ELECTRONIC DELAY CIRCUITS

CIRCUITS ELECTRONIQUES TEMPORISATEURS

English Abstract

ABSTRACT OF THE DISCLOSURE
A delayed action circuit including input connections, a voltage - limiting circuit
connected to the input connections, a resistance - capacitance integrating network
connected to the voltage-limiting circuit and a threshold circuit connected to
the integrating network, characterised in that the threshold circuit has a control
input connected to the input connections for controlling its threshold voltage in
response to the peak voltage of any signal applied to the input connections and
thereby providing a longer delay in response to a higher peak input voltage.

Claims

WHAT I CLAIM IS: -
1. A fuze circuit for an explosive device comprising an impact
transducer for producing a sustained voltage in response to an impact,
such that a higher voltage will be produced in response to a hard impact
and a lower voltage in response to a soft impact, and a delayed-action
detonator circuit connected to the impact transducer, the detonator
circuit including a voltage limiting circuit connected to receive the
sustained voltage and adapted to derive therefrom a predetermined voltage;
a resistance-capacitance integrating network connected to the voltage
limiting circuit to receive the predetermined voltage and to derive
therefrom an increasing voltage; and a threshold circuit connected to
the integrating network to receive the increasing voltage and to produce
a detonating signal when the increasing voltage reaches a threshold
voltage derived from the sustained voltage and said detonating circuit
being adapted to produce a detonating signal in response to the sustained
voltage after a delay following the impact.
2. A fuze circuit as claimed in claim 1 wherein the threshold circuit
includes a programmable unijunction transistor having its gate electrode
connected to receive a voltage whose magnitude is dependent on the
magnitude of the sustained voltage.
3. A fuze circuit as claimed in claim 2 wherein the gate electrode
is connected to an intermediate point in a resistive potential divider
chain which is connected to receive the sustained voltage.
4. A fuze circuit as claimed in claim 3 wherein a voltage limiter
is connected to the gate electrode so that the threshold voltage cannot
exceed the maximum value of the increasing voltage.
5. A fuze circuit as claimed in any of claim 1, 2 or 3, wherein
the impact transducer comprises a piezo-electric transducer device,
connected via a rectifier to a storage capacitor, the sustained voltage
being the voltage developed on the storage capacitor.

6. A fuze circuit as claimed in any of claim 1, 2 or 3, wherein
the detonating signal is applied to a switching device connected in
series with a detonator device so as to cause the sustained voltage
to be applied to the detonator device when the detonating signal is
produced, thus activating the detonator.
7. A fuze circuit as claimed in any of claim 1, 2 or 3 in which
the impact transducer is arranged to act as a power supply so that no
separate power supply is required.
8. A fuze circuit as claimed in claim 1, 2 or 4, where said impact
transducer comprises a piezo-electric transducer device, connected via
a rectifier to a storage capacitor, the sustained voltage being the
voltage developed on the storage capacitor, and wherein said impact
transducer is arranged to act as a power supply so that no separate
power supply is required.

Description

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This inven-tion rela-tes to electronic delay circuits and in particular
to delayed switch circuits whereby a switch, which may be an electronic
switch~ is closed in response to a stimulus~ the switch being closed
after so~e predetermined d~lay following the application of the stimulus.
In a known type of delayed swi-tch circuit the stimulus provides a
voltage across a resistor and a timing capacitor connected in series.
A threshold circuit is connected to the timing capacitor and is
constructed so that it will effectively close a circuit when the voltage
across the timing capacitor reaches some predetermined value. The
delay between the application of the stimulus and the closing of the
circuit depends on the applied voltage, a larger voltage producing a
shorter delay. If a constant delay switch circuit is required, the
delay being approximately independent of the strength of the stimulus,
the voltage provided by the stimulus can be applied to the timing
capacitor through a voltage-limiting network. ~or example the voltage
can be applied to a Zener diode and a resistor in series and the voltage
across the Zener diode can be used to oharge the timing capacitor.
According to the present invention a delayed action circuit includes
input connections, a voltage-limiti~g circuit connected to the input
connections, a resistance-capacitance in-tegrating network connected
to the voltage-limiting circuit~ and a threshold circuit connected to
the integrating network~ characterised in that the threshold CiICUit
has a control input connected to the input connections for controlling
its threshold voltage in response to the peak voltage of any signal
applied to the input connections and thereby providing a longer delay
in response to a higher peak input voltage.

