GB2082813A - Audible warning system - Google Patents

Abstract

A system for generating an audible warning signal has a voltage controlled oscillator controlled by a signal generator whose output periodic signal pattern is preprogrammable to produce a preselected warning signal pattern from the oscillator. The signal is gated through a multiplexer and applied to a number of remote loudspeaker transducer units in a sequence preselected by a clock pulse control of the multiplexer. Alternatively, the signal is transmitted to the transducer units along a common output line together with selected code signals which enable selected ones of the transducer units responsive to the code signals. The power of the warning signal received at each loudspeaker is controlled by a respective attenuator controlled in dependence on ambient light or sound level conditions. <IMAGE>

Description

SPECIFICATION Audible warning system The present invention relates to audible warning systems.

Audible warning systems of the type which are used in distributed machinery complexes such as in quarries and on factory floors are generally designed merely to provide a sound with an intensity considerably greater than the inherent background noise caused by machinery and the like. This type of warning system has considerable disadvantages, one major disadvantage being that while such warning systems provide a warning sound of sufficient intensity in a prescribed area the sound generally carries for some considerable distance outside the area and can cause considerable disturbance and distress to people outside the prescribed area, particularly at night in residential areas. In rural areas such high intensity sounds can seriously affect the breeding performance and health of livestock.In addition, such sounds can cause considerable shock and distress to personnel working in the prescribed area, particularly if one happens to be standing close to a loudspeaker or tannoy system when the warning sound is given. There is, in such instances also the possibility of an accident arising where a person is carrying out a particularly dangerous operation requiring is full concentration. In hospitals, laboratories and offices there can be even greater discrepancy between the alarm level and the ambient noise level.

The present invention seeks to provide an improved audible warning system.

Accordingly, the present invention provides a system for generating an audible warning signal, the system comprising a source of an electrical signal, said source being programmable to provide a preselected one of a number of signal patterns; a plurality of electro-mechanical transducers for converting said signal to an audible warning signal; and means coupling said source to said electro-mechanical transducers.

Advantageously the coupling means comprises a multiplexer for switching said signal sequentially to each of said electro-mechanical transducers.

The coupling means also includes a power amplifier with conveniently variable gain to vary the intensity of sound generated by the electromechanical transducers. preferably means are provided for automatically varying the gain of the power amplifier in dependence upon, for example, the ambient sound intensity or ambient light intensity, the latter allowing for a reduction in the audible warning sound intensity during the night.

An override time controlled switch may also be incorporated. An over-ride time controlled switch may be additionally incorporated.

In a preferred embodiment of the present invention the signal source is capable of producing a swept frequency signal or a single frequency signal with a variable temporal pattern to the signal, each of these being preselectable by an operator.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates a preferred embodiment of an audible warning system according to the present invention; and Figure 2 illustrates a modification of the audible warning system of Figure 1.

The system 10 illustrated in Figure 1 comprises a control unit 12, a signal source 14, a plurality of electro-mechanical transducers 1 6 (only one of which is shown in the drawing) and means 1 8 coupling the signal source 14 to the electromechanical transducers 1 6. The control unit 12, signal source 14 and coupling means 1 8 are conveniently arranged in a common housing which may be located at a suitable control point in an area or zone which is to be covered by the system.

The control unit comprises a power supply unit 20 which supplies power for the signal source and coupling means and may conveniently also provide power on a power rail 22 to the signal source and coupling means of other sub-alarm systems such as flashing light systems. Such subsystems may conveniently be used where different audible warning signals are required for different areas of a zone and where independent control of such areas is desired. The power supply unit 20 is controlled by a trigger unit 24 which is conveniently activated to energise the power supply unit for a preselected period, thus controlling the time period during which the audible warning signal is sounded.This time period may be adjustable to suit specific requirements and the trigger unit may be actuated either manually or automatically by a control signal generated, for example, by the start-up of a machine line such as a conveyor belt in a quarry.

This ensures that the warning signal is sounded immediately the machinery is activated.

Alternatively, a preset delay can be built in to the machinery power supply to ensure that the warning signal is sounded a preset time before the machinery is activated.

