WO2004064003A1

WO2004064003A1 - An electronic device detects and deactivates proximy electronic equipment of an area having restrictions for the use

Info

Publication number: WO2004064003A1
Application number: PCT/SE2003/000010
Authority: WO
Inventors: Ian James Forster; Peter Robert George Horrell; David J. Puleston; Gunnar Ahlberg
Original assignee: Envirotainer Ab
Priority date: 2003-01-08
Filing date: 2003-01-08
Publication date: 2004-07-29
Also published as: AU2003201791A1

Abstract

An electronic device having a detector that detects a signal indicative of the proximity of an area having restrictions for the use of certain electronic equipment, such as a transportation vessel or an intrinsically-safe area. The detector detects the presence of a signal that is emitted by e.g. a transportation vessel or a beacon associated with the restricted area. The detector may shut-off or in any other way disable any filed-emitting device comprised in the electronic device if the detector receives a signal that is indicative of the proximity of the protected area. The electronic device further comprises a self-check generator that emits a signal that can be detected by the detector. If the detector is operating properly, the detector will successfully receive the signal emitted by the generator. If a fault in the detector operation is discovered, the field-emitting device can be precautionary disabled.

Description

An electronic device detects and deactivates proximy electronic equipment of an area having restrictions for the,- use.

TECHNICAL FIELD

The present invention relates in general to security functionality of electronic equipment and in particular to proximity detectors, detecting the proximity of an area having restrictions for the use of certain electronic equipment, such as a transportation vessel or an intrinsically-safe area.

BACKGROUND

In certain areas, the use of certain electronic equipment may cause severe problems. It may for instance be desirable for certain electronic devices to be deactivated when being on board or in proximity to a transportation vessel. For example, different aviation administrations have restrictions on use of certain electronic devices emitting radio frequency electromagnetic signals on an aircraft during its operation. The emitted electromagnetic fields could potentially interfere with the aircraft systems, such as its navigation and/ or communication systems.

Furthermore, in a hospital, some treatment or analysis equipment may be disturbed in its operation by radio signals originating e.g. from portable electronic equipment. An active or idle mobile telephone may in the worst case cause a malfunctioning of life-maintaining equipment. Similarly, in e.g. laboratories or advanced production facilities, interfering electromagnetic fields may cause damages, which in turn may result in large economical losses.

In an "intrinsically-safe" area, all electrical or electronic equipment has to be classified as "intrinsically safe". This means that the equipment operates at a low voltage and is designed safe, regardless of short circuits, ground, over- voltage, equipment damage or component failure. A wide range of industries such as, for example, electric utilities, power plants, oil refineries, off shore oil rigs, gas ethylene companies, chemical plants, coal mining operations, coal prep plants and transfer stations, gas pipelines, plastic manufacturers, granaries, etc. present very hazardous environments, in which electrical equipment must be used. Because of these dangerous environments, various standards have been imposed for the design of electrical equipment for hazardous areas. Electronic equipment, not being intrinsically safe has to be deactivated or turned off before entering into such areas.

In order to prohibit interference between electronic equipment coming into the vicinity of such areas and the sensitive equipment within such areas, there are two main approaches of security functionality. One approach relies on detectors at the entrance to such areas, detecting specific properties associated with interfering electronic equipment. An alarm or automatic shut-off signal is emitted when interfering electronic equipment is detected. This approach has the disadvantage that an electronic equipment may be shut off when entering the area but can be turned on at a later occasion.

The other security functionality approach is to supply the electronic devices themselves with a proximity detector, detecting the proximity of an area having restrictions for the use of certain electronic equipment. Certain specific properties of the area are monitored and the interfering means of the electronic device is forced to be turned off. There are a large number of possible detectors. A number of possible proximity detectors are described in the patent US 6,281,797.

The electronic equipment can be divided into two main groups. The first group consists of personally portable devices, such as mobile telephones, laptop computers, pagers, personal digital assistant devices etc. These devices are assumed to be brought into the area by a person, carrying the electronic device, being in possession of the equipment. For this group of electronic equipment, the possessor may assist in the shutting-off procedure. The second group of electronic equipment consists of transported electronic equipment brought into the areas as cargo, in packages, as mail etc., where the person performing the actual entering action does not need to be aware of the existence of the electronic equipment. In such cases, fully automatic shut-off procedures have to be utilised.

For instance, many shipping companies attach tracking devices having some kind of field-emitting communication systems (also known as "tracking devices") to shipping containers to track their actual geographic location. This allows the shipping company to determine the geographic location of the container as it moves between the origination and destination points to determine whether the goods inside the container are on time, late, or somehow misplaced. Such systems are e.g. described in the international patent application WO 0175700.

