GB2082862A - Improvements Relating to Timing Circuits - Google Patents

Abstract

A circuit arrangement for timing a delay between functions, such as the time delay between the launching of a chaff-dispensing projectile and the dispensing of chaff by said projectile comprises tuned circuit means responsive to an electrical signal for predetermined frequency which has a duration for determining said delay between functions and further comprises means conditioned 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 the analogue system shown, a first frequency AC signal charges 8 via rectifier 7 to provide d.c. power. A different frequency to which 9, 10 are tuned, operates switch 11, thereby charging 13 at current I, for time T1. Subsequently switch 18 is closed to discharge 13 at current I2, the delay time being the time taken for Vc to fall to reference voltage VR, when 22 is energised by switch 21. Timing functions may alternatively be provided digitally. <IMAGE>

Description

SPECIFICATION Improvements Relating to Timing Circuits This invention relates 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 chaff-dispensing projectiles employed for radar decoy purposes.

According to the present invention there is provided an electrical circuit arrangement for timing a delay between functions, said circuit arrangement comprising tuned circuit means responsive to an electrical signal of predetermined frequency which has a duration for determining said delay between functions, means conditioned 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 predetermined low level for the measurement of said time delay at the expiration of which an electrical output is provided to initiate the second of said functions.

In an alternative circuit arrangement for carrying out 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 detonation or firing of a rocket motor for the projectile whilst another 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 aforesaid 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 arrangement 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 1; 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.

Referring to Figure 1 the circuit arrangement shown within 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 foy the dispensing of chaff in response to the firing of a charge and the consequential 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.

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 transformer 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 by utilized inter alia for providing electrical energy for the firing of a charge for initiating the dispensing of chaff from 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, T1, 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 T1 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 11 derived from capacitor 8 to flow for time T1 into a timing capacitor 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. I,T,. For launching the projectile a third frequency signal (e.g. 1 5 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 1 5 and a capacitor 1 6 selectively responds so that the signal effects ignition of the rocket motor of the projectile by igniting a match-head firing device 1 7. The rocket motor is accordingly ignited and the projectile will be launched from the launching barrel.

Assuming the launch is satisfactory an inertia switch 1 8 included in the timing circuit 12 will be operated immediately after launch due to the acceleration of the projectile and this switch will then effectively 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 1 8 may be produced by electrical means as will hereinafter be described.

As will be seen from the circuit diagram operation of the inertia switch 1 8 closes a circuit for the discharge of the capacitor 13 through a resistor 1 9 so that a substantially constant current 12 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 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 pressure.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 1 3 is given by: Cc=l 1T Discharge of capacitor C to predetermined voltage Vc is given by CD=l2T2 where T2 is the time delay between launch and chaff dispensing.

Thus IT=12T I T 11 b T2= 12 If l=10 mA and 12=0.1 mA Then T2=1 00 T, 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 timing circuit arrangement described above and contained within the box 12 in Figure 1.

In the case of this digital timing circuit arrangement it will be seen by reference to Figure 3 that the pulse of duration 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 V0 therefor from a potential divider 25, 26 and responds to the rectified pulse signal to provide a dc pulse output of duration T1 as shown which is then utilized to enable a first clock pulse generator 27 (Figure 2) providing a first frequency pulse output (e.g. 1 60 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 T1 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 T1 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 output from the counter 28 may be utilized to operate an FET 21 (Figure 1) which as described with reference to Figure 1 then closes a discharge circuit for the storage capacitor 8 which discharges 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 provide 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 1 st count position to end position at 1.6 KHz Now T,=time taken to step counter to 1 st count position at 1 60 KHz.

If counter has 8000 count positions and 1 st count position is at 1 500 then 6500 T 1.6 KHz and 1500 T,= 160 KHz Therefore, (6500x 1 60) T2=T1 (1.6x1500) T2=T, 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 commenced so as to prevent the detonation of the charge of chaff dispensing purposes under conditions of faulty launching.

Moreover, in the case of the digital timing 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 provided for.

Claims (11)

Claims

1. An electrical circuit arrangernent for timing a delay between the performance of functions, said circuit arrangement comprising tuned circuit means responsive to an electrical signal of predetermined frequency which has a duration for determining said delay between the performance of functions, means conditioned 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.

2. An electrical circuit arrangement as claimed in claim 1, in which the means conditioned in dependence upon the time delay between the performance of said functions comprises 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 predetermined low level for the measurement of said time delay at the expiration of which an electrical output is provided to initiate the performance of the second of said functions.

3. An electrical circuit arrangement as claimed in claim 1, in which the means conditioned in dependence upon the requisite time delay comprises counter means arranged to be stepped to a predetermined count position thereof indicative of the requisite time delay between the performance of functions and subsequently rendered effective when the first of the functions is performed to step progressively at a predetermined rate to an output position whereas an output for causing the execution of the other of said functions is derived from the counting means at the expiration of the time delay.

4. A chaff-dispensing projectile comprising a circuit arrangement as claimed in any preceding claim for timing an interval between the launch of the projectile and the dispensing of chaff therefrom, in which the projectile comprises part of an inductive coupling device through which an electrical signal of a predetermined frequency for causing the timed circuit to respond is transmitted from a projectile launching barrel.

5. A chaff-dispensing projectile as claimed in claim 4, in which a rocket motor is arranged to be fired in response to an electrical signal transmitted to the projectile through the inductive coupling device and having a predetermined frequency different from that of the signal for timing purposes.

6. A chaff-dispensing projectile as claimed in claim 4 or claim 5, in which capacitor means for providing electrical power required for detonating a charge which initiates a chaff-dispensing operation when the time delay expires to produce an electrical output from the timing means is arranged to be charged by an electrical signal which is transmitted to the capacitor means through the inductive coupling device from the launching barrel for the projectile and which has a frequency different from the signal utilised for timing purposes.

7. A chaff-dispensing projectile as claimed in any of claims 4 to 6, in which the inductive coupling device comprises a transformer with dust cores having its secondary embodied in the projectile.

8. A chaff-dispensing projectile as claimed in any of claims 4 to 7, in which the projectile includes inertia switch means operable at launch to render the means conditioned in dependence upon the time delay between launch and chaff dispensing operable to commence timing of said delay.

9. A chaff-dispensing projectile as claimed in claim 8, in which the inertia switch means includes latching means which prevents interruption of the timing operation once the intertia switch means has operated.

1 0. A timing circuit arrangement according to, claim 1, substantially as described with reference to Figure 1 of the accompanying drawings.

11. A chaff-dispensing projectile substantially as hereinbefore described with reference to the accompanying drawings.