Sentry 73 Noise Limiter

Environmental noise control sound limiter, standard unit. Enables venue operators to regulate noise levels to meet local authorities requirements. The Formula Sound Sentry MKII usually controls mains power via a relay or contactor (Contactor Not Included - Available Separately - Click Here For Details). Unit features a large bar graph display with Linear, C or Bass weighting options.

Delivery usually 1-2 working days.


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The Sentry Mk2 is the second generation of this product offering more facilities than the original Sentry. The Sentry Mk2 incorporates a measuring microphone inside the unit making it virtually tamperproof. Provision is made to connect an external microphone if required.

A large illuminated bargraph display is incorporated into the unit. The unit should be installed in a position where it can be clearly seen so the artiste has full knowledge of the levels at which he is working. If the noise level drives the display to full scale, which is all the green, amber and red lights lit, after a period of time the power will be turned off. The time period is adjustable between 10 to 70 seconds. Power can only be restored manually by pressing a reset button.

The Sentry is used in conjunction with a contactor or relay usually to control mains power. The connection between the two is at low voltage so the contactor can be located in a fuse cupboard and wired to control all the sockets in the vicinity. (Contactor Not Included - Available Separately - Click Here For Details).

The Sentry has a security loop facility which can be connected to a relay controlled by the fire alarm or switches that detect open fire doors or windows to ensure that the soundproofing of the venue is not impaired. Magnetic reed switches similar to the ones used in intruder alarms can be used as detectors. If the loop circuit is open the Sentry will switch off and it will not be possible to reset the Sentry until the circuit is closed.

The Sentry Mk2 also has provision to operate at two different levels, which may be selected remotely or by switches operated by open doors and windows, or an optional time switch. This allows the unit to cater for changes in noise type (e.g. disco or live music) or changes in surroundings (e.g. a venue situated near offices requiring stricter control during office hours.) An integral timer which automatically switches between the two sound levels is available as an optional extra.

The combination of the security loop to switch off completely and the second level function provides for most situations to be catered for.

A counter which is not resetable is also offered as an option. The counter records the number of times the unit has been reset.

To keep the Sentry system as versatile as possible connectors are fitted which allow the connection of several optional features, including remote reset switches, warning lamps, slave displays, etc.

The Sentry when supplied for entertainment venues can be internally selected to work on a linear or 'C' scale or on Bass. This should be used where Bass, i.e. low frequency noise is the problem. When this option is selected a 300Hz low pass filter with a 12dB per octave slope is inserted in the measuring circuit.

Dimensions: Width (including hinges) 320mm, Depth 120mm, Height 261mm

Note: A sound level meter will be required if you wish to set the trigger level to a specific sound pressure (dB) level - Click here for details.

Download Sentry Instruction Manual