Dräger Polytron 8900 UGLD Instructions For Use Manual page 9

3.2 Feature description
Polytron 8000 instruments are housed in a rugged stainless
steel enclosure for indoor and outdoor applications.
The flameproof / explosion proof enclosure provides three ¾"
NPT openings, which can be used for field wiring or direct
attachment of a sensor.
Polytron 8900 UGLD consists of an ultrasonic sensor (remote
or integrated) and the transmitter. The ultrasonic sensor
detects the ultrasonic sound level of the surrounding areas.
The detected ultrasound is then indicated as dB (re 20 µPa)
or percentage of full scale measuring range on the display
and the analog interface.
Level of ultrasound, status messages, and menu choices are
displayed on a backlit graphic LC-display and 3 colored LEDs.
Navigation through the menu is done by taping a magnetic
wand on the glass at the appropriate indicator. The instrument
can be configured, calibrated and maintained non-intrusively
without declassifying the area.
The instrument can be operated as current source or sink.
With the optional remote sensing head, the ultrasonic sensor
can be mounted at a distance of up to 30 m from the
transmitter.
3.3 Intended use
Polytron 8900 UGLD is an explosion proof instrument for
continuous ultrasonic gas leak detection (Ultrasonic Gas Leak
Detection = UGLD).
Dräger Polytron 8900 UGLD can be used to build large and
complex monitoring systems if sufficient power supply and a
sufficient number of HART/4-20 mA input channels are
available in a suitable Programmable Logic Controller (PLC),
e.g. Dräger REGARD 7000.
The instrument can be connected through a sealed conduit or
approved cable gland to a Dräger monitoring system or a
PLC.
The instrument is designed to be installed in permanent
locations and is approved for use in hazardous, classified
areas.
A mapping survey of the installation site should be conducted
to determine environmental conditions. With the obtained data
the instrument is commissioned.
3.4 Ultrasonic gas leak detection (UGLD)
Pressurized gas leaks (minimum pressure 2 bar / 29 psi)
generate both acoustic and ultrasound. Airborne ultrasound
has a frequency range of approx. 16 kHz to >100 kHz.
Dräger Polytron 8900 UGLD frequency range extends from
16 kHz to >80 kHz.
There are three primary factors that influence the intensity of
the ultrasound signal:
– Physical size of the leak (mass flow)
– Pressure drop between the pressurized vessel or pipeline
and the surrounding atmosphere.
– Properties of leaking gas
Instructions for use |
Dräger Polytron
®
8900 UGLD Firmware version ≥ 4.0.x
Gases with lower molecular mass (or higher speed of
sound) appear louder.
Ultrasound travels at the speed of sound and is only slightly
influenced by wind or strong air currents. Thus, the instrument
detects pressurized gas leaks that point detectors could miss
due to environmental conditions. The position of the gas leak
relative to the instrument does not significantly affect the
ability of the system to detect leaks.
Size and ultrasound distribution of a leak
Wind
UGLD
3.4.1 Gas leaks
Point detectors detect gas concentrations (e.g. ppm, %LEL).
UGLD transmitters indicate a change of sound in a known
environment. This is likely to be the onset of a hazard caused
by a leak.
Ultrasound emitted by gas leaks is proportional to the leak
rate. Leak rate is also called mass flow rate and describes the
amount of gas released over time [kg/s].
3.4.2 Background noise
Background noise is recurrent noise from running machinery
or other sound sources that emit ultrasound.
To increase the range, look for a location with as little
background signal as possible (< 54 dB re 20 µPa).
3.4.3 Alarm settings
The instrument displays the ultrasonic sound level in dB.
Alarm threshold
Alarm threshold should be based on the max. recurrent
background noise level. Short lasting, background noise
peaks may conflict with a lower required alarm threshold. For
such cases, an alarm delay can be set.
Dräger recommends the following alarm thresholds.
– Alarm A1: 6 dB above max. recurrent background noise.
– Alarm A2 can be set as a second escalation stage.
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Description
10 % LEL
50 % LEL
100 % LEL
Gas leak
9