Halma Crowcon Xgard Assembly instructions

Installation, operating
and maintenance
instructions
Xgard
Gas Detectors
M07249
Issue 8 October 2007

2
•Xgard gas detectors must be installed, operated and maintained in
strict accordance with these instructions, warnings, label information,
and within the limitations stated.
• The lid on flameproof versions of Xgard must be kept tightly closed
until power to the detector is isolated otherwise ignition of a
flammable atmosphere can occur. Before removing the cover for
maintenance or calibration purposes, ensure the surrounding
atmosphere is free of flammable gases or vapours.
•Xgard detectors are designed to detect gases or vapours in air, and
not inert or oxygen deficient atmospheres. Xgard oxygen detectors
can measure in oxygen deficient atmospheres.
• Electrochemical cells used in toxic and oxygen versions of Xgard
contain small volumes of corrosive electrolyte. Care should be
observed when replacing cells to ensure that the electrolyte does not
come into contact with skin or eyes.
• Maintenance and calibration operations must only be performed by
qualified service personnel.
• Only genuine Crowcon replacement parts must be used, substitute
components may invalidate the certification and warranty of the
detector.
•Xgard detectors must be protected from extreme vibration, and direct
sunlight in hot environments as this may cause the temperature of the
detector to rise above its specified limits and cause premature failure.
A sunshade is available for Xgard.
• This equipment must not be used in a Carbon Disulphide atmosphere.
•Xgard Types 2, 3, 5 & 6 are certified for use in atmospheres that may
contain flammable dusts. They will not however detect the presence
of flammable dust, and the response of the gas sensor may be
compromised by becoming blocked in a dusty environment. Xgard
detectors should be inspected regularly if used in a dusty
environment.
Safety information

3
Hazardous area classifications:
Zone 0: An area classified as Zone 0 will have ignitable concentrations
of flammable gases, vapours or liquids either continuously
present or present for long periods of time under normal
operating conditions. Intrinsically Safe (Exia) detectors are
suitable for use in Zone 0, provided they are connected via a
suitable zener barrier or galvanic isolator.
Zone 1: An area classified as Zone 1 is likely to have ignitable
concentrations of flammable gases, vapours or liquids present
under normal operating conditions. Flameproof (Exd) detectors
are suitable for use in Zone 1. Intrinsically Safe (Exia) detectors
are suitable for use in Zone 1, provided they are connected via
a suitable zener barrier or galvanic isolator.
Zone 2: An area classified as Zone 2 is not likely to have ignitable
concentrations of flammable gases, vapours or liquids present
under normal operating conditions. Flameproof (Exd) detectors
are suitable for use in Zone 2. Intrinsically Safe (Exia) detectors
are suitable for use in Zone 2, provided they are connected via
a suitable zener barrier or galvanic isolator.
Notes:
In North America ‘Divisions’ are used to categorise risk where:
Division 1 is equivalent to Zone 0 or 1
Division 2 is equivalent to Zone 2
Under European ATEX rules hazardous area equipment has been
redefined under ‘equipment categories’ where:
Equipment Category 1 is suitable for Zone 0
Equipment Category 2 is suitable for Zone 1
Equipment Category 3 is suitable for Zone 2
Safety information

