Formula Sound SENTRY MK2 User manual

SENTRYMK2
SOUNDLEVELCONTROL
USERSMANUAL

2
Sentry MK 2
ENVIRONMENTAL NOISE CONTROL SYSTEM
FUNDAMENTALS
Noise nuisance legislation requires sound levels to be controlled within limits, for licensed premises it
is increasingly a condition of licensing that equipment to control sound levels is in place.
Where artists (such as DJ’s or Bands) bring in their own sound equipment the only way to control
sound levels is to control the mains power ring used for the sound equipment.
Installing a contactor into the mains power ring (requires qualified electrician) used to supply power to
the sound equipment and using a Sentry MK2 to monitor sound levels and control the contactor
provides control of maximum music levels.
The Sentry is designed to monitor sound levels and provide a trigger when a preset sound level is
exceeded, this trigger will normally be used to trip a contactor removing the mains power supply to
the music system. When the Sentry trips the contactor there is a short (about 3 seconds) delay
before the system can be reset, before pushing the reset button always check that it is safe to do so
(eg amps turned down so no sudden surge).
The Sentry should be mounted opposite the performing area where the performers can see it. It
should be mounted on a solid wall away from doors and some distance from where speakers will be
mounted. If the Sentry is to be mounted on a wooden or plasterboard wall an external microphone is
likely to be required as wooden/plasterboards are prone to vibration which will be picked up by the
internal microphone.
In a basic installation a permanent power feed is required to the Sentry which then supplies the
control voltage to the contactor to hold it in, when the sound level exceeds the set level for about 10
seconds or more the Sentry triggers the removal of the control voltage to the contactor. The contactor
opens and the mains supply to the music system is removed.
If you are using our Contactor use the low voltage output from the Sentry which is the first
two terminals on the grey connectors. You can use thin low voltage cable (bell wire alarm cable
etc) the current requirement is very low, this connects to the two terminals on the printed circuit board
located at the end of the contactor case. The polarity is not critical.
DO NOT CONNECT MAINS INTO THE PRINTED CIRCUIT BOARD CONNECTORS WITHIN THE
CONTACTOR CASE.
When power is applied to the Sentry the reset light will be lit and no contactor control voltage will be
present. Resetting the unit will cause the light to go out and the contol voltages to be present.
The allowable noise level must be adjusted on site by using the multi turn pre-set labelled
ADJ 1 at the bottom left of the circuit board usually 1-2 turns up or down from the factory setting will
provide more than enough adjustment for most applications.
The Sentry can have two levels set; if for example; the allowed level is different for day and night or
weekdays/weekends then a switch (or timer) may be used to change to a second setting.

3
Sentry MK 2
ENVIRONMENTAL NOISE CONTROL SYSTEM
Features
A choice of internal microphone (supplied factory fitted as standard) or external microphone (with
or without phantom power) may be selected. External microphone not included.
A choice of weighting filters (A, C, BASS) or no weighting filter (LIN)
Two sound level thresholds may be set, level 1 (default) and level 2. Switching from level 1 to
level 2 can be done on a switch or a timer
Security loop (eg for fire alarm or fire doors)
Anti-tamper microphone circuitry is incorporated with a front panel indicator.
Dual mains voltage operation is standard (internally switchable)
Case provides easy connections via cable entry knock-outs and screw terminals
Fire alarm interface
Pair of isolated relay contacts
Large display plus ability to power mains 60W warning light
Will drive low voltage or mains contactor
Slave display option
Remote reset option (push button or keyswitch)
Factory set to about 20 seconds just over limit before tripping
AT1 option allowing sound levels to be controlled.
General Detail
Any function that can be controlled by a relay or switch can be controlled by the Sentry. These may
include disconnecting loudspeakers, switching passive attenuators to reduce system volume or acting
as the trigger into an active attenuator system as well as operating a contactor to remove the power
supply.
The Sentry may also be used as a stand alone display unit indicating sound pressure levels or in
industrial applications to switch on warning lamps or illuminated signs advising the use of ear
defenders when the safe noise level is exceeded.
Our technical department is always on hand to advise when unusual applications are encountered.