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The threshold circllit may include a programm~ble unijunction
transistor (~JT) having its gate electrode connected to receive a
voltage derived from the input signal and its source electrode
connected to receive an output from the integrating network.
The gate voltage may be derived from the input signal by
means of a network inclu~ ng a Zener diode, the network being such
that the gate voltage cannot exceed the maximum voltage to which the
capacitance of the integrating network can be charged.
The delayed action circuit may be incorporated into ~nelectronic
fuze for an explosive device in which the input signal is provided
by the rectified output of a piezo~electric transducer and in which
the closing of a switch circuit effected by the delayed action
circuit operates a detonator. The voltage output of the transducer
D~ay act as a power 9Upply for the detonator so that no separate power
supply is required.
An embodiment of the invention will now be described by way of
example only with reference to the accompanying drawing which is a
circuit diagram of an electronic fuze for an explosive device.
The circuit shown is suitably positioned within an explosive
device (not shown) such as a bomb.
A piezo-electric transducer 1 is ~o positioned within ~he bomb
(not shown) that it will receive a mechanical blow when the bomb
impacts with a target. The mechanical force of the blow i9 converted
by the transducer 1 to an electrical voltage the magnitude of which
is related to the magnitude of the mechanical force.

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The voltage output of the piezo-electric transducer 1 is
rectified by a diode bridge 2 and applied to a storage capacitor 3.
A resistor 4 and a Zener diode 5 are connected in series across -the
storage capacitor 3 and the voltage across the Zener diode 5 is
applied to a resistor 6 and a timing capacitor 7 connected in series.
In parallel with the storage capacitor 3 is a potential divider
chain comprising two resistors 8 and 9 in series. A Zener diode 10
is connected in parallel with the resistor 9 so as to limit the
output voltage of the potential divider which is applied as a gate
voltage to a PU~ 11. In parallel with the timing capacitor 7 is a
resistor 12 connected in series with the main current path -through
the PUT 11. The voltage developed across the resis-tor 12 is
applied to a gate input of a silicon controlled rectifier (SCR) 14.
~he main current path of the SCR 14 is connected in series with a
detonator 15 and together they are connected in parallel with the
storage capacitor 3. ~ .-
In operation, wh0n the bomb impacts a target of a given material~the rectified output of the transducer charges the storage capacitor 3
to a corresponding voltage level. The stored charge provides the
stimulus voltage for the delayed switch and also the power supply for
the detonator 15. ~he resistor 4 and the Zener diode 5 provide a
voltage which is substantially independent of the magnitude of the
stimulus voltage from which the timing capacitor 7 is charged through
the resistor 6. The resistors 8 and 9 and the Zener diode 10 derive
a gate voltage for the PU~ 11 which is proportional to the stimulus
voltage up to a predetermined value of the stimulus vol-tage determined

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by the Zener diode 10 and is substantially constant for higher values.
The threshold vol-tage of the PU~ controlled by the gate voltage,
so that a higher stimulus vol-tage, up -to the predetex~ined value, will
raise the threshold voltage.
~ hen the ~oltage across the timing capacitor 7 reaches the
threshold voltage, the PUT 11 will become conducting and a voltage
will be developed across the resistor 12 which will cause the SCR 14
to become conductive. The storage capacitor 3 will then discharge
through the detonator 15. The capacitor 13 prevents transients from
reaching the SCR 14 and causing premature detonation. The higher the
tbleshold voltage the longer will be the time delay before the
threshold voltage is reached. Hence the stimulus voltage controls the
time delay between the occurrence ofthe stimulus and the detonation,
so that a larger stimulus causes a longer delay.
Many variations and modifications of the embodiment described
will suggest themsélves to those skilled in the art. For example
the bridge rectifier circuit 2 can be replaced by a diode in series
with the input ofthe delay circuit. ~his arrangement is more
suitable if the output of -the transducer 1 is expected to be a series
of pulses since then the storage capacitor 3 will become charged to a
voltage proportional to the magnitude o~ the largest of these pulses.
A Zener diode may also be placed in parallel with the storage
capacitor 3 to limit the maximum voltage that can be applied across
the SCR 14 to a value less than the maximum rated forward blocking
voltage of the SCR 14.
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