GB2547038A

GB2547038A - An interlock system

Info

Publication number: GB2547038A
Application number: GB1602157.8A
Authority: GB
Inventors: Trice Michael; Johnson Robert
Original assignee: Fortress Interlocks Ltd
Current assignee: Fortress Interlocks Ltd
Priority date: 2016-02-05
Filing date: 2016-02-05
Publication date: 2017-08-09
Anticipated expiration: 2036-02-05
Also published as: WO2017134443A3; GB2547038B; WO2017134443A2; GB201602157D0

Abstract

An interlock system, a communication system, and a transceiver are provided. The interlock system 10 comprises: a first part 12 including a transmitter 30; and a second part 14 including a receiver 50. The first part 12 is configured to be held in a position adjacent the second part 14. The transmitter 30 and receiver 50 are configured to operate using an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz and are disposed on opposing sides of a barrier 20. A signal from the transmitter 30 for identifying the first part 12 is receivable by the receiver 50 through the barrier 20. A pipework system, a bursting disc, a portable sensor and a method of fitting an interlock system are also provided.

Description

Title: An interlock system Description of Invention

Embodiments of the present invention relate to an interlock system and a communication system. More particularly some embodiments relate to interlock and communication systems using a communication method which allows communication of data through a barrier.

Interlock systems are well known for their applications in many environments, to ensure greater safety. Generally, an interlock system forces certain events to occur in a specified sequence and/or prevent a machine from operating when it is not safe to do so. For example, in an industrial environment interlocks are used to prevent machines from being operated in a way which may injure a user or cause damage to equipment. Typically, a safety housing (such as a safety fence or other types of guard) prevents direct access to a machine, such that operation can be controlled (or stopped completely) by the interlock system when, for example, an access panel or door into the safety housing is open or may be opened (i.e. when a person may be within the housing).

Interlock systems often use a “trapped key” system. There are two main types of trapped key system which are used to limit access into the safety housing (i.e. access to a machine), these are safety locks and access locks. A safety lock is configured such that when the door is closed and locked, and the machine is operating, the safety key is held in an interlock key dock unit. When the safety key is removed from the interlock key dock unit (for example, so that the safety key can be used to unlock the access door), a switch is tripped in the interlock system which prevents power from being supplied to the machine. Hence, the machine cannot operate when the safety key is not in the interlock key dock unit. When the safety key is returned to the interlock key dock unit, the power is enabled and the machine can begin or recommence operation.

Access locks are used improve the safety to a safety lock. An access key is used to stop the safety key(s) of a safety lock from being removed. For example, a site manager may have the access key on their person, and when they are present at the interlock key dock unit they insert their access key into the unit. This allows the other key(s) to be removed and the machine will stop operating and the safety housing may be opened. The access key may only be removed once all of the safety key(s) have been reinserted.

Various trapped key interlock systems exist which may require, for example, the use of multiple keys which provide a logical control mechanism for forcing a sequence of events through the trapping and releasing of various of the keys. Additionally, the trapping/releasing of keys may be provided by a solenoid, which is controlled using a safety PLC (programmable logic controller) or other device. Hence, the interlock system controls aspects of the operation of a machine or machines and/or the gaining of access to a safety housing for a machine.

Interlock systems may also include a head assembly and tongue actuator. Typically, the head assembly is secured to a surface (for example, a door frame or hatch cover) and the tongue actuator is secured to another surface which interacts with the first surface (for example, the moveable portion of the door or hatch), so that when the door is closed, the tongue actuator is received by the head assembly, and when the door is open, the tongue actuator is not received by the head assembly. The door can be locked in the closed position with the tongue actuator retained by the head assembly. A trapped key system, as described above, may be used to ensure that the door is locked in the closed position before any power can be delivered to a machine accessed through the door. A problem with current tongue actuator and head assembly interlock systems is that a particular industrial site may have many interlock systems which use substantially identical tongue actuators. Thus, a single head assembly will accept a tongue actuator which may not be the tongue actuator associated with that head assembly (for example, a spare tongue actuator may be used) such that the head assembly incorrectly detects that a door is closed when it is, in fact, still open. This may result in the safety of the interlock system being compromised because a machine may be allowed to operate when it is not safe to do so (i.e. even though the door may still be open or unlocked).

According to a first aspect of the invention we provide an interlock system comprising: a first part including a transmitter; and a second part including a receiver; whereby the first part is configured to be held in a position adjacent the second part, and wherein the transmitter and receiver are configured to operate using an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz and are disposed on opposing sides of a barrier, such that a signal from the transmitter for identifying the first part is receivable by the receiver, through the barrier.

The first part may be held in a position abutting at least a portion of the second part. The first part may be held in a position with an air gap between the first part and the second part.

The first part may be lockable in the position in which it is held.

The barrier may be at least partially formed by a portion the first part. The barrier may be at least partially formed by a portion of the second part. The barrier may be at least partially formed by a portion of both the first part and the second part.

The transmitter may be embedded in the first part and/or the receiver may be embedded in the second part.

The barrier may be approximately 3mm thick.

At least a portion of the first part may be received in at least a portion of the second part.

The first part may be a tongue actuator and the second part may be a head assembly.

The first part may be secured to a door and the second part may be secured to a door frame.

The transmitter and/or the receiver may operate at frequency below about 10kHz. A data transfer rate between the transmitter and the receiver may be about 250bps.

The receiver of the second part may have an activation time to register the transmitter and process a signal for identifying the first part. The activation time may be substantially between about 100ms and 500ms.

The receiver of the second part may have a reading time in which the receiver processes a signal fault. The reading time may be between about 10 and 30 seconds. The reading time may be longer than the activation time.

The receiver may have a trip time in which to indicate that a transmitter has been removed. The trip time may be less than or equal to around 100ms.

The signal for identifying the first part may be a 10bit code.

The transmitter of the first part may have a high Q factor.

The receiver of the second part may include two controllers to process the signal transmitted from the transmitter independently.

The receiver may further include a filter which may increase the distance at which the transmitted signal from the transmitter is received.

The receiver may further include a distance sensor which may be configured to sense a distance between the transmitter and the receiver. The receiver may include a predetermined limit which may specify the maximum distance at which the receiver will process a signal from the transmitter.

In accordance with a second aspect of the invention we provide a communication system for a safety system comprising: a transmitter; and a receiver; wherein the transmitter and receiver are configured to operate using an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz and are disposed on opposing sides of a barrier, such that a signal from the transmitter for identifying the first part is receivable by the receiver, through the barrier.

The receiver may have an activation time to register the transmitter and process the signal from the transmitter. The activation time may be substantially between about 100ms and 500ms.

The receiver may have a reading time in which the receiver processes a signal fault. The reading time may be between about 10 and 30 seconds. The reading time may be longer than the activation time.

The signal transmitted by the transmitter may be a 10bit code.

The transmitter may have a high Q factor.

The receiver may include two controllers which may process the signal transmitted from the transmitter independently.

The barrier may be approximately 3mm thick.

In accordance with a third aspect of the invention, we provide a pipework system including a communication system according to the second aspect of the invention.

The pipework system may further include: a holder configured to hold a burst disc with respect to a conduit such that when a fluid pressure in the conduit exceeds a predetermined level the burst disc is rupturable to relieve the fluid pressure in the conduit, wherein the receiver is connectable to or embedded within the holder such that the receiver is configured to receive the signal from the transmitter which is connectable to or embedded within the burst disc.

In accordance with fourth aspect of the invention, we provide a burst disc for a pipework system in accordance with the third aspect of the invention wherein the burst disc is configured to be connected to the transmitter or wherein the burst disc is embedded within the burst disc.

In accordance with fifth aspect of the invention, we provide a portable sensor device for use with a communication system according to the second aspect of the invention or a pipework system in accordance with the third aspect of the invention or a burst disc in accordance with the fourth aspect of the invention, wherein the portable sensor device includes the receiver.

