GB2159000A - Conrolled inductive coupling device - Google Patents

Description

SPECIFICATION A controlled inductive coupling device This invention relates to a controlled inductive coupling device wherein the capability of the device to transmitelectrical energyfrom a primary circuit to a secondary circuit inductively linked to said primary circuit can be controlled. The invention also includes a method of controlling the transmission of electrical energyfrom a primary circuitto a secondary circuit inductively coupled thereto. The invention is especially advantageous when applied to control thetransmis- sion of firing energy from an electrical source such as a blasting machine, inductively linked to the electrical firing circuit of an ignition element, for example, the electricfusehead of an electric detonator.

Electric detonator assemblies adapted for inductive coupling to an electrical firing energy source are marketed widely by Nobel's Explosive Company Limited underthe Registered Trade Mark'Magnadet', the blasting system using such detonators being generally described as the'Magnadet'system. In this blasting system an encased resistive ignition element of an electric detonator for detonating the blasting charge has its two terminais connected respectivelyto the ends of a continuous conductorwire which extends outside the detonator casing. The external portion of the conductor wire is fully insulated and is wound as a secondary winding of 3-5 turns on a ferrite ring core, which isusuallytermed atoroid (although it is generally a flat cylindrical section of a tube and it may have shapes other than circular, such as rec tangular or multi-angular). Forfiring the detonator an insulated conductorwire is threaded as a single loop primary winding through one or more toroid ring cores and connected to a suitable source of A. C. firing current. These inductivelycoupled detonators are described in United Kingdom PatentSpecifications Nos. 2022222Aand 2109512A.

Inductivelycoupled'Magnadet'detonators are advantageous in many blasting operations because of their convenience in connecting for use and their high degree of safetyfrom premature ignition by stray electric currents and static electricity. The inductive coupling can be designedto befrequencyselectiveso that signals outside a designed band within a range of about 10to 100 kHzwill be effectively attenuated to preventthem firing the ignition element. Thus in general such detonators are designed to pass efficiently a signal of 10-20 kHzand in use are usedwith a blasting machine (exploder) generating a current within this frequency band. The safety characteristics therefore ensure safetyfrom all the common sources of dangerous electric currents. Howeverthe detonators are necessarily not protected against a spurious signal having a frequency within the designed frequency band and are therefore at some riskfrom such a signal when the primary conductorwire is in position in thetoroidal core and especiallywhen the primary wire is connected to the firing source. Since it is often necessaryto position explosive charges and 'Magnadet'detonators in shotholes for a considerable period of time before blasting and, moreover, the primary wire is connected to the firing source for some time before blasting, it would be advantageous if the detonators were completely safe from all currents untilthetimeforfiring.

It is an object of this invention to provide an inductive coupling devicewhose currenttransmitting capabilitycan be controlled in orderto prevent currents above a predetermined value being transmitted through the device. Afurther object is to provide an inductive device for connecting an A. C. firing sourceto an electric ignition elementwherein the currenttransmitting capability ofthe device can be controlled so asto maintainthetransmitted current belowthe firing current until firing of the ignition element is desired.

In accordance with the invention an inductive coupling device for coupling a primarycircuitto a secondary circuit, comprises a magnetically permeable coreto which each of said circuits may be inductively coupled, and means to apply a steady magneticfield within at least a portion of the said core, the intensity of the said magneticfield within said core being variable to effect control of the transmission of electrical energyfrom the primaryto the secondary circuit.

The means to applythe magneticfield maycom- prise one or more magnets, preferably permanent magnets. The magnet (s) may advantageously be movable with respect to the said core to vary the field intensity. With such an arrangementthe magnetic field can be maintained within the magnetically permeable core until the transmission of current is required and then reduced or removed by relative movement of the magnet and core.

The said permanent magnet advantageously has its poles disposed so thatthey may both simultaneously be in close proximityto the magnetically permeable core.

The means to apply the magneticfield should preferably be capable of magnetically saturating the magnetically permeable core, thereby rendering the device incapable of passing any significant current when the magneticfield is applied within the core.

The magnetically permeable core is advantageously a ferrite core and is preferably a ring core, hereinaftertermed atoroidal core ortoroid.

In using the coupling device of the invention at least one of said primary and secondary circuits is coupled as a winding of at least oneturn through a magnetical ly permeable ring core and the primary circuit is connected to an A. C. source. When the core is a toroidal core at least one of said circuits may be coupled as a single strand of wire threaded through the said toroid. When the magneticfield intensity within the core is at a high value the transmission of electrical energy from the primary to the secondary circuit is inhibited but asthefield intensity is reduced the energy transmission increases.