4
Operation
The Sentry features a large bar-graph VU meter with 23dB range to give a good visual indication of
the noise level in a venue.
While the meter is operating in the green section, with even an occasional peak into the red, there is
no cause for concern. Factory set the Sentry has about 20 seconds delay when limit is just exceeded
before power is removed to allow performers time to reduce sound levels.
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 (about 20 seconds factory set) 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 reset button. The Sentry will now be reset 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 reset.
Check that it is safe to do so (eg are amps turned down).
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.
All connections and adjustments are located beneath the removable cover plate (below the display).
Non reusable security labels are supplied with each unit to help detect unauthorised tampering.
Level 2
Level 2 is selected by shorting the 2 marked terminals on the Sentry grey connector strip. Switch may
be via switch or relay etc, the timer option is detailed below. The allowed level at weekends or
evenings may be different so the level 2 facility allows a quick switch.
Opening windows and/or doors allows more sound out of a venue, setting level 1 about 6dB lower
than level 2 and using magnet relays on doors/windows as the level 2 switch means running at level
2 (louder) as long as doors/windows shut and dropping to level 1 if opened.

5
Remote reset options
Remote reset controls are available in either push button or keyswitch format, the reset control can
then be mounted as desired eg behind the bar or in the managers office.
Mic Tamper
With Int(ernal) mic(rophone) selected the internal microphone is monitored for tampering, if Ext(ernal)
mi(crophone) is selected the external microphone is monitored for tampering. A front panel LED
indicator will show MIC TAMPER if the microphone has been tampered with and the Sentry will trip
the contactor, the Sentry will not reset until MIC TAMPER indicator is off.
If Mic tamper is illuminated with Internal microphone selected the internal microphone is probably
damaged and you will need to contact your installer or Formula Sound.
The Sentry will switch off if the Mic tamper or Security loop indicators are illuminated.
Security loop
The security loop feature is provided on two terminals behind the removable cover plate, while the
two terminals are linked the Sentry will operate but if the link is broken (for more than half a second)
the Sentry will trip.
This feature can be used as in any circumstance that the Sentry is required to be tripped, eg fire
doors can be fitted with a magnetic relay so that if the fire doors open the relay breaks the circuit and
the Sentry is tripped.
A front panel LED indicator will show SECURITY LOOP if the link between the two terminals is
broken and the Sentry will trip the contactor, the Sentry will not reset until the link is restored (LED
indicator off).
Time levels exceed limit before the Sentry trips
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.
Fire alarm interface
The fire alarm interface option allows the Sentry to be interfaced to a fire alarm, the interface can be
set to accepted a trigger of voltage applied (up to 24V), voltage removed, contacts closing or contacts
opening. Factory setting is “voltage applied”.
Isolated contacts
A pair of relay contacts that are normally open and close when the unit trips allow other equipment to
be switched if required (contacts can be normally closed if required).

6
Timer option
A timer option is available allowing the setting of two different levels at different times of the day or
week. The timer may for example be set to switch to level 2 at 11pm which may be a quieter level.
This option is factory fitted, although an external version will be available in the near future, contact
Formula Sound for details.
Counter option
The counter option counts the number of times the Sentry has tripped. This option is factory fitted.