In the published US patent application US 2002/0017989, a proximity detector is used to automatically deactivate such tracking devices upon entrance into a transportation vessel. However, a problem may occur if the frequency detector fails to operate. The proximity detector may then fail to recognise the proximity of a transportation vessel. If the proximity detector fails, the field-emitting and/ or tracking device systems will not be deactivated, thereby constituting a potential interference risk with the transportation vessel systems.

SUMMARY

A general problem with prior-art proximity detector systems is that they are crucially dependent to rely on the proper operation of the detector itself.

An object of the present invention is thus to provide proximity detector systems with a self-checking feature to determine if the proximity detector used is operating properly and if the safety functions may rely on the output from the proximity detector. A further object of the present invention is to provide such self-checking features, which do not interfere with the actual safety functions of the electronic device itself and possible other electronic equipment in the vicinity.

The above objects are achieved by devices and methods according to the accompanying claims. In general, an electronic device for sensing the proximity of an area having restrictions for the use of certain electronic equipment comprises a control system, a proximity detector and a generator. The proximity detector is arranged for receiving signals having characteristics indicative to the proximity of the area in question. The generator is arranged for emitting self-check signals of the same kind as is used by the proximity detector. When the generator is controlled to operate it is thus possible to determine if the proximity detector operates properly. If a malfunctioning of the proximity detector is determined, the means being potentially interfering with systems in the area is preferably precautionary disabled.

In one embodiment, the disabling function is locked during the time period when the generator operates in order to prevent self-disabling. In an alternative embodiment, the disabling function is performed only if the proximity detector indicates a proximity to the area during a time period longer than a predetermined value. In this embodiment, the generator is operated during time periods being shorter than this predetermined value. This arrangement prevents both the own generator and generators on neighbouring devices to cause any disabling functions.

Self-checking is preferably performed at disappearance of a proximity indication from the proximity detector and/or intermittently. The proximity detector and generator preferably detects/ generates acoustic and/ or electromagnetic signals, where the latter choice is the most preferred. In preferred embodiments, provisions for detecting detuning of the proximity detector are included.

The invention is generally applicable to all areas having restrictions for the use of certain electronic equipment, but is particularly beneficial in connection to transport vessels. More particularly, the present is best suited for proximity detection of aircraft.

The movable objects can in a general case be any objects having an electronic device that potentially may disturb equipment in the area. Furthermore, transported electronic equipment is of special interest, since they are more dependent on automatic safety systems. In particular, the present invention is best suited for tracking devices of transportation containers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of components of an embodiment of an electronic device according to the present invention;

FIG. 2 A is a schematic diagram of a cellular phone having a field-emitting device;

FIG. 2B is a schematic diagram of a personal digital assistant having a field-emitting device;

FIG. 2C is a schematic diagram of a laptop computer having a field- emitting device;

FIG. 3 is a perspective view of an aircraft container having a tracking device according to the present invention;

FIG. 4 is a flowchart describing the process of detection of a transportation vessel according to prior art;

FIG. 5 is a flowchart describing the process of detection of a transportation vessel according to one embodiment of the present invention;

FIG. 6 is a schematic illustration of an electromagnetic field detector with a self-checking electromagnetic field generator according to the present invention; FIG. 7 is a schematic illustration of an electromagnetic field detector arrangement having orthogonal element; and

FIG. 8 is a schematic illustration of an electromagnetic field detector with a phase-locked-loop circuit.

DETAILED DESCRIPTION

Referring to the drawings in general, it will be understood that the illustrations are for the purpose of describing preferred embodiments of the invention and are not intended to limit the invention to the details thereof.

Figure 1 schematically illustrates a typical electronic device 100 according to one embodiment of the present invention. The electronic device 100 or an object to which the electronic device 100 is associated emits or generates an electric, magnetic or electromagnetic field that may be interfering with e.g. aircraft systems. The electronic device 100 includes a control system 101 that includes a microprocessor 102 operatively connected with a memory 104, an input/ output interface 106 and a timer circuit 108. The microprocessor 102 interfaces with devices outside the control system 101 through the input/ output interface 106. If the microprocessor 102 needs to carry out instructions or operations based on time, the microprocessor 102 uses the timer circuit 108.