Product overview
Xgard are a family of gas detectors for monitoring a very wide range of
toxic and flammable gases and oxygen. Xgard are available as either
Intrinsically Safe (Exia) or Flameproof (Exd) detectors, dependant upon
sensor type and customer preference. Intrinsically Safe versions are
suitable for use in Zone 0, 1 or 2 hazardous areas when used with a
suitable Zener barrier or galvanic isolator. Flameproof versions are suitable
for use in Zone 1 or 2 hazardous areas.
Please refer to the certification label on the detector junction box to
identify the type of certification that relates to the product supplied.
Hazardous area definitions are shown in the Hazardous area
classifications section on page 3.
Note: if no certification label is fitted to the junction box, the
detector is not certified for use in hazardous areas.
4
Overview
Vmax=32v Wmax =10W
WARNING Do not open when
an explosive atmosphere
Baseefa04ATEX0024X
1180 II 2GD
IECEx BAS 05.0043X
Xgard
OX14 1DY
Gas Detector
Ex d IIC T4
Ex d IIC T6
a
a
40 C T +50 C
40 C T +80 C
o
o
<
<
<
<
o
o
40 C T +80 C
40 C T +50 C
EEx d IIC T4
EEx d IIC T6
o
o
<
<
<
a
a
<o
o
is present
T80 C Tamb = 50 C T110 C Tamb = 80 C
o
oo
o
Ex tD A21 IP6x
Xgard ATEX and IECEx
Flameproof
40 C T + 55 C
Ui=28v Pi=1.2W
Baseefa04ATEX0115X
Xgard
Ex ia IIC T4
1180
Gas Detector
<
o
<
a
o
OX14 1DY
IECEx BAS 05.0042X
STATIC HAZARD
CLEAN ONLY WITH A
DAMP CLOTH
II1G
Xgard ATEX and IECEx
Intrinsically Safe
Xgard Intrinsically Safe  Type 1 UL
Class I, Groups A, B, C and D Haz. Loc when installed in accordance with control
CROWCON XGARD GAS DETECTOR TYPE 1
understand and adhere to the manufacturer's live maintenance procedures.
Safety. To prevent ignition of flammable or combustible atmospheres read,
drawing No S-4838-A3. WARNING Substitution of Components May Impair Intrinsic
Securite Intriseque. Classified as to Intrinsic Safety For use in
-40°C < Ta < +55°C T4
OXYGEN
XX
Exia
Vmax: 28V, Pmax: 1.2W, Ci: 15.6nF, Li: 0uH
C
A
L
C
I
S
S
66Y6
US
D
I
F
E
Diagram 1: Xgard certification labels
Xgard UL Flameproof
Class 2 1030VDC Wmax=10W
CLASS I, DIVISION 1, GROUPS B, C, & D
AS TO RISK OF FIRE, ELECTRIC SHOCK & EXPLOSIVE HAZARDS ONLY.
WARNING To reduce the risk of ignition of Hazardous Atmosheres
disconnect the equipment from the supply circuit before opening.
Keep assy tightly closed when in operation. Conduit runs must have
40ºF T +176ºF T4
CROWCON
sealing fitting connected within 18 inches of enclosure.
40ºF T +122ºF T6
XGARD GAS DETECTOR TYPE
<
<
a
<
<
a
2006
C
L
S
A
I
S
66Y6
E
I
F
D
drawing No S-4838-A3. WARNING Substitution of Components May Impair Intrinsic
-40°C<Ta<+55°C T4
CROWCON XGARD GAS DETECTOR TYPE 1
XX
Safety. To prevent ignition of flammable or combustible atmospheres read,
understand and adhere to the manufacturer's live maintenance procedures.
Vmax:28V, Pmax:1.2W, Imax:150mA, Ci:14.4nF, Li:0 uH
Securite Intriseque. Classified as to Intrinsic Safety For use in
Class I, Groups A, B, C and D Haz. Loc when installed in accordance with control
TOXIC Exia
66Y6
C
C
L
A
S
S
I
F
I
E
D

