GB2220823A - Electromagnetic warning system - Google Patents

Abstract

An electromagnetic warning system 10 for miners working in underground mines 100 comprises: a transmitter unit 11, for transmitting an ultra-low frequency signal 54 through the strata 101 that define the mine openings 102; an ultra-low frequency micro-circuit receiver unit 12 equipped with antenna 50 which is tuned to the frequency of the transmitter unit 11 for producing a warning signal to the miners within an underground mine 100. The receiver may be powered from the battery of a miners cap lamp or a vehicle or a powered piece of equipment. The antenna 50 may comprise a high permeability ferrite core and tuned by capacitors in series with the antenna. The warning may be provided via a flicker in the lamp, audibly via a speaker or vehicle horn. An LCD screen may also be associated with the receiver. <IMAGE>

Description

ELECTROMAGNETIC FIRE WARNING SYSTEM FOR UNDERGROUND MINES The present invention relates generally to the field of mine safety devides and more particularly to detection systems for sensing.underground mine fires.

The rapid warning to miners of the occurrence of a mine fire is necessary for prompt mine evacuation before the fire has time to spread. The principal safety hazard associated with underground mine fires is the rapid spread of smoke and toxic fire gases throughout the mine's workings. Even miners who are quite far removed from the fire itself (up to several miles) can be exposed to life threatening concentrations of these combustion products within minutes. This occurs because the mine's ventilation systems, which continuously supplies fresh air to the mine, can circulate the combustion products from a mine fire with equal efficiency. In case of fire underground, the recommended course of action is to evacuate as quickly as possible. Over the years, only a tiny fraction of the survivors of underground fires have done so by remaining underground.The overwhelming majority have survived because they evacuated.

Given the need for rapid evacuation, it is clear that reliable and timely fire warning signaling systems are essential. In typical above-ground occupancies, conventional fire alarms such as bells, gongs, lights, whistles, public address announcements, and even "word-of-mouth" are sufficient. However, in underground mines, these methods are generally not suitable, and are therefore seldom used.

Underground mines are characterized by workers who are widely scattered over very large areas with little or no means of communication between groups or individuals. Even a short separation distance between the worker and an audible or visual alarm would render the alarm useless, especially if the worker was not in direct line-of-sight of the alarm or was using noisy equipment. In many mines, working areas are completely isolated, without links to any other part of the mine by telephone, power cable, compressed air line, conveyors, rail, or any other continuous or semi-continuous medium, over which a warning signal could be transmitted. And most mines are so large that the cost of installing a conventional signaling system would be prohibitive.

The spread of toxic combustion products is a time-dependent threat to miners, and rapid warning is necessary to avoid a time delay before allowing miners to exit the danger zone. In high-back room-and-pillar mines where diesel equipment is used and there are few, if any, conductors, a "through-the-earth" fire warning system would be inexpensive and easy to install.

The principle disadvantages of the prior art of underground fire warning systems are inherent slowness, vulnerability to damage, and limited mine coverage. The most common fire warning system in hard roc mines utilizes the above mentioned ventilation system to transport the fire warning signal. Known as the "stench system", it operates by releasing an odoriferous chemical (the same chemical used to odorize natural gas) into the mine's ventilation and/or compressed air streams. When the miners detect the odor, they immediately begin to evacuate according to a pre-arranged evacuation plan.

The principal disadvantages of the stench system are the time required for the odor to reach the farthest work places and the tendency for some parts of a mine to be consistently missed altogether. These problems are particularly acute in mines with openings having large cross-sectional areas, and therefore, extremely slow ventilation velocity. Under certain conditions, a fire can even generate its own ventilation forces which are counter to the mine's ventilation, further slowing down or reversing the flow of stench.

The deficiencies of the stench system are well known, however, due to the lack of a superior alternative, it is still the most commonly used system. Considerable research effort has been directed toward the development of wireless radio frequency signaling systems, however, each has inherent disadvantages which have precluded their widespread use in mines. Ultra-high frequency systems (UHF), due to their negligible through-the-rock transmission capabilities, are limited to line-of-sight applications. Once a miner travels around a corner such that the "pocket pager" type receiving antenna is not in a direct line-of-sight with the transmitting antenna, the wireless communication link is broken. In order to achieve mine-wide coverage for the warning system, it therefore becomes necessary to install transmitting antenna through virtually the entire mine.In large mines which might comprise several hundred miles of workings, the cost of such an installation would be prohibitive.

A second radio frequency system as disclosed in U.S.

Patent No. 4,495,495 operates in the medium frequency bands (MF). Although it too has limited through-the-rock transmission capabilities, it has an advantage over UHF systems in that specialized transmitting antenna are not required.