The electronic device 100 may also contain a tracking device 117, also referred to as a positioning system or global positioning system (GPS) receiver. These terms are used interchangeably herein. The tracking device 117 receives signals being interpretable as positioning information representing the location of the electronic device 100. The actual operation of a GPS system is well known by anyone skilled in the art, and is e.g. mentioned in US 5,648,763 or US 6,281,797.

The positioning information is received by the microprocessor 102 through the input/ output interface 106. The microprocessor 102 may store the positioning information in memory 104. The microprocessor 102 may also send the positioning information received from the tracking system 117 to a remote communication device 112 via the input/ output interface 106. The remote communication device 112 is a typical example of a field-emitting device 105, since it transmits information using wireless communications. A general field-emitting device 105 emits signals, e.g. electromagnetic signals, which potentially may interfere with different control systems. The remote communication device 112 is in this embodiment designed to communicate the positioning information to a remote site 130.

A power system 110 supplies power to the electronic device 100. The power system 1 10 is coupled to the electronic device 100 so that field-emitting device 105 functions can operate regardless of whether the electronic device 100 is in the presence of an external power source. However, the power system 110 may also be connected to external power as well. The microprocessor 102 controls which devices within and/ or associated with the electronic device 100 receive power by controlling the distribution of the power system 110.

An electromagnetic field detector 1 18 is utilised to determine the proximity of a transportation vessel, i.e. the electromagnetic field detector 118 is in this embodiment a proximity detector. The electromagnetic field detector 118 is designed to detect an electromagnetic signal having characteristics, e.g. a frequency or frequency distribution indicative of the proximity of a transportation vessel. The electromagnetic signal may be emitted by a transportation vessel as a normal by-product of its operation, such as signals emitted from communication systems or powering systems, for example. The electromagnetic signal may also be emitted by an electromagnetic frequency beacon contained inside or in proximity to the transportation vessel.

By way of example, Figures 2A, 2B and 2C illustrate examples of objects, in these cases electronic devices 10, that contain a field-emitting device 105 and which may be used with the present invention. Figure 2A is an illustration of a typical cellular or mobile phone 10A. The cellular phone 10A contains a field-emitting device 105A in the form of communication electronics that communicates data in the form of electromagnetic signals in the radio frequency range. Figure 2B is an illustration of a typical personal digital assistant 10B that includes a field-emitting device 105B in the form of a radio-frequency transmitter/ receiver. Figure 2C is an illustration of a typical laptop computer IOC that includes a field-emitting device 105C in the form of a monitor display. All of the aforementioned objects 10A, 10B, 10C may include an electronic device 100 having a control system 101 similar to that illustrated in Figure 1 to deactivate their respective field-emitting devices 105A, 105B, 105C and/ or other systems upon detection of the proximity of a transportation vessel.

Figure 3 illustrates another type of electronic device 100 that may be used in accordance with the present invention. This is an example of a transported electronic equipment, while Figs. 2A-2C are examples of personally portable devices. An object, in this embodiment a container 10, is provided that is especially suited for the cargo hold of a transportation vessel, and in particular to the cargo hold of an aircraft. An electronic device 100 containing a tracking device 117 and a remote communication device 112, is associated with the container 10 for determining its geographical position during the shipping process. The tracking device 117 and/ or remote communication device 112 may be placed internally within the electronic device 100 or the tracking device 117 and/ or remote communication device 112 may be placed on the container 10 and/or on an outer surface of the container 10. The tracking device 117 and/ or remote communication device 1 12 is placed in a position such that it will not interfere with or be damaged by the material handling systems used for loading the cargo hold.

Figure 4 illustrates a flow diagram of a typical operation of a prior art proximity detector system when the electromagnetic field detector 118 is used to determine if an electronic device 100 is in proximity to the transportation vessel. The operation starts (step 300) and a field-emitting device 105 is operated (step 302). Control system 101 receives any detected electromagnetic signals present that are received by the electromagnetic field detector 118 (step 304). The control system 101 determines, based on information received from the electromagnetic field detector 1 18, whether the electronic device 100 is in proximity to the transport vessel (decision step 306). If the control system 101 determines that the electronic device 100 is not in proximity to the transportation vessel, the process is repeated. Even if the flow diagram indicates a specified order, it should be understood that step 302 and steps 304, 306 in practice are performed independently. If the control system 101 determines that the electronic device 100 is in proximity to the transportation vessel, the control system 101 performs a deactivation procedure for its field-emitting device(s) 105 and/ or any other systems desired (step 308). The procedure ends in step 310.

From Fig. 4, it is seen that deactivation procedure will only take place after a positive detection of electromagnetic signals indicating proximity of a protected area.

