GB1604012A

GB1604012A - Electrical devices for initiating explosions

Info

Publication number: GB1604012A
Application number: GB3750776A
Authority: GB
Original assignee: ARBRA INSTR Ltd
Current assignee: ARBRA INSTR Ltd
Priority date: 1977-09-08
Filing date: 1976-03-09
Publication date: 1981-12-02

Description

(54) IMPROVEMENTS IN AND RELATING TO ELECTRICAL DEVICES FOR INITIATING EXPLOSIONS (71) We, ARBRA INSTRUMENTS LIM ITED, a British company of George Street, Whitchurch, Shropshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to electrical devices for initiating explosions. Such devices are commonly termed exploders.

Exploders are used in a number of environments and one such environment is a coal mine or other underground working. When used underground there is a risk that in addition to causing the explosion desired, the electrical energy will also ignite gases existing underground such as firedamp.

The present invention provides an exploder comprising a hand operated electromechanical generator, a pulse generating circuit, resistance measuring circuit, two output terminals, and switching means for connecting the generator to either the pulse generating circuit or the measuring circuit and for connecting that circuit connected to the generator also to the output terminals, the circuit not connected to the generator being isolated from the output terminals.

The embodiment of the invention to be described has been designed to operate safely underground.

Features and advantages of the present invention will become apparent from the following description of an embodiment given by way of example when taken in conjunction with the accompanying drawing, which shows a circuit diagram of an exploder.

An exploder comprises a generator 10, a firing circuit II in the form of a pulse generating circuit and an ohmmeter circuit 12 housed in a single case. The generator is hand cranked and supplies power for both the firing and the ohmmeter circuits.

The exploder is of the so-called automatic type in as much as the firing circuit will produce a pulse of electrical energy once a storage capacitor 14 has accumulated sufficient charge. This is achieved by including a switch device in the power line from the capacitor 14 and triggering the switch device when the capacitor 14 has accumulated sufficient charge. As shown the switch device is a controlled rectifier device 15 but it could be a power transistor. The rectifier device 15 is rendered conductive by a signal from the trigger circuit indicated generally by the reference numeral 16. The trigger circuit comprises a voltage divider consisting of three resistors and a diac 17 which supplies the primary winding of a transformer 18, the secondary of which is in the gate circuit of the controlled rectifier, device 15.

For use underground, especially in coal mines, the output pulse of energy from the capacitor 14 is limited in duration by a timer circuit indicated generally by reference numeral 20. The duration of the output pulse is chosen depending on the gases encountered underground. For example, it is known that a pulse of duration of4 milliseconds or less will not ignite firedamp. The circuit 20 is designed to allow a pulse of electrical energy of 4 milliseconds duration. This is achieved by rendering conductive a controlled rectifier device 21 after 4 milliseconds so as to short the output from the capacitor 14.

A visual indication is given of the correct functioning of the firing circuit. This is necessary because the exploder as mentioned above is automatic. The visual indication is given by a lamp circuit 24 which includes a neon lamp 25. Because a pulse of only 4 milliseconds is applied to the lamp circuit 24, it is necessary to attenuate this pulse so that the lighting of the neon lamp 25 can be seen by the operator of the exploder. This is achieved by storing charge on a capacitor 26 during the 4 millisecond period and dis charging the capacitor through the neon lamp for a period of time sufficient for the lighting of the neon lamp to be noticed by the operator. In this case the lamp is arranged to be lit for approximately 2 seconds.

As mentioned previously, an ohmmeter circuit 12 is provided in the exploder housing and it also receives its power from the generator 10. The ohmmeter circuit 12 is used to check the integrity of the wiring connecting the exploder to the various charges of explosives to be detonated. In order to protect the ohmmeter circuit 12 from the high power pulse produced by the firing circuit 11 and in order to prevent accidental firing when testing the integrity of the line, two interlocked switches 30 and 31 are provided, one at the input of the circuits Il and 12 and the other at the outputs of the circuits.

