Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
PHN 6873
1040700
The invention relates to an arrangement provided
with at least two series-arranged combustion flash bulbs
which bulbs can be ignited one after the other and in
which each of the bulbs includes a heating wire and an ig-
nition paste, a means being provided in at least one bulb
to render the internal resistance of said bulb one ohm at
a maximum after flashing, the thermal capacities of the
heating wires of the bulbs being substantially equal.
The thermal capacity of the heating wire is
understood to mean the energy (for example, expressed in
wattsecond or in joule) to be produced with an electrical
current through this heating wire in order to raise the
temperature of this wire by one degree Celsius.
In the said flash bulbs it is important how much
energy must be produced to bring the heating wire from the
ambient temperature to the ignition temperature of the ig-
nition paste.
Since the time interval between the initiation
of the current through the heating wire and the moment of
reaching the ignition temperature of the ignition paste is
very short~ namely in the order of 0.5 millisecond, the
heat conducted away from the thin heating wires commonly
used for this purpose is negligibly small during this time
interval. This means that the required energy for bringing
the heating wire from the ambient temperature (room
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PHN 6873
1040700
temperature) to the ignition temperature of the
ignition paste is substantially equal to the product of
the above-mentioned thermal capacity and the difference
between the said ignition temperature and the ambient
temperature.
A known arrangement of the kind mentioned above
is described, for example, in applicant's Canadian
Patent No. 906,564 issued August 1, 1972.
A drawback of the said known arrangement is that
prior to flashing the greater part of the heating wires
of the bulbs is to be shunted by branches which have
a relatively low resistive value. This is necessary
to provide the next bulb to be flashed with current.
This, however, makes the electrical circuit of the known
arrangement complicated.
The invention has for its object to provide an
arrangement of the kind described in the preamble which
does not have the said drawback or has this drawback
to a lesser extent.
According to the invention an arrangement provided
with at least two series-arranged combustion flash bulbs
in which said bulbs can be ignited one after the other
and in which each of the bulbs includes a heating wire
and an ignition paste, while a means is present in at
least one bulb to render the internal resistance of
said bulb one ohm at a maximum after flashing and
the termal capacities of the heating wires of the bulbs
being substantially equal, is characterized in that
PHN 6873
1040700
prior to flashing the resistive values of the heating wires
of the bulbs are different and this in such a manner that
- when arraying the bulbs in accordance with a decreasing
resistance - the heating wire of a subseguent bulb is
60 % at a maximum of the resistance of the heating wire of
the preceding bulb.
An advantage of this arrangement is that the elec-
trical circuit thereof may be very simple. In fact, this
circuit may only consist of a series arrangement of the
relevant bulbs, while the connection conductors substantially
do not include any further resistors.
A supply source is of course also required. It
may consist of, for example, a battery whose terminals are
connected by the said series arrangement of bulbs. However,
this leads to very fast successive flashing of the bulbs
which may be desired, for example, for stroboscopic purposes.
Due to the higher thermal development the bulb including the
heating wire which had the highest resistance flashes first
and subsequently the bulb flashes which includes the
heating wire having the highest resistance but one, etc.
It is to be noted that it is known per se to
give the flash bulbs of an arrangement provided with some
flash bulbs a different resistance, for example, from
United States Patent Specification 3,518,487. In this case,
however, a parallel arrangement of bulbs was concerned in
which external resistors had been added to each bulb.
In a preferred embodiment according to the in-
; vention, which is provided with a supply capacitor
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PHN 6873
lV4~)700
chargeable with an auxiliary device the capacitance of the
supply capacitor has been chosen to be so low that the
residual charge still present after flashing of a bulb in
this supply capacitor corresponds to a quantity of energy
which after multiplication by Rh is smaller than the energy
required at that moment to ignite the remaining unflashed
bulb having the highest resistance in the arrangement,
where:
Rh is the resistive value of the heating wire of the said
unflashed bulb having the highest resistance and
Rt is the total resistive value of the discharge circuit
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of the supply capacitor.
