Crowcon TXgard-IS Plus Istruzioni per il montaggio
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TXgard
MANUAL
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JUNHO 2013
TXgard-IS+
Intrinsically Safe
Toxic and Oxygen Gas Detectors
Loop Powered Electrochemical and Galvanic Sensor Types Only
Installation, operating and
maintenance instructions, M07214
Issue 7 January 2010
Contents
1 Introduction .................................................................................. 5
Product overview ........................................................................................ 5
Product description ..................................................................................... 5
2 Installation ................................................................................... 8
General ....................................................................................................... 8
Mounting ..................................................................................................... 9
Cabling requirement ................................................................................... 9
Electrical connections ............................................................................... 10
3 Operation ................................................................................... 13
The operator display panel and keypad ................................................... 13
Using the TXgard-IS+ menus ................................................................... 14
4 Commissioning .......................................................................... 16
Commissioning procedure:
Toxic gas detectors .................................................................................. 16
Commissioning procedure:
Oxygen detector ....................................................................................... 21
5 Maintenance .............................................................................. 24
Routine maintenance ................................................................................ 24
Sensor replacement and servicing of detectors ....................................... 24
6 Fault finding ............................................................................... 26
Appendices
Appendix A
Wiring the TXgard-IS+ to Crowcon control equipment ............ 31
Appendix B
TXgard-IS+ specification.......................................................... 35
Appendix C
Spare parts .............................................................................. 37
Appendix D
Menu system............................................................................ 38
Appendix E
4-20 mA Loops......................................................................... 46
Appendix F
Cabling requirement................................................................. 48
Appendix G
Sensor limitations..................................................................... 51
Warranty Statement................................................................. 51
Introduction TXgard-IS+
Issue 7 5
1 INTRODUCTION
1.1 Product overview
TXgard-IS+ is an Intrinsically Safe detector for toxic gases or oxygen. It is
suitable for use in Zone 0, 1 or 2, or Division 1/Division 2 hazardous areas
when used with a suitable Zener barrier or galvanic isolator.
TXgard-IS+ is designed to detect a wide range of gases when fitted with
the appropriate electrochemical sensor. Gases include oxygen, carbon
monoxide and hydrogen sulphide. For a full list of supported sensors,
please contact Crowcon.
TXgard-IS+ is a loop-powered instrument providing a 4-20 mA signal
suitable for direct connection to a control panel. Unlike most other 4-20 mA
gas detectors featuring operator display panel (LCD) and keypads, it
combines its power and signal in just two wires, so only one barrier is
required. The instruments are supplied with the mA pre-calibrated, so the
mA does not need re-calibration in the field. The keypad and operator
display panel allow access to many powerful features to help installation
and maintenance, such as:
•true one man calibration
•signal current can be ramped to a desired value to help set-up
control panels
•configurable fault and inhibit currents
•configurable display options
•displaying line voltage - no need to access test points inside
unit
1.2 Product description
TXgard-IS+ comprises of two main parts. The junction box contains the
circuitry, including the PCBs, an operator display panel and keypad. The
sensor is contained in the sensor housing. “Figure 1.1” on page 6.
The sensor comes in a re-usable bayonet sensor housing which is
standard for all gas sensors.
The sensor housing screws into an M20 entry on the junction box.
All electrical connections to the detector are made through the terminal
blocks on the baseboard J2 and J4 (see and in “Figure 1.1” on
page 5). The junction box of TXgard-IS+ has one top-entry M20 cable
TXgard-IS+ Introduction
6 Issue 7
entry for customer use as standard. Side entry versions and gland
adapters are available (contact Crowcon for details).
The Personality Module , mounted on the baseboard, comes in two
varieties: Toxic and Oxygen. It converts the sensor output into a standard
signal which can be interpreted by the processor. The Personality Module
contains a memory chip with calibration data for the associated sensor.
When replacing a sensor, it is not necessary to change the Personality
Module; you simply rezero (Note: not necessary for O2 sensor) and
recalibrate, and the Personality Module stores the new calibration
constants.
When the detector is powered through a suitable Zener barrier or galvanic
isolator, the system is certified Ex ia IIC T4.
Figure 1.1: TXgard-IS+ fitted with toxic sensor
Important
TXgard-IS+ is designed for use in Zone 0, 1 or 2, or Division 1/Division 2
hazardous areas and is certified Ex 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. TXgard-IS+ should be inspected regularly if used in a dusty
environment. For further information, please contact Crowcon.
Before carrying out any installation work, ensure that local
regulations and site procedures are followed.