In accordance with a sixth aspect of the invention we provide a transceiver for a communication system or an interlock system which is configured to receive an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz, and transmit a modulated backscatter signal substantially between about 1 kHz and about 30kHz which corresponds to a predetermined identifier code.

In accordance with a seventh aspect of the invention we provide a transceiver for a communication system or an interlock system which is configured to transmit an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz, and receive a modulated backscatter signal substantially between about 1kHz and about 30kHz which corresponds to a predetermined identifier code.

In accordance with a eighth aspect of the invention we provide a part for an interlock system including a transceiver in accordance with either the sixth or seventh aspects of the invention.

In accordance with a further aspect of the invention we provide a method of fitting an interlock system in accordance with the first aspect of the invention, or of fitting a part in accordance with the eighth aspect of the invention including the step of fitting at least one part to a safety housing.

The present invention seeks to alleviate one or more problems associated with known interlock systems.

Embodiments of the invention will now be described by way of example only with reference to the accompanying figures, of which: FIGURE 1 is a perspective view of part of an interlock system in accordance with an embodiment of the invention; FIGURE 2 is a perspective view of a second part of an interlock system in accordance with an embodiment of the invention; FIGURE 3 is a perspective view of a first part of an interlock system in accordance with an embodiment of the invention; FIGURE 4 is a side view of part of an interlock system in accordance with an embodiment of the invention; FIGURE 5 is a block diagram illustrating parts of a communication system in accordance with an embodiment of the invention; FIGURE 6 is a block diagram illustrating parts of a communication system in accordance with an embodiment of the invention; FIGURE 7 is a perspective view of parts of an interlock system in accordance with an embodiment of the invention; FIGURE 8 shows parts of an interlock system in accordance with an embodiment of the invention; FIGURE 9 shows a side view of a pipework system in accordance with an embodiment of the invention; and FIGURE 10 shows a side view of a sensor device in accordance with an embodiment of the invention.

With reference to the accompanying figures, an embodiment of an interlock system 10 and a communication system 100 for a safety system is shown. The safety system may be an interlock system 10, or pipework system 200, or other type of safety system in which the communication system 100 is used.

Whilst some embodiments of the present invention are specifically described with reference to an interlock system 10, all of these teachings apply equally to other forms of safety system and should be construed accordingly.

In some other embodiments, the interlock system 10 includes a first part 12 having a transmitter 30 and a second part 14 having a receiver 50. The transmitter 30 is configured to transmit a signal which is receivable by the receiver 50 for confirming the identity of the transmitter 30. In some embodiments, the receiver 50 may be configured to output a signal to a master controller (i.e. a controller that controls one or more aspects of different interlocking systems), which indicates a status of the interlock system 10 (i.e. whether the first part 12 is the correct part).

The first part 12 is configured to be held in a position adjacent the second part 14 (e.g. so that the first part 12 and the second part 14 can communicate). In particular, in some embodiments, the interlock system 10 may form part of a safety mechanism that is used in or around machinery to prevent or restrict unsafe use. For example, the first part 12 may be provided on a safety housing door and the second part 14 may be provided on a door frame, so that when the safety housing door is closed the first part 12 is held adjacent, and may be received in, the second part 14. In some embodiments, the first part 12 may be locked in place adjacent the second part 14 or the first part 12 may be received and locked inside the second part 14.

The communication system 100 may include the transmitter 30 and receiver 50, which are configured to communicate using an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz. The transmitter 30 and receiver 50 are disposed on opposing sides of a barrier 20 which may form part of the interlock system 10 and is discussed in more detail below.

The transmitter 30 may be configured to transmit a signal, for identifying the first part 12. The signal transmitted by the transmitter 30 is receivable by the receiver 50 through the barrier 20 and the receiver 50 may be configured to process the signal to determine the identity of the transmitter 30 (and, hence, the first part 12).

Accordingly, the signal transmitted by the transmitter 30 may represent an identifier or signature for the transmitter 30 and/or first part 12. For example, an identifier may be a digitally encoded identifier, which may be a coded character string or a bit code (the identifier may be between 10 and 20 bits, and may a 10 bit code), which provides a unique or substantially unique identifier for that transmitter 30 and/or first part 12 (in some embodiments, the bit code may be a binary bit code). A signature may be a characteristic of the signal which can be compared in the receiver 50, or another device coupled to the receiver 50, to one or more stored signatures (each of which may be associated with a respective transmitter 30 and/or first part 12) to determine the identity of the transmitter 30 and/or first part 12.

The identifier may be stored in a transmitter memory module 36a of the transmitter 30. In the case of a signature, this may be dependent on an inherent property of part of the transmitter 30 (such as the shape, length, or material properties of a transmitter antenna 32 of the transmitter).

In some embodiments, there may be more than one first part 12 present in a warehouse or facility. In these and some other embodiments, each transmitter 30 and/or first part 12 may be associated with a different identifier which is transmitted by the transmitter 30. Accordingly, the receiver 50 may process the signal transmitted by the transmitter 30 (and received at the receiver 50) to confirm that the first part 12 is the correct part for interaction with the second part 14 with which the receiver 50 is associated. Accordingly, each receiver 50 may be associated with an identifier so that the receiver 50 can determine whether or not the received identifier from the transmitter 30 is the correct identifier (i.e. that the transmitter 30 is associated with the first part 12 which is correct for interaction with the second part 14). The receiver 50 may, therefore, store the associated identifier in a receiver memory module 58c of the receiver 50 and the processing of the received identifier by the receiver 50 may include comparison of the received identifier with the stored identifier in the receiver 50 (a match between the received and stored identifiers indicating that the correct first part 12 is attempting to interact, or is interacting with, the correct second part 14).

In some embodiments, a device coupled to the receiver 50 performs the processing and may be associated with an identifier in a similar manner.

In some embodiments, the identifier associated with the receiver 50 may be considered to be an authorised identifier because receipt (from the transmitter 30) of the authorised identifier indicates that the first part 12 (with which the transmitter 30 is associated) is authorised for interaction with the second part 14 (with which the receiver 50 is associated). In some embodiments, there is more than one authorised identifier associated with the receiver 50 (or device coupled thereto). This may, therefore, be considered to be a whitelist of authorised identifiers.

In some embodiments, the barrier 20 through which the signal is transmitted and received is at least partially formed by a portion of the first part 12 and/or a portion of the second part 14.

In other words, the barrier 20 may be a portion of the first and/or second part 12, 14. For example, the transmitter 30 may be embedded in a portion of the first part 12 during manufacturing. The receiver 30 may also be embedded in a portion of the second part 14 during manufacturing.

In some embodiments, this embedding is achieved by the provision of a cavity in the first part 12 which is configured to house the transmitter 30 and/or a cavity in the second part 14 which is configured to house the receiver 50. Once the transmitter 30 and/or receiver 50 are housed in their respective cavities, the cavities may be closed with respective covers to inhibit or substantially prevent removal of the transmitter 30 and/or receiver 50 from their cavities.

The transmitter 30 and/or receiver 50 may be bonded to a wall of the first part 12 and/or second part 14, as the case may be, by a suitable adhesive.

As will be appreciated, therefore, the transmitter 30 may be carried by the first part 12 and the receiver 50 may be carried by the second part 14.

In some embodiments, the barrier 20 is a metal material, for example, the barrier 20 may be steel or stainless steel. High purity stainless steel (such as SAE grade 316) may be used as it is more resistant to attack from chemicals and less prone to corrosion.

In some embodiments, the total thickness of the barrier 20 may be between around 1mm and 6mm.

