TROLEX STX3241 Toxic Gas Sensor Installation Guide
- June 16, 2024
- Trolex
Table of Contents
TROLEX STX3241 Toxic Gas Sensor
INSTALLATION & OPERATING DATA
PRINCIPAL OPERATINGFEATURES
Fixed gas sensors for the detection of toxic gases present in the atmosphere.
High accuracy electrochemical sensing elements for a wide range of toxic gases.
LCD readout of gas concentration with OVER RANGE indication.
Convenient calibration of ZERO and SPAN via front mounted potentiometers.
Output signal versions:- 4 to 20 mA or 0.4 to 2 V.
Reinforced Polymer – EMC protected and proof against electrostatic charge.
Intrinsically safe for use in Group I hazardous areas.
Optional format with remote mounted gas sensing module in robust metal housing.
APPLICATION
Fixed gas monitoring for point-source hazards and per imeter protection in
arduous duty and exposed locations.
Safety protection for toxic gas risk occurring in hazardous areas and general
industrial applications.
A range of primary instrumentation and monitoring modules is available from Trolex to which the sensors can be directly connected to provide a flexible choice of display and control functions.
TRIP AMPLIFIER
for use with analogue output sensors.
CONFIGURABLE SENSOR CONTROLLER
for monitoring up to 8 analogue output sensors.
COMMANDER DISTRIBUTEDI/O SYSTEM
for large scale general plant monitoring systems and the mining and tunnelling
industries.
DIMENSIONS
S TX3241.01 TOXIC GAS SENSOR/TRANSMITTER
STX3241.01.84 TOXIC GAS SENSOR/TRANSMITTER with Remote Gas Sensing Module.
TECHNICAL DETAILS
Specification
Ambient Temperature Limits: –10 to +40°C.
Humidity: 15 to 90% non condensing.
Storage Temperature Limits: –20 to +60°C.
Ambient Pressure Limits: 1 bar ± 100 mbar absolute.
Protection Classification: Dust & waterproof to IP66. Gas inlet port to
IP54.
Housing Material: Reinforced Polymer – EMC protected and proof against
electrostatic charge.
Sensing Principle: Electrochemical cell.
Cell Operating Life: >2 years (in clean atmosphere).
Electrical Connections: 4 mm barrier/clamp terminals.
Information Display: Graphic LCD.
Vibration Limits (BS2011): 10 to 100 Hz, 0.25 mm pk. 100 to 600 Hz, 2 g
pk.
Impact Limits: 20 joules (housing).
Net Weight: 450 g.
Certification: EEx ia I M1.
| TOXIC GASES ELECTROCHEMICAL CELLS
---|---
| | | SENSING RANGE| LINEARITY| DRIFT| REPEATABILITY| RESPONSE
TIME T63%
| OPERATING
LIFE*
CO| STX3241.01.250.50| CARBON MONO XIDE| 0 to 50 ppm| ±2% FS| 2%
month