7
Mounting Position
The Sentry should be mounted on a flat solid surface preferably where it can be seen by the persons
affected by its use (D.J., band, etc.) and away from doors. It should be located in a position where it
cannot be tampered with, e.g. A minimum of 8 feet (2.5 metres) from the floor, ideally on a wall
facing the sound source. It is not necessary to have a microphone suspended above the band or
dance floor. If the Sentry can hear the sound source above the background noise the unit can be
calibrated accordingly.
Avoid positions that are too close to the sound source e.g. in a typical concert room with the stage
area at one end the Sentry should be positioned centrally away from the stage at a minimum
distance equal to the stage width. If there is more than one source of sound, e.g. several instruments
in a band the Sentry should ideally be at a position equal distance from each instrument. (see Fig1)
Ideal Position
w
“A” x “W”
Sentry Stage
At least 2.5m y
From Floor level
z
Fig 1
Distance “A” should never be less than distance “W”.
Poor Positioning
W
X
Stage
Position (B)
Y
Sentry Sentry
Z
Better position Poor position
Fig 2
In Fig 2 the instruments Y & Z will appear louder to the Sentry than instruments W & X. Moving the
Sentry back away from the stage to position (B) will minimise the problem
In order to help solve difficult location problems provision is now included to connect a remote
microphone to the Sentry MK2. See Drg No 879 for more details.

8
Cable Entry and Fixing
Read this section fully before proceeding
Customising the box. Cable entry knock outs are provided on the rear and bottom faces of the unit,
using the rear cable entry’s can result in a very neat installation. Select the cable entry positions to
be used and remove the appropriate knock outs. (A small flat blade screwdriver on the perimeter of
the hole will assist prizing out the blanking plugs.) Remove any sharp edges that may damage
cables or use protective grommets (not supplied)
NOTE: - Use a separate cable entry for mains connections. Always keep low voltage cables away
from mains cables and connections.
Fastening the unit. The unit is secured to a wall by 3 screws (not supplied). The top centre screw
locates in a key hole slot on the back of the unit.
The Sentry will require a mains power supply that is not controlled by the contactor, this should be in
place before fastening the unit to the wall.
Use No. 10 or 12 screws with round heads 1.5" (38mm) minimum length. Brick or masonry walls will
require drilling and plugging in the usual manner.
First remove the cover below the display to expose the bottom mounting screw holes, these are
located in the bottom corners of the case. Fit the top centre screw 30 mm down from the required top
case position, leave this screw approx. 1.5mm proud of the mounting face.
The unit may now be suspended on this screw while the two bottom mounting screw positions are
marked out (ensure that the unit is captive on the screw head so it cannot fall). Fit the bottom two
mounting screws.
Check that the unit is secure,cannot fall, and is not loose on the screws.
In high risk areas security screws should be utilised to prevent the unit from being removed.
Wiring For Applications Controlling the Mains Power.
All mains wiring must be installed in accordance with IEEE Regulations. If after reading these
instructions you are not sure how to proceed you should seek help from a qualified
electrician.
Overview
The Sentry provides outputs to control a contactor or relay which in turn will control the mains supply.
This strategy allows the Sentry to be mounted in the most suitable position for noise measuring whilst
the mains switching equipment (the relay or contactor) can be mounted in the most convenient
position for switching the mains power (fuse cupboard, etc).
A 32amp fully fused boxed contactor with low voltage interface has been designed for use with the
Sentry and is available from Formula Sound Ltd.
The Sentry also provides connections to use a mains coil contactor with a maximum coil consumption
of 60VA.