Fig. 5 illustrates a flow diagram of an embodiment of a proximity detector system according to the present invention when the electromagnetic field detector 118 is used to determine if an electronic device 100 is in proximity to the transportation vessel. Steps 300 to 310 are similar as in Fig. 4. However, if nor proximity to a transportation vessel is detected in step 306, the procedure continues to step 312. In step 312, the electronic device itself generates an electromagnetic signal. This electromagnetic signal resembles a typical signal emitted by the transport vessel. In step 314, another detection of an electromagnetic signal is performed. If the detector operates properly, this detection will give an indication of proximity to a transport vessel, since the generator in step 314 has emitted such a signal. In step 316 it is decided if an indication of a relevant electromagnetic signal has been detected or not. If a relevant signal is detected, the detector operates properly and the procedure can be repeated again. However, if no relevant signal is detected, one or several parts of the electronic device are malfunctioning. As a precautionary measure, the field-emitting device should in such case also be shut-off, and the procedure continues to step 308. In the case of a detector error initiated shut-off, it is preferred if the shut-off is of a more permanent type, that only may be revoked by a user action.

Even if the flow diagram indicates a specified order, it should be understood that step 302, steps 304, 306 and steps 312-316 in practice are performed independently.

The electronic device 100 is configured to determine if it is in proximity to a transportation vessel, such as an aircraft transportation vessel, by detecting electromagnetic signals emitted by the transportation vessel during its normal operation. An aircraft with jet engines may produce specific electromagnetic signals during operations such as take off, landing, taxiing and pre-flight checks.

Figure 6 illustrates an electromagnetic field detector 118 according to one embodiment of the present invention, for detecting an electromagnetic signal in the range of 400 Hz. Aircraft power systems use an AC 400 Hz power distribution system that is somewhat unique to aircraft systems. An electromagnetic field detector 118 that detects a signal at approximately 400 Hz may thus be used to indicate that the electronic device 100 is in proximity to a transportation vessel and that any field-emitting devices 105 associated with the electronic device should be deactivated.

When the 400 Hz signal is detected by the control system 101, as illustrated in Fig. 6, the control system 101 causes a power switch 408 coupled to the control system 101 to disconnect power from the power system 110 to selected portions of the electronic device 100. The power switch 408 is one possible example of a deactivation means, for prohibiting the potentially interfering signals, interfering with vital operations within the area of interest, to be emitted from the field-emitting device. Many other types of deactivation means are also possible. The electromagnetic field detector 118 is comprised of a detector coil 400 that is broadly tuned to receive a 400 Hz electromagnetic signal, transforming it to an electric signal. The detector coil 400 is coupled to an amplifier and filter 402. The amplifier and filter 402 conditions the electric signal by amplifying low frequencies and by a bandpass filter limit the response to the 400 Hz region. In this manner, other irrelevant and/ or disturbing frequency components, e.g. 50 or 60 Hz, can be suppressed.

The amplifier and filter 402 passes the conditioned signal to threshold detector 404. The threshold detector 404 passes the signal through to the control system 101 if it has a level exceeding a reference threshold value. The threshold level may be based on total energy of the signal or on voltage and/ or current, individually. The threshold value is selected to suppress most situations involving only noise, but to pass through a signal when a significant 400 Hz signal is present. The threshold detector 404 may be comprised of a rectifier and low pass filter or integrator, which provides an outgoing voltage in proportion to the level of the incoming signal.

If the signal is above the threshold value, it is passed on to a digital filter 406 in the control system 101 to smooth the signal so that it may be input into a power switch 408 to control the power system 110. The power switch 408 may be a digital switch that generates a true and false condition, in this embodiment a CMOS transistor. The default condition of the power switch 408 is isolated, so that if the power system fails to supply the control system, the field- emitting devices are isolated.

According to an embodiment of the present invention, the electronic device also contains a self-checking 400 Hz electromagnetic field generator 420. The generator (420) is thus arranged for emitting self-check signals having substantially similar characteristics as said characteristics that are indicative of the proximity of the transportation vessel. In this embodiment, the 400 Hz electromagnetic field generator 420 is also coupled to the control system 101. The 400 Hz electromagnetic field generator 420 is arranged in such a way that an emitted field easily should be detected by the detector coil 400. Periodically, the 400 Hz electromagnetic field generator 420 is activated by a self-check functionality of the control system 101 to emit a 400 Hz electromagnetic signal. If the electromagnetic field detector 118 is operating properly, the 400 Hz signal emitted by the generator 420 will be detected. The control system 101 will receive a corresponding signal from the electromagnetic field detector 118 with minimal delay. In this manner, a self- check functionality of the control system 101 is able to determine that the electromagnetic field detector 118 is operating properly.

