Placement / Detection Coverage - Dräger Polytron 8900 UGLD Notice D'utilisation

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en Description
Alarm threshold
Alarm threshold should be based on the continuous
background noise level. The default alarm thresholds of the
instrument must not be used.
Dräger recommends the following alarm thresholds.
– Alarm A1: 6 dB or 11% measurement range above
continuous background noise.
Increase alarm threshold to 16% above continuous
background noise if a significant decrease in ambient
temperature (< - 20 °C / < - 4 °F) is expected.
– Alarm A2 can be set if necessary.
In the example, A1 is triggered at 20 % and A2 is triggered at
31 %.
110 dB = 100 %
50 dB
+ 12 dB
+ 6 dB
Alarm delays
Alarm delay represents the time the measured signal needs to
be beyond the defined alarm threshold in order to trigger an
alarm.
Alarm delays avoid false alarms by ignoring spurious sound
peaks. Spurious ultra sound peaks can be generated e. g. by
the fizz of detaching compressed air hoses, pressure release
valves or the jingling of tools falling to the ground. Such
sounds do not trigger an alarm although the sensor detects
sound levels that breach the alarm thresholds for a short time.
The alarm delay in which no alarm is triggered should be
optimized for each installation.
Dräger recommends alarm delays of 10-30 seconds
depending on the duration of spurious ultrasound events.
The instrument does not yet support alarm delays. Alarm
delays need to be configured through the control unit (e. g.
®
Dräger REGARD 7000 or a PLC).
10
A1
level

3.4.4 Placement / detection coverage

A2 at
72 dB ≈ 31 %
Instruments are normally installed at heights of 3-5 m (approx.
10- 16 ft.) above possible gas leak locations.
The recommendation that the instruments have to be installed
A1 at
66 dB ≈ 20 %
above possible gas leaks may result in installations awkward
to reach for maintenance and configuration.
The optional remote sensing head that can be installed
remotely from the transmitter allows the display to be easily
accessible for configuration. Remote sensor cables are
available in lengths of 5 m, 15 m, and 30 m (approx. 15 ft., 50
Background
noise level
ft. and 100 ft). The remote sensing head can also be used to
60 dB ≈ 9 %
avoid interferences such as vibrations or precipitation.
Placement of the ultrasonic sensor should not be obstructed
by solid objects like walls or pipework. Such obstacles might
deflect or absorb the ultrasound on its way to the instrument.
To optimize installation the sensor surface can be pointed at
different directions.
UGLD
Sound
level
Delay Delay 1
Delay reset
Instructions for use |
Dräger Polytron
Delay 2 A2
A1
Time
Remote sensing head
Gas leak
®
8900 UGLD