Rt also includes the possible internal resistance
;l of the supply capacitor.
lS An advantage of this preferred embodiment is
that no double flashing (that is to say: two bulbs flashing
almost simultaneously) can occur. This is advantageous when
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taking photographs.
The different resistive values of the flash
bulbs (prior to flashing) may be realised, for example,
by using a plurality of parallel-arranged heating wires
in the bulbs in which, for example, the length of the
heating wires is shortened to maintain the thermal capacity
constant. These wires may then be made of, for example,
the same material, but in one bulb of the arrangement
the number of parallel heating wires may be chosen to be
- different from that in other bulbs of the arrangement. In-
stead of several parallel heating wires it is of course
,
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1040700
alternatively possible to use one heating wire having a larger
thickness.
In a further special embodiment of an arrangement ac-
cording to the invention the material of the heating wire of
a bulb is different from the materials of the heating wires of
the other bulbs.
An advantage thereof is that one heating wire which
is not too thick may be sufficient for each bulb. This sim-
plifies the manufacture of the bulbs.
In a very special embodiment of an arrangement ac-
cording to the invention the heating wire of one bulb is made
of an alloy known under the trade mark "kanthal" and the
heating wires of the other bulbs are made of alloys known as
chromel, alumel and molybdenum, the first two being trade marks.
The compositions of kanthal, chromel and alumel are
as follows:
Element Kanthal Alumel Chromel
Aluminium 4.5% 1-2%
Carbon 0.09~ balance ~0.1%
Chromium 22.6% - 9-11%
Cobalt 2.0%
Copper - - 0.1%
Iron balance - ~0.5%
Manganese - 2-4% c 2.5%
Nickel - 94~ 87%
Silicon - 1/2 - 1 1/2 ~ 0.5%
Others - - -0.2%
An advantage of this embodiment is that the specific
heats of these materials (conductors) are fairly close so that
also in case of mutually equal length and diameter of the heat-
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1040700
ing wire the thermal capacity of the bulbs may be reasonably
equal and the resistive values may be sufficiently different
from each other.
In a further preferred embodiment of an arrangement
S according to the invention the said means - to render the
internal resistance of a bulb after flashing to a maximum
of one ohm - consists of an electrically conducting bush
surrounding the supply conductors of the heating wire at
an area located within the bulb, which bush melts upon flash-
ing thereby shortcircuiting said supply conductors.
An advantage of this preferred embodiment ts that
switching over to a subsequent bulb may be very
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PHN 6873
~040700
reliable.
The invention will further be described with
reference to a drawing.
Fig. 1 is a diagrammatical view of an electrical
circuit of an arrangement according to the invention.
Fig. 2 is a longitudinal cross-section through
one of the combustion flash bulbs of the arrangement of
Fig, 1.
In Fig. 1, 1 and 2 are input terminals intended to
be connected to a charge device of the capacitor 3 including
a resistor. The electrodes of the capacitor 3 are connected
by means of a series arrangement of a switch 8 and four
low-voltage combustion flash bulbs 4, 5, 6 and 7.
The construction of these bulbs 4 to 6 is sub-
stantially identical. Fig. 2 shows such a bulb.
In Fig. 2, 10 is an envelope which is provided
with two leadthrough conductors 11 and 12. These also
pass through a bead 13 in which a metal bush 14 is an-
chored. A heating wire 15 is present between the ends of
the conductors 11 and 12 present in the envelope 10. The
length of the bulb is approximately 25 mm and its diameter
is approximately 9 mm.
The length of the heating wire 15 is approximately
1,4 mm and its diameter is approximately 25 microns.
In bulb 4 (see Fig. 1) the heating wire was made
of kanthal, in bulb 5 it was chromel, in bulb 6 alumel and
in bulb 7 molybdenum.