9
Installation
In the room that is to be controlled identify all mains sockets and establish which mains ring (or rings)
they are on. Select and install a suitable contactor in that mains ring, if there is more than one ring
you will require as many contactors as there are rings. Ensure the contactor is adequate for the
power rating of the ring(s).
A 32amp fully fused boxed contactor with low voltage interface has been designed for use with the
Sentry and is available from Formula Sound Ltd, also a dual version is available from Formula Sound
which will control two 32 amp rings.
In very large installations, it is a simple matter to make 1 contactor control many others
of whatever current rating is required.
Connect the contactor control back to the Sentry using appropriate cable and connections depending
on the type of contactor used.
Connections
All connections to the Sentry are located beneath the lower removable front cover (below the
display). On this cover is also mounted the reset button which connects to the printed circuit board
via a 2 pin plug (and temporarily may be easily disconnected). See Drg No 879.for more details.
Connect the Sentry to a suitable mains outlet using the terminals labelled “Mains In” and ensure that
the earth is also connected. The mains consumption is approximately 1 amp at 240V - a 5 amp
lighting feed could be utilised. Connect via an isolating switch or removable plug socket arrangement
so that the unit can be isolated when necessary.
For use on 120V the consumption will be approximately 2amps
ENSURE THAT THE MAINS SUPPLY IS NOT THE SAME AS THAT CONTROLLED BY THE
CONTACTOR.
Warning Lamp
Provision to switch a mains warning lamp to a maximum of 60VA is provided. The lamp can be of
any style considered suitable but must have a maximum consumption of 60VA (60 watts). It is
connected to the mains outlet terminals labelled "warning lamp". Alternatively a relay or contactor
may be used to switch other lamps as required. Good wiring practice should be observed.
Remote Reset
Detail on page 12
Setting the Permissible Volume Level
Adjustment of allowable noise level is made by adjusting the pre-sets ADJ 1 and ADJ 2. These are
located beneath the removable cover at the left hand end of the unit. They are 10-turn pre-sets to
provide fine adjustment. ADJ1 sets the normal operating level, ADJ 2 sets the level for a second
threshold (Level 2) which can be initiated remotely. An indicator on the front panel will show when
level 2 is selected. Take care when making adjustments and use a small screw driver. Try to make

10
adjustments when the noise level is displayed on the bar graph meter as you will be able to see the
changes displayed on the meter.
The adjustment pre-sets have a slipping clutch at the end of travel to prevent damage. But this can
cause confusion if the pre-set is at the end of travel as it then appears to do nothing (this is not
usually a problem once you know about it).
The actual sound pressure level (SPL) at which the unit operates can only be determined by
measuring the noise level using a calibrated sound pressure level meter and adjusting the unit
accordingly. Play music at the maximum required level (monitor with SPL meter) and adjust ADJ1 so
the “LIMIT” LED’s (right hand of display) are going on and off. A small increase in the music level will
now trip the system after about 20 seconds, level 1 is now set. Repeat for level 2 if the second level
is also to be used.
Alternatively the unit may be adjusted using trial and error but this should be used only as a
temporary measure or last resort. Measuring the sound level and setting to a limit agreed with the
local area official is the only recommended method.
An internal measuring microphone is fitted which will be suitable for most applications but should the
need arise an external microphone can be connected. The external microphone may be a moving
coil type, capacitor or electret. Microphone phantom power is provided and may be selected as
required. Select a microphone with the required frequency response and polar response. (Please
telephone our technical department if help is required).
NOTES:- If the unit is to be used in an entertainment venue to control a band or disco use a meter
with either a linear scale or 'C' weighting response.
The frequency response of the measuring circuit of the Sentry may be selected to be, Linear (Flat
response) ‘C’ (conventional C scale), Bass (LP filter @ 300Hz 12dB per octave slope) or A weighting.
see Drg No 879.
'A' weighting is a frequency response curve that resembles the human ear response. It is much more
sensitive in the mid 500Hz - 5 kHz region. It is not recommended for entertainment venues as it is
less sensitive to the bass regions and bass regions travel most and annoy neighbours more. Most
industrial applications will need A weighting.
SECURITY LABELS ARE PROVIDED. THESE SHOULD BE FITTED TO COVER
THE SCREW HEADS HOLDING THE REMOVABLE COVER IN PLACE AND WILL
REVEAL ANY UNAUTHORISED ATTEMPT TO CHANGE THE THRESHOLDS
ALWAYS FIT SECURITY LABELS AFTER ADJUSTMENTS HAVE BEEN MADE.
EXTRA LABELS ARE AVAILABLE FROM FORMULA SOUND IF REQUIRED.
Remember that the acoustic characteristics of a venue will change depending on the number of
people in it. Our experience has shown that it is always advisable to take readings when the venue is
in use. It would be a wise precaution to allow in your costings for a site visit during opening hours to
take measurements and make final adjustments.

