1
1.1 Product overview
TXgard-Plus is a flameproof toxic and oxygen gas detector
suitable for use in zone 1 or 2 hazardous areas. It is designed to detect
the following gases when fitted with the appropriate electrochemical
sensor:
Gas
Range
Type
Hydrogen sulphide
0–25 ppm
Toxic
Carbon monoxide
0–250 ppm
Toxic
Ammonia
0–50 ppm
Toxic
Oxygen
0–25% vv
Oxygen
Sulphur dioxide
0–10 ppm
Toxic
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 fitted
with optional alarm and fault relays.
1.2 Product description
TXgard-Plus comprises four parts; 96HD sensor housing, junction box, amplifier
and terminal board. Diagram 1 details TXgard-Plus. The overall assembly is
certified EEx d IIC T6 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 amplifier plugs into the terminal board, and is held in place by two
captive screws. The amplifier 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
amplifier 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.
TXgard
-Plus
Flameproof
Toxic and Oxygen
Gas Detector
with Non-intrusive One-man Calibration
1. INTRODUCTION
Instructions
Diagram 1
: TXgard Plus general arrangement
TAMPER PROOF
GRUB SCREW
(1.5mm ALLEN KEY)
STEADY ON
INDICATES
ZERO/ CAL
MODE
ACTIVATED
EXTERNAL
EARTH POINT
"UP"
M20 (
1
/
2
" NPT)
CABLE ENTRY
UNITS
M20 (
1
/
2
" NPT)
CABLE ENTRY
115 (4
1
/
2
")
HEIGHT = 115 (4
1
/
2
")
All dimensions in mm unless otherwise stated
83 (3
1
/
4
")
200 (8")
135 (5
5
/
16
")
LOCAL
DISPLAY
FLASHING
INDICATES
4-20mA/RELAYS
INHIBITED
ALARM 1 & 2
ADJUSTMENT
POTS
4 OFF
FIXING HOLES
O 6mm (
1
/
4
")
STATUS
LED
"DOWN"
ppm
TXgard
-Plus
Relay version only
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 LED
Relay
Comment*
state
indication
states*
Normal
Steady green
AL1 - Off
Gas level < AL1
operation
AL2 - Off
Current output = 4–20 mA
FAULT - On
Normal
Steady red
AL1 - On
AL1 < gas level < AL2
operation
AL2 - Off
Current output = 4–20 mA
(alarm 1)
FAULT - On
Normal
Flashing red
AL1 - On
Gas level > AL2
operation
AL2 - On
Current output = 4–20 mA
(alarm 2)
FAULT - On
Over-range
Flashing red
AL1 - On
Gas level > full scale
AL2 - On
Display backlight flashes
FAULT - On
Current output = 24 mA
Zero/calibration
Flashing green
Configuration
Latched until reset by ‘MENU’
mode
dependent
Current output = 2 mA
(see section 2)
(4 mA option)
Detector
Steady amber
AL1 - Off
Current output = 0 mA
fault
AL2 - Off
FAULT - Off
*See section 2 for AL1 and AL2 standard settings
Table 1: LED status indicator summary
.
