EP0072825A1

EP0072825A1 - Electronic warning system

Info

Publication number: EP0072825A1
Application number: EP19820900552
Authority: EP
Inventors: Anthony Roland Coppen; Roger Force
Original assignee: Blue Circle Industries PLC
Current assignee: Blue Circle Industries PLC
Priority date: 1981-02-18
Filing date: 1982-02-18
Publication date: 1983-03-02
Also published as: WO1982002971A1; GB2107908A; DK455582A; AU8140182A; JPS58500091A

Abstract

Systeme d'alarme electronique comprenant un generateur de signaux, un amplificateur de puissance et au moins un haut-parleur. Des moyens peuvent etre prevus pour regler la sortie acoustique totale de l'amplificateur, pour regler le niveau de chaque haut-parleur et pour faire varier le niveau total suivant l'heure de la journee. Une pluralite de haut-parleurs, de preference directionnels, peuvent etre branches de maniere a fonctionner sequentiellement au moyen d'une operation de multiplexage. Le systeme peut produire un avertissement sonore de la mise en marche imminente d'une machine ou d'une installation tout en reduisant au minimum le niveau de bruit sur le lieu de travail ou dans son environnement immediat.Electronic alarm system comprising a signal generator, a power amplifier and at least one loudspeaker. Means may be provided for adjusting the total acoustic output of the amplifier, for adjusting the level of each speaker and for varying the total level according to the time of day. A plurality of loudspeakers, preferably directional, can be connected so as to operate sequentially by means of a multiplexing operation. The system can produce an audible warning of the imminent start-up of a machine or installation while minimizing the noise level at the workplace or in its immediate environment.

Description

ELECTRONIC WARNING SYSTEM

Field of the invention

The present invention relates to an electronic warning system, especially to such a system that emits an alarm (warning sound) of variable intensity and frequency.

Background to the invention

Warning devices are required in many industrial situations in order to give warning to personnel that machinery is about to start. Such devices have geπerally been of the vibrating diaphragm or siren type, having a fixed acoustic output, operated automatically from a contact at the main switch panel of machinery. In order to allow time for personnel to move clear, the start-up of the machinery is delayed for a given period after the alarm has been sounded.

These prior-art warning devices can be satisfactory insofar as they, meet the audible warning requirements of alarms. However, these devices are generally not adjustable for overall noise level, frequency or directivity and therefore suffer from the disadvantage that their performance cannot be optimised for any one specific task or position. Furthermore, the fixed acoustic output, which is often unmodulated, and the omnidirectional radiation characteristics of conventional warning devices can give rise to the environmental problem of excessive noise levels beyond the boundary of the works site, thereby causing considerable annoyance to residents in the neighbourhood, the problem being especially acute at night. Clearly, there is a need for a warning device or system that emits a satisfactory on-site warning signal whilst achieving an acceptable level of noise at the site boundary. It would also be desirable for such a warning system to be more flexible in operation than warning devices of the conventional types. Summary of the invention

According to the present invention, an electronic warning system comprises a signal generator, a power amplifier and at least one loudspeaker.

The system according to the present invention overcomes the limitations of the conventional warning devices by enabling. the alarm operating level, its acoustic frequency, its modulation pattern and its direction to be varied, thus providing the facility to optimise the audible impact on the personnel on the site whilst minimising the impact at the site boundary. The present system is suitable for both single and multiple signal source applications and is particularly suitable for applications - such as long conveyor belts, production lines, railways and hospitals - requiring multiple alarms from one contactor.

Although the overall output is determined by the setting of the volume control of the power amplifier, it is desirable to provide means whereby the output level from the or each loudspeaker can be pre-set.

It is also preferred to provide means whereby the frequency of the signal can be adjusted in order to achieve an optimum contrast between the warning signal generated and the background noise. It is also preferred to incorporate means for adjusting the alarm temporal pattern in order to achieve optimum detectability and recognition. Thus, an amplitude and frequency modulating device may be provided in order to provide the required pattern (e.g. a characteristic wailing, hi-lo or pulsed sound, etc.).