Transmission signals parasitically couple into any continuous or semi-continuous metallic conductors present. Thus, a receiver need only be within line-of-sight of any such conductor (power line, water line, rail, compressed air pipe, etc.) for the system to operate. The disadvantages of the MF system are that the receiving antenna are quite large and cumbersome (worn like a vest with large batteries in the pockets), and that many modern mines which utilize diesel-powered mobile equipment don't have continuous or semi-continuous metallic conductors installed throughout the mine. They may be present in certain locations, but too many areas would be left unprotected, and those miners working in remote parts of the mine may not be made aware of the existence of a mine fire.

The use of stench in the ventilation system in high-back room-and-pillar mines where air movement is slow can result in excessive time delay in sending a fire warning to underground miners. A fire warning system using wire for warning signal transmission can be destroyed when rock falls or explosions break the wire. Conventional fire warning systems are usually expensive to install in a mine, and therefore, the mine company may only install them where the majority of miners are working and those miners working in remote parts of the mine may not be in close proximity to a fire warning device and fail to be alerted to the existence of a mine fire.

As a consequence of the foregoing situation, there has existed a longstanding need among those concerned with the development of mine safety detection systems for a lightweight compact receiver apparatus that would not be dependent upon transmission signals traveling via omnipresent secondary wave guides, and which would simply rely upon the electromagnetic through-the-earth transmission of the receiver signal.

Briefly stated, the electromagnetic fire warning system for underground mines that forms the basis of the present invention comprises a conventional ultra-low frequency electromagnetic signal transmitting unit and a micro-circuit receiver unit.

The signal transmitting unit is positioned at or near the surface of an underground mine such that the ultra-low;.frequency electromagnetic signal will be transmitted directly through the strata that define the mine tunnels, passageways and chambers.

The microcircuit receiver unit is coupled to a tuned ferrite core receiving antenna which has been resonantly tuned with the transmitting unit by placing capacitance of appropriate size in series with the receiver.

The power for the receiver unit is coupled with miners cap lamp batteries, so that a reliable power supply is both readily available; and, the additional weight of the receiver unit to the miners person is minimized to the greatest extent possible.

Furthermore, the receiver unit is further adapted to be operably connected to the miners cap lamp to produce a visual signal; and/or provided with a warbler to produce an audible signal for warning the miner of an unsafe condition.

In addition, in an alternate version of the preferred embodiment the receiver unit might also be provided with a liquid crystal screen such that a digital readout of encoded information could be produced on the receiver via a frequency modulated transmission signal on the carrier wave from the transmission unit.

These and other objects, advantages, and novel features of the invention will become apparent from the detailed description of the best mode for carrying out the preferred embodiment of the invention which follows; particularly when considered in conjunction with the accompanying drawings, wherein: Fig. 1 is a combined schematic and circuit diagram of the transmitter unit and the receiver unit of this invention; Fig. 2 is a perspective view of the receiver unit in combination with the power supply for a miners cap lamp; and, Fig. 3 is an enlarged cross-sectional detail view of the receiver antenna.

As can be seen by reference to the drawings and in particular to Fig. 1, the electromagnetic fire warning system for underground mines, which forms the basis of the present invention is designated generally by the reference numeral (10). The fire warning system (10) comprises in general: a transmitter unit (11) and a receiver unit (12). These units will now be described in seriatim fashion.

As shown in Fig. 1, the transmitter unit (11) comprises a conventional ultra-low frequency transmitter (50) including a signal generator (51), an audio frequency range amplifier (52) and an antenna (53) for transmitting an ultra-low frequency signal (54). The transmitter (50) is disposed adjacent the surface of an underground mine (100) and will propagate the ultra-low frequency signals (54) through the strata (101) which defines the mine openings (102) for a distance of up to several miles, depending on the size and power of the aboveground transmitter unit (11).

The receiver unit (12) comprises a micro-circuit receiver (19) whose circuitry (20) is depicted in Fig. 1 and a receiver antenna (60) depicted in Fig. 2; wherein, the receiver (19) and the antenna (60) are operatively associated with a miners cap lamp apparatus (80), as will be described in greater detail further on in the specification.

As shown in Fig. 1, the receiver circuitry (20) of the present invention is response to frequencies of from 300 to 10,000 Hz receives an input signal from the ferrite core antenna (50) through the terminals (E3 and E4) whereupon the signal passes into a transformer (11), which transfers the signal into the circuitry (20).

The ultra-low frequency signal then passes through a four stage amplification arrangement before being transmitted to the output of a speaker at terminals (E5 and E6). The power is provided to the receiver circuitry (20) by a D.C. voltage source at terminal E7; wherein, the circuitry (20) is grounded at terminal E8. In addition, a volume control means is generally connected at terminals El and E2.

The first amplifier (U1A) receives the signal at its inverter input from the transformer (T1) and through use of its clamped feedback loop (R5 and C4) amplifies the signal before passing it to the second amplifier (U1D).

The second (U1D) and third (U1C) amplifiers increase the strength of the signal in a well recognized manner; wherein, the only difference in the circuitry between the second and third stages being the presence of diodes (CR3) and (CR4) in the feedback loop of the third amplifier (U1C).