In some embodiments, the barrier 20 may be a few millimetres thick (for example, the barrier 20 may be approximately 3mm thick). The barrier 20 need not necessarily be made entirely of a single portion of material. For example, the first part 12 may provide some of the barrier 20 (for example, around 1.5mm) and the second part 14 may also provide some of the barrier 20 (for example, also about 1.5mm). Hence, the barrier 20 may comprise different proportions of the first part 12 and the second part 14 (not limited to each providing around 50% of the barrier 20). In some embodiments, a third part (other than the first part 12 and second part 14) forms part of the barrier 20 such that this third part (or a portion of it) is located between the adjacent first and second parts 12, 14. This third part may abut both the first and second parts 12, 14 and may also be formed of a metal such as steel or stainless steel.

The first and second parts 12, 14 could take a number of different forms in accordance with embodiments of the invention. The forms described herein are given as examples only and embodiments of the invention may encompass the use of the transmitter 30 and receiver 50 in other forms of part 12,14.

On processing the received identifier, the receiver 50 may be configured to output a signal to another device of the interlock system 10, that signal may be representative of the received identifier being determined to belong to a transmitter 30 associated with the correct first part 12, it may be representative of the received identifier not being determined to belong to a transmitter 30 associated with the correct first part 12, or it may be representative of the received identifier (so that another device of the interlock system 10 can determine whether or not the transmitter 30 is associated with the correct first part 12).

The interlock system 10 may, therefore, be configured to use the signal output by the receiver 50 in order to control one or more aspects of the operation of the interlock system 10 - which may include the activation or deactivation of machinery, the activation or deactivation of an alarm, or the completion of a logic stage of a larger logic sequence of the interlock system 10, for example.

Embodiments of the present invention may be used with a number of different configurations of first and second parts 12,14. Indeed, some embodiments may be used in relation interlock systems 10 in which a first part 12 must be identified as the correct locking part with respect to a second part 14. There are numerous different examples of such scenarios is interlock systems 20 and only a few examples are provided.

In some embodiments, for example, the first part 12 is received in a recess 22 of the second part 14. The first part may be a tongue actuator 12 and the second part may be a head assembly 14. In this example, the tongue actuator 12 is receivable in the recess 22 of the head assembly 14. In some embodiments, the tongue actuator 12 is in the form of a pin which may have a generally circular, square, rectangular, pentagonal, hexagonal, or octagonal cross-section, for example.

In some embodiments, the first part 12 is held in a position abutting at least a portion of the second part 14 (i.e. the first part 12 and the second part 14 may touch). However, in other embodiments the first part 12 may be held in a position which includes an air gap between the first part 12 and the second part 14. As described above, in some embodiments, a third part may be interposed between the first and second parts 12,14.

In some embodiments, the second part 14 may also include a locking mechanism (not shown) which locks the first part 12 in the held position relative to the second part 14. For example, the first part 12 may include a feature, such as a protrusion or recess, which is engageable by a part of the locking mechanism to inhibit or substantially prevent movement of the first part 12 with respect to the second part 14 out of the held position.

The locking mechanism may be controlled by a key unit 26. A key 26a may be provided from a trapped key system 28 which only allows the key 26a to be released when a correct sequence of steps is performed (i.e. when a logic sequence of the interlock system 10 is followed). The key 26a may be used to lock/unlock the locking mechanism of the second part 14 and, hence, allow the first part 12 to be moved away from the second part 14 (e.g. out of engagement, abutment, or receipt). In some embodiments, a controller or safety PLC (safety programmable logic) may control trapping and/or releasing of the key unit 26 using a solenoid.

The key 26a may, in some embodiments, be the first part 12 and the locking mechanism may, in such embodiments, be the second part 14 (such that the transmitter 30 may be coupled to the key 26a and the receiver 50 may be coupled to the locking mechanism). Accordingly, the identity of the key 26a may be determined using the transmitter 30 and receiver 50 (in addition to or instead of any mechanical determination through the use of a keyed surface of the key 26a with a profile which is identifiable by the locking mechanism). In some embodiments, the trapped key system 28 includes one or more key receivers 28a in a key docking unit 28b. The or each key receiver 28a may include a receiver 50 which is configured to receive the identifier from the transmitter 30 associated with the key 26a to determine if that key 26a is the correct key 26a for that key receiver 28a.

The transmitter 30 and receiver 50 could take a number of different forms. For example, in some embodiments, the transmitter 30 includes a transmitter antenna 32 and a transmitter signal processing system 34,36,38. The transmitter signal processing system 34,36,38 may include one or more of a rectifier 34, a controller 36 (which may be a micro-controller 36) and a modulator 38. The transmitter signal processing system 34,36,38 may also include the transmitter memory module 36a which may be part of the controller 36, for example.

The transmitter signal processing system 34,36,38 is configured to process a signal for transmission using the transmitter antenna 32. This signal may be the signal representing the identifier for the transmitter 30 (and hence the associated first part 12).

In some embodiments, the receiver 50 includes a receiver antenna 52 and a receiver signal processing system 54,56,58. The receiver signal processing system 54, 56, 58 may include one or more of a driver 54, a filter 56, and a controller 58 (which may be a micro-controller 58). The controller 58 may be configured to output a decision (e.g. a decision representative of whether the correct identifier has been received) and/or may be configured to output that identifier or a signal representative of the identifier.

Accordingly, the receiver signal processing system 54,56,58 is configured to process a signal received, from the transmitter 30, via the receiver antenna 52. This signal may be the signal representing the identifier for the transmitter 30 (and hence the associated first part 12). The receiver signal processing system 54,56,58 may perform one or more operations on the received signal in order to assist in determining the identifier from the signal - e.g. performing one or more extraction, filtering, and/or amplification processes on the signal. In some embodiments, the receiver signal processing system 54,56,58 is configured to extract the identifier and to compare the identifier to the stored identifier or identifiers associated with authorised transmitters 30 (and first parts 12). In some embodiments, the receiver signal processing system 54,56,58 is configured to extract the identifier and the comparison is performed by another device coupled to the receiver 50.

In some embodiments, the receiver signal processing system 54,56,58 is also configured to generate a carrier signal for transmission using the receiver antenna 52 (e.g. to the transmitter 30). The receiver antenna 52 may, therefore, be configured for use in transmitting the carrier signal as well as in receiving the signal from the transmitter 30.

In some embodiments, a pair of receiver antennae 52 is provided - one of use in transmitting the carrier signal and one for use in receiving the signal from the transmitter 30.

The driver 56 of the receiver signal processing system 54,56,58 may, in some embodiments, be configured to drive the receiver antenna 52 with the carrier signal.

Accordingly, in some embodiments, the transmitter 30 may be a passive device. In such embodiments, the transmitter 30 may transmit a modulated backscatter signal (“the signal” which represents the identifier) to the receiver 50. As a passive device, the transmitter 30 may not include an integrated power source, so first the receiver 50 may need to provide power to the transmitter 30 such that a signal can be transmitted.

In some embodiments, the receiver 50 emits an electromagnetic signal between about 1kHz and about 30kHz (which may be the carrier signal emitted via the receiver antenna 52 and driven by the receiver signal processing system 54,56,58 (e.g. by the driver 54)).

The carrier signal may be received by the transmitter 30 to induce an electrical current in electrical components of the transmitter 30. In some embodiments, the current (and, therefore, the voltage) generated in the transmitter 30, by the carrier signal, provides power for the transmitter 30.

The transmitter 30 may modulate the carrier signal (e.g. using the modulator 38) and reflects the modulated signal towards the receiver 50 (e.g. via the receiver antenna 52). The modulation corresponds to an identifier such that the modulated signal represents the identifier. In some embodiments, the modulation corresponding to the identifier may be at a frequency between around 200Hz and 4kHz. The receiver 50 receives the modulated signal (i.e. the modulated backscatter signal) from the transmitter 30, and processes the received (and modulated) signal to determine the identifier.

In some embodiments, the transmitter antenna 32 may include a tuned inductor-capacitor parallel circuit. The transmitter antenna 32 may use a parallel circuit rather than a series circuit, so that at a resonant frequency of the transmitter antenna 32 the impedance is high (e.g. at a maximum) and, consequently, the voltage across the transmitter antenna 32 is also high (e.g. at a maximum).