If the control system 101 does not receive a corresponding signal from the electromagnetic field detector 118, the control system 101 will assume that the electromagnetic field detector 1 18 is not operating properly. (In reality, the broken component could be present anywhere in the loop from the control system 101, via the generator 420, the electromagnetic field detector 118 and back to the control system 101.)

If the electronic device is a personally portable device, the control system 101 may emit an audio or visual alarm to the user, indicating a malfunction of the detector 118. If the detector malfunction is discovered after a certain period when no transportation vessel signals are detected, it is fairly safe to assume that the electronic device is not in proximity of a transportation vessel. In such cases, an alarm may be communicated through the remote communication device 112 to a remote site 130. However, if the malfunction is discovered shortly after the disappearance of a transportation vessel specific signal, the disappearance may be caused by the malfunction itself and the electronic device may still be on board of the transportation vessel. Any wireless communication should in such a case be avoided.

If there is any risk for interference, the detected error could be recorded in the memory 104 in order for an operator to retrieve at a later occasion. Moreover, since the detector is assumed to be broken, no external signals are detectable, and the field-emitting device may be allowed to be erroneously reactivated. In such a situation, it is, as indicated in Fig. 5, preferred if the field-emitting device is precautionary deactivated as long as the detector is assumed to be broken.

The emission of the self-check signal is preferably initiated in two ways. The first way is by an intermittent procedure during such time periods when no transportation vessel specific signal is detected. The other ways is to initiate the emission of a self-check signal at or shortly after the disappearance of a transportation vessel specific signal. Basically, no self-check has to be performed when a transportation vessel specific signal is indeed detected.

The regular emission initiation may be controlled by the control system in a number of ways. In one embodiment, the control system 101 sets a timer. The control system 101 polls the count of the timer to determine if the timer has expired. When the timer expires, the control system 101 causes the generator 420 to generate a self-check signal. The timer is preferably only counted down if no transportation vessel specific signal is present.

Once the control system 101 detects the lack of receipt of the signal from the detector 1 18, the control system 101 will cause the generator 420 to emit a self-check signal to be picked up by the detector 118. This is to ensure that the lack or receipt of the frequency signal is not due to an inoperable detector 1 18.

In one embodiment of the present invention, the control system 101 is arranged to interrupt any signal sent from the control system 101 to the power switch 408 during the emission from the electromagnetic field generator 420. This interruption is intended to minimise any risk for the power switch 408 to switch off the field-emitting device 105 just as a result of the electromagnetic field emitted from the electromagnetic field generator 420. The interruption functions as an override of the overall detector operation when its operability is checked. This prevents the proximity detector system to activate itself during self-checking. In particular, this works well together with systems that do not perform any self-checks while receiving a true electromagnetic signal from the transport vessel.

The electromagnetic field generator 420 and the electromagnetic field detector 118 are preferably arranged in such a way that even a relatively weak generated field may be detected. Typically the generator 420 and detector 118 are arranged close to each other and in such a way that the generated field is not attenuated by any unnecessary external means. If only relative weak generated fields have to be used, the interference between two devices 100 according to the present invention situated in the vicinity of each other may be reduced.

However, in some cases, there might be an overhearing from one object having a proximity detector device according to the present invention to another object having a proximity detector device operating at the same frequency. When one control system 101 initiates a field emission from the generator 420, this electromagnetic field may be sensed by the neighbouring one and interpreted as if a transportation vessel would be proximate. In such a way, interference between different devices could case unwanted deactivation of the field-emitting devices 105.

In another embodiment of the present invention, this drawback is prevented. In this embodiment, the control system 101 requires that a detected electromagnetic signal of the right frequency should be present for at least a predetermined period of time. If the detected signal is present only during shorter time periods, this is not interpreted as coming from any transport vessel. The predetermined time could be of almost any value, but a value in the order from a few seconds up to half a minute would operate well. During moving the object, the electromagnetic field from e.g. a transportation vessel will be present for a considerable time, in particular if the object is loaded into the transportation vessel. This delaying of the deactivation a couple of second will not be crucial. At the same time, by letting the emitted electromagnetic field from the generator 420 have a duration considerably shorter that this predetermined value, there is no risk that the self-check signal should cause any false deactivation neither in its own device nor a neighbouring one. At the same time, there is enough time to determine if the actual detector system operates properly.