11
Security Loop
Provision to connect a security loop is provided. This may be required for fire doors/alarm or
emergency cut off etc. Magnetically operated reed switches of the type used in intruder alarms are
most convenient for this application on doors or a simple emergency switch. If this facility is not
required a wire link must be connected to allow the Sentry to work normally. (see Drg No 879). A
front panel indicator shows if the security loop is opened.
Tampering
If you find that you have problems with unauthorised persons security screws are available to
replace the cover retaining screws,a special key is also supplied for the fitting and removal of
these screws. Contact FORMULA SOUND sales office for more details.
Internal Settings
Several optional settings are available internally. These are shown on drawing Drg No 879.
Internal/External Microphone Selection and Phantom power
This is accomplished by the position of three jumper plugs on pin headers. Take care to move
jumpers and ensure that they connect correctly. The positions are shown on drawing Drg No 879.
Weighting Selection
The position of jumper plugs select the response on the measuring microphone. The positions are
shown on the P.C.B. Ensure that the jumpers are seated correctly.
Special weighting options are possible - contact Formula Sound for further details.
External Microphone connection
A 3 way terminal strip is provided for the connection of a remote microphone. The microphone
should be low impedance, balanced and good quality twin screened cable should be used for the
connections. Contact Formula Sound if you are unsure.
Led Indicators
Outputs are provided for remote led indicators: - MIC TAMPER, LEVEL 2, WARNING, RESET
REQUIRED. If more than two leds are to be connected they share a common terminal. Led current
limiting resistors are not required. Leds may be connected directly. These outputs are also sufficient
to drive a contactor with low voltage interface if required.
Timer Adjustment
The period of time that noise "over limit" is tolerated before the unit trips out is variable over the range
of 10 - 70 seconds. If adjustment is required locate the timer pre-set from Drg No 879 and adjust with
a small terminal screwdriver as required. You may have to wait up to 70 seconds for the timing
capacitor to discharge before new timer settings will take place.

12
Fire alarm interface
The fire alarm interface jumpers setting the mode of operation are located beneath the display panel.
To access first switch off power to the unit, open the perspex display cover and remove the screws
from the display panel. Drop the display panel forward a couple of inches and reach in to release the
ribbon cable connector attaching the display assembly to the main unit.
The fire alarm interface connector and settings are located top right corner, on the PCB there is a
legend “FIRE ALRM”.
To set the mode of operation first set the jumpers for voltage sensing or contacts sensing (“VOLTS
SENSE” and “CONT SENSE”). If the fire alarm is applying or removing a voltage then set for “VOLTS
SENSE”, if the fire alarm is closing or opening contacts set for “CONT SENSE”.
If voltage sensing is selected next set voltage applied or voltage removed (“V.A” or “V.R.”).
If contact sensing is selected set for contacts normally closed or contacts normally open (located by
legend “CONTACTS” and “N.C.” or “N.O.”).
Replace the display, the ribbon cable connector is keyed so ensure it goes it the correct way round (if
you feel any resistance when pressing home the connector it may be in the wrong way round).
Switch the Sentry on and reset it, perform a fire alarm test to ensure the Sentry trips when the fire
alarm operates.
Remote Reset
A remote reset facility can be added by connecting a momentary action push button or key switch.
Site this in a Manager's office or behind the bar or other suitable location.
Formula Sound offer both remote push button (074P) and remote keyswitch (074K) options in a grey
plastic lighting style surface mount box. Connection of either 074P or 074K is as follows:
Open the remote reset box and the connections are on the back of the front panel as shown below.
SWITCH
LED COMMON -VE
RESET
RESET REQUIRED
LED +VE
WARNING LED +VE
The box contains LED’s that show if the Sentry is tripped (reset required) or if the sound level is near
the limit (warning).
Behind the panel below the main display is a grey connector strip (see drwg 879 later in manual).
To connect LED’s and switch a 5 core wire is required (low voltage dc and low current), a 6 core
microphone cable would be suitable.
Connect the “RESET SWITCH” terminals to the Sentry terminals marked “N” (Remote reset switch)
on drwg 879.

