Magnetodynamic and exponential hornelectronic si-rens have high frequency sound output suitable for shortdistance use.In general, electronic sirens have the following advantages over electronic motor sirens: -low power consumption -greater sound output -variable tone in the sound frequency (i.e. modulated, bi-tone, or multi-tone)-cyclic and pause option -intermittent sound option -progressive sound option controlling the level of thefinal blast-continuous operation -combined audible/visual signal option. Horns and bells produce distinct sounds which areeasily distinguishable from typical everyday sounds.They have low frequencies and are suitable for a variety of signalling applications especially long distance, short call signals or danger signals. They produce a continuous sound that can be changed to intermittent by using an electronic modulator (ME). Electric motor sirens have a short duty cycle, produce asingle tone sound and reach their specified operating fre- quency quickly.A single sound is very effective but can, after a short time, loose effectiveness as the human ear may become accustomed to it.A more effective method of audible alarm can be obtained by applying an elec- tronic modulator (ME) which would allow a modulated or intermittent sound.

SPECIFICATIONS

• European Machine Directive 89/392 requires the installation of appropriate audible and visual warning devices asan essential safety requirement for the operator in industrial environments.• European norms EN457 and EN842 (machine protection: audible and visual danger signalling) specify the technical,design and functional characteristics the audible and visual signal must have to be effective, i.e. audible or visible, distinguishable and unequivocal.•SIRENAacoustic (electric and electronic sirens, bells and industrial horns) and luminous devices (continuous,blinking, rotating and flashing beacons) conform in every aspect to the technical and functional requirements of Norms EN457 and EN842.•The installation of Sirena’s range of audible and visual products onto machines conforms in every way to thesafety standards set out in current norms.

GUIDELINES FOR INTERPRETATION AND APPLICATION OF THE NORMS - ACOUSTIC LINE

Current international standards for safety require theinstallation of an audible warning device in order to attract the attention of the operator and to indicate a dangerous or emergency situation.These standards have specific rules regarding the instal-lation of audible warning devices in industrial environ- ments.Two important factors determine the capability of the sound to be heard in any environment: -the distance between the audible warning deviceand the operator-the existing ambient noise .The suitability of an audible alarm for a specific applica-tion is determined by its specification, i.e.: -sound output DECIBEL (dB)-sound frequency HERTZ (Hz). International standards for industrial warning devices haveestablished minimum differential sound output levels that must be complied with. The dB level of the siren mustbe at least 15 dB higher than that of the measuredambient noise. The siren must, however, have a minimumsound output of 65 dB PHONOMETER . The sound frequency of thesiren, at the point where the sound output is greatest, must differ as much as possible to the frequency of the ambient noise.Sound frequency, however, must be between 300 and 3000 Hz.The use of a is necessary to measureambient sound levels, in order to comply with these regulations and to select the most suitable siren. Once this data is available the selection of a siren can be done very simply, by using the data shown in the Sirena catalo- gueand by making the required adjustments to compen- sate for the ambient noise levels. The sound output dB (A) levels of Sirena’s audible warning devices are accurately measured in an anechoic testing chamber at a distance of one meter from the axis of the device.The ratings given in the Sirena catalogue for electric mo-tor sirens give a maximum sound output. This is also valid for the horns and electronic sirens.The Hz frequencies shown in the Sirena cataloguerefer to a specific frequency for the electric motor and electronic sirens, and for a range of applicable frequen-cies for the other types of warning devices, i.e. horns and electronic sirens.Further information regarding the sound spectrum ofSirena’s range of audible warning devices is available on request. When selecting an audible warning device the sound spectrum of the siren must be superimposed upon the sound spectrum of the ambient noise. The differential dB level and the differential frequencies are therefore im- mediately recognised.Additional factors to be considered when selecting anaudible warning device: 4