Note: Descriptions are shown in the official language in which they were submitted.
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I MP ROVE MENT S RE LAT I NG TO T I MI NG C I RC U I TS .
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This invention r~lates to timing circuit arrangements
and is especially, but not exclusively, applicable to
timing circuit arrangements for timing a delay between the
launching and the release of chaff from so-called
chaLf-dispensing pro~ectiles employed for radar decoy
puzposes.
According to the present invention there is provided
an electrical circuit arrange~.ent for timing a delay
between the performance fllnctions, said circuit arrangement
comprising tuned circuit means responsive to an electrical
signal of predetermined frequency which has a duration 'or
determining said delay between functions, means conditione
in dependence upon the duration of said signal and means
effective when the first of said functions is performed to
cause the conditioned means to respond for the timing of
said delay.
In one arrangement for carrying out the present
invention in an analogue mode the means conditioned in
dependence upon the time delay between functions may
comprise capacitor means arranged to be charged to a level
dependent upon the requisite time delay between functions
and subsequently discharged at a predetermined rate and to
a predeter~ined low level for the measurement of said time
delay at the expiration of which an electrical output is
provided to initiate the second of ~aid functions.
Jn a.. alternative circuit arrange~ent for carrying out
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the present invention digitally the means conditioned in dependence
upon the requisite time delay may comprise counter means arranged
to be stepped to a predetermined count position thereof indicative
of the requisite time delay between functions and subsequently
rendered effective when the first of the aforesaid functions is
performed to step progressively at a predetermined rate to an
output position whereat an output for causing the execution of
the other of said functions is derived from said counting means
at the expiration of said time delay.
The digital timing arrangement just above described may
well be significantly smaller and cheaper than the analogue
arrangement described.
As will be appreciated from the foregoing the timing
circuit arrangement according to the present invention may have
many different applications but its incorporation for example in
a chaff-dispensing projectile for timing an interval between the
launching of the projectile and the dispensing therefrom of chaff
is especially envisaged. In such an application the electrical
signal, the duration of which predetermines the time delay between
the launching of the projectile and the initiation of a chaff
dispensing operation and to which the tuned circuit responds, may
be applied to the projectile from a projectile launching barrel
through an inductive coupling device. The coupling device may
also serve to transmit to the projectile electrical signals of
different frequencies to that utilised for timing purposes. For
instance, one of these signals may be utilized for causing detona-
tion or firing of a rocket motor for the projectile whilst another
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may serve to charge capacitor means for providing electrical power
required inter alia for detonating a charge which initiates a
chaff-dispensing operation when the time delay expires as afore-
said to produce an electrical output from the timing circuit means.
By way of example the present invention will now be
described with reference to the accompanying drawings in which;
Figure 1 shows a schematic circuit diagram of a chaff
dispensing projectile embodying an analogue timing circuit arrange-
ment for timing a delay between the launching of the projectile
and the detonation of a charge therein for initiating the chaff-
dispensing operation;
Figure 2 shows an alternative digital timing circuit
arrangement to that shown in Figure l;
Figure 3 shows a circuit for operating one of the clock
pulse generators of Figure 2; and,
Figure 4 shows a circuit for maintaining operation of the
other of the clock pulse generators of Figure 2 should an inertia
switch of the projectile restore before the charge for initiating
the chaff-dispensing operation is detonated.
Referr~ng to Figure 1 the circuit arrangement shown with-
in the dotted line box 1 is embodied in a self-propelled projectile
having a rocket motor and carrying chaff in the nose portion which
is arranged to be separated from the projectile for the dispensing
of chaff in response to the firing of a charge and the conse-
quential operation of a gas generator~ This projectile is adapted
to be launched from a launching barrel which has associated with
it the circuit arrangement shown within the dotted box 2.
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The circuit arrangement within the box 2 comprises signal
generating means 3 for generating electrical signals at three
different frequencies (e.g. 5, 15, and 20 KHz). These signals
will be selectively applied as hereinafter described to the primary
4 of an inductive coupling device 5, such as a txansformer with
dust cores, the secondary of which indicated at 6 is embodied in
a chaff-carrying projectile to be launched from the aforesaid
launching barrel which embodies the primary 4.
Preparatory to launching the chaff-carrying projectile a
first frequency signal (e.g. 5 KHz) from the generating means 3
is selectively applied to the projectile through the inductive
coupling device 5. This signal is rectified by means of a half-
wave rectifier 7 and serves to charge a storage capacitor 8 which
will subsequently be utilized inter alia for providing electrical
energy for the firing of a charge for initiating the dispensing
of chaff fxom nose part of the projectile.
After this initial capacitor charging operation a second
frequency signal (e.g. 20 KHz) derived from the generating means
is then applied to the projectile though the inductive coupling
device 5. The duration of this signal pulse, Tl, say, will
determine the time delay between the launch of the projectile and
the detonation of the charge carried by the projectile for chaff
dispensing purposes. A tuned circuit comprising an inductor 9
and capacitor 10 responds selectively to the signal pulse of
duration Tl so that the pulse operates an electrical switch 11 of
an analogue timing circuit shown within the chain line box 12.
Operation of switch 11 allows a substantially constant current I
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derived from capacitor 8 to flow for time Tl into a timing capaci-
tor 13 through resistor 14. At this juncture the time delay
between launch and chaff dispensing has effectively been stored in
the timing circuit since the charge on capacitor 10 is given by
IlTl. For launching the projectile a third frequency signal
(e.g. 15 KHz) derived from the signal generating means 3 is applied
to the projectile through the inductive coupling device 5. To
this signal a further tuned circuit comprising inductor 15 and a
capacitor 16 selectively responds so that the signal effects
ignition of the rocket motor of the projectile by igniting a match-
head firing device 17. The rocket motor is accordingly ignited
and the projectile will be launched from the launching barrel.
