1. INTRODUCTION
2. INSTALLATION
1.1 Product overview
CIRRUS is a dual wavelength, fixed point, infrared gas detector for
the detection of C1 to C8 hydrocarbons in the range 0-100% LEL. It
is designed for continuous operation in the harshest of
environments where speed of response and accuracy are essential.
Cirrus is powered by 24 V dc and provides a 4-20 mA signal (sink or
source) proportional to the gas concentration. The unit is certified
flameproof and may be fitted in zone 1 or 2 hazardous environments.
For å list of gases which can be detected using Cirrus please
contact Crowcon.
1.2 Product description
Cirrus comprises two main parts, the docking station and IR detector.
Diagram 1 shows the overall general arrangement of Cirrus. All housings
are manufactured from 316 stainless steel and when assembled form an
explosion proof detector for use in zone 1 or 2 hazardous environments.
Cirrus is certified EEx d IIC T6 and UL Class 1, Zones 1 & 2, EEx d IIC
T6. For a list of gases which can be detected using Cirrus, please
contact Crowcon.
All field cables are terminated at the docking station which can
be supplied independently of the main detector. When supplied
separately the docking station is fitted with a temporary dust cover. This
cover is uncertified, so the docking station can only be installed in a
hazardous area and cabled to, ready for fitting of the detector during
commissioning, if a hot-work permit applies. This ensures that cabling
can be carried out in advance of commissioning so reducing the risk of
damage to the detector. As standard the docking station is supplied with
one female M20 entry (alternative entries are available upon request).
Terminals for up to 2.5 mm2 cable are provided for all connections.
Diagram 2 shows the docking station general arrangement. Provision is
made for the attachment of identification tags as required.
WARNING
Cirrus is designed for use in Zone 1 and 2 hazardous areas, and is
certified EEx d IIC T6 and UL Class 1, Zones 1 & 2, EEx d IIC T6.
Installation must be in accordance with the recognised standards of
the appropriate authority in the country concerned. For further
information please contact Crowcon. Prior to carrying out any
installation work ensure local regulations and site procedures are
followed.
2.1 Location
There are no rules which dictate the siting and location of detectors,
however, considerable guidance is available from BS6959: 1988 – ‘British
Standard Code of Practice for the Selection, Installation, Use and
Maintenance of Apparatus for the Detection and Measurement of
Combustible Gases’. Similar international codes of practice may be used
where applicable. In addition certain regulatory bodies publish
specifications giving minimum gas detection requirements for specific
applications.
The detector should be mounted where the gas is most likely to
be present, note the following points when locating gas detectors:
•
To detect gases which are lighter than air (eg. methane), detectors
should be mounted at high level.
•
To detect heavier than air gases (eg. butane) detectors should be
mounted at low level.
•
Consider the possible damage caused by natural events eg. rain or
flooding.
•
Consider ease of access for functional testing and servicing.
•
Consider how the escaping gas may behave due to natural or forced
air currents. Mount detectors in ventilation ducts if appropriate.
•
Consider the process conditions. Butane is normally heavier than air,
but if released from a process line which is at an elevated
temperature and/or pressure, the gas may rise rather than fall.
The placement of sensors should be determined following
advice of experts having specialist knowledge of gas dispersion, the plant
processing equipment as well as safety and engineering issues. The
agreement reached on the locations of sensors should be recorded.
Crowcon would be pleased to assist in the selection and siting of gas
detectors.
2.2 Mounting
Diagram 1 shows the mounting arrangement of Cirrus. The docking
station may be installed early in the construction phase of the plant and
the detector connected during commissioning of the system. This
minimises the risk of damage or contamination of Cirrus due to
construction work.
Cirrus is mounted at the designated site with the optical axis of
the detector horizontal (±15º). The weatherproof cover has been designed
to allow maximum gas flow into the optical chamber in this position so
providing the best speed of response while ensuring a high degree of dust
and water ingress protection. If Cirrus is used with the optional flow
adaptor, non horizontal mounting is possible.
2.3 Cabling requirement
Cabling to Cirrus must be in accordance with the recognised standards
of the appropriate authority in the country concerned and meet the
electrical requirements of the detector. Crowcon recommend the use of
steel wire armoured (SWA) cable and suitable explosion proof glands
must be used. Alternative cabling techniques, such as steel conduit, may
be acceptable provided appropriate standards are met.
Cirrus requires a DC supply in the range 12-32 volts at 4 Watts.
Care should be taken to ensure the minimum DC supply of 12 volts is
observed at the detector taking into account the voltage drop due to
cable resistance.
For example, a nominal DC supply at the control panel of 24
volts has a guaranteed minimum supply of 18 volts. The maximum
voltage drop allowed is therefore 6 volts. Cirrus can demand up to 370
mA and so the maximum loop resistance allowed is 16 Ohms. A 1.5 mm
2
cable will typically allow cable runs up to 660 m. Table 1 below shows
maximum cable distances given typical cable parameters. The
acceptable cross sectional area of cable used is 0.5 to 2.5 mm
2
.
C.S.A. (mm
2
)
Resistance (Ohms per km)
Max. Distance (km)
Cable
Loop
1.0
18.1
36.2
440
1.5
12.1
24.2
660
2.5
7.4
14.8
1080
Table 1:
Maximum cable distances for typical cables
Table 1 is provided for guidance only, actual cable parameters
for each application should be used to calculate maximum cable
distances.
2.4 Electrical Connection
Cirrus has two possible electrical configurations; Current source 4-20 mA
and Current sink 4-20 mA.
As standard, Cirrus is supplied configured as a current source
unless specified otherwise when ordering. For details of how to change
this configuration in the field, contact Crowcon.
Refer to diagram 2 for terminal layout and diagram 3 for
electrical connections. Terminals are designated as follows:
1.
24 V dc (nominal)
4.
RS 485 A
2.
0 V
5.
RS 485 B
3.
4-20 mA signal
1
2
3
4
5
6
1. INTRODUCTION
2. INSTALLATION
Gas Detection You Can Trust
Gas Detection Y ou Can T
rust
instructions
Diagram 1:
Cirrus general arrangement
Diagram 2:
Docking station general arrangement
The IR detector includes the electrical compartment, optical chamber
and weatherproof cover (optional). Cirrus is calibrated at the factory to
detect the target gas specified when ordering. An optional pre-calibrated
filter can be fitted into the detector. This filter is automatically switched
into the path of the infrared beam to check whether or not the detector is
working correctly. The test is invoked automatically by the processor and
is totally trnsparent to the user. If the detector fails this test, a fault signal
is raised. The specification sheet provided with each detector should be
consulted to determine the unit’s specific functionality.
Part No C01625
Cirrus
Fixed Point
Infrared
Flammable Gas
Detector
Installation, operating and maintenance
instructions, M07184
1180
Issue 3 03/03
Crowcon Detection Instruments Ltd
2 Blacklands Wa
y
Abingdon Business Park
Abingdon
Oxfordshire OX14 1DY ,
UK
T el:
+44 (0)1235 553057
Fax:
+44 (0)1235 553062
email:
sales@crowcon.com
internet:
http://www.crowcon.com
NPT