With the present system, central control of the or each loudspeaker can be achieved. Thus, it is preferred to pass the signal. from the amplifier through a multiplex coding unit, each loudspeaker being provided with a specific multiplex decoding unit. By this means, it is possible to arrange that a plurality of loudspeakers operate in a given sequence. This arrangement is particularly advantageous in the case, for example, where warning is to be given of the starting up of a long conveyor belt (which, in a quarry could be as long as 800 metres or more). Sequential operation of loudspeakers sited at predetermined intervals along the length of the conveyor belt would ensure that adequate warning is given to operatives, whilst avoiding an excessive acoustic total output at any given point in time. Brief description of the drawing The single accompanying figure represents a block diagram of a warning system in accordance with the present invention. Description of preferred embodiments

As illustrated in the accompanying drawing, a preferred embodiment of the present invention comprises a variable-frequency signal generator and a power amplifier providing a suitable output signal to one or more remotely sited loudspeakers. The alarm signal is produced in the signal generator and is then modulated by a programme selector in order to provide the means for optimising froth frequency and modulation for any background noise level. The acoustic output of the system is adjustable in three distinctly separate ways in order to achieve an optimum operating level and noise/warning contrast.

Firstly, the overall acoustic output of the system is adjusted via the main amplifier gain (volume) control.

Secondly, the level of each individual loudspeaker is separately adjustable, by means of a secondary volume control, up to the maximum level set by the main amplifier level control. In practice, this is checked with a sound-level meter midway between two units to ensure that an adequate noise-to-background level is obtained. A value of 30 dB has proved satisfactory. Alternatively, the output of each individual loudspeaker could be electronically controlled to any desired level above the ambient noise level, by using the loudspeaker itself or an associated transducer as a feedback device.

Thirdly, a programmable timer is incorporated in order to provide the facility of varying the overall level to produce an optimum setting both for day and for night operation. This last feature is particularly important as background levels often drop by 10 dB or more at night, during which period any high industrial boundary noise levels are most likely to give rise to complaint (see British Standard (BS) 4142 - Method of Rating Industrial Noise. Affecting Mixed Residential and Industrial Areas).

It has proved satisfactory to set the level at -10 dB for the night period. The system of the present invention can be used in applications where only one loudspeaker is required. However, the present system is particularly advantageous in applications requiring two or more warning devices associated with a particular item of plant, it being necessary only to extend the number of remotely sited loudspeaker units.

In the case of a system having a plurality or an array of loudspeakers, the individual speakers can be operated either simultaneously or in a desired sequence As shown in the accompanying drawing, a multiplex coding unit and multiplex decoding units are provided, whereby sequential operation of the loudspeakers can be achieved. The multiplexing technique allows individual adjustment of volume for each loudspeaker and also the use of a single pair of signal wires, thus avoiding the need for multiple wiring for each loudspeaker. It is preferred that directional loudspeakers be employed to emit the alarm signal. The choice of directional loudspeakers allows an additional degree of control by permitting adjustment to the polar distribution of the s oundfield produced; this enhances the alarm signal in the preferred direction and minimises its effect in other directions.

A period timer is provided in order that the duration of the alarm can be pre-set as required to suit the time delay for the specific application. A warning system according to the present invention can be designed as a direct replacement of an existing alarm and can be arranged to be operated by the same contact at the main switch panel of the machinery or plant. The signal (or tone) generator can be of any suitable design, but is preferably adjustable or programmable.

The multiplex switching can be operated by frequency or pulse selection, the latter method being preferred if a large number of speakers are used.

In the above-described embodiments, the signals are transmitted to the loudspeakers by wires. However, it will be readily understood that the invention applies also to other systems, e.g. radio-controlled systems.

Claims

Cl aims

1. An. electronic warning system characterised in that it comprises a signal generator, a power amplifier and at least one loudspeaker.

2. A system according to claim 1, characterised in that it comprises means for modulating the frequency of the signal from the signal generator.

3. A system according to claim 1 or 2, characterised in that it comprises means for modulating the signal from the signal generator.

4. A system according to claim 1, 2 or 3, characterised in that it comprises means for varying the gain of the amplifier.

5. A system according to any one of claims 1 to 4, characterised in that the or each loudspeaker is provided with a means for adjusting its output.

6. A system according to any one of claims 1 to 5, characterised in that means are provided to adjust the acoustic output according to the time of day and/or the ambient noise level.

7. A system according to any one of claims 1 to 6 , characterised in that it comprises a plurality of loudspeakers.

8. A system according to claim 7, characterised in that it comprises a multiplex coding unit for the signal. each loudspeaker being provided with a multiplex decoding unit, whereby sequential operation of the loudspeakers can be achieved.

9. An electronic warning system substantially as hereinbefore described and as illustrated in the accompanying drawing.

10. The use of a system according to any one of claims 1 to 3 to emit an alarm to warn personnel of the imminent start-up of machinery or plant.