This invention relates to loudspeakers and in particular provides loudspeakers for emergency public address in remote or hazardous areas such as on off-shore oil/gas platforms and drilling rigs.
Loudspeakers are often used in hazardous areas to provide audible warnings as an integral part of the safety features of the area. In the event of any serious accidents or emergency procedures it is imperative that the work-force and any emergency teams can be given precise information regarding the incident and what steps must be taken such as decks to be cleared or, in the event of a serious fire, the procedure and route for the installation to be evacuated. In such circumstances it is imperative that the loudspeakers function for as long as possible in emergency conditions especially during fire as lives may be lost if such loudspeaker equipment is affected by a fire.
At present, the control electronics for the public address speakers are generally located in a safe area on the installation and cables are run from this area to the speakers. The loudspeakers are then controlled from a remote location such as a radio room or control room.
The present arrangement uses large amounts of cabling which is susceptible to damage during an emergency such as an explosion or fire on deck.
EP-A-0180423 describes a system for remotely adjusting a parameter of an electrical circuit within an enclosure in which sensors are mounted on respective explosion proof housings containing microprocessor circuitry for operating signals from the sensors. The signals are transmitted to a central control unit. A remote hand held unit is provided for individually setting the operating parameters of the circuitry.
The present invention therefore aims to overcome the disadvantages of known loudspeaker equipment and to provide a loudspeaker which will continue to function in hazardous conditions.
According to one aspect of the present invention there is provided a remote controlled loudspeaker comprising a main housing; an explosion proof body located within the main housing; closure means for the body; means for sealing the closure means in position; an aperture in one end of the main housing through which the body extends; means for sealing the body within the aperture and means for controlling the loudspeaker, the control means being provided within the body such that in the event of an emergency the loudspeaker may continue to operate from a remote location.
Sealing means are provided to seal the explosion-proof body within the loudspeaker. The sealing means may be in the form of silicone rubber o-rings and a sintered disc.
One embodiment of the present invention will be described with reference to and as shown in the accompanying drawings, in which:
Referring now to the figures there is described a loudspeaker 1 comprising a main housing 2 having a cylindrical portion 3 and a frustoconical horn portion 4. The housing 2 is formed of an anti-static compound (CENELEC EN 50014-6). One end 5 of the housing 2, remote from the frustoconical portion 4, is provided with a cover portion 6 which is sealed in position by a silicone rubber o-ring 7.
A flame-proof, explosion-proof body 8 made from aluminium alloy (DS-4261 equal to LM6) is located within the cylindrical portion 3 of the housing. The body 8 extends through an aperture 9 in the main housing 2 within the horn 4 of the housing 2 and is sealed by a cork sealing gasket 10 and a silicone rubber o-ring 11 and sintered disc 17. At the other end of the housing 2 the body 8 is closed by an explosion-proof enclosure cap 12 and is sealed by a further silicone o-ring 13 within the cylindrical portion 3 of the housing 2.
An antenna (not shown) is provided within the cover portion 6 of the housing 2. A bracket 14 is fixed to the main housing 2 by a suitable fixing means such as a screw 15. The loudspeaker may be mounted in any desired location.
The control electronics 16 for the loudspeaker are located within the explosion-proof body 8 and are described below.
As shown in Figure 2, an RF carrier set to the correct frequency is received by an RF unit 17. The modulation from the receiver 17 is then passed to a processor unit 18 where it is fed to a CTCSS decoder. This is programmed for detection of one of 38 standard sub-audible tones. If a tone is detected, the audio signal is then filtered to remove any high frequency noise and passed to a mute circuit 19. The mute circuit 19 ensures that in a condition of no received carrier into the receiver 17, no unwanted noise is fed to the last amplifier. From the volume control the audio signal is fed to a power amplifier which then feeds the signal to the speaker.
In an enhanced version of the control electronics as shown in figure 3, after the signal is passed through the mute circuit 19 it is fed to an electronic volume control and a DTMF receiver 20 (or decoder).
To enable the audio paths in this embodiment, the correct DTMF sequence must be received, which upon being decoded is fed to an 8 bit Micro Controller 21. Here it is checked for validity and also checked to establish ident, as each unit has its own individual ident no. If all the above parameters are met then the MCU 21 carries out such commands as change channel on radio, adjust volume level, turn CTCSS decoder on/off, unmute speaker, and generate emergency alarms.
When the audio path has been opened by the MCU 21 then the speech is fed to the power amplifier which then feeds the speaker.
It can be appreciated that in the event of an emergency such as a fire or explosion the loudspeaker 1 as described above may be operated from a remote location such as a helicopter in the area. Vital instructions may be given to personnel on the installation thus aiding evacuation from the area.
Furthermore, as the control electronics for each loudspeaker are provided within the explosion-proof body 8 inside the individual loudspeaker housing this eliminates the requirements for lengthy 100 volt line audio transmission cables which are prone to damage in the event of an explosion or serious fire. Each speaker is a "stand-alone" unit, no audio interconnection wires are necessary as with conventional systems.
Power to the unit may be fed via an uninterrupted power supply from the installation source or via a custom designed unit which would trickle charge from the installation mains and revert to emergency supply when the said mains supply is lost. The custom UPS would be likewise explosion proof and located as close to the loudspeaker as to maximise safety.
It is to be understood that the loudspeaker as described above may be located in any area where it is advantageous for public address announcements.