Crowcon TXgard-IS+ Manuale
Contents
1 INTRODUCTION ....................................................................... 1
Product overview.................................................................. 1
Product description............................................................... 1
2 INSTALLATION.......................................................................... 4
General ................................................................................ 4
Mounting............................................................................. 5
Cabling requirement............................................................. 5
Electrical connections ........................................................... 6
3 OPERATION............................................................................ 10
The operator display panel and keypad............................... 10
Using the TXgard-IS+ menus............................................... 11
4 COMMISSIONING .................................................................. 14
Commissioning procedure: ................................................ 14
Commissioning procedure: ................................................ 20
5 MAINTENANCE...................................................................... 23
Routine maintenance.......................................................... 23
Sensor replacement and servicing of detectors.................... 23
6 FAULT FINDING ...................................................................... 25
Appendices
APPENDIX A.............................................................................. 31
WIRING THE TXGARD-IS+ TO CROWCON CONTROL
EQUIPMENT........................................................................ 31
APPENDIX B.............................................................................. 35
TXGARD-IS+ SPECIFICATION............................................... 35
APPENDIX C.............................................................................. 37
SPARE PARTS AND ACCESSORIES ....................................... 37
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APPENDIX D.............................................................................. 38
MENU SYSTEM................................................................... 38
APPENDIX E .............................................................................. 48
4-20 mA LOOPS ................................................................. 48
APPENDIX F .............................................................................. 50
CABLING REQUIREMENT .................................................... 50
APPENDIX G ............................................................................ 53
SENSOR LIMITATIONS ......................................................... 53
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TXgard-IS+ Introduction
1
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:
• trueonemancalibration
• signalcurrentcanberampedtoadesiredvaluetohelpset-up
control panels
• congurablefaultandinhibitcurrents
• congurabledisplayoptions
• displayinglinevoltage-noneedtoaccesstestpointsinsideunit
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 on page 2.
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.
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Introduction TXgard-IS+
2
All electrical connections to the detector are made through the terminal
blocks on the baseboard J2 and J4 (see and in Figure 1). The
junction box of TXgard-IS+ has one top-entry M20 cable 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.
J4
TP1
+
TP2
–
J2
CONNECTION TO
CONTROL PANEL
40-200mV
TEST POINTS
RED
BLU
GRN
M20CABLE ENTRY
BASE BOARD
PERSONALITY
MODULE
SENSOR
HOUSING
Some baseboards may have
J4 in this orientation
Figure 1: TXgard-IS+ fitted with toxic sensor
Important
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TXgard-IS+ Introduction
3
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.
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
Abingdon, United Kingdom, OX14 4SD
GAS DETECTOR
TXgard-IS+
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Installation TXgard-IS+
4
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:
• Todetectgasesthatarelighterthanair,detectorsshouldbe
mounted at high level. Crowcon recommends the use of a
Collector Cone (part no. C01051).
• Todetectgasesthatareheavierthanair,detectorsshouldbe
mounted at low level.
• Todetectgaseswithsimilarweighttoair,forexample,hydrogen
sulphide, mount the detector at normal breathing height.
• Whenlocatingdetectors,considerthepossibledamagecausedby
natural events such as rain or flooding. For detectors mounted
outdoors, Crowcon recommends the use of a spray deflector (part
no. C01338).
• Mountingofoxygendetectorsrequiresknowledgeofthegas
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.
• Considereaseofaccessforfunctionaltestingandservicing.
• Considerhowtheescapinggasmaybehaveduetonaturalor
forced air currents. Mount detectors in ventilation ducts if
appropriate.
• Considertheprocessconditions.Gasesthatarenormallyheavier
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
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TXgard-IS+ Installation
5
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.
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.
TXgard-IS+
5 ppm
4.3mA
CO
OK
124 92
122
38
104
104
Figure 2: TXgard-IS+ dimensions
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.
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Installation TXgard-IS+
6
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 1 shows maximum cable distances given typical
cable parameters (See Appendix F for more information).
Table 1: Maximum cable distances for typical cables
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
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 on page 2. 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 3 on page 7 , 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.
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