It may, in some embodiments, be advantageous to tune the transmitter antenna 32 in this configuration because even when there is only a weak link between the transmitter antenna 32 and the receiver 50, the carrier signal may still induce enough power in the transmitter 30 for it to operate. In other words, the range of the transmission of the carrier signal is relatively large. In other words, in some embodiments, an inductor-capacitor parallel circuit may improve the range of the transmitter antenna 32 over an inductor-capacitor series circuit (which could still be used in some embodiments).

In some embodiments, the resonant frequency of the transmitter antenna 32 may be tuned such that it matches the frequency of the carrier signal emitted from the receiver 50. When both the receiver 50 and the transmitter 30 operate at the same frequency, the receiver antenna 52 and the transmitter antenna 32 have a highest relative coupling between them (and, in turn, the largest amount of power is transferred to the transmitter 30 from the receiver 50). This may help to ensure that the transmitter 30 produces a relatively high power modulated backscatter signal to be received by the receiver 50.

In an electrical resonant circuit, a Q factor represents the effect of electrical resistance on the resonance of the circuit. In a series circuit, the Q factor is equal to 1/RV(L/C), where R is resistance, L is inductance and C is capacitance of the circuit. In a parallel circuit, the Q factor is calculated by RV(C/L), where R,C and L are as above. The Q factor is related to the bandwidth of a resonant circuit, so that the higher the Q factor the narrower the bandwidth.

In some embodiments, the Q factor of the transmitter antenna 32 is lower than the Q factor of the receiver antenna 52. Thus, the bandwidth of the transmitter antenna 32 may be wider than the bandwidth of the receiver antenna 52. This may help to prevent issues caused by a mismatch between the transmitter antenna 32 and the receiver antenna 52 because the transmitter antenna 32 will function over a greater range of bandwidths than the receiver antenna 52 emits. In some embodiments, the Q factor may be in the range of between around 4 and around 16. In some embodiments, the Q factor may be about 10, for example.

As mentioned above, in some embodiments, the transmitter antenna 32 may include an inductor-capacitor series circuit, rather than an inductor-capacitor parallel circuit.

As will be understood, the carrier signal induces a signal in the transmitter antenna 32 and the induced signal may be referred to as a power signal herein.

The transmitter signal processing system 54, 56, 58 may include the rectifier 34 which may be configured to rectify the power signal received via the transmitter antenna 32.

In some embodiments, the rectifier 34 of the transmitter 30 may convert the power signal in the form of an induced AC voltage, which is generated in the transmitter antenna 32 by the carrier signal emitted by the receiver 50, into a DC voltage. This may enable, for example, other components of the transmitter signal processing system 54,56,58 to operate and/or to be simplified.

The DC voltage may be useable, for example, by the modulator 38 and/or controller 36. In some embodiments, the rectifier 34 may be a bridge rectifier (which may convert more of the AC voltage than other rectifier topologies). However, it should be appreciated that many rectifier topologies are known in the art which may be suitable (e.g. a half-wave rectifier or other configuration may be used to convert the AC voltage into a DC voltage).

The DC voltage output of the rectifier 34 may be referred to herein as a rectified power signal.

In some embodiments, the rectifier 34 may include a capacitor (not shown) connected in parallel with the output of the rectifier 34. The capacitor may act to stabilise (i.e. smooth) the rectified power signal.

In some embodiments, a DC-DC converter (not shown) is provided. The rectified power signal from the rectifier 34 may vary from around OV to around 60V, which may be damaging to the controller 36. Therefore, the DC-DC converter, if provided, may further stabilise or regulate the voltage supplied to the controller 36.

Of course, as little power should be lost in the operation of the DC-DC converter as possible. In some embodiments, one or more low drop out linear voltage regulators may be used as the DC-DC converter (although, other convertors such as buck convertors could also be used, since they are efficient when an input voltage does not need a large reduction (e.g. when the input voltage is relatively low)). Nevertheless, in some embodiments, low drop out linear voltages regulators may be more efficient when the voltage requires a large reduction (e.g. when the input voltage is relatively high).

There may be a desire, for example, to select a suitable regulator which prevents unwanted heating of the transmitter 30 and/or reduces the use of extra components in the transmitter 30 which may increase the overall size of the transmitter 30.

The DC-DC converter, if provided will receive the rectified power signal from the rectifier 34 and output the rectified power signal (but this output signal will be voltage regulated).

In some embodiments, the controller 36 may provide a modulation signal which is supplied to the modulator 38.

In some embodiments, the controller 36 may not need to provide any additional functionality other than the ability to store an identifier and provide a modulation signal to the modulator 38, in order to transmit the modulated backscatter signal. In some embodiments, the identifier is stored in the transmitter memory module 36a and, therefore, the controller 36 may be configured to access the identifier from the transmitter memory module 36a (which may be part of the controller 36 or separate from the controller 36). The controller 36 may be configured to generate the modulation signal wherein the modulation signal is dependent on the identifier and, therefore, represents the identifier.

As will be appreciated, the operation of the controller 36 (and any transmitter memory module 36a) may be powered using the rectified power signal.

The modulator 38 is configured to receive the modulation signal from the controller 36 and to modulate an aspect of the operation of the transmitter antenna 32 to alter backscattered electromagnetic radiation. Accordingly, the modulator 38 may be configured to modulate the power signal.

In some embodiments, the modulator 38 may, for example, short circuit the transmitter antenna 32 which changes the amount of backscatter radiation reflected back at the receiver 50.

The modulator 38 may also be powered using the rectified power signal. In some embodiments, the modulator 38 only requires a relatively low amount of power to operate - to enable operation when there is only weak coupling between the transmitter 30 and receiver 50 (e.g. when the transmitter 30 is further away from the receiver 50).

In some embodiments, the modulator 38 may modulate the voltage in the transmitter 30 after it has been rectified by the rectifier 34. In other words, the modulator 38 may modulate the rectified power signal. This may be advantageous in some embodiments because a DC signal (i.e. the rectified power signal) is easier to modulate than the AC carrier signal (i.e. the power signal received from the receiver 52). Modulation of the rectified power signal may, again, be achieved by short circuiting the output of the rectifier 34.

Various different forms of modulator 38 may be used in accordance with embodiments, for example, a Darlington pair or Darlington transistor may be used (particularly in embodiments in which the input current is very low), or a standard transistor or a MOSFET could also be used.

In summary, in some embodiments, the transmitter 30 may receive a carrier signal from the receiver 50, which induces a current and voltage in the transmitter 30 (i.e. the power signal). The power signal may be rectified and converted to a suitable power supply for the controller 36 and/or modulator 38 (i.e. the rectified power signal). The controller 36 may provide a modulation signal corresponding to (i.e. representing) an identifier, to the modulator 38. The modulator 38 may use the modulation signal to modify the operation of the transmitter (e.g. the power signal or rectified power signal), so that the identifier is transmitted back to the receiver 50 in a modulated backscatter signal.

In some embodiments, the receiver antenna 52 may be an inductor-capacitor series circuit. The circuit is tuned, so that a resonant frequency of the receiver antenna 52 is at the required carrier signal frequency. This means that the receiver antenna 52 impedance is low (e.g. at a minimum) when operating at the carrier frequency, so that the current flowing through the receiver antenna 52 is relatively high (e.g. at a maximum). This creates a electromagnetic field that is relatively large (e.g. at a maximum size) because the electromagnetic field is proportional to the current through the inductor.

In some embodiments, the receiver antenna 52 may have a high Q factor, so that the receiver antenna 52 has a relatively high powered electromagnetic field over a narrow bandwidth. In some embodiments, the Q factor is between around 4 and around 16. In some embodiments, the Q factor may be around 10.