Figure 7 illustrates another aspect of the detector 118. In this configuration, the detector 118 is capable of receiving signals independent of its orientation. The detector 118 includes three receiving elements 440, orthogonal to each other in three directions for use as a detector 118. The receiving elements 440 may be coils with tuned circuits to detect desired frequencies of electromagnetic fields, or magnetometers designed to sensitively measure AC field strengths.

The purpose of including more than one receiving element 440 and placing a plurality of receiving elements 440 orthogonal to each other is to create an orientation-independent receiving structure to ensure that signals are picked up regardless of the orientation of the electronic device 100 and/ or the detector 118. A summer 441 sums the squares of the signal patterns from the receiving elements 440 to eliminate any nulls.

The summed signals from the summer 441 are received by the control system 101. If the control system 101 detects a significant signal from the receiving elements 440 that are tuned to receive 400 Hz signals, the control system 101 is programmed to recognise that the electronic device 100 is in proximity to a transportation vessel and to perform the deactivation procedure. The summer 441 may also be contained inside of the control system 101 rather than a separate device from the control system 101.

A spectrum analyser may also be used as an electromagnetic field detector 1 18 to determine the presence of a particular frequency. This may be performed as described in the patent US 3,418,574. The spectrum analyser scans a band of signal frequencies in order to determine the frequency spectrum within a certain frequency band of any signal emitted by a transportation vessel. There are other methods of detecting particular electromagnetic signals so as to provide an electromagnetic field detector 118, and the preferred embodiments are not intended to limit the present invention from using such other methods.

An electromagnetic field beacon may also be used with the present invention to detect a transportation vessel or other area of interest. An electromagnetic beacon is a cooperative device that is proposefully placed in proximity to e.g. a transportation vessel or other area having restrictions for the use of certain electronic equipment to emit an electromagnetic signal to be detected by the electromagnetic field detector 118. An electromagnetic beacon may be desirable if the transportation vessel or protected area of interest does not emit a specific electromagnetic signal that can be uniquely detected by the electromagnetic field detector 118.

The electromagnetic beacon may be configured to emit an electromagnetic signal that is the same that is naturally emitted by e.g. a transportation vessel. In this manner, the electromagnetic field detector 118 will be capable of detecting an electromagnetic signal indicative of the proximity of a transportation vessel from either the transportation vessel itself, the electromagnetic beacon, or both. This particular configuration adds an extra measure of reliability and accuracy.

In one embodiment, the control system 101 determines if the electromagnetic field detector 118 is becoming or is de-tuned due to a change or failure in one of its components. Depending on the particular change or failure in the electromagnetic field detector 118, the electromagnetic field detector 118 may still detect signals emitted from the electromagnetic field generator 420. However, the electromagnetic field detector 118 may not receive such signals at the desired strength, and at the strength sufficient to pass through the threshold detector 404 and/ or surpass the control system's 101 threshold value.

The control system 101 cause the electromagnetic field generator 420 to emit a band of frequencies close to the centre frequency of the electromagnetic field detector 118 during the self-checking process. The control system 101 then determines the reception strength and noise level received by the electromagnetic field detector 118 for each of the frequencies in the band. If the control system 101 determines that the electromagnetic field detector 118 is not detecting the desired frequency at the correct threshold value or strength, the control system 101 can adjust the threshold detector 404 and/ or its settings in memory 104 so that the control system 101 properly receives an indication that the electromagnetic field detector 118 received an electromagnetic field signal even though the components and/ or tuning of the electromagnetic field detector 118 may have been altered and /or failed over time. If the control system 101 determines that such alteration or failure is significant enough to justify the reporting of an error, the control system 101 may then emit an alarm or communicate this error through the remote communication device 1 12 to the remote site 130, as previously described.

In another embodiment, the electromagnetic field detector 118 contains a phase-locked-loop (PLL) circuit. The threshold detector 404 is comprised of components to create a PLL circuit. In one embodiment, the threshold detector 404 with PLL circuit is the LMC567 CMOS tone decoder. Use of a PLL circuit ensures that the electromagnetic field detector 118 first determines that the electromagnetic field signal received from the detector coil 400 is substantially the same in frequency and phase over a given period of time, known as a "locked" condition, before the electromagnetic field detector 118 outputs a signal to the digital filter 406 indicating that an electromagnetic signal has been detected indicative of the proximity of a transportation vessel. A basic PLL circuit includes a phase and frequency detector that compares the phase of a reference signal received by the detector coil 400 to a voltage- controlled oscillator (VCO). The VCO generated by an output of the phase and reference detector is a signal in proportion to the phase difference of the reference signal and the output of the VCO. The direct current component of this output signal is used as the input voltage for the VCO. The output of the VCO is fed back to the phase and frequency detector for comparison to the reference signal that in turn controls the VCO frequency to minimise the phase difference. Therefore, the frequency and the phase of the reference signal and the VCO signal are made the same by this negative feedback indicative of a "locked" condition if the reference signal does not wander.