The signal source comprises a voltage controlled oscillator 26 whose output is coupled through a gate 28 to the coupling means 18. The voltage controlled oscillator 26 is controlled by a waveform generator 30 which applies a voltage of a preselected waveform to the voltage controlled oscillator 26 to generate a preselected output signal from the oscillator 26. A number of different waveform patterns may be provided by the generator 30. For example a square-wave or pulsed signal which varies between a high and a low voltage, when applied to the voltage controlled oscillator 26 produces a "Hl-LO output signal whose frequency varies abruptly between relatively high and low values.The ratio of the time period of the high frequency to low frequency portions of the output signal depend, of course, on the mark to space ratio of the square-wave or pulsed wave form from the generator 30 and can be varied to suit "on-site" requirements. A further type of wave form which may be provided by the generator 30 is a saw-tooth waveform which sweeps the oscillator 26 from a high frequency to a low frequency, or vice versa. Again the frequency of the saw-tooth wave form may be varied. As will be appreciated, the variations in wave form which may be generated by the generator 30 to control the output frequency signal of the oscillator 26 are considerable and the aforementioned two signals are merely exemplary of these. The particular waveform pattern produced by the generator 30 may be chosen for optimum effect in the area to be covered by the system.The waveform pattern generator 30 also conveniently provides a pulsed output signal of preselectable mark to space ratio to control the gate 28 in an open-close manner. This enables the electrical signal to be controlled to provide an alternating sound no-sound warning signal.

Each electro-mechanical transducer 1 6 comprises a loud speaker 32. Although only one loudspeaker 32 is shown the loudspeakers are conveniently provided in pairs to compensate for possible failure of one loudspeaker in each pair.

The loudspeaker is coupled to the coupling means by way of an attenuator 34, the attenuation of which may be continuously variable or stepped.

The attenuator 34 allows the intensity of the sound generated by the loud speaker 32 to be varied to suit ambient conditions and to produce the optimum sound signal to noise ratio for a particular warning signal. Each loudspeaker is conveniently directional in its field characteristics to reduce the sound spread outside the controlled area.

The coupling means comprises a power amplifier 36 which drives a multiplexer 38. The latter has a number of output lines each of which is connected to a respective electro-mechanical transducer 1 6. The multiplexer 38 is conveniently in the form of a multi-stage ring counter with an adjustable reset facility and driving V--MOS signal switches. The signal from the signal source 14 is applied through the power amplifier 36 to the multiplexer 38 which in turn may apply the signal to all of the electro-mechanical transducers 1 6 simultaneously or sequentially.Sequential energisation of the electro-mechanical transducers 1 6 maintains the net sound power produced at a minimum level to reduce the spread of sound outside the control area to a minimum while providing an optimum audible warning signal throughout the area. The multiplexer 38 is driven by a clock generator 40 whose pulse rate is adjustable to vary the on-time of each transducer 16.

Switching the output of the power amplifier 36 by the multiplexer 38 may give rise to transient signals being generated when the signal from the signal source 1 4 is present at the instant the output of the power amplifier 36 is switched from one transducer 16 to the next transducer. Such transients might in certain circumstances damage the power amplifier and in order to avoid this risk the signal source 14 is connected to the power amplifier 36 by way of an interrupt gate 42 which is conveniently controlled by the clock 40. The latter closes the gate 42 to block the signal from the signal source 14 immediately prior to switching of the power amplifier output and opens the gate 42 immediateiy after switching.This ensures that at the instant the power amplifier output is switched from one transducer to the next the amplifier output is quiescent thus avoiding the generation of transients. The inclusion of the interrupt gate 42 is a precautionary measure and normally may not be necessary.

The gain or output power of the power amplifier 36 may be controlled either manually or automatically by suitable control means which monitor, for example, the ambient sound level and adjusts the amplifier gain or power output accordingly. The control means may additionally or alternatively be light sensitive and arranged to reduce the gain or power output of the amplifier 36 during the night when generally ambient noise levels are reduced. A day-night time-switch may be incorporated.

The use of a large number of low power rated loud speakers 32 rather than a small number of large power rated loud speakers is also effective in ensuring a minimum spread of sound outside the area under control. In addition, control of the signal applied to each individual loud speaker may be effected by suitable control means which samples ambient noise levels and adjusts the attenuator 34 to vary the signal accordingly to ensure that the sound level generated by the loud speaker is not in excess of that required for optimum warning.

The provisions for control of the sound level generated by the preferred system together with the possibility of sequentially and successively energising the loud speakers allows an improved control of the environmental effect of the system without prejudicing the necessary safety considerations. In addition the provision for control of the type of warning signal generated enables the system to be tailored to suit individual installation requirements.

An information panel 44 is conveniently coupled to the multiplexer 38 to provide an operator of the system with information regarding the operation of the system, for example by indicating the operation or non-operation of a transducer 1 6 and to warn of failure of any part of the system. This is configured as a 'green band'/'red-band' indication.

Where very large scale systems are required it is economic to use a single continuous channel output from the system power amplifier with all speaker units being driven from the one line.

Figure 2 illustrates a modification to the system of Figure 1. Parts of the two systems of Figures 1 and 2 serving the same or similar functions are given the same reference numbers with those of Figure 2 being primed. An alarm signal is fed through an interrupter gate 42' and a power amplifier 36' which may be similar to the gate and amplifier of Figure 1 to a status detector 60 which replaces the multiplexer 38 of Figure 1. The power amplifier 36' has a second input to which a coded signal can be fed from a coded tone generator 62.