5
Each type of Xgard detector is identified by a label fitted on the junction
box body. Please quote the ‘model number’, ‘gas range’ and ‘sensor
type’ when contacting Crowcon for advice or spares.
This manual covers all versions of Xgard, care should be taken to ensure
that the correct section is referenced according to the type of detector
used. The Xgard detector type is detailed on the product label. The Xgard
range is as shown:
Type 1: Intrinsically safe toxic and oxygen gas detector
Type 2: Flameproof toxic and oxygen gas detector
Type 3: Flameproof flammable gas detector
Type 4: Flameproof high temperature flammable gas detector
Type 5: Flameproof flammable gas detector with 420mA output
Type 6: Flameproof thermal conductivity type gas detector
Product description
Xgard comprises of a universal assembly to accommodate the full range
of toxic, flammable and oxygen gas sensors. The assembly comprises
five main parts; the junction box, junction box lid, amplifier/terminal PCB,
sensor PCB and sensor retainer. These are shown in exploded form in
Diagram 3.
A cover is fitted over the amplifier PCB to provide protection when the
junction box is opened. This cover is designed to allow access to all cable
terminals, test points and potentiometers without the need for removal.
The junction box is available in three versions: Glassfilled Nylon for
Xgard Type 1; Corrosionresistant aluminium for all Types; or 316
Stainless Steel for all Types. The junction box is supplied with 1 x M20,
1/2" or 3/4"NPT cable gland entry, on the right hand side for customer use.
The junction box is suitable for fixing on the wall or ceiling using M6
fixings. Cable gland adaptors are available if required (see Spare parts
and accessories section).
Overview

M20, 1/2” or 3/4” NPT cable entry
6
Overview
Slots to suit M6 or 1/4” fixings
155.5 Overall
Height 111
36 Slot
CRS
146 CRS
166.3 Overall
Slots to suit M6
or 1/4” fixings for
ceiling mount
All dimensions in millimetres
Diagram 2: Xgard dimensioned view

Diagram 3: Xgard exploded view (part numbers shown in brackets where applicable.
For part numbers not shown, see Spares and Accessories on page 59)
7
Overview
Grub screw
Grub screw
Certification label
PCB cover
(M04770)
Enclosure
base
Sensor seal
Sensor retainer Oring
(M04828)
Sensor retainer
Lid Oring
(M04829)
Amplifier PCB
Sensor module

8
Table of contents
Type 1  Intrinsically safe toxic and oxygen gas detector . . . . . . . .9
1. Introduction ......................................................................................9
2. Installation ......................................................................................10
3. Operation........................................................................................13
4. Specification...................................................................................16
Type 2  Flameproof toxic and oxygen gas detector . . . . . . . . . . .17
1. Introduction ....................................................................................17
2. Installation ......................................................................................18
3. Operation........................................................................................21
4. Specification...................................................................................24
Type 3  Flameproof flammable gas detector . . . . . . . . . . . . . . . . .25
1. Introduction ....................................................................................25
2. Installation ......................................................................................26
3. Operation........................................................................................29
4. Specification...................................................................................32
Type 4  Flameproof high temperature flammable gas detector . .33
1. Introduction ....................................................................................33
2. Installation ......................................................................................34
3. Operation........................................................................................37
4. Specification...................................................................................40
Type 5  Flameproof flammable gas detector with 420mA output41
1. Introduction ....................................................................................41
2. Installation ......................................................................................42
3. Operation........................................................................................45
4. Specification...................................................................................49
Type 6  Flameproof thermal conductivity type gas detector . . . .50
1. Introduction ....................................................................................50
2. Installation ......................................................................................51
3. Operation........................................................................................54
4. Specification...................................................................................58
Spare parts and accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Appendix: Sensor limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

9
1.1 Intrinsically safe toxic and oxygen gas detector
This version of Xgard is an Intrinsically safe looppowered (currentsink)
420 mA toxic or oxygen gas detector, designed to detect a wide range
of gases when fitted with the appropriate electrochemical sensor. The
detector is certified II 1 G EEx ia IIC T4, and is suitable for use in
Zone 0, Zone 1 and Zone 2 hazardous areas when used with a suitable
Zener barrier or galvanic isolator.
Electrical connections to the detector are made via the terminal block on
the amplifier PCB shown below. The amplifier provides power to the
sensor, and converts the sensor signal into a 420 mA signal for
connection to a control panel.
Diagram 4: Xgard Type 1 PCB layout
(Shown with PCB cover removed).
1. Introduction Xgard Type 1
Internal
grounding
terminal
(earth)
Test
points
Set zero
Run
Links for Crowcon
use (toxic version
only)
Supple
mental
external
grounding
terminal
(earth)