As illustrated in Figure 8, the electromagnetic signal is detected by the detector coil 400 and passes through the amplifier and filter 402. The signal is converted into a logic signal by the converter 450 and is input into the phase and frequency comparator 452. The phase and frequency comparator 452 also contains an integrated output that generates a signal that is filtered by a filter 458 and is input into a voltage-controlled oscillator (VCO) 456. The signal from the VCO 456 is divided by two by a frequency divider 454 and then input back into the phase and frequency comparator 452. The VCO 456 operates at twice the input frequency to avoid radiation from the VCO 456 blocking the input sensitivity of the phase and frequency comparator 452, but the VCO 456 could be designed to operate at one times the input frequency without need for the frequency divider 454. The VCO 456 could also be designed to operate at any factor times the input frequency so long as an appropriate frequency divider 454 is used.

When a frequency signal indicative of the proximity of a transportation vessel is received and when an adequate signal-to-noise ratio inside the integration time of the filter 458 is received, the VCO 456 moves into a phase-locked condition. When the phase and frequency comparator 452 detects the locked condition, it outputs a signal to the digital filter 406 to indicate that the electromagnetic field detector 118 has detected a signal indicative of the proximity of a transportation vessel.

The invention is generally applicable to all areas having restrictions for the use of certain electronic equipment. Such areas could e.g. include hospitals, sensitive laboratories, intrinsically-safe areas, where actual damage may be caused by the field-emitting devices. However, it would also be applicable to areas in which the use of e.g. mobile phones are unwanted, such as theatres, recreation areas, resting areas etc., where no harm is caused, except for the annoying use itself. The present invention is, however, particularly beneficial in connection to transport vessels. Transportation control systems become more and more complex and since huge numbers of objects and persons are transported, the need is increasingly growing. More particularly, the present is best suited for proximity detection of aircraft, since the influence on security systems in such cases may have catastrophic results.

The movable objects can in a general case be any objects having an electronic device that potentially may disturb equipment in the area. Obvious candidates are personal portable devices, such as mobile phones, laptop computers etc. Transported electronic equipment is of special interest, since they are more dependent on automatic safety systems. When such systems are loaded onto e.g. an aircraft, there are in general no persons available for deactivating any field-emission devices manually. In particular, the present invention is best suited for tracking devices of transportation containers.

The present invention is applicable to proximity detector systems operating according to very different principles. In principle, all possible kinds of signals, being typical for the area of interest could be used. The detector and self-check generator should of course operate according to the same principle. The most preferred principle is the use of electromagnetic signals, which are easy to generate and easy to detect and analyse. However, there are also other possibilities. Acoustic signals could e.g. be very typical for certain engines or motors, and such signals could then be used for proximity detection. The self-check generator will in such a case by a loudspeaker or other audible signal generator.

It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.

Claims

1. Movable object (10; 10A-C), comprising: an electronic device (100) for sensing the proximity of an area having restrictions for the use of certain electronic equipment, said electronic device (100) in turn comprising: control system (101); and detector (1 18) connected to said control system (101) for receiving signals having characteristics indicative to the proximity of said area, characterised in that said electronic device (100) further comprises: generator (420) connected to said control system (101) for emitting self- check signals having substantially similar characteristics as said characteristics indicative of the proximity of said area; said control system (101) in turn comprising self-check means, arranged for causing said generator (420) to emit said self-check signals and for determining if said detector (118) detects said emitted self-check signals.

2. Movable object according to claim 1, characterised in that said control system (101) further comprising deactivation means (408), deactivating functions of said object (10; 10A-C) and/ or electronic device (100) interfering with vital operations in said area if said detector (118) receives said signals having characteristics indicative to the proximity of said area.

3. Movable object according to claim 2, characterised in that said deactivation means (408) is arranged to perform said deactivating if said detector (118) receives said signals having characteristics indicative to the proximity of said area during a time period exceeding a predetermined time.

4. Movable object according to claim 3, characterised in that said control system (101) is arranged to cause said generator (420) to emit during a time period shorter than said predetermined time.

5. Movable object according to claim 2, characterised in that said deactivation means (408) is further arranged to neglect detection of said signals having characteristics indicative to the proximity of said area during operation of said generator (420).