Switch 30 comprises a normally closed set of contacts 30a at the input to the ohmmeter circuit 12 and a normally open set of contacts 30b at the input to the firing circuit 11. The switch 31 comprises a normally closed set of contacts 31 a at the output of the ohmmeter circuit 12 and a normally open set of contacts 3 lb at the outputs of the firing circuit 11. The centre poles 31 c of the switch 31 are connected to output terminals of the exploder.

Both switches 30, 31 are operated simultaneously by a single push button. Thus, the circuit normally rests with the ohmmeter circuit 12 in circuit and the firing 11 isolated.

The wires connecting the exploder to the charge to be detonated are attached to the exploder by a terminal arrangement which ensures two handed operation of the exploder.

The terminal arrangement comprises three apertures provided in one wall of the exploder case.

A contact receiving member of insulating material is received in the exploder case and is provided with conductive terminal posts.

The contact receiving member is provided with a screw-threaded hole which receives a correspondingly screw-threaded shaft projecting through one of the apertures and provided with connecting means for connecting the shaft to an actuating handle. The shaft is fixed against axial movement but can be rotated by the handle so as to move the contact receiving member within the chamber and hence move the posts.

The posts are provided with wire receiving means in the form of holes in such a position that when the posts are retracted, wires in the holes will be clamped between the periphery of the holes and the wall of the exploder case or conductive bushings in the other two of the apertures. Electrical connection between the wires and the contacts 31 c of the circuit shown in the drawing is made in any convenient manner such as by means of flying leads between the posts and the contacts 31 c.

Thus, in use, wires are placed in the holes in the posts and the handle rotated. This firstly retracts the posts to clamp the wires against the posts and then rotates the armature of the generator. If a relatively flexible material such as nylon is used for the contact receiving member, a self-equalizing clamping action can be achieved by bending of the contact receiving member to ensure that both the wires are fully clamped in the holes.

In operation, no wires are connected to the output terminal posts of the exploder and the exploder is tested by depressing the push button and cranking the generator until the neon lamp flashes on. By depressing the push button, only the firing circuit is connected to the generator, the ohmmeter circuit being isolated. Once the operator is satisfied the exploder is functioning correctly, the wires connecting the exploder to the various charges to be exploded are connected to the output terminals of the exploder in the manner described above. Without the push button being depressed, the generator is cranked which passes a small current down the wires from the ohmmeter circuit 12, the firing circuit 11 being isolated.Once the operator is satisfied as to the integrity of the firing line, the push button is again depressed and the generator cranked until the neon lamp indicates that the exploder has operated.

It will be appreciated that the case of the exploder, and also the housing member for the output terminal posts, have to be rigid and comply with the existing safety requirements. At present we use a case and housing member made from rigid plastics material for example polycarbonate.

Various modifications may be made. For example, instead of using a single transformer with two secondary windings and a heavy duty switch, it is possible to use two transformers, one for the resistance measuring circuit and one for the firing circuit. This allows a lighter rated switch to be used.

Further the terminal posts can be either fully or only partially retracted into the housing member.

WHAT WE CLAIM IS: 1. An exploder comprising a hand-operated electromechanical generator, a pulse generating circuit, a resistance measuring circuit, two output terminals, and switching means for connecting the generator to either the pulse generating circuit or the measuring circuit and for connecting that circuit connected to the generator also to the output terminals, the circuit not connected to the generator being isolated from the output terminals.