10
WARNING
This detector is designed for use in Zone 0, Zone 1 and Zone 2
hazardous areas, and is certified II 1 G EEx ia IIC T4 when
used with a suitable Zener barrier or galvanic isolator.
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
The detector should be mounted where the gas to be detected is most
likely to be present. The following points should be noted when locating
gas detectors:
• To detect gases which are lighter than air, detectors should be
mounted at high level and Crowcon recommend the use of a collector
cone (Part No. C01051) and accessory adaptor (Part No. M04666).
• To detect heavier than air gases, detectors should be mounted at low
level.
• When locating detectors consider the possible damage caused by
natural events e.g. rain or flooding. For detectors mounted outdoors
Crowcon recommend the use of a Spray Deflector (Part No. C01052)
and accessory adaptor (Part No. M04666).
• Mounting of oxygen detectors requires knowledge of the gas
displacing the oxygen. For example, carbon dioxide is heavier than air
and collects in low lying areas. It will displace oxygen and so detectors
should be placed at low level.
• 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. For example, ammonia is normally
lighter than air, but if released from a cooling system, the gas may fall
rather than rise.
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. Installation Xgard Type 1

11
2.2 Mounting
Xgard should be installed at the designated location with the sensor
pointing down. This ensures that dust or water will not collect on the
sensor and stop gas entering the cell. The mounting detail is shown in
Diagram 2. Care should be taken when installing the detector to avoid
damaging the painted surface of the junction box and sensor retainer.
2.3 Cabling requirement
Cabling to Xgard 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 2core screened cable with a minimum
crosssectional area of 0.5 mm2(20awg). Suitable weatherproof cable glands
must be used. Intrinsically Safe cables should be identified by some means,
for example coloured blue. Alternative cabling techniques such as steel
conduit may be acceptable provided appropriate standards are met.
Xgard requires a dc supply of 830 V and is loop powered (if mounted in
a hazardous area, do not apply a voltage higher than the maximum rating
of the Zener barrier, typically 28 V). Ensure there is a minimum of 8 V at
the detector, taking into account the voltage drop due to cable resistance,
the Zener barrier (if fitted) and the sense resistance of the control panel to
which it is connected.
For example, a nominal dc supply at the control panel of 24 V has a
guaranteed minimum supply of 19.5 V. The circuit may demand up to 20
mA. Given a sense resistor in the control panel of 232 Ohms the
maximum voltage drop allowed due to cable resistance is 6.8 V. The
maximum loop resistance allowed is 340 Ohms (approx.).
A 1.5 mm2cable will typically allow cable runs up to 14 km. Table 1 below
shows the maximum cable distances given typical cable parameters.
C.S.A. Resistance Max. Distance Max. Distance with 330 ž
(Ohms per km) (km) Zener barrier km
mm2Awg Cable Loop
1.0 17 18.1 36.2 9.4 0.35
1.5 15 12.1 24.2 14 0.5
2.5 13 7.4 14.8 23 0.85
Table 1: Maximum cable distances for typical cables
The acceptable cross sectional area of cable used is 0.5 to 2.5 mm2
(20 to 13awg). The table is provided for guidance only, actual cable
parameters for each application should be used to calculate
maximum cable distances.
2. Installation Xgard Type 1