The system clock 40' controls both the generator 62 and the status detector 60 and the latter is connected to the system output line, conveniently a twin wire output line to which a number of transducer units 1 6' are connected. Each unit comprises a loudspeaker 32' coupled through a switch and adjustable volume control 64 to the output line. This is controlled by a tone decoder 66 also coupled to the output line, power for the tone decoder being derived through a rectifier power supply 68 from the signal on the output line.

The operation of the system of Figure 2 is similar to that of Figure 1 with the alarm signal being applied to the system output line. However, in order to select one of the transducer units to be energised a coded signal is also transmitted along the output line with the alarm signal. Each tone decoder 66 of the speaker units responds to a respective unique coded signal to close the associated loudspeaker switch 64, the loudspeaker 32' then being energised by the alarm signal on the output line. The coded signal is generated by the coded tone generator 62 which applies an ultrasonic carrier signal modulated by the coded signal to an input of the power amplifier 36'. Sequential operation of any number of the loudspeaker units in any preferred order can be effected simply by generating the respective coded signals in the desired sequence.The codes transmitted by the tone generator may be manually selectable or automatically selected in any desired sequence by means of a preprogrammed control 70 for the tone generator 62. The operating period for each loudspeaker unit can also be controlled simply by preselecting the transmission period of the unit coded signal. As will be appreciated, therefore the system of Figure 3 provides a high degree of versatility and control of the loudspeaker units. In addition, the various subsidiary functions described in relation to the system of Figure 1, such as control of the loudspeaker outputs in dependence on ambiemt noise, may also be provided in the system of Figure 2. The versatility of a system according to the present invention allows it to be tailored to suit user requirements and makes it particularly effective in environments such as hospitals and the like where one set of personnel might need to be warned of a possible emergency situation without alarming others. In that respect the system may also be used as an information system with different warning sounds conveying different information.

Claims (14)

1. A system for generating an audible warning signal, the system comprising a source of an electrical signal, said source being programmable to provide a preselected one of a number of signal patterns; a plurality of transducer units for converting said signal to an audible warning signal; and means coupling said source to said units, said means being operable for selectively energising said transducer units.

2. A system as claimed in Claim 1 wherein said signal source comprises a variable frequency signal generator and means for controlling the frequency of said signal generator in a preselectably variable manner.

3. A system as claimed in Claim 2 wherein said signal generator comprises a voltage controlled oscillator and said control means comprises a signal generator coupled to said oscillator for applying a tuning signal having a preselectable waveform to said oscillator.

4. A system as claimed in Claim 2 or 3 wherein the output of said signal generator is coupled to said coupling means by way of a gating circuit and said control means is coupled to said gating circuit for switching said gating circuit alternatively between open and closed states so as to provide a pulsed audible warning signal.

5. A system as claimed in any of Claims 1 to 4 wherein each transducer unit comprises a loudspeaker coupled to said coupling means by way of a variable altenuator.

6. A system as claimed in Claim 5 wherein said altenuator includes a sensor operable to monitor the level of at least one of ambient sound and light and adjust the attenuator in dependence thereon.

7. A system as claimed in any of claims 1 to 6 wherein said coupling means comprises a variable gain power amplifier including means for automatically adjusting the gain thereof for preselected time periods.

8. A system as claimed in any of claims 1 to 7 wherein said coupling means comprises a multiplexer coupling said signal source to each said transducer unit and control means operable to control said multiplexer for applying the signal from said signal source to said transducer units in a preselectable pattern.

9. A system as claimed in claim 8 wherein said control means is operable to control said multiplexer to apply said signal sequentially to each said transducer unit.

10. A system as claimed in claim 8 or 9 wherein said control means is coupled to a gating circuit coupling said signal source to an amplifier in said coupling means, said control means being operable to close said gating circuit momentarily during switching of said multiplexer output.

11. A system as claimed in claim 8,9 or 10 wherein said multiplexer comprises a ring counter and said control means comprises a pulse generator.

12. A system as claimed in any of claims 1 to 7 wherein said coupling means is coupled to the transducer units by a common signal line and comprises a code generator for transmitting any one or more of a plurality of preselectable codes signals along said line and wherein each transducer unit has a decoder operable to detect a respective one of said code signals and open a gating circuit coupling said line to a loudspeaker of said unit to enable generation of said audible warning signal by said loudspeaker.

13. A system as claimed in claim 12 wherein said code generator is operable to transmit said code signals or modulation on an ultrasonic carrier' signal.

14. A system as claimed in claim 12 or 13 wherein said code generator is operable to transmit said code signals in a presslectable repetitive sequence.

1 5. A system for generating an audible warning signal substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.