6. Movable object according to any of the claims 2 to 5, characterised in that said deactivation means (408) is further arranged to deactivate said functions if said control system (101) indicates detector (118) failure.

7. Movable object according to any of the claims 2 to 6, characterised in that said deactivation means (408) is further arranged to reduce or turn off emission of electromagnetic radiation from said object (10) or electronic device (100).

8. Movable object according to claim 7, characterised in that said deactivation means (408) is further arranged to reducing or turning off emission of radio frequency electromagnetic radiation from said object (10) or electronic device (100).

9. Movable object according to any of the claim 1 to 8, characterised in that said control system (101) is arranged to initiate said generator (420) to emit if said signals having characteristics indicative to the proximity of said area disappear.

10. Movable object according to any of the claim 1 to 9, characterised in that said control system (101) is arranged to initiate said generator (420) to emit intermittently if no said signals having characteristics indicative to the proximity of said area are detected.

11. Movable object according to any of the claims 1 to 10, characterised in that said movable object is transported electronic equipment.

12. Movable object according to any of the claims 1 to 11, characterised in that said movable object is a container having a tracking device associated with it.

13. Movable object according to any of the claims 1 to 10, characterised in that said movable object is a personal portable equipment (10A-C).

14. Movable object according to any of the claims 1 to 13, characterised in that said electronic device (100) is a position- tracking device.

15. Movable object according to any of the claims 1 to 14, characterised in that said area is a transport vessel.

16. Movable object according to claim 15, characterised in that said transport vessel is an aircraft.

17. Movable object according to any of the claims 1 to 14, characterised in that said area is an intrinsically-safe area.

18. Movable object according to any of the claims 1 to 17, characterised in that said detector is an electromagnetic field detector (118).

19. Movable object according to claim 18, characterised in that said electromagnetic field detector (118) is arranged to detect frequencies in a frequency range around 400 Hz.

20. Movable object according to any of the claims 1 to 17, characterised in that said detector is an acoustic detector.

21. Movable object according to any of the claims 1 to 20, characterised in that said generator (420) is arranged to emit signals within a frequency band and said control system (101) is arranged to detect any detuning of said detector (118).

22. Electronic device (100) for sensing the proximity of an area having restrictions for the use of certain electronic equipment, said electronic device (100) in turn comprising: control system (101); and detector (118) connected to said control system (101) for receiving signals having characteristics indicative to the proximity of said area, characterised in that said electronic device (100) further comprises: generator (420) connected to said control system (101) for emitting self- check signals having substantially similar characteristics as said characteristics indicative of the proximity of said area; said control system (101) in turn comprising self-check means, arranged for causing said generator (420) to emit said self-check signals and for determining if said detector (118) detects said emitted self-check signals.

23. Method for proximity detector self-checking, comprising the step of: detecting signals having characteristics indicative to the proximity of an area having restrictions for the use of certain electronic equipment, characterised by the further steps of: emitting self-check signals having substantially similar characteristics as said characteristics indicative of the proximity of said area; and verifying a proper operation of said proximity detector by determining if said emitted self-check signals are detected.

24. Method according to claim 23, characterised by the further step of deactivating functions interfering with vital operations in said area if said signals having characteristics indicative to the proximity of said area are received.

25. Method according to claim 24, characterised in that said step of deactivating is performed if said signals having characteristics indicative to the proximity of said area are received during a time period exceeding a predetermined time.

26 Method according to claim 25, characterised in that said emitting step takes place during a time period shorter than said predetermined time.

27. Method according to claim 24, characterised in that said step of deactivating is inhibited during said step of emitting.

28. Method according to any of the claims 24 to 27, characterised in that said step of deactivating is further performed if said step of verifying indicates detector (118) failure.

29. Method according to any of the claims 24 to 28, characterised in that said step of deactivating comprises reducing or turning off emission of electromagnetic radiation.

30. Method according to any of the claim 23 to 29, characterised in that said step of emitting is initiated if said signals having characteristics indicative to the proximity of said area disappear.

31. Method according to any of the claim 23 to 30, characterised in that said step of emitting is initiated intermittently if no said signals having characteristics indicative to the proximity of said area are detected.

32. Method according to any of the claims 23 to 31, characterised in that said signals are electromagnetic signals.

33. Method according to claim 32, characterised in that said electromagnetic signal has a frequency in a frequency range around 400 Hz.

34. Method according to any of the claims 23 to 31, characterised in that said signals are acoustic signals.