12
2.4 Electrical connections
All connections are made via the screw terminal block mounted on the
amplifier PCB in the junction box. The terminals are marked ‘+’ and ‘’
and correct polarity should be observed when connecting the detector to
control equipment. This version of Xgard is a 420 mA current sink
device, and requires a dc supply of 830 V.
Note: The internal grounding terminal (see diagram 4) shall be used as the
grounding means of the Xgard gas detector. The external grounding
terminal ( see diagram 4) is only a supplemental bonding connection, and
is only to be used where local authorities permit or require such a
connection. To limit radio interference, the junction box and cable armour
should be grounded (earthed) at the control panel. Ensure the earth
connection is provided in a safe area only, so as to avoid earth loops and
maintain I. S. certification.
Diagram 5: Xgard Type 1 electrical connections
2. Installation Xgard Type 1
Pepperl & Fuchs 
Z715 / Z728
1
2
8
7
SIG
MTL
715+ / 728+
3
4
1
2
SIG
1
3
8
7
Pepperl & Fuchs
1211
2
1
12
11
MTL
5041
1314
SIG
SIG
KF D2-CR-Exl.30200
Pepperl & Fuchs and MTL galvanic isolators
Xgard Type 1 PCB Control Panel
I.S. Earth
I.S. Earth
Earth
Earth
Control Panel
SAFE AREAHAZARDOUS AREA
Pepperl & Fuchs and MTL Zener barriers
Xgard Type 1 PCB
24V dc
Supply
24V dc
Supply
SAFE AREA
HAZARDOUS AREA

13
WARNING
Prior to carrying out any work ensure local regulations and
site procedures are followed. Never attempt to open the
detector or junction box when flammable gas is present.
Ensure that the associated control panel is inhibited so as to
prevent false alarms.
3.1a Commissioning procedure
– toxic types only
1. Open the junction box of the detector by
unscrewing the lid in an anticlockwise
direction (having loosened the retaining grub
screw first).
2. Check that all electrical connections have been made and are correct
as per Diagram 5.
3. Apply power to the detector and ensure the minimum supply voltage
of 8 V dc is present at the ‘+’ and ‘’ terminals of the detector.
4. Leave the detector to stabilise for at least 1 hour, dependant upon
sensor type.
5. Connect a digital volt meter (DVM) to the test points on the amplifier
PCB.
Note: At the test points, Zero will read 40 mV = 4 mA.
Full scale deflection will read 200 mV = 20 mA.
Zeroing the detector
6. Ensure you are in clean air. Adjust the ‘ZERO’ pot on the amplifier
(which is accessible via a hole in the PCB cover) until the DVM reads
40 mV. Check that the control equipment display reads zero.
Calibrating the detector
7. Apply calibration gas (concentration should be at least 50% of sensor
fullscale) to the detector at a flow rate of 0.5  1 litre/minute via a flow
adaptor (Part No. C03005). Contact Crowcon for the supply of
calibration gas.
8. Allow the gas reading to stabilise (usually 30 to 60 seconds) and adjust
the ‘CAL’ pot until the DVM reads the appropriate reading. To calculate
the reading use the formula and example below:
(160
Range x Gas )+ 40 = mV setting
Example: calibrating a 0250 ppm carbon monoxide sensor using
150 ppm gas.
3. Operation Xgard Type 1
NB Glassfilled Nylon
junction boxes do not
include a grub screw.

14
(160
250 x 150 )+ 40 = 136 mV
9. If the control equipment display requires adjustment consult the
operating manual for the equipment.
10.Remove the gas and allow the sensor to completely settle before re
checking the zero setting.
11.Close the junction box of the detector ensuring that the lid is securely
tightened, and the grubscrew is secured.
12.The detector is now operational.
3.1b Commissioning procedure
– oxygen type only
1. Follow steps 1 to 5 given in 3.1a above.
Zeroing the detector
2. Remove the amplifier PCB covers and move the LINK on the amplifier
board from ‘RUN’ to ‘SET ZERO’. Adjust the ‘ZERO’ pot on the
amplifier until the DVM reads 40 mV. Check that the control equipment
display reads zero.
Calibrating the detector
3. With normal clean air present at the detector, replace the LINK to ‘RUN’
on the amplifier board, adjust the ‘CAL’ pot until the DVM reads 174 mV,
(20.9% O2). Leave the LINK in ‘RUN’ position and refit the PCB cover.
4. If the control equipment display requires adjustment consult the
operating manual for the equipment.
5. Follow steps 11 and 12 given in 3.1a above. The detector is now
operational.
3.2 Routine maintenance
The operational life of the sensors depends on the application, frequency
and amount of gas being seen. Under normal conditions (6 monthly
calibration with periodic exposure to CAL gas) the life expectancy of the
toxic sensors is 23 years. Oxygen sensors must be replaced every two
years.
Site practices will dictate the frequency with which detectors are tested.
Crowcon would recommend that detectors be gas tested at least every 6
months and recalibrated as necessary. To recalibrate a detector follow
the steps given in 3.1 above. The calibration frequency should be
increased in environments subject to extreme heat and/or dust, and
where gas is frequently present.
3. Operation Xgard Type 1