Forfiring an ignition elementwith the device, the primary circuit has an inputconnected to an A. C. firing source and the secondary circuit has an output connected to beat last one ignition element. The primary circuit may be single-strand closed loop threaded through one orseveral toroidal cores each core being inductively coupled to at least one secon darywinding in serieswith the ignition element.

The invention also includes a method of controlling thetransmission ofelectrical energyfrom a primary circuitto a secondary circuit, the circuits being inductively coupled to a magnetically permeable core, in which method a steady magneticfield is applied within at least a portion of the core when suppression of energy transmission is desired and the magnetic field is reduced when energy transmission is desired.

The magneticfield is advantageously applied by a magnet which is movable with respectto the core and when energy transmission is desired the magnet is moved from a position in which the core lies within the magneticfield of said magnetto a position in which the core is effectively outside said magneticfield.

The method may advantageously be used as a method of arming an ignition elementwherein the primary circuit is an A. C. firing circuit and the secondary circuit includes at leastone ignition element, the ignition element (s) being maintained in a safe condition bythe application of the magneticfield until firing of the element (s) is required and then armed by reduction or removal ofthe magneticfield to permit subsequent ignition of the elementwhen A. C. energy is passed through the primarycircuit.

The invention is further illustrated bythe preferred embodimentwhich is hereinafterdescribed, byway of example, with reference to the accompanying draw ingswherein, Figure 1 shows diagrammatically an inductively (transformer) coupled electric detonatorfiring circuit assembly.

Figure 2 showsthe assembly of Fig. 1 with a magneticfield established within the transformer core, Figure 3 shows the assembly of Fig. 2 with the magneticfield effectivelywithdrawn from the trans formercore ; Figure 4shows a test circuit diagram for testing the efficiency of a transformer coupling ; and Figure 5 shows graphs of the secondary circuit currentwith various magneticfield intensities within the core of the inductive coupling device of the assembly of Fig. 1.

The assembly of Fig. 1 as a'Magnadet'electric detonatorfiring circuit comprising a ferrite toroid 1 to which an electric detonator 2 is coupled by a secondary circuit 3 and an A. C. generator4 is coupled by a primary circuit 5. The secondary circuit 3 comprises three turns of insulated wire around the core1 andtheprimarycircuit5comprisesasingle loop of insulated wirethrough the toroid 1. In normal use the detonator is fired by generating firing current in the generator 4 at a frequency within the range which the toroid is designed to transmit effectively.

In the assembly as shown in Fig. 2 two permanent magnets 6 are positioned respectively on opposite sidesofthetoroid 1 and in close proximitythereto, with both poles (12,13) of each magnet close to the toroid 1. With the magnets 6 in this position the coupling efficiency of the toroid 1 is temporarily reduced so that current supplied by the generator4 is not transmitted to the detonator 2. The efficiency is most effectively reduced by having the poles of one magnet positioned facing like poles of the other magnetthrough toroid. When the detonator 2 is to be firedthe magnets 6 are removed from the vicinity of the toroid 1 as shown in Fig. 3, whereupon the coupling efficiency of the toroid 1 is restored to its originafvalue and firing energy rnay be transmitted from the generator4 to the detonator 2.

The effectiveness of the magnets 6 in reducing the coupling efficiency of a toroid 1 wastested irtthe circuit arrangement of Fig. 4. In the test circuita variable frequency A. C. generator 9 was connected to provide inputto a power amplifier8. The A. C. output from the ampiifier8 was fed through a primary circuit 10 coupled to, atoroid 1 by a single loop (as in Fig.. 1). A secondary circuitll coupted to thetoroidi bytnrea turns of wire (as in Fig. 1) was connected to a resistive load 7 of 1 ohm, which corresponds approximately with the resistance of the ignition element inthe electric detonator 2.

The following Table gives the secondary circuit currents measuredat different frequencies for a primary circuit of 6amps using (a) no magnet (as in fig. 1), (b) one magnet, and (c) two magnets (as in Fig.

2) positioned closetothetoroid 1. The magnetswere 'Eclipse' (R. T. M.) E852'Maxi Magnets'having a closed circuitflux density of approximately 630 gauss.