In some embodiments, the transmitter antenna 32 and the receiver antenna 52 may be tuned (i.e. the transmitter antenna 32 and the receiver antenna 52 operate at similar resonant frequencies) so that a maximum amount of power is transferrable between the transmitter 30 and the receiver 50.

The high Q factor of the receiver antenna 52 in some embodiments may mean that other components (such as, capacitors and resistors) within the receiver antenna 52 require a relatively high voltage rating in order to provide the Q factor (see equation above).

In some embodiments, the Q factor will not exceed 20 because as the Q factor increases the bandwidth of the receiver antenna 52 decreases. This means any mismatch between the receiver antenna 52 and transmitter antenna 32 may result in a failure of the overall system 100.

In some embodiments, the driver 54 may force the receiver antenna 52 to oscillate at the resonant frequency of the receiver antenna 52. The driver 54 may receive an input from the controller 58 to control its operation and the driver 54 may output a driving signal at an operational frequency, which is between about 1 kHz and about 30 kHz. This driving signal causes the carrier signal to be output from the receiver antenna 52 (in some embodiments the driving signal and the carrier signal may be considered to be one and the same).

The driver 54 may be a configuration of transistors, such as MOSFETs or BJTs, in a push-pull arrangement, for example. However, other configurations could be used in the driver 54, such as a common source/emitter or a common drain/collector configuration.

As will be understood, in some embodiments, the controller 58 provides an input to the driver 54 and the driver 54 drives the receiver antenna 52 at its resonant frequency, so that the receiver 50 emits the carrier signal, to power the transmitter 30.

The transmitter 30, in turn, may transmit the modulated backscatter signal to the receiver 50.

The modulated backscatter signal is received by the receiver 50 through the receiver antenna 52. In particular, the modulated backscatter signal induces an electric current in the receiver antenna 52. This induced signal will be referred to as the received modulated backscatter signal.

The received modulated backscatter signal may be passed through the filter 56 and onto the controller 58.

In some embodiments, the filter 56 is configured to extract the identifier from the received modulated backscatter signal.

Some embodiments of the filter 56 are described with reference to figure 6.

In some embodiments, the filter 56 includes a buffer and scale block or module 61 which is configured to reduce a voltage of the signal from the receiver antenna 52 (the signal which includes the received modulated backscatter signal and which may be a relatively high voltage). For example, the buffer and scale block or module 61 may be configured to reduce the signal voltage to a level which is within the input operating voltage of an op-amp or other analogue filtering device. In other words, the buffer and scale block or module 61 may be configured to scale the received signal.

In some embodiments, the buffer and scale block or module 61 may be configured to centre or shift the signal which it receives (which includes the received modulated backscatter signal) about a virtual ground, if required.

In some embodiments, the buffer and scale block or module 61 may be configured to buffer the signal which it receives. This buffering may help to reduce or eliminate interference with the resonance of the receiver antenna 52 (which could cause the system 100 to fail).

The buffer and scale block or module 61 is configured to output the buffered and/or scaled signal (and potentially centred or shifted signal) for filtering and amplification in a filter and amplification sub-system 561 of the filter 56. The filter and amplification sub-system 561 may be configured to receive the signal from the buffer and scale block or module 61 and to filter from that signal one or more parts (e.g. frequencies) of the signal which are not the received modulated backscatter signal. For example, the filter and amplification subsystem 561 may be configured to perform one or more high-pass, low-pass, or band-pass filter operations to attenuate parts of the signal which are not within the frequency range of the received modulated backscattered signal.

The filter and amplification sub-system 561 may be further configured to amplify the resulting filtered signal, or parts thereof, for further processing.

Other operations which the filter and amplification sub-system 561 may be configured to perform include shifting the signal, to be centred on a different voltage level, for example.

The filter and amplification sub-system 561 may be configured to perform a digitising process to convert the analogue signal into a digital signal (suitable to be sent to the controller 58a of the receiver 50, for example). The filter and amplification sub-system 561 may be configured, therefore, to output a digital version of the received modulated backscatter signal (i.e. a digital backscatter signal which represents the identifier of the transmitter 20).

In some embodiments of the filter and amplification sub-system 561, a positive part of the signal which it receives may be processed in a positive amplitude envelope module 62a and a negative part of the signal which it receives may be processed in a negative amplitude envelope module 62b. The positive and negative amplitude envelope modules 62a, 62b are configured to generate respective envelope signals (positive and negative respectively); the identifier from the transmitter 30 being represented by information encoded within the amplitude envelopes of the signal being processed in some embodiments.

Both envelope modules 62a, 62b may operate in parallel with one another and may pass their respective output envelope signals to respective high pass filter and level shift modules 63.

Each high pass filter module 63 may be configured to attenuate low frequency signals within the two envelope signals - including any DC components of the envelope signals.

The operating frequency of the envelope modules 62a, 62b is selected in order to attenuate the components of the signal being processed which are at or around the carrier signal frequency and so as not to attenuate substantially the part of the signal being processed which originates from the received modulated backscatter signal (which may, as described above, have already undergone some processing steps). In other words, the frequency components of the processed signal at or around the carrier signal frequency are attenuated and the received modulated backscatter signal is passed.

As will be appreciated, if the carrier frequency and the frequency of the received modulated backscatter signal are too close to each other, then filtering of the carrier frequency components from the signal without substantial attenuation of the received modulated backscatter signal may be difficult. Therefore, the system 100 may be designed to provide separation between the frequencies of these two signals. The bit rate is, of course, dependent on the frequency of the received modulated backscatter signal and so the bit rate may also be limited by the need to achieve suitable separation of the frequencies of the two signals. The separation of the two frequencies may be dependent on the characteristics of the filter and amplification sub-system 561 - such as the shape of the frequency response curve of one or more filters used in the sub-system 561.

The positive and negative amplitude envelopes 62a,62b may be summed together in a summing module 64 of the filter and amplification sub-system 561 in order to produce a signal generally representative of received modulated backscatter signal and, therefore, also generally representative of the identifier of the transmitter 30.

The summing module 64 may be useful in some embodiments to produce a signal with greater amplitude and a better signal-to-noise ratio than might be achievable using on the positive or negative envelope alone.

The signal output by the summing module 64 will be referred to as the summed identifier signal.

In some embodiments, the filter and amplification sub-system 561 may include a low pass filter 65 may be used to remove one or more remaining carrier signal frequency components from the summed identifier signal and potentially other high frequency noise.

The summed identifier signal (whether or not it has passed through the low pass filter 65) may have relatively low amplitude due to the carrier signal having been largely or entirely removed.

This may be exasperated, in some embodiments, by the ratio between amplitudes of the carrier signal and received modulated backscatter signal being low because the system 100 requires high power and high Q factor, to transmit through the barrier 20 (i.e. the carrier signal is much bigger in amplitude than the variations due to the modulation).

In some embodiments, an amplifier module 66 is provided as part of the filter and amplification sub-system 561. The amplifier module 66 may be configured to increase amplitude of the summed identifier signal (which may or may not have been through the low pass filter 65). The level of amplification will be selected to provide a signal which is readable by a Schmitt trigger 67 or other digitising module. The Schmitt trigger 67 or other digitising module may be configured to produce a digital signal representative of the identifier of the transmitter 30 that can be processed by a controller 58.

The level of amplification may be selected such that any amplification of the noise is unlikely to impact the operation of the Schmitt trigger 67 or the correct digitising of the signal representative of the identifier of the transmitter 30.

As will be appreciated, the digital signal representative of the identifier of the transmitter 30 may be encoded characters or a short bit string (for example, a 10 bit string) forming the identifier, for example (the bits may be binary bits). In some embodiments, the controller 58 is configured to perform one or more additional processing steps on the digital signal in order to extract the identifier.

In some embodiments the filter and amplification sub-system 561 may include a level shifter 68 which is configured to receive the digital signal and to shift the voltage of the digital signal for use by the controller 58 and/or other digital components of the receiver 50 and/or one or more devices coupled to the receiver 50.