15
When performing maintenance on Xgard, ensure that the sensor retainer
and junction box lid Orings are present and in good condition to maintain
the ingress protection of the product. See the ‘Spare parts and
accessories’ section for the part numbers of replacement Orings.
3.3 Sensor replacement/servicing of detectors
Xgard uses a modular design, which makes replacement of sensors
extremely simple. Replacement sensors are supplied fitted to a sensor
PCB to allow simple plugin installation. An exploded view of Xgard is
given in Diagram 3. The following procedure may be followed when
servicing a Xgard detector.
WARNING
This work should be carried out by Crowcon or an approved
service centre unless suitable training has been received.
1. Switch off and isolate power to the detector requiring attention.
2. Open the junction box of the detector by unscrewing the lid in an anti
clockwise direction (having loosened the retaining grubscrew first).
3. Unscrew the sensor retainer and remove the sensor and sensor PCB.
4. Fit the replacement sensor (having checked that the part number
matches that stated on the detector junction box label), taking care to
align the locating pins correctly with the slots in the junction box.
5. Refit the sensor retainer.
6. Follow the Commissioning Procedure given in 3.1.
Storage Instructions: The sensor used in this detector has a maximum
nonpowered storage life of 3 months. Sensors stored within a detector
for longer than 3 months prior to commissioning may not last for the full
expected operational life. The warranty period for the sensor begins from
the date of shipment from Crowcon. Detectors should be stored in a cool
and dry environment where temperatures remain within the 020°C range.
Cleaning: When cleaning Glassfilled Nylon junction boxes use a damp
rather than dry cloth to avoid building up static electricity.
3. Operation Xgard Type 1

16
Junction box material ATEX: Glassfilled nylon
UL Version: Aluminium
316 Stainless Steel (optional)
Dimensions 156 x 166 x 111 mm (6.1 x 6.5 x 4.3 inches)
Weight Alumnium: 1 kg (2.2 lbs)
Glassfilled Nylon: 0.5 kg (1.1lb)
Stainless Steel: 3.1 kg (6.8lbs) approx.
Operating voltage 8–30 V dc
Output 420 mA Sink (loop powered)
Fault signal < 3 mA
Operating temperature 20°C to +50°C (4°F to +122°F)
dependant upon sensor type
Humidity 0–90% RH, non condensing
Degree of protection IP65, IP66 (when fitted with a weatherproof cap)
Explosion protection Intrinsically Safe
Approval code ATEX II 1 G EEx ia IIC T4
IECEx BAS 05.0042X
Tamb = 40°C to 55°C
UL& cUL Class I, Division 1, Groups A, B, C & D
Safety certificate no. ATEX Baseefa04ATEX0115X
Standards EN50014, EN50020, UL913
Zones Certified for use in Zone 0, Zone 1 or Zone 2
(see hazardous area classifications section)
Gas groups IIA, IIB, IIC (UL groups A, B, C, D)
EMC EN50270
Marine Approval Oxygen detectors only: MED (Marine
Equipment Directive 96/98/EC).
4. Specification Xgard Type 1

17
1.1 Flameproof toxic and oxygen gas detector
This version of Xgard is a Flameproof looppowered (currentsink)
420 mA toxic or oxygen gas detector, designed to detect a wide range
of gases when fitted with the appropriate electrochemical sensor. The
detector is certified II 2 GD EExd IIC T6, and is suitable for use in
Zone 1 and Zone 2 hazardous areas.
Electrical connections to the detector are made via the terminal block on
the amplifier PCB shown below. The amplifier provides power to the
sensor, and converts the sensor signal into a 420 mA signal for
connection to a control panel.
Diagram 6: Xgard Type 2 PCB layout
(Shown with PCB cover removed).
1. Introduction Xgard Type 2
Internal
grounding
terminal
(earth)
Test
points
Set zero Run
Links for Crowcon
use (toxic version
only)
Supple
mental
external
grounding
terminal
(earth)