J4
TP1
+
TP2
–
J2
CONNECTION TO
CONTROL PANEL
40-200mV
TEST POINTS
RED
BLU
GRN
M20 CABLE ENTRY
BASE BOARD
PERSONALITY
MODULE
SENSOR
HOUSING
Some baseboards may have
J4 in this orientation
Introduction TXgard-IS+
Issue 7 7
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
TXgardIS+ ATEX, UL and IECEx Intrinsically safe
GAS DETECTOR
TXgard-IS+
TXgard-IS+ Installation
8 Issue 7
2 INSTALLATION
2.1 General
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 that are lighter than air, detectors should be
mounted at high level. Crowcon recommends the use of a
Collector Cone (part no. C01051).
•To detect gases that are heavier than air, detectors should be
mounted at low level.
•To detect gases with similar weight to air, for example,
hydrogen sulphide, mount the detector at normal breathing
height.
•When locating detectors, consider the possible damage
caused by natural events such as rain or flooding. For
detectors mounted outdoors, Crowcon recommends the use of
a spray deflector (part no. C01338).
•Mounting of oxygen detectors requires knowledge of the gas
displacing the oxygen. For example, carbon dioxide is heavier
than air and displaces oxygen at low level. Under these
circumstances oxygen 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. Gases that are normally
heavier than air, but are released from a process line that is at
a high temperature and/or under pressure, may rise rather than
fall. Ammonia released from a cooling system may fall rather
than rise.
The placement of the sensors should be decided following the advice of
experts with specialist knowledge of gas dispersion, experts with
knowledge of the process plant system and equipment involved, and
safety and engineering personnel. The agreement reached on the
locations of sensors should be recorded. Crowcon is pleased to assist
in the selection and siting of gas detectors.
Installation TXgard-IS+
Issue 7 9
2.2 Mounting
TXgard-IS+ should be installed at the location with the detector pointing
down. This ensures that dust or water will not collect on the sensor and
stop gas entering the detector.
Figure 2.1: TXgard-IS+ dimmensions
2.3 Cabling requirement
Cabling to TXgard-IS+ must be in accordance with the recognised
standards of the appropriate authority in the country concerned, and must
also meet the electrical requirements of the detector. Crowcon
recommends the use of 2-core twisted pair cable, but there is no particular
restriction as long as it can supply 8 V at 20 mA to the instrument terminals.
Suitable weatherproof glands must be used. Cable should be identified as
being intrinsically safe by some means, for example, by having a blue outer
sheath. Alternative cabling techniques, such as steel conduit, may be
acceptable provided that appropriate standards are met.
TXgard-IS+ requires a dc supply of 8-32 V and is loop powered.
(If mounting in a hazardous area, do not use a higher voltage than the
Zener barrier’s rating, usually 28 V). Ensure there is a minimum supply 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. "Table 2.1" on page 10, shows maximum cable distances
given typical cable parameters (See appendix F for more information).
TXgard-IS+ Installation
10 Issue 7
Table 2.1: Maximum cable distances for typical cables
The acceptable cross-sectional area of cable used is 1.0 to 2.5 mm2.
The table is provided for guidance only. Actual cable parameters for
each application should be used to calculate maximum cable
distance. Assume each termination is 0.5 Ω.
2.4 Electrical connections
All connections to the 4-20 mA loop, and sensor, are made via the screw
terminal connectors mounted on the baseboard in the junction box. “Figure
1.1” on page 6. For further information on how 4-20 mA current loops work,
see "Appendix E". For a worked example of how to calculate if the cable is
suitable, please see “Appendix F”.
“Figure 2.2” below, shows the baseboard in detail. The terminals marked
J4 should be connected to the control equipment using the appropriate +
and – terminals. For further details of wiring the TXgard-IS+ to Crowcon
equipment see "Appendix A".
Figure 2.2: Baseboard
Cross-sectional
area (mm2)
Typical resistance
(Ωper km)
Maximum
distance (km)
Cable Loop
1.0 18.1 36.2 2.2
1.5 12.1 24.2 3.3
2.5 7.4 14.8 5.4
Some baseboards
may have J4 in
this orientation
Installation TXgard-IS+
Issue 7 11
TXgard-IS+ is a 4-20 mA sink, loop-powered device designed to work in
safe and hazardous zones 0, 1 and 2 areas when used in conjunction with
an appropriate barrier. Figures 2.3, 2.4 and 2.5 summarise the electrical
connections.
SAFE AREA
Figure 2.3: Electrical connections for safe area
HAZARDOUS AREA
Note: An IS earth connection must be supplied in the safe area, so
as to avoid earth loops and to maintain IS certification.
Figure 2.4: Electrical connections using Zener barrier
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