flashers is to
be done with the system operating and is a recognition by the FAA
of limitations in known strobe light circuits.
The FAA specifies that no arcing is to occur during any intensity
step change and to minimize arcing, all of the known prior art
devices have provided a bleeder resistor in parallel with each of
the flash capacitors which discharge the capacitors during the
two-second shutdown to a level low enough so that arcing between
switch contacts does not occur when the switches are opened to
remove the capacitor from the strobe lamp. Power shutdown has also
been required when it is desired to increase the strobe lamp light
intensity, due to electrical arcing which occurs when an uncharged
flash capacitor is coupled across the power supply and strobe
lamp.
SUMMARY OF THE INVENTION
Applicant has discovered that by placing the switch contact between
the low side of the power supply and the capacitor rather than
between the high side of the power supply line and the capacitor,
electrical arcing between switch contacts is substantially reduced.
Thus, the requirement for a power shutdown to change intensity
levels may be eliminated.
In accordance with the invention, the flash capacitors are coupled
at one end to the high voltage or ungrounded side of the power
supply. The other side of the capacitor is coupled through a
normally open relay contact, i.e., a relay contact which is open
when the relay coil is unenergized, to the low side of the power
supply line or ground, and the junction between the normally open
relay contact and the capacitor is coupled to one side of a
normally closed relay contact, i.e., a relay contact which is
closed when the relay coil is unenergized. The other side of the
normally closed relay contact is coupled through a bleeder resistor
to the one side of the capacitor connected to the high voltage line
of the power supply. Both sets of relay contacts are controlled by
a common relay coil and are arranged such that the closed contact
always breaks its connection prior to the open contact closing.
While although a single-pole, double-throw relay switch contact
could be utilized in place of the two separate sets of relay
contacts, applicant has discovered that the operating life of each
set of contacts of the single-pole single-throw relay is
substantially greater than the contact life of a single-pole,
double-throw relay switch.
A principal object of the present invention is the provision of a
variable intensity strobe light circuit in which the intensity may
be changed without removing power from the unit to add or remove
flash capacitors.
Another object of the present invention is to provide a variable
intensity strobe light circuit in which the switch contacts for
controlling the circuit connections between the flash capacitors
and the strobe lamp are coupled between the low voltage side of the
power supply and the flash capacitors, thereby substantially
reducing arcing during switching.
A further object of the present invention is to provide a variable
intensity strobe light circuit in which separate sets of contacts
are utilized for discharging the flash capacitors and for adding or
removing from flash capacitors across the strobe lamp, thereby
increasing the operative life of the unit.
BRIEF DESCRIPTION OF THE DRAWING
Further features and advantages of the invention will be apparent
from the following description taken in connection with the
accompanying drawing, which is a circuit schematic of a preferred
embodiment of the variable intensity strobe light circuit of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, a circuit schematic of a preferred
embodiment of the strobe light circuit of the present invention is
shown in which a gaseous discharge or strobe lamp 10 is
repetitively fired in response to application of trigger signals
applied to its firing electrode 12.
Strobe lamp 10 has a cathode 32 coupled to a low voltage side or
terminal 16 of a DC power supply, generally designated by reference
numeral 18, which is connected to ground reference potential at 20,
and an anode 34 coupled to a high voltage side 26 of power supply
18. Each time a trigger pulse is applied to firing electrode 12,
strobe lamp 10 breaks down and momentarily conducts a surge current
from anode 34 to cathode 32. The intensity with which strobe lamp
10 lights is directly related to the magnitude of the surge current
which, in turn, is directly proportional to the amount of
capacitance coupled across strobe lamp 10 between its anode 34 and
cathode 32.
The surge current is supplied from power supply 18, a minimum
intensity level flash capacitor 36 and a selected one or both of
flash capacitors 38 and 40. Flash capacitor 36 is always coupled
across strobe lamp 10 and thus provides the minimum surge current
corresponding to the lowest intensity level. During the period
between flashes of lamp 10, flash capacitor 36 charges from DC
power supply 18, and when lamp 10 is fired it discharges through
the lamp thereby providing the necessary surge current.