Assuming the launch is satisfactory an inertia switch 18
included in the timing circuit 12 will be operated immediately
after launch due to the acceleration of the projectile and this
switch will then effec~ively be latched so that it cannot interrupt
the timing operation before the nose of the projectile has been
separated for chaff dispensing purposes. This effective latching
of the inertia switch 18 may be produced by electrical means as
will hereinafter be described.
As will be seen from the circuit diagram operation of the
inertia switch 18 closes a circuit for the discharge of the
capacitor 13 through a resistor 19 so that a substantially constant
current I2 flows therethrough. The voltage Vc as the capacitor 13
discharges is compared with a reference voltage VR by a comparator
20 which provides an output effective to turn on an FET 21 when
the voltage Vc reaches a predetermined low level. The conduction
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of the FET 21 completes a discharge circuit for the capacitor 8
and the ignition of a match-head detonator 22 which detonates a
charge for initiating the dispensing of chaff from the projectile
in response to the separation of the nose part of the projectile
by gas p.ressure. In order to prevent the comparator 20 producing
an output signal which would prematurely turn on the FET 21 the
comparator 20 will be disabled until the inertia switch 18
operates.
As previously mentioned the charge on the capacitor 13
is given by:-
CC = Il Tl
Discharge of capacitor C to predetermined voltage Vc isgiven by CD = I2 T2 where T2 is the time delay between launch and
chaff dispensing.
Thus Il Tl = I2 T2
T2 = Il Tl
I2
If Il = lOmA and I2 = O.lmA
Then T2 = lOOTl
As will be appreciated from the foregoing description the
timing circuit will not be rendered operative to commence timing
and consequently chaff dispensing will not take place if the launch
is unsatisfactory as indicated by the failure of the inertia switch
to operate.
The present invention also provides a digital timing
circuit arrangement which will now be described with reference to
Figures 2 to 4 and which may be used instead of the analogue
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timing circuit arrangement described above and contained within
the box 12 in Figure 1.
In the case of ~his digital timing circuit arrangement
it will be seen by reference to Figure 3 that the pulse of dura-
tion T1 to which the tuned circuit 9, 10 (Figure 1) responds is
rectified by rectifier 23 and then fed to a comparator 24 which
derives a reference signal V therefor from a potential divider
25, 26 and responds to the rectified pulse signal to provide a dc
pulse output of duration Tl as shown which is then utilized to
enable a first clock pulse generator 27 (Figure 2) providing a
first frequenc~ pulse output (e.g. 160 KHz). The output from this
clock pulse generator 27 steps a counter 28 through an OR gate 29
to a position corresponding to the duration Tl of the timing pulse.
When an inertia switch 30 (Figure 4) operates consequent
upon the satisfactory launching of the projectile a clock pulse
generator 31 (Figure 2) is operated for producing a second
frequency pulse output (e.g. 1.6 KHz). This second frequency
pulse output passes through the OR gate 29 and drives the counter
28 forward from its count position corresponding to the duration
Tl of the timing pulse to the end or output position thereof at
which an electrical output is derived from the counter. The time
taken to step the counter 28 from the first count position
referred to to the end position corresponds to the time delay
; between the projectile launch and detonation of the charge for
initiating chaff-dispensing. To achieve this detonation the out-
put from the counter 28 may be utilized to operate an FET 21
(Figure 13 which as described with reference to Figure 1 then
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closes a discharge circuit for the storage capacitor 8 which dis-
charges through a match-head detonator 22.
In the digital timing circuit arrangement described
operation of the inertia switch 30 (Figure 4) may be arranged to
cause a capacitor 32 to be charged from the storage capacitor 8
(Figure 1) over a supply line 33 through resistor 34. The charge
on the capacitor 32 causes a comparator 35 to prGvide an output
for enabling the clock generator 31 to operate. Should the inertia
switch 30 restore after its initial operation the capacitor 32 will
be discharged very slowly through a high value resistor 36 to
maintain the clock pulse generator 31 in operation for at least
the delay period being timed between the launch of the projectile
and the detonation of the charge for chaff dispensing purposes.
In operation of the digital timing circuit arrangement
the time delay T2 is given by:
T2 = time taken to step counter from 1st count position to end
position at 1.6 KHz
Now Tl = time taken to step counter to 1st count position at
160 KHz.
If counter has 8000 count positions and 1st count position
is at 1500 then
T2 = 6500 and
1.6KHz
T = 1500. Therefore, T = T (6500 x 160)
1 2 1 (1.6 x 1500)
160 KHz T2 = T1 433.3
It will be apparent from both of the embodiments described with
reference to the drawings that the failure of the inertia switch
to operate due to a faulty launch will prevent the time delay being
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commenced so as to prevent the detonation of the charge of chaff
dispensing purposes under conditions of faulty launching. More-
over, in the case of the digital ~iming circuit arrangement
failure of the first clock pulse generator 27 (Figure 2) to be
enabled so that the counter 28 is stepped to a count position
will not cause premature and hazardous detonation of the charge
for chaff dispensing since the second clock pulse generator 31
will cause the counter to step through the full counting sequence
(e.g. 8000 positions) before the charge for chaff dispensing is
ignited. In this way a time delay in excess of the normal time
delay will be provied for.