PHN 6873
iO4~700
The table below states further data on these
four heating wires. As the volumina of the wires were equal
the ratio of the specific heat (see the table) also indicates
the ratio of the thermal capacity of these wires.
TABLE
Data on the heating wire
Lamp ~ length thickness Resistive Specific heat Temperature
No. heating mm nicrons value at in Joule/cub- coefficient
wire room tenp ic mm/C. (~)/C.
(in ohm)
l4 Kanthal 1.4 25 4.1 3.35.10 3 6,4.10 5
Chromel 1.4 25 2.0 3.93.10 3 32.10 5
6 Alumel 1.4 25 0.8 4.50.10 3 188.10 5
7 ¦Hnuolybde- 1.4 I ~1 0.2 ¦ 2.26.10 3
The temperature coefficients included in the last
column of this table are positive for the four heating wire
materials considered. This means that for an increasing tem-
perature the resistive values of the heating wires increase.
This is favourable because this means that - in the series
arrangement of bulbs considered - the resistance of the
heating wire of the bulb at the instant of flashing that bulb,
(which heating wire is then at a temperature of approximately
500C) is considerably higher than that of the heating wire
of the bulb to be flashed next (which consequently has a
;~ temperature which is several hundred degrees Celsius lower).
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The occurrence of double flashes is then substantially ex-
cluded.
PHN 6873
, .
1~40700
This favourable influence of the positive character
of the temperature coefficients is slightly less if the
bulbs having a low resistive value of the heating wire
(at room temperature) have the highest temperature coeffi-
S cients. This is the case in the embodiment described
hereinafter. The safety margin for preventing double flashes
is, however, amply sufficient in this case too.
In the envelope 10 of Fig. 2 some ignition paste
was present on the heating wire 15. That paste has an
ignition temperature of approximately 500C. Furthermore
the envelope was filled with a wire filling (16) of
zirconium.
The capacitor 3 (see Fig. 1) had a capacitance of
approximately 200 /u Farad. This capacitor was charged
to 6 Volt. When the switch 8 closed fDr the first t~me
; the bulb 4 flashed. At a subsequent renewed charge of the
capacitor 3, and a renewed closure of the switch 8, the
bulb 5 flashed etc.
By flashing a bulb an interconnection between the
leadthrough conductors (11 and 12) of this bulb was esta-
blished by the bush 14 engaging these conductors which
bush melted as a result of the thermal development. The
interconnection obtained had a negligibly small resistance.
Other modifications of giving a flashed bulb
a low resistance are likewise feasible.
Immediately after flashing the bulb 4 the resi-
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dual voltage of the capacitor 8 was approximately 0.3 Volt
while the temperature of the heating wire of bulb 5
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PHN 6873
1040700
had increased to approximately 200C. This residual charge
of the capacitor 8 was insufficient to heat the heating
wire of the bulb 5 to 500C (being the ignition temperature
of the paste).
This may also be explained as follows. Immediately
after flashing the bulb 4 the residual energy in the
capacitor was:
1/2 CV2 = 9 . 10-6 Joule.
The quotient Rh was 2/3 at a maximum at that
moment so that at a maximum 2/3 . 9 . 10 6 Joule = 6. 10 6
Joule was applied to the next bulb (bulb 5).
Considering the specific heat and the dimensions
of the heating wire of chromel, of this bulb 5 (see the
table), this may at most lead to an increase in the tem-
perature of this wire by some degrees Celsius. In fact,
the number of Joules necessary to raise the chromel wire
by one degree of Celcius in temperature is:
Volume x specific heat =
; [1/4 ~ (25 . 10-3)2 . 1.4 ] x [3.93 . 10-3~ Joule is
approximately 3. 10-6 Joule.
An important advantage of an arrangement according
to the invention is that all the parts to be heated, for
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example, for interconnection are present within the bulb
envelopes so that their operation is very reliable.
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