Formula Sound SENTRY MK2 User Manual - Page 3
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Operation
The Sentry features a large bar-graph VU meter with 23dB range to give a visual indication of the
noise level in a venue. This has the advantage over other units in that anyone can see the volume
level and can see how their actions are contributing to this level. While the meter is operating in
the green section, with even an occasional peak into the red, there is no cause for concern.
The Sentry will operate within the range 80dB - 120dB and may be pre-set to anywhere in this
range. Provision is included to operate at 2 different levels, for instance at different times of day.
This selection can be performed manually or automatically by a time switch. A front panel
indicator shows when level 2 is selected.
If a mains warning lamp is connected it will operate at the same point as the two red sections of
the meter. These are labelled "WARNING".
If the noise level is high enough to light the "OVER LIMIT" section of the meter (three red sections)
the noise has exceeded the allowable limit. If this is allowed to continue for more than the set time
period the unit will trip and remove the power to the contactor or relay. Visual indication of this is
provided above the reset button.
When the unit is first powered up the RESET indicator will be lit - wait for a few seconds and
press the re-set button. The Sentry will now be re-set and ready for normal operation.
The action of the timing circuit means that continually exceeding the limit even for short periods
may eventually trip the unit.
The unit has to be manually reset to restore power and this will only be possible after a short time.
The reset time is determined by the amount by which the unit is driven over limit. e.g. tripping the
unit by just exceeding the limit will result in a short period of a few seconds before reset is
possible. Tripping the unit by grossly exceeding the limit will require a longer period before reset
is possible.
NOTE. It is important that a check is made before the unit is re-set.
Check that it is safe to do so
.
Audio systems generally need to be powered up in a specific order. In an audio system
comprising of different components amplifiers, mixers, etc. a general rule is to switch power
amplifiers off first and on last to avoid possible loudspeaker damage. Therefore a band or D.J.
may need to turn off amplification equipment to protect loudspeakers before the power is
restored.
Mic Tamper
An anti-tamper circuit is incorporated which if enabled will detect the presence of tape etc. placed
on the case above the internal microphone in an attempt to artificially raise the internally set
threshold. To enable this function adjust the T.S. preset (X) on Drg 879. (turn the pre-set to
approx the 11 o'clock position. External microphones being disconnected will also be detected
by a seperate circuit. A front panel indicator will show MIC TAMPER.
The Sentry will switch off if the Mic tamper or Security loop indicators are illuminated.
All connections and adjustments are located beneath the removable cover plate. None reusable
security labels are supplied with each unit to help ensure that unauthorised tampering is detected.
Timer
The period of time that noise "over limit" is tolerated before the unit trips out is variable over the
range of 10 - 70 seconds. A pre-set is provided to adjust this should it be necessary - the factory
setting is approx. 20 seconds.
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