The observationsgiven intheTable are shown graphically in Fig. 5. These results showthat overthe frequency range 5 to 50 kHz the secondary current can be substantially reduced bythe magnets. Thus the transmission of sufficient energy to fire an inductively coupled detonator, which usually required a minimum firing current of about 1 amp., can be readily prevented bythe application of a steady magnetic field within the core of the inductive coupling.

TABLE

SECONDARY CURENT (AttPS) S) Frequency No One kHz Magnet Magnets ; S1. 230. 1400009, 10 1. 77 0. 33 0. 0002 15'I. 85 0. 48 t 0. 003a, 20 1. 90 0. 66 0. 0042 251. 900. 770. 005S 30 1. 90 0. 87 0. 0066 401. 90l. OX. O. QQ8 501. 911. 230. 0108 CLAMS 1. An inductive coupling deviceforcoupling a primary circuit to a secondarycircuit, comprising a magnetically permeable core to which each of said circuits may be inductivelycoupled and means to apply a steady magnetic field within at least a portion of the said core, the intensity of the said magnetic field within said core being variable to effect control ofthetransmission ofelectrical energyfrom the primary to the secondary circuit.

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

Claims (16)

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

   source and the secondary circuit has an output connected to beat last one ignition element. The primary circuit may be single-strand closed loop threaded through one orseveral toroidal cores each core being inductively coupled to at least one secon darywinding in serieswith the ignition element.

   The invention also includes a method of controlling thetransmission ofelectrical energyfrom a primary circuitto a secondary circuit, the circuits being inductively coupled to a magnetically permeable core, in which method a steady magneticfield is applied within at least a portion of the core when suppression of energy transmission is desired and the magnetic field is reduced when energy transmission is desired.

   The magneticfield is advantageously applied by a magnet which is movable with respectto the core and when energy transmission is desired the magnet is moved from a position in which the core lies within the magneticfield of said magnetto a position in which the core is effectively outside said magneticfield.

   The method may advantageously be used as a method of arming an ignition elementwherein the primary circuit is an A. C. firing circuit and the secondary circuit includes at leastone ignition element, the ignition element (s) being maintained in a safe condition bythe application of the magneticfield until firing of the element (s) is required and then armed by reduction or removal ofthe magneticfield to permit subsequent ignition of the elementwhen A. C. energy is passed through the primarycircuit.

   The invention is further illustrated bythe preferred embodimentwhich is hereinafterdescribed, byway of example, with reference to the accompanying draw ingswherein, Figure 1 shows diagrammatically an inductively (transformer) coupled electric detonatorfiring circuit assembly.

   Figure 2 showsthe assembly of Fig. 1 with a magneticfield established within the transformer core, Figure 3 shows the assembly of Fig. 2 with the magneticfield effectivelywithdrawn from the trans formercore ; Figure 4shows a test circuit diagram for testing the efficiency of a transformer coupling ; and Figure 5 shows graphs of the secondary circuit currentwith various magneticfield intensities within the core of the inductive coupling device of the assembly of Fig. 1.

   The assembly of Fig. 1 as a'Magnadet'electric detonatorfiring circuit comprising a ferrite toroid 1 to which an electric detonator 2 is coupled by a secondary circuit 3 and an A. C. generator4 is coupled by a primary circuit 5. The secondary circuit 3 comprises three turns of insulated wire around the core1 andtheprimarycircuit5comprisesasingle loop of insulated wirethrough the toroid 1. In normal use the detonator is fired by generating firing current in the generator 4 at a frequency within the range which the toroid is designed to transmit effectively.

   In the assembly as shown in Fig. 2 two permanent magnets 6 are positioned respectively on opposite sidesofthetoroid 1 and in close proximitythereto, with both poles (12,13) of each magnet close to the toroid 1. With the magnets 6 in this position the coupling efficiency of the toroid 1 is temporarily reduced so that current supplied by the generator4 is not transmitted to the detonator 2. The efficiency is most effectively reduced by having the poles of one magnet positioned facing like poles of the other magnetthrough toroid. When the detonator 2 is to be firedthe magnets 6 are removed from the vicinity of the toroid 1 as shown in Fig. 3, whereupon the coupling efficiency of the toroid 1 is restored to its originafvalue and firing energy rnay be transmitted from the generator4 to the detonator 2.

   The effectiveness of the magnets 6 in reducing the coupling efficiency of a toroid 1 wastested irtthe circuit arrangement of Fig. 4. In the test circuita variable frequency A. C. generator 9 was connected to provide inputto a power amplifier8. The A. C. output from the ampiifier8 was fed through a primary circuit 10 coupled to, atoroid 1 by a single loop (as in Fig.. 1). A secondary circuitll coupted to thetoroidi bytnrea turns of wire (as in Fig. 1) was connected to a resistive load 7 of 1 ohm, which corresponds approximately with the resistance of the ignition element inthe electric detonator 2.

