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• The basic electronic circuits and components

required to make an electronic fuze are discussed in the following.

(a) Antenna: This is generally a loop type antenna

used to radiate the RF waves received from RF oscillator. Fuze body also forms a part of antenna and helps to radiate the RF waves. The design of

antenna and fundamentals of wave propagation can be found in F.1 and F.2 of Bibliography.

4.3 Basic elements of electronic fuzes:

(b) Radio frequency generator, transmitter and receiver: An oscillator circuit is used to generate

the RF waves of required frequency, which are to be transmitted through antenna. This is a combined

transmitter and receiver/detector, which sends out waves of radio frequency and receives them again after reflection from the target.

4.3 Basic elements of electronic fuzes:

• The interaction of the waves produces ripple

impulses of audio frequency. The design principles of various communication systems can be studied in detail in F.3 and F.4 of Bibliography

4.3 Basic elements of electronic fuzes:

(c) Signal processor unit: This is generally an audio frequency amplifier circuit. This is called signal

processor unit, as it amplifies the weak audio

frequency signal received by detector. The output of signal processor unit is a trigger pulse, which is

utilized by firing circuit to trigger its electronic

switch. The detailed study of analog circuit and their design can be found in F.5 and F.6 of Bibliography.

4.3 Basic elements of electronic fuzes:

(d) Electronic Time delay circuit: This is a counter

based time delay circuit, which provides the necessary time delay after firing to the time of

function of fuze. Depending on the requirement time delay circuit can be of simple or complex nature.

Simple time delay circuit contains a single counter, which will have a fix count and hence a single time delay (e.g. fix 10 seconds ± tolerance) of specified amount can be achieved.

4.3 Basic elements of electronic fuzes:

• If more than one-time delay options are required, multiple counter circuit with a selectable switch is required. For example, if one wants to have a fuze with a time delay options of 10 sec or 50 sec or 100 sec ± tolerance, then three counter circuit with a

selectable switch would be required. Further if one wants a range of time delay e.g. from 0 sec to 200

sec ± tolerance, then a programmable counter circuit would be needed.

4.3 Basic elements of electronic fuzes:

• The timer circuits can also be implemented on

FPGA (Field Programmable Gate Array). FPGA can be used to implement any digital logic circuit

required by user and as the name suggests it can be programmed at field i.e. by user at his requirement. The detailed study of various digital logic circuits and their design principles can be found in F.7 of Bibliography.

4.3 Basic elements of electronic fuzes:

(e) Electronic safety circuit: This is generally an

electronic time delay circuit which enables the firing mechanism after some specified time to ensure that fuze does not function prematurely in any case.

4.3 Basic elements of electronic fuzes:

(f) Power supply: Power supply is generally a reserve type of

primary battery with the electrolyte contained in a glass ampoule, which is broken by set – back force on firing the gun. It acts as a safety mechanism as it prevents the

electronic circuit from getting power and hence preventing any premature or accidental explosion. Air driven

alternators are also used as source of power supply in

electronic fuzes now a days. Air driven alternator utilizes the airflow in the fuze to generate the required electric voltage

4.3 Basic elements of electronic fuzes:

(g) Impact switch: This switch is normally open

while handling and transporting the fuze. It closes when fuze is fired and hits any hard object. This switch is placed in the path of condenser of firing circuit and electric detonator. When the switch

closes, it allows the condenser to get discharge into electric detonator. It is a mechanical switch and is used in electronic point detonation fuze or in fuzes where point detonation action is required as back up mode if the fuze does not function in its set mode.

4.3 Basic elements of electronic fuzes:

(h) Firing circuit: It consists of a grid condenser,

electronic switch (Thyristor, or MOSFET transistor or thyratron), and electric detonator. The electric

detonator is a bridge wire element some times also referred to as an electronic blasting cap. The bridge wire element consisted of small metal wire or a thin strip of carbon film in parallel with a total resistance value of about 700 to 15, 000 ohms.

4.3 Basic elements of electronic

fuzes:

• Electronic switch is closed on receipt of trigger pulse of appropriate magnitude from audio amplifier circuit and the grid condenser is discharged into electric detonator to

4.3 Basic elements of electronic fuzes:

(i) Safety switch and mechanical arming/safety systems: The safety switch is used to connect the

two entities on experiencing a force such as

acceleration force of certain magnitude or spin of certain rpm or air flow of certain magnitude. This is a mechanical system, similar to one used in

4.3 Basic elements of electronic fuzes:

• To make a particular type of electronic fuze the required modules are implemented on Printed Circuit Board (PCB) and interfaced to have the required fuze action. The modules can be

implemented in a single PCB or more than one

PCB. The electronic modules are individually tested and then interfaced with the rest of the sub-

assemblies to make the complete fuze. The complete fuze is then tested for the required