In some embodiments, the filter 56 may include all of the components discussed above (as part of the filter and amplification module 561 or otherwise). However, not all components are required for the receiver 50 of all embodiments. In some embodiments, the filter 56 does not use positive and negative amplitude envelope modules 62a,62b, as one amplitude envelope module (generating one envelope) may be sufficient. In some embodiments, the high pass filter(s) 63 is/are not needed. In some embodiments, the low pass filter 65 may not be required.

It should also be appreciated that not all of the filtering is necessarily performed by physical devices. Digital filtering could be implemented in part of the controller 58 or otherwise.

In summary, the receiver antenna 52 may be driven by the driver 54 to generate a carrier signal which may power the transmitter 30. The receiver 52 may receive a signal transmitted by the transmitter 30. The signal may be passed through the filter 56 to convert the signal into readable data for the controller 58. As will be appreciated, the digital signal may not always be representative of the identifier of the transmitter 30 because the transmitter 30 may not be within range of the receiver 50, for example. Therefore, the digital signal is conveys data to the controller 58 which may then be processed by the controller 58 (or other device) to determine whether that data includes an identifier and if that identifier is the identifier of the correct transmitter 30 (as discussed above).

In some embodiments, the receiver 50 may also include a distance sensor 70 which is configured to detect how far away the transmitter 30 is from the receiver 50.

The distance sensor 70 is configured to use the amplitude of the received modulated backscatter signal to determine an indication of the distance of the transmitter 30 from the receiver 50. In particular, the distance sensor 70 may be configured to use the signal which has been partially processed by the filter 56 (e.g. by the filter and amplification sub-system 561) to determine the distance of the transmitter 30 from the receiver 50.

In some embodiments, the distance sensor 70 may be configured to receive the summed identifier signal to determine the distance of the transmitter 30 from the receiver 50.

In some embodiments, the distance sensor 70 may be configured to use the summed identifier signal after amplification by the amplifier module 66. As such the distance sensor 70 may be connected to the amplifier module 66.

The distance sensor 70 may include a buffer 72, a positive amplitude envelope module 73, a low pass filter 74 and a level shifter 75. The distance sensor 70 may process the summed identifier signal (or other signal being used to determine the distance) by buffering the signal and extracting a positive amplitude envelope of the signal using the buffer 72 and the positive amplitude envelope module 73. The positive amplitude envelope may be passed through the low pass filter 74, so that only a low frequency signal remains (i.e. a near DC signal) - this signal represents the amplitude of the received modulated backscatter signal received by the receiver 50. The amplitude of this signal increases as the transmitter 30 is brought closer to the receiver 50, and hence the distance between the transmitter 30 and the receiver 50 can be detected by comparison to one or more predetermined threshold amplitudes. This comparison may be performed by the controller 58a of the receiver 50, for example. The predetermined threshold amplitudes may be determined during a calibration operation and may be stored in the receiver memory module 58c in some embodiments.

In some embodiments, the distance sensor 70 may be used to stop the receiver 50 from trying to read and process the signal from the transmitter when the transmitter 30 is positioned at the edge of a detectable range. In some embodiments, the maximum read range is around 20mm. This may be advantageous because the signal received by the transmitter 30 at the edge of the detectable range may be intermittent and if the receiver 50 (or device coupled thereto) tries to process an incomplete signal then the system 10 may output erratic decisions (i.e. the system may flip between a safe decision where a machine may begin operation and an unsafe decision where the machine may not begin operation).

In some embodiments, the distance sensor 70 may be used to limit the range of the receiver 50 artificially (for example, until the transmitter is around 18mm from the receiver 50). The receiver 50 may be configured to have a default range in which it will process signals received by the transmitter 30 (e.g. a range within a “detectable” range). This may be beneficial because it sets a maximum distance that the first part 12 may be distanced from the second part 14 before the receiver 50 will process any signal.

In some embodiments, a read range of around 18 to 20 mm may be too large, since a finger is typically smaller than this distance. It may be desired to set the read range to a shorter distance (for example, 10mm), in order to inhibit the insertion of fingers through a gap in the safety housing and/or between the first part 12 and the second part 14.

In some embodiments, the receiver 50 may include a second controller 58b (which may be a micro-controller) to process the signal received from the transmitter 30 in parallel with the controller 58a. The second controller 58b may be used to verify the result of the first controller 58a and ensure that the correct identifier is processed. This may be advantageous because the second controller 58b provides redundancy.

The electromagnetic signal frequency selection may be an important aspect of the interlock system 10. At higher frequencies (e.g. between 125kHz and 13MHz) the skin depth of some barriers, in particular metal, is very small. For example, 316 stainless steel has a skin depth of about 1.2mm at a frequency of 125kHz and about 0.1mm at 13MHz, and Aluminium has a skin depth of about 0.2mm at a frequency of 125kHz and 0.02mm at 13MHz By skin depth we mean the distance an electromagnetic signal will penetrate a material (the “normal” definition of skin depth). A small skin depth results in the electromagnetic signal not being able to penetrate through the barrier 20, since the strength of an electromagnetic signal is reduced by around 70%, per skin depth that the signal travels through. The thickness of the barrier 20 can be reduced; however, this introduces a number of issues. For example, a thin barrier is hard to produce reliably, and increases the manufacturing costs; additionally a thin wall is structurally weak (which is not a desired feature of an interlock system 10 which may require strength to provide some of the safety aspects).

For example, an interlock system 10 with a total barrier depth of 3mm was tested. The barrier 20 was split into two portions, as described earlier, and the first part 12 provided 1.5mm of the barrier and the second part 14 provided the remaining 1.5mm. Signals of different frequencies were tested, to measure the maximum air gap that the signal remains receivable by the receiver 50 (i.e. the signal is emitted from the transmitter 30 and travels through the barrier 20 formed by the first part 12, through air between the first and second parts 12,14, and through the second part of the barrier 20 formed by the second part 14). It was found that at a frequency of 12 kHz the signal travelled across a 2mm air gap, at a frequency of 8 kHz the signal travelled across a 10mm air gap, and at a frequency of 5 kHz the signal travelled across a 20mm air gap.

As the frequency of the electromagnetic signal is reduced, the corresponding skin depth of the material increases (i.e. the signal is able to penetrate the material by a greater distance). In some embodiments, the frequency of the electromagnetic signal may be selected such that it will penetrate a desired thickness of barrier 20 (and/or the maximum thickness that a barrier 20 may be made is largely dependent on the frequency of the electromagnetic signal). However, the lower the operating (i.e. carrier signal) frequency, the lower the data transfer rate will be (since the system relies on modulating the carrier signal to transmit the identifier). In some embodiments, the receiver 50 processes the identifier of the first part 12 to ensure the correct part 12 is present. If the data transfer rate is low then the receiver 50 may take too long to receive the signal from the transmitter 30 and the interlock system 10 may not operate correctly (which may be dangerous).

Accordingly, in some embodiments, the frequency of the carrier signal (and, in some embodiments, the signal emitted by the transmitter 30) may be less than about 30kHz, less than about 15kHz, less than about 10kHz, or less than about 5kHz. As will be appreciated different applications of the invention will require different barrier 20 thicknesses in order to provide sufficient protection for the transmitter 30 and for the receiver 50. The thickness of the barrier 20 may need to be adequate to protect against mechanical shock or, for example, exposure to chemicals (which may be corrosive chemicals). The barrier thickness may decrease over time (e.g. due to exposure to corrosive chemicals). Similarly, the maximum air gap may be dependent on the specific application - for example, dependent on the predictability (and reliability) of the proximity of the transmitter 30 and receiver 50, during use.

In some embodiments, the receiver 50 may have an activation time which is the time in which the receiver 50 recognises whether the transmitter 30 is present or not and the identifying code and processes the identifying code to confirm the correct part 12 is present. The activation time may be between about 100ms and about 500ms.