The fourth amplifier (U2) provides the final amplification stage before passing the signal to the output of a speaker at E5 and E6. The thrice amplified signal is passed from the inverting output of the third amplifier (U1C) to the direct input. of the final amplifier (U2) for final amplification before passing it to a speaker.

The power supply for the receiver circuitry (20) is input at E7. The power to the various amplifier stages is directed through respective input and output connections of each of the amplifier stages.

As can best be seen by reference to Fig. 2, the receiver (19) is operatively-disposed intermediate the battery power supply (81) and the lamp (84) of a miners cap lamp assembly (80); wherein, the receiver antenna (60) is contained in the housing (19') of the micro-circuit receiver (19); and, wherein the output of the receiver (19) may be adapted to interrupt the power from the battery power supply (81) thru the power cable (82) in a well recognized manner, to cause the lamp (84) to flicker as a warning to the mine of an unsafe condition.

In addition, as indicated in Figs. 1 and 2, the output of the micro-circuit receiver (19) is also adapted to be connected to a speaker (70); whereby, an audio signal may be transmitted through the speaker (70) to the miner to warn the miner in situations; wherein, the bright lights within certain portions of the mine would render a flickering light signal ineffective due to the high intensity ambient lighting.

Turning now to Fig. 3, it can be seen that the receiver antenna (60) is provided with a short cylindrical antenna housing (60') and comprises a high-permeability ferrite core member (61) surrounded by a plurality of coils (62) of conductive wire (63) such as enameled copper wire, or the like, -to form a receiver antenna which may be tuned to the frequency of the transmitting antenna (53) (e.g. 2,000 Hz). Tuning is accomplished by placing capacitance'of apprqpriate size in series with the receiver antenna (60) to achieve a resonant frequency of choice. The wound ferrite core antenna (60) can be wound with wire adequate to achieve 100 millihenrys inductance, if required. The receiver (19) is preferably powered by the existing lamp battery (81), and therefore, is very portable and convenient to carry on ones person.

In an alternate embodiment of the invention (not shown), the apparatus (10) also contemplates the provision of a liquid crystal screen associated with the receiver (19) such that a digital printout of encoded information may be transmitted to the receiver (19) by a frequency modulated carrier wave signal (54) from'the transmitter unit (50).

In an additional alternate embodiment of the invention (not shown), the apparatus including encased ultra-low frequency receiver and ferrite core receiving antenna might be mounted on a vehicle or powered piece of equipment used in underground mining and be powered by the battery contained in such vehicle or piece of equipment. The warning signal might then be used to initiate a flickering of the vehicle lights or sound the horn thereby alerting the operator to the existence of a mine emergency. Encoded information might be made available to the vehicle operator as described for the cap lamp battery version of the apparatus.

By now it should be appreciated that the principal advantage of the present invention over the prior art systems are its relatively low cost as a fire warning system, its speed in alerting the miner, its superior survivability in cases of a mine disaster, the mobility of the receiver allowing roving miners in remote parts of the mine to be made aware of the presence of a fire, its light weight, and its assured power supply; since cap lamp batteries are recharged each 24-hour period and checked daily. The rapidity with which a fire warning is made evident to a miner, minimizes the miners exposure to toxic fire gases. These gases may overcome the miner before he dons his self-rescuer if there is valuable time lost in sending the fire warning, or if the warning system were to be damaged by fall of rock or explosion.

Having thereby described the subject matter of this invention, it should be obvious that many substitutions, modifications, and variations of the invention are possible in light of the above teachings. It is, therefore, to be understood.that the invention as taught and described herein is only to be limited to the extent of the breadth and scope of the appended claims.

Claims (6)

Claims:

1. An electromagnetic warning system for miners in underground mines wherein the miners are equipped with batter; powered cap lamps and wherein the warning system comprises: a transmitting unit including a conventional ultra-low frequency transmitter disposed adjacent to the surface of an underground mine and having a transmission frequency range of from 300 to 10,000 Hz; whereby the signal produced by the ultra-low frequency transmitter will be propagated through the strata surrqunding the mine openings; and, a receiving unit comprising a micro-circuit receiver powered from the battery of said battery powered cap lamp and operatively coupled to an ultra-low frequency antenna; wherein the antenna is tuned in resonance with the output of said ultra-low frequency transmitter.

2. The warning system as in claim 1 wherein said ultra-low frequency antenna comprises: a a high permeability ferrite core wound with conductive wre.

3. The warning system as in claim 2 wherein said antenna is tuned in resonance with thqoutput of said low-frequency transmitter by placing capacitors of appropriate size in series with said antenna.

4. The warning system as in claim 1 wherein said receiving unit is further provided with means responsive to the output of the transmitting unit for producing a visual signal to warn a miner.

5. The warning system as in claim 1 wherein said receiving unit is further provided with means responsive to the output of the transmitting unit for producing an audible signal to warn a miner.

6. An electromagnetic warning system substantially as herein described with reference to and as shown in the accompanying drawings.