1818
WARNING
This detector is designed for use in Zone 1 and Zone 2
hazardous areas, and is certified II 2 GD EExd 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
The detector should be mounted where the gas to be detected is most
likely to be present. The following points should be noted when locating
gas detectors:
• To detect gases which are lighter than air, detectors should be
mounted at high level and Crowcon recommend the use of a collector
cone (Part No. C01051) and accessory adaptor (Part No. M04666).
• To detect heavier than air gases, detectors should be mounted at low
level.
• When locating detectors consider the possible damage caused by
natural events e.g. rain or flooding. For detectors mounted outdoors
Crowcon recommend the use of a Spray Deflector (Part No. C01052)
and accessory adaptor (Part No. M04666).
• Mounting of oxygen detectors requires knowledge of the gas
displacing the oxygen. For example, carbon dioxide is heavier than air
and collects in low lying areas. It will displace oxygen and so detectors
should be placed at low level.
• 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. For example, ammonia is normally
lighter than air, but if released from a cooling system, the gas may fall
rather than rise.
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. Installation Xgard Type 2

19
2.2 Mounting
Xgard should be installed at the designated location with the sensor
pointing down. This ensures that dust or water will not collect on the
sensor and stop gas entering the cell. The mounting detail is shown in
Diagram 2. Care should be taken when installing the detector to avoid
damaging the painted surface of the junction box and sensor retainer.
2.3 Cabling requirement
Cabling to Xgard 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.
Xgard requires a dc supply of 830 V and is loop powered. Ensure there
is a minimum of 8 V at the detector, taking into account the voltage drop
due to cable resistance and the sense resistance of the control panel to
which it is connected.
For example, a nominal dc supply at the control panel of 24 V has a
guaranteed minimum supply of 19.5 V. The circuit may demand up to
20 mA. Given a sense resistor in the control panel of 232 Ohms the
maximum voltage drop allowed due to cable resistance is 6.8 V. The
maximum loop resistance allowed is 340 Ohms (approx.).
A 1.5 mm2cable will typically allow cable runs up to 14 km. Table 2 below
shows the maximum cable distances given typical cable parameters.
C.S.A. Resistance (Ohms per km) Max. Distance (km)
mm2Awg Cable Loop
1.0 17 18.1 36.2 9.4
1.5 15 12.1 24.2 14
2.5 13 7.4 14.8 23
Table 2: Maximum cable distances for typical cables
The acceptable cross sectional area of cable used is 0.5 to 2.5 mm2
(20 to 13awg). The table is provided for guidance only, actual cable
parameters for each application should be used to calculate
maximum cable distances.
2. Installation Xgard Type 2

20
2.4 Electrical connections
All connections are made via the screw terminal block mounted on the
amplifier PCB in the junction box. The terminals are marked ‘+’ and ‘’
and correct polarity should be observed when connecting the detector to
control equipment. This version of Xgard is a 420 mA current sink
device, and requires a dc supply of 830 V.
Note: The internal grounding terminal (see diagram 6) shall be used as the
grounding means of the Xgard gas detector. The external grounding
terminal (see diagram 6) is only a supplemental bonding connection, and
is only to be used where local authorities permit or require such a
connection. To limit radio frequency interference, the junction box and
cable armour should be grounded (earthed) at the control panel. Ensure
the earth connection is in a safe area only, so as to avoid earth loops.
Diagram 7: Xgard Type 2 electrical connections
2. Installation Xgard Type 2
SIG
Xgard Type 2 PCB Control Panel
Earth
830 V dc
420 mA
(Source)