In some embodiments, the receiver 50 has a read time. The read time is used when the receiver 50 detects a signal but that signal may have a fault (e.g. the identifier is incorrect or garbled - an incorrect code may be received when an incorrect part 12 is present or if a signal from a correct part 12 suffers from interference). The read time may be longer than the activation time, since the receiver 50 may need to process multiple iterations of the identifier to ascertain a correct status (i.e. whether there is truly an incorrect part 12 present and a user may be trying to bypass the system 10 or the system 10 is suffering interference and the system 10 is safe to operate). In some embodiments, the read time is between about 10 and 30 seconds.

In some embodiments, the receiver 50 may have a trip time. The trip time is the time the receiver 50 takes to indicate that a part 12 has been removed. For example, when the part 12 is present, the receiver 50 will continuously receive multiple signals from the transmitter 30 which indicates that the part 12 is present and the system 10 is safe. The receiver 50 may need to react quickly when it is no longer receiving signals from the transmitter 30 (i.e. when the part 12 has been removed). In some embodiments, the trip time is a maximum of 100ms.

Low operating frequencies are difficult to achieve in small physical spaces because as the frequency decreases the inductor and capacitor in an antenna must increase in inductance and capacitance respectively and, therefore, size. The Q factor also has an effect on the physical side of the components; a high Q factor may require high inductance and a low capacitance and resistance (and a large inductance requires a larger inductor). In some embodiments, the diameter of wire used in the inductor may be varied to provide an appropriate Q factor.

In some embodiments, the carrier signal (and hence the modulated backscatter signal) of the system 10 may be about 10kHz and the transfer rate may be between around 125bps to 2kbps (and may be around 250bps). This provides a system 10 which will operate through a stainless steel barrier. It should be appreciated that a system intended for use with a barrier 20 of a different material may need to use a different frequency and/or a different transfer rate. The optimum frequency for the system 10 may depend on one or more of the following factors: the amount of data required to be transmitted in a certain time frame, the range/distance at which the system 10 is required to work over, the physical size of the system 10, the type of material that the system 10 must transmit the signal through, the local noise sources which may interfere with the operation of the system 10, and the individual component ratings and costs of putting the communication system together.

In some embodiments, the receiver 50 may also be a transmitter which is configured to transmit an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz. The receiver 50 may also be configured to receive a modulated backscatter signal substantially between about 1kHz and 30kHz (which includes a predetermined identifier using a modulation frequency between about 200Hz and 4kHz). In some embodiments, the transmitter 30 may also include a receiver which receives an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz and the transmitter 30 may also be configured to transmit a modulated backscatter signal substantially between 1kHz and 30kHz (which includes a predetermined identifier using a modulation frequency between about 200Hz and 4kHz).

Some embodiments of the present invention provide an interlock system 10 which allows the identification of a specific first part 12. For example, if the first part 12 is a tongue actuator and the second part 14 is a head assembly. The system 10 can identify if the wrong tongue actuator is being used in the head assembly. This improves the safety of the system 10, because a machine cannot operate unless the correct tongue actuator is linked with the head assembly (and, hence, it is ensured an access port or door is closed before operation commences). Therefore, the interlock system 10 is harder to defeat (i.e. bypass) and more tamper proof than previous systems.

In some embodiments, the transmitter 30 is not a passive device but is an active device - meaning that it has its own power source and need to obtain power from the carrier signal. Accordingly, the transmitter 30 may include a power source - such as a battery - or a connection configured to be coupled to a power supply - such as a mains electricity supply. In such embodiments, it will be appreciated that the components of the transmitter 30 concerned with obtaining useable power from the carrier signal may be omitted. Instead, the transmitter 30 may include a transmitter driver (not shown) which is configured to generate a signal representing the identifier (i.e. generally corresponding to the modulated backscatter signal discussed above. Similarly, in such embodiments, the receiver 50 need not include the components required to remove the carrier signal from the signal being processed to extract the received modulated backscatter signal. The receiver 50 may, however, still include one or more filters and amplifiers in order to filter and amplify the signal for conversion into a digital signal - generally as described above in relation to other embodiments.

It will be understood that many of the above embodiments have been described in relation to the transmission of an identifier from the transmitter 30 to the receiver 50. However, the same techniques may be used in relation to the transmission of other data - in addition to or instead of the identifier. For example, the data may include event information such as the number of actuations of a particular part of the interlock system 10 (e.g. the number of times the transmitter 30 has come into range of the receiver 50 from a position outside this range), time stamp information, and the like.

The communication system 100 may also be used in relation to other systems. For example, it may be used to improve the safety and/or diagnostics of safety valves in a pipework system 200. Burst discs 210 are used in pipework systems 200 to limit the level of fluid pressure in at least part of the pipework system 200.

The burst disc 210 may be configured to withstand up to a predetermined fluid pressure, when the fluid pressure (e.g. a fluid pressure differential across the disc) exceeds the predetermined fluid pressure then the burst disc 210 is configured to rupture. Accordingly, the burst disc 210 may be formed of a material of a predetermined thickness - with different thicknesses of the same material providing different predetermined fluid pressures at which that disc will rupture.

The burst disc 210 may be held in a holder 212 within an inner bore 222 of a pipe 220 (which may be part of a safety module for the pipework system 200) - or provided with respect to another form of conduit. During operation of the pipework system 200 if the predetermined fluid pressure is exceeded, the burst disc 210 ruptures (i.e. the excess pressure is relieved via the ruptured burst disc 210 (via a downstream passage accessible when the burst disc 210 ruptures). The holder 212 may be configured to allow removal of the ruptured burst disc 210 and replacement with a new burst disc 210.

The thickness/material of the burst disc 210 may vary depending on the industrial application/type pipework system (e.g. what diameter of pipe is used and the operating temperature of the pipework system 200), how much pressure the burst disc 210 must be able to withstand (i.e. the thicker a disc is the more pressure it should be able to withstand).

In some embodiments, the transmitter 30 may be connected to/embedded within the burst disc 210. The receiver 50 may be connected to/embedded within the holder 212. When a burst disc 210 (and the transmitter 30) is placed in the holder 212, the receiver 50 may operate in the same way as discussed above in order to identify the burst disc 210 and confirm that a suitable burst disc 210 has been installed. This is advantageous because, if a non-suitable burst disc 210 is installed, the safety of the pipework system 200 may be compromised (for example, if a thicker burst disc 210 is installed than that required, then the pipework system 200 may be exposed to pressures that are too high because the thicker burst disc 210 does not rupture at the pressure required). This may be a particular risk in situations in which there is a plurality of burst discs 210 which are all of a similar form (e.g. shape and size) and so are easily confused.

If a non-suitable burst disc 210 is installed, the receiver 50 may produce an alarm (for example, an alarm sound or warning light), and/or the receiver 50 may send a signal to a central control to indicate that the pipework system 200 has a fault and should not be used.

In some embodiments, the receiver 50 may be configurable to allow different types of burst discs 210 (e.g. different thicknesses and/or materials, etc.) to be determined as the correct burst disc 210. This allows flexibility in the use of the pipework system 200 because the receiver 50 can be reset by a user to accept a different type of burst disc 210. The receiver 50 may be configured to accept two or more identifiers which relate to different burst discs types and so the receiver 50 may allow variation in the burst discs 210 installed.

It should be appreciated that a pipework system 200 may not have the same time pressure as embodiments of the interlock system 10 described above. As such the transmitter 30 of the burst disc 210 may be configured to transmit a large amount of data (i.e. a much longer identifier code) because the receiver 50 may not need to process the entire code in fewer than 500ms (for example, the code may include additional burst disc data, such as manufacture date and/or holder type, etc.).

Additionally, a portable sensor device 250 may also be used. The portable sensor device 250 may also include a receiver 50, so that the portable sensor device 250 may be held adjacent/in the vicinity of an installed burst disc 210. This may allow the pipework system 200 to be checked by a user to make sure that appropriate burst discs 210 are installed in multiple locations.