Flash capacitors 38 and 40 operate in an identical fashion as flash
capacitor 36 when they are connected across lamp 10 through their
respective normally open, relay contacts RL2-1, controlled by relay
coil RL2, and RL3-1, controlled by relay coil RL3. These normally
open, relay contacts are coupled between the low voltage side 16 of
power supply 18 and their associated capacitors to minimize
arcing.
To discharge capacitors 38 and 40 two bleeder resistors 42 and 44
are provided. Bleeder resistor 42 is coupled across flash capacitor
38 through normally closed relay contacts RL2-2, controlled by
relay coil RL2, and bleeder resistor 44 is coupled across flash
capacitor 40 through normally closed relay contacts RL3-2 which are
controlled by relay coil RL3. The normally closed relay contacts
are connected to the low voltage side of their respective
capacitors to minimize arcing between the relay contacts.
The light intensity may be remotely controlled by selectively
energizing relays RL2 and RL3 by means of intensity control switch
46. Intensity control switch 46 is preferably a two section, three
position rotary switch with sections 47 and 48, each having a
rotary contact switchable between three stationary contacts
designated Lo, Mand H for low, medium and high intensity. The
rotary contact of both sections is coupled at one side to a
suitable source of relay power V.sub.R. The medium and high
position contacts of section 47 are coupled to relay coil RL2, and
the high position contact of section 48 is coupled to relay coil
RL3. When switch 47 is in the Lo position as shown in the drawing,
neither relay is energized and the surge current is provided solely
by flash capacitor 36 and power supply 18 which corresponds to the
lowest intensity level. With switch 47 in the M position, relay RL2
is energized to open normally closed relay contact RL2-2 to remove
the shunt circuit across capacitor 38 and to close relay contact
RL2-1 to connect flash capacitor 38 across lamp 10 and power supply
18. The two sets of contacts of both relays RL2 and RL3 are
designed such that the conducting set of contacts, i.e., the
contacts which are in a closed position, always open before the
other contact closes. This is necessary to prevent shorting which
would otherwise occur. With relay RL2 energized, surge current is
supplied by both flash capacitors 36 and 38, and the strobe lamp
flashes at a medium intensity level. With switch 46 in the H
position, both relays RL2 and RL3 are energized and surge current
is supplied by all three flash capacitors to flash strobe lamp 10
at the highest intensity level.
Power for the circuit may be provided by any suitable AC power
source 54, such as the 60 hertz, 110 or 220 VAC current. The
requisite DC voltage may be obtained by means of a step-up
transformer 56, the secondary winding output of which is rectified
by a full wave rectifier circuit 58.
To discharge capacitor 36 when power is removed, a bleeder resistor
60 is provided. Bleeder resistor 60 is coupled across capacitor 36
through a normally closed relay contact RL4-1 that is controlled by
a relay coil RL4 which, in turn, is coupled across the AC source
through a single-pole, double-throw power switch 62. When switch 62
is closed, relay RL4 is energized and the normally closed relay
contact RL4-1 opens to remove the bleeder capacitor 60 from across
flash capacitor 36. However, when power is removed, normally closed
relay contact RL4-1 reverts to its normally closed position to
shunt capacitor 36 which discharges through bleeder resistor
60.
The trigger signals at firing electrode 12 are generated in
response to corresponding trigger signals developed from a suitable
trigger source 14 which repetitively energizes single-pole,
double-throw relay RL1. One side of the relay contact of relay RL1
is coupled to the low voltage terminal side 16 of DC power supply
18. The other side of the relay contact is coupled to a junction
between two resistors 22 and 24 which are connected in series
across power supply 18 between the low voltage side 16 and high
voltage side 26 of power supply 18. The junction between resistors
22 and 24 is coupled, in turn, to firing electrode 12 through a
coupling capacitor and a step-up autotransformer, generally
designated by reference numeral 30, having a coil portion 31 and a
coil portion 33. Each time the contacts of relay RL1 open,
capacitor 28 is charged, and when the contacts of relay RL1 close,
capacitor 28 is discharged through autotransformer coil portion 33
which induces a high voltage across autotransformer 30 that is
applied between firing electrode 12 and cathode 32.
* * * * *