Crowcon TXgard-Plus Installation and operating instructions

Installation, Operation and Maintenance Instructions
M07194
Issue 6
April 2018
TXgard-Plus
Flameproof Toxic and Oxygen Gas Detector

TXgard-Plus Introduction
1
1 Introduction
1.1 Product overview
TXgard-Plus is a ameproof toxic and oxygen gas detector suitable for
use in zone 1 or 2 hazardous areas. It is designed to detect toxic gases
and oxygen using a range of electrochemical sensors. A local display and
magnetically operated switches allow non-intrusive one-man calibration
without a hot work permit. Powered by 24 V dc (nominally) TXgard-
Plus provides a 4-20 mA signal (sink or source) proportional to the gas
concentration and can also be tted with optional alarm and fault relays.
For a list of gases that can be detected, please contact Crowcon.
1.2 Product description
TXgard-Plus comprises four parts; 96HD sensor housing, junction box,
amplier and terminal board. Diagram 1 details Txgard-Plus. The overall
assembly is certied Ex db IIC T6 Gb in Europe and Class 1, Zones 1&2
AEx d IIC T6 in the USA.
The 96HD sensor housing is a modular stainless steel assembly that
dismantles to allow plug in sensors to be replaced easily (see Diagram
4). The assembly screws into an M20 entry on the junction box.
The junction box is manufactured from marine grade alloy and is
supplied with 2 x M20 (1/2” NPT for USA) cable entries for customer
use. Alternative cable entries are available from Crowcon.
The amplier plugs into the terminal board, and is held in place by
two captive screws. The amplier provides power to the sensor, local
display and controls, and a 4-20 mA signal proportional to the gas
concentration for connection to a control panel. To remove, turn screws
anti-clockwise and use them to pull amplier out of the enclosure.
All electrical connections are made via the terminal board mounted in
the base of the junction box (see Diagram 2). Optional alarm relays (AL1
& AL2) and one fault relay (FAULT) are mounted on the terminal board
which may be used to drive local warning devices or connect TXgard-
Plus to a control panel.

Introduction TXgard-Plus
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1.3 Status Indication
TXgard-Plus includes a local display and status LED, visible through
the junction box window, see Diagram 1. The display shows the gas
concentration and current mode of operation ie. NORMAL, ZERO or
CAL. The LED shows the current alarm state of the detector. This is
summarised in Table 1.
Operational
state
LED
indication
Relay states* Comment*
Normal
operation
Steady green AL1 - O
AL2 - O
FAULT - On
Gas level < AL1
Current output = 4-20 mA
Normal
operation
(ALARM 1)
Steady red AL1 - On
AL2 - O
FAULT - On
Gas level > AL1 < AL2
Current output = 4-20 mA
Normal
operation
(ALARM 2)
Flashing red AL1 - On
AL2 - On
FAULT - On
Gas level > AL2
Current output = 4-20 mA
Over-range Flashing red AL1 - On
AL2 - On
FAULT - On
Gas level > full scale
Display backlight ashes
Current output = 24 mA
Zero/
calibration
mode
Flashing
green
Conguration
dependent
(see section 2)
Latched until reset via 'MENU'
Current output = 2 mA
4 mA option)
Detector fault Steady
amber
AL1 - O
AL2 - O
FAULT - O
Current output = 0 mA
*See section 2 for AL1 and AL2 standard settings
= Relay version only
Table 1: LED status indicator summary.

TXgard-Plus Introduction
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Diagram 1: TXgard Plus general arrangement

Introduction TXgard-Plus
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Diagram 2: Terminal and amplier layouts

TXgard-Plus Detector configuration
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2. Detector conguration
2.1 Standard conguration
As standard, TXgard-Plus is factory set as follows:
Current source with 0 mA = Fault
2 mA = Inhibit ie. Zero/Cal mode
4-20 mA = Normal operation
24 mA = Over-range clamp
AL1 relay Alarm level 1, see Table 3
Normally de-energised, energising on alarm
Contact normally open (NO), closing on alarm
AL2 relay Alarm level 2, see Table 3
Normally de-energised, energising on alarm
Contact normally open (NO), closing on alarm
FAULT relay Normally energised, de-energised on fault
Contact normally closed (NC), opening on
fault
Alarm/fault relays automatically reset when alarm or fault has cleared.
INHIBIT Normally selected, ie. when CAL/ZERO
selected current output is forced to 2mA and
relays are held in normal/no alarm state.
Table 2: Standard conguration for TXgard-Plus.

Detector configuration TXgard-Plus
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Table 3 details standard alarm points for the available gases and ranges.
Gas Range* AL1* AL2*
Hydrogen sulphide 0-25 ppm 5 ppm 10 ppm
Carbon monoxide 0-250 ppm 30 ppm 200 ppm
Oxygen 0-25% vv 19% vv 17% vv
*Alternative ranges and alarm set points must be specied when ordering
Table 3: Standard ranges and alarm set points.
Location of links are shown in Diagram 2.
2.2 4-20mA options
To change current source output to sink, set switch to ‘SK’ position. To
change Inhibit from 2 mA to 4 mA, t link to‘4’position.
2.3 Relay options
To change AL1 or AL2 relay from NO to NC, t link in the ‘NC’ position.
To change FAULT relay from NC to NO, t link in the “NO” position.
2.4 Inhibit options
To not inhibit 4-20 mA signal and relays, t link to ‘N’and link to‘4’.

TXgard-Plus Installation
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3. Installation
WARNING
TXgard-Plus is designed for use in Zone 1 and 2 hazardous areas
and is certified Ex db IIC T6 Gb (AEx d IIC T6 in USA). Installation
must be in accordance with the recognised standards of the
appropriate authority in the country concerned. For more
information contact Crowcon. Prior to carrying out any work
ensure local regulations and site procedures are followed.
3.1 Location
There are no rules which dictate the siting and location of detectors,
however, considerable guidance is available from BS EN 60079-29-
2:2015 ‘Explosive atmospheres. Gas detectors. Selection, installation,
use and maintenance of detectors for ammable gases and oxygen’.
In the USA refer to the National Electrical Code. Similar international
codes of practice may be used where applicable. In addition certain
regulatory bodies publish specications giving minimum gas detection
requirements for specic applications.
The detector should be mounted where the gas 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).
• To detect heavier than air gases (eg hydrogen sulphide), detectors
should be mounted at low level.
• When locating detectors consider the possible damage caused by
natural events e.g. rain or ooding. For detectors mounted outdoors
Crowcon recommend the use of a Weatherproof Cap (Part No.
C01442).
• 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.

Installation TXgard-Plus
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• Consider the process conditions (ie whether gas within a process is at
high temperature or high pressure)
Detector placement 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.
3.2 Mounting
The mounting detail of TXgard-Plus is given in Diagram 1. TXgard-
Plus should be installed at the designated location with the detector
pointing down. This ensures that dust or water will not collect on the
sinter and stop gas entering the detector.
3.3 Cabling requirement
Cabling to TXgard-Plus 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.
TXgard-Plus requires a dc supply of 12-30 V at up to 100 mA. Ensure
the minimum dc supply of 12 V 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 V has
a guaranteed minimum supply of 20V. The maximum voltage drop
allowed is therefore 8V. TXgard-Plus can demand up to 100 mA and
so the maximum loop resistance allowed is 80 Ohms. A 1.0 mm2 cable
will typically allow cable runs up to 2000m. Table 4 shows maximum
cable distances given typical cable parameters.