13
Connect the LED terminals to the Sentry terminals marked “J” (LED INDICATORS) on drwg 879,
note LED COMMON is connected to the Sentry terminal marked “EARTH”.
Contactor
Details of the contactor are shown on drawing 755 towards the back of the manual.
AT1 option
An optional add on is available which can manage sound levels, the AT1 connects to the Sentry and
provided the audio is signal is routed through the AT1 before going to the system amplier(s) the
Sentry and AT1 will control levels just below the threshold that the Sentry has been set to.
Remote display option
A remote display option is available, this is mounted in an identical box but contains only the Sentry
display circuitry and connects to the “Slave display” terminals.

14
Summary
The Sentry will monitor sound levels and provide a trigger when a set sound level has been exceeded
for about 20 seconds, typically the trigger will be used to operate a contactor.
In an audio application (music) the Sentry will normally be used where performers bring in their own
equipment, the mains power supply for this equipment will be put under the control of the Sentry by
means of a mains contactor. Where mains power is to be controlled the mains ring(s) are identified
and a contactor(s) are installed (by a qualified electrician) to control those rings.
In an industrial application the Sentry may be used to indicate ear defenders are required or remove
power to a piece of machinery, An “A” weighting filter will often be used in this situation.
The Sentry should be mounted on a solid wall, away from doors and opposite the source of the
sound. The display should be visable to performers or machine operators. If the Sentry cannot be
mounted on a solid wall away from doors then an external microphone can be used.
Two levels may be set (eg day and night or weekdays and weekends may require different levels),
switching between levels may be done by switch, keyswitch or timer.
There is a choice of filters, for music either Linear or Bass will be used (Bass tends to travel and
therefore is a greater cause of noise nuisance) and for industrial “A” weighting should be used.
The fire alarm interface allows the Sentry to be interfaced with the fire alarm. The security loop may
be used to trip the system if fire doors are opened.
Adding a Formula Sound AT1 to the Sentry can allow the music level to be controlled providing the
music can be routed through the AT1 beofre going to the amplifiers.
A simple method of setting the level for a music venue is to play music at the maximum allowable
level (ensure speakers are where visitors will place them), the maximum allowable level is
determined by the environmental health officer but will typically be either a level just audible in a
neighbours premises or a set level at the boundary of the premises.
With the music at the maximum allowable level adjust the Sentry (Adj 1) to be between “warning” and
“Over limit” on the display.
Note: Reducing the amount of sound escaping from a venue will generally increase the sound level
the venue is allowed to operate at, doors, windows, direction and mounting of speakers all affect
sound levels from a venue.
FORMULA SOUND LTD.
UNIT 23; STADIUM BUSINESS CENTRE
NORTH END ROAD
WEMBLEY
MIDDLESEX
HA9 0AT
TEL: [phone]
FAX: [phone]
Email [email protected]
www.formula-sound.com

1
FORMULA SOUND LIMITED
UNIT 23; STADIUM BUSINESS CENTRE; NORTH END ROAD; WEMBLEY; MIDDLESEX; HA9 0AT
TELEPHONE [phone] FAX [phone]
www.formula-sound.co.uk email [email protected]
E.U. CERTIFICATE OF CONFORMITY
We declare that the products listed conform to the following directives and standards
89/336/EEC amended by 92/31/EEC and 93/68/EEC
BS EN 50082-1 BS EN 50081-1
PRODUCT TYPE
SENTRY MK2
The CE mark was first applied in 1995
Signed B. J. Penaligon General Manager
Attention
The attention of the specifier, purchaser, installer, or user is drawn to the fact that good wiring practice must be
observed when connecting the above equipment. Good quality connectors and screened cables must be used
for all audio connections. Twin screened cables should be used for all balanced lines.
THIS EQUIPMENT MUST BE EARTHED
CONSULT THE USERS MANUAL FOR TECHNICAL DETAILS