2. An exploder according to claim 1,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. charging the capacitor through the neon lamp for a period of time sufficient for the lighting of the neon lamp to be noticed by the operator. In this case the lamp is arranged to be lit for approximately 2 seconds. As mentioned previously, an ohmmeter circuit 12 is provided in the exploder housing and it also receives its power from the generator 10. The ohmmeter circuit 12 is used to check the integrity of the wiring connecting the exploder to the various charges of explosives to be detonated. In order to protect the ohmmeter circuit 12 from the high power pulse produced by the firing circuit 11 and in order to prevent accidental firing when testing the integrity of the line, two interlocked switches 30 and 31 are provided, one at the input of the circuits Il and 12 and the other at the outputs of the circuits. Switch 30 comprises a normally closed set of contacts 30a at the input to the ohmmeter circuit 12 and a normally open set of contacts 30b at the input to the firing circuit 11. The switch 31 comprises a normally closed set of contacts 31 a at the output of the ohmmeter circuit 12 and a normally open set of contacts 3 lb at the outputs of the firing circuit 11. The centre poles 31 c of the switch 31 are connected to output terminals of the exploder. Both switches 30, 31 are operated simultaneously by a single push button. Thus, the circuit normally rests with the ohmmeter circuit 12 in circuit and the firing 11 isolated. The wires connecting the exploder to the charge to be detonated are attached to the exploder by a terminal arrangement which ensures two handed operation of the exploder. The terminal arrangement comprises three apertures provided in one wall of the exploder case. A contact receiving member of insulating material is received in the exploder case and is provided with conductive terminal posts. The contact receiving member is provided with a screw-threaded hole which receives a correspondingly screw-threaded shaft projecting through one of the apertures and provided with connecting means for connecting the shaft to an actuating handle. The shaft is fixed against axial movement but can be rotated by the handle so as to move the contact receiving member within the chamber and hence move the posts. The posts are provided with wire receiving means in the form of holes in such a position that when the posts are retracted, wires in the holes will be clamped between the periphery of the holes and the wall of the exploder case or conductive bushings in the other two of the apertures. Electrical connection between the wires and the contacts 31 c of the circuit shown in the drawing is made in any convenient manner such as by means of flying leads between the posts and the contacts 31 c. Thus, in use, wires are placed in the holes in the posts and the handle rotated. This firstly retracts the posts to clamp the wires against the posts and then rotates the armature of the generator. If a relatively flexible material such as nylon is used for the contact receiving member, a self-equalizing clamping action can be achieved by bending of the contact receiving member to ensure that both the wires are fully clamped in the holes. In operation, no wires are connected to the output terminal posts of the exploder and the exploder is tested by depressing the push button and cranking the generator until the neon lamp flashes on. By depressing the push button, only the firing circuit is connected to the generator, the ohmmeter circuit being isolated. Once the operator is satisfied the exploder is functioning correctly, the wires connecting the exploder to the various charges to be exploded are connected to the output terminals of the exploder in the manner described above. Without the push button being depressed, the generator is cranked which passes a small current down the wires from the ohmmeter circuit 12, the firing circuit 11 being isolated.Once the operator is satisfied as to the integrity of the firing line, the push button is again depressed and the generator cranked until the neon lamp indicates that the exploder has operated. It will be appreciated that the case of the exploder, and also the housing member for the output terminal posts, have to be rigid and comply with the existing safety requirements. At present we use a case and housing member made from rigid plastics material for example polycarbonate. Various modifications may be made. For example, instead of using a single transformer with two secondary windings and a heavy duty switch, it is possible to use two transformers, one for the resistance measuring circuit and one for the firing circuit. This allows a lighter rated switch to be used. Further the terminal posts can be either fully or only partially retracted into the housing member. WHAT WE CLAIM IS:

1. An exploder comprising a hand-operated electromechanical generator, a pulse generating circuit, a resistance measuring circuit, two output terminals, and switching means for connecting the generator to either the pulse generating circuit or the measuring circuit and for connecting that circuit connected to the generator also to the output terminals, the circuit not connected to the generator being isolated from the output terminals.

2. An exploder according to claim 1,

wherein voltage amplifying means is provided between the generator and the pulse generating circuit and between the generator and the measuring circuit.

3. An exploder according to claim 2, wherein the voltage amplifying means comprises a transformer with two secondary windings, one for each of the circuits.

4. An exploder according to claim 3, wherein the voltage amplifying means comprises two transformers, one for each of the circuits.

5. An exploder according to any one of the preceding claims, wherein the exploder has a housing and the output terminals are retractable at least partially into the housing.

6. An exploder according to claim 5, wherein the output terminals are arranged to be retracted on initial hand-cranking.

7. An exploder according to any one of the preceding claims, wherein the switching means is arranged normally to connect the measuring circuit to the generator and to the output terminals.

8. An exploder substantially as hereinbefore described with reference to the accompanying drawing.