The portable sensor device 250 may also be used to identify burst discs 210 before they are installed. For example, if a user has a container holding multiple different types of burst disc 210, they need to be able to identify which, out of the container, is suitable for installation. The sensor device 250 may provide a method of identifying burst discs 210 prior to installation. The portable sensor device 250 may be configured to output a visual and/or audible indication of the identified burst disc 210 - e.g. an indication of the type of burst disc 210 and/or the predetermined fluid pressure at which that burst disc 21 is configured to rupture.

It should be appreciated that embodiments described with reference to the interlock system 10, communication system 100 or the pipework system 200 may be combined with embodiments described in relation to other systems unless otherwise stated. For example, the portable sensor device 250 may be used in relation to the interlock system 10 described above.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. An interlock system comprising: a first part including a transmitter; and a second part including a receiver; whereby the first part is configured to be held in a position adjacent the second part, and wherein the transmitter and receiver are configured to operate using an electromagnetic signal at a frequency substantially between about 1 kHz and about 30kHz and are disposed on opposing sides of a barrier, such that a signal from the transmitter for identifying the first part is receivable by the receiver, through the barrier.

2. An interlock system according to claim 1 wherein the first part is held in a position abutting at least a portion of the second part.

3. An interlock system according to claim 1 wherein the first part is held in a position with an air gap between the first part and the second part.

4. An interlock system according to any of the preceding claims wherein the first part is lockable in the position in which it is held.

5. An interlock system according to any of the preceding claims wherein the barrier is at least partially formed by a portion the first part.

6. An interlock system according to any of the preceding claims wherein the barrier is at least partially formed by a portion of the second part.

7. An interlock system according to claims 5 or 6 wherein the barrier is at least partially formed by a portion of both the first part and the second part.

8. An interlock system according to any of the preceding claims wherein the transmitter is embedded in the first part and/or the receiver is embedded in the second part.

9. An interlock system according to any of the preceding claims wherein the barrier is approximately 3mm thick.

10. An interlock system according to any of the preceding claims wherein at least a portion of the first part is received in at least a portion of the second part.

11. An interlock system according to claim 10 wherein the first part is a tongue actuator and the second part is a head assembly.

12. An interlock system according to any of the preceding claims wherein the first part is secured to a door and the second part is secured to a door frame.

13. An interlock system according to any of the preceding claims wherein the transmitter and/or the receiver operate at frequency below about 10kHz.

14. An interlock system according to any of the preceding claims wherein a data transfer rate between the transmitter and the receiver is about 250bps.

15. An interlock system according to any of the preceding claims wherein the receiver of the second part has an activation time to register the transmitter and process a signal for identifying the first part.

16. An interlock system according to claim 15 wherein the activation time is substantially between about 100ms and 500ms.

17. An interlock system according to any of the preceding claims wherein the receiver of the second part has a reading time in which the receiver processes a signal fault.

18. An interlock system according to claim 18 wherein the reading time is between about 10 and 30 seconds.

19. An interlock system according to claims 15 or 16 and 17 or 18 wherein the reading time is longer than the activation time.

20. An interlock system according to any of the preceding claims wherein the receiver has a trip time in which to indicate that a transmitter has been removed.

21. An interlock system according to claim 20 wherein the trip time is less than or equal to around 100ms.

22. An interlock system according to any of the preceding claims wherein the signal for identifying the first part is a 10bit code.

23. An interlock system according to any of the preceding claims wherein the transmitter of the first part has a high Q factor.

24. An interlock system according to any of the preceding claims wherein the receiver of the second part includes two controllers to process the signal transmitted from the transmitter independently.

25. An interlock system according to any of the preceding claims wherein the receiver further includes a filter to increase the distance at which the transmitted signal from the transmitter is received.

26. An interlock system according to any of the preceding claims wherein the receiver further includes a distance sensor which is configured to sense a distance between the transmitter and the receiver.

27. An interlock system according to claim 26 wherein the receiver includes a predetermined limit which specifies the maximum distance at which the receiver will process a signal from the transmitter.

28. A communication system for a safety system comprising: a transmitter; and a receiver; wherein the transmitter and receiver are configured to operate using an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz and are disposed on opposing sides of a barrier, such that a signal from the transmitter is receivable by the receiver, through the barrier.

29. A communication system according to claim 28 wherein the transmitter and/or the receiver operate at frequency below about 10kHz.

30. A communication system according to claims 28 or 29 wherein a data transfer rate between the transmitter and the receiver is about 250bps.

31. A communication system according to claims 28 to 30 wherein the receiver has an activation time to register the transmitter and process the signal from the transmitter.

32. A communication system according to claim 31 wherein the activation time is substantially between about 100ms and 500ms.

33. A communication system according to claims 28 to 32 wherein the receiver has a reading time in which the receiver processes a signal fault.

34. A communication system according to claim 33 wherein the reading time is between about 10 and 30 seconds.

35. A communication system according to claims 33 or 34 when dependent on claims 31 or 32 wherein the reading time is longer than the activation time.

36. A communication system according to claims 28 to 35 wherein the receiver has a trip time in which to indicate that a transmitter has been removed.

37. A communication system according to claim 36 wherein the trip time is less than or equal to around 100ms.

38. A communication system according to claims 28 to 37 wherein the signal transmitted by the transmitter is a 10bit code.

39. A communication system according to claims 28 to 38 wherein the transmitter has a high Q factor.

40. A communication system according to claims 28 to 39 wherein the receiver includes two controllers to process the signal transmitted from the transmitter independently.

41. A communication system according to claims 28 to 40 wherein the receiver further includes a filter to increase the distance at which the transmitted signal from the transmitter is received.

42. A communication system according to claims 28 to 41 wherein the receiver further includes a distance sensor which is configured to sense a distance between the transmitter and the receiver.

43. A communication system according to claim 42 wherein the receiver includes a predetermined limit which specifies the maximum distance at which the receiver will process a signal from the transmitter.

44. A communication system according to any of the claims 28 to 43 wherein the barrier is approximately 3mm thick.

45. A pipework system including a communication system according to any of claims 28 to 44.

46. A pipework system according to claim 45, further including: a holder configured to hold a burst disc with respect to a conduit such that when a fluid pressure in the conduit exceeds a predetermined level the burst disc is rupturable to relieve the fluid pressure in the conduit, wherein the receiver is connectable to or embedded within the holder such that the receiver is configured to receive the signal from the transmitter which is connectable to or embedded within the burst disc.

47. A bursting disc for a pipework system according to claim 46, wherein the burst disc is configured to be connected to the transmitter or wherein the burst disc is embedded within the bursting disc.

48. A portable sensor device for use with a communication system according to any of claims 28 to 44 or a pipework system according to claim 45 or 46, wherein the portable sensor device includes the receiver.

49. A transceiver for a communication system or an interlock system which is configured to receive an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz, and transmit a modulated backscatter signal substantially between about 1kHz and about 30kHz which corresponds to a predetermined identifier code.

50. A transceiver for a communication system or an interlock system which is configured to transmit an electromagnetic signal at a frequency substantially between about 1kHz and about 30kHz, and receive a modulated backscatter signal substantially between about 1kHz and about 30kHz which corresponds to a predetermined identifier code.

51. A part for an interlock system including a transceiver according to claims 49 or 50.

52. A method of fitting an interlock system according to any claims 1 to 27, or of fitting a part according to claim 51 including the step of fitting at least one part to a safety housing.

53. An interlock system, a communication system, a transceiver, a part or a method of fitting substantially as herein described and/or with reference to the accompanying drawings.

54. A pipework system or a bursting disc substantially as herein described and/or with reference to the accompanying drawings.

55. Any novel feature or combination of features substantially as herein described and/or with reference to the accompanying drawings.