2
2. DETECTOR CONFIGURATION
Table 3 details standard alarm points for the available gases and ranges.
Gas
Range*
AL1*
AL2*
Hydrogen sulphide
0–25 ppm
10 ppm
20 ppm
Carbon monoxide
0–250 ppm
30 ppm
100 ppm
Ammonia
0–50 ppm
10 ppm
25 ppm
Oxygen
0–25% vv
19% vv
17% vv
Sulphur dioxide
0–10 ppm
2 ppm
5 ppm
* Alternative ranges and alarm set points must be specified when ordering
Table 3: Standard ranges and alarm set points.
Location of links are shown in Diagram 2.
2.2 4–20 mA options
To change current source output to sink, set switch to ‘SK’ position.
To change Inhibit from 2 mA to 4 mA, fit link to ‘4’ position.
2.3 Relay options
To change AL1 or AL2 relay from NO to NC, fit link in the ‘NC’ position.
To change FAULT relay from NC to NO, fit link in the ‘NO’ position.
2.4 Inhibit options
To not inhibit 4-20 mA signal and relays, fit link to ‘N’ and link to ‘4’.
3. INSTALLATION
Diagram 2
: Terminal and amplifier layouts
CONTACT
REVERSING
LINKS
TO
96HD
SENSOR
4-20mA
10-30V
0V
RL3
RL2
RL1
ALARM 2
12
4
SENSOR
56
3
OXYGEN
OUTPUT
SK
SR
OTHER
CONTROL
EQUIPMENT
ALARM2
RELAY
CONTACTS
INTERNAL TERMINAL LAYOUT
= ALARM RELAY VERSION ONLY
REAR VIEW OF
AMPLIFIER
FAUL
T
ALARM1
ALARM
4mA
OUTPUT OPTIONS
TEST
POINT
40-200 mV
INHIBIT
N
Y
17 4 2
GAS
RANGE
ALARM
ALARM 1
78
9
10
11
12
ISOLATE
0V
GND
NC NO
NC NO
NO NC
GND
ISOLATE
LINK
ALARM1
FAULT
ALARM
SET POTS
USED FOR
OXYGEN TXGARD.
FOR TOXIC LINK
SET TO OTHER
2.1 Standard configuration
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
(if fitted)
• Alarm level 1, see Table 3
• Normally de-energised, energising on alarm
• Contact normally open (NO), closing on
alarm
AL2 relay
(if fitted)
• Alarm level 2, see Table 3
• Normally de-energised, energising on alarm
• Contact normally open (NO), opening on
alarm
FAULT relay
(if fitted)
• Normally energised, de-energising 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 configuration for TXgard-Plus
.
WARNING
TXgard-Plus is designed for use in Zone 1 and 2 hazardous areas and
is certified EEx d IIC T6 (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 BS6959:1988 – ‘British Standard
Code of Practice for the Selection, Installation, Use and Maintenance of
Apparatus for the Detection and Measurement of Combustible Gases’. In the
USA refer to the National Electrical Code (NEC 1999). Similar international
codes of practice may be used where applicable. In addition certain regulatory
bodies publish specifications giving minimum gas detection requirements for
specific 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 e.g. ammonia, 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 e.g. sulphur dioxide, detectors should be
mounted at low level.
•
When locating detectors consider the possible damage caused by natural
events eg. rain or flooding. For detectors mounted outdoors Crowcon
recommend using 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.
• Consider the process conditions. Ammonia is normally lighter than air, but
if released from a process line which is cooled and/or under pressure the
gas may fall rather than rise.