   The following Table gives the secondary circuit currents measuredat different frequencies for a primary circuit of 6amps using (a) no magnet (as in fig. 1), (b) one magnet, and (c) two magnets (as in Fig.

   2) positioned closetothetoroid 1. The magnetswere 'Eclipse' (R. T. M.) E852'Maxi Magnets'having a closed circuitflux density of approximately 630 gauss.

   The observationsgiven intheTable are shown graphically in Fig. 5. These results showthat overthe frequency range 5 to 50 kHz the secondary current can be substantially reduced bythe magnets. Thus the transmission of sufficient energy to fire an inductively coupled detonator, which usually required a minimum firing current of about 1 amp., can be readily prevented bythe application of a steady magnetic field within the core of the inductive coupling.

   TABLE

   SECONDARY CURENT (AttPS) S) Frequency No One kHz Magnet Magnets ; S1. 230. 1400009, 10 1. 77 0. 33 0. 0002 15'I. 85 0. 48 t 0. 003a, 20 1. 90 0. 66 0. 0042 251. 900. 770. 005S 30 1. 90 0. 87 0. 0066 401. 90l. OX. O. QQ8 501. 911. 230. 0108 CLAMS 1. An inductive coupling deviceforcoupling a primary circuit to a secondarycircuit, comprising a magnetically permeable core to which each of said circuits may be inductivelycoupled and means to apply a steady magnetic field within at least a portion of the said core, the intensity of the said magnetic field within said core being variable to effect control ofthetransmission ofelectrical energyfrom the primary to the secondary circuit.
2. 2. A coupling device as claimed in claim 1 wherein the meansto apply the magneticfield comprises at least one magnet.
3. 3. A coupling device as claimed in claim 2 wherein the said magnet is movable with respect to the core sothatthe magneticfield intensitycan bevaried by relative movement of the magnet and core.
4. 4. A coupling device as claimed in claim 2 or claim 3 wherein the said magnet is a permanent magnet.
5. 5. A coupling device as claimed in claim 4wherein the said permanent magnet has its poles disposed so thatthey may both simultaneously be in close proximitytothe magnetically permeable core.
6. 6. A coupling device as claimed in any one of claims 1 to 6 inclusive wherein the means to apply the magneticfield is capable of magnetically saturating the magnetically permeable core.
7. 7. A coupling device as claimed in any one of claims 1 to 6 inclusive wherein the magnetically permeable core is a ferrite core.
8. 8. A coupling device as claimed in any one of claims 1 to 7 inclusive wherein the core is a ring core.
9. 9. A coupling device as claimed in claim 8 wherein at least one of said circuits may be coupled as a winding of at least one turn through said ring core.
10. 10. A coupling device as claimed in claim 8 or claim 9wherein at leastone ofsaid circuits may be coupled as a single strand of wire threaded through the said ring core.
11. 11. A coupling device as claimed in any one of claims 1 to 10 inclusive having a primary circuit and a secondary circuit coupled to the core, the primary circuit having an input connected to an A. C. source and the secondary circuit having an output connected to at least one ignition element.
12. 12. A method of controlling the transmission of electrical energy from a primary circuitto a secondary circuit, the circuits being inductively coupled to a magnetically permeable core, in which method a steady magneticfield is applied within at least a portion of the core when suppression of energy transmission is desired andthe magneticfield is reduced when energy transmission is desired.
13. 13. A method is claimed in claim 12 wherein the magnetic field is applied by a magnet which is movablewith respecttothecorefrom a position in which the core lies withing the magnetic field of said magnetto a position in which the core is effectively outside said magneticfield.
14. 14. A method as claimed in claim 12 or 13which is a method of arming an ignition elementwherein the primary circuit is an A. C. firing circuit and the secondary circuit includes at least one ignition element, the ignition element (s) being maintained in a safe condition by the application of the magnetic field until firing of the element (s) is required and then armed by reduction or removal orthe magneticfield to permit subsequent ignition of the element when A. C. energy is passed through the primary circuit.
15. 15. A coupling device substantially as described herein with reference to the accompanying drawings.
16. 16. A method of controlling the transmission of electrical energy from a primary circuit to a secon dary circuit inductively coupled thereto, substantially as described herein with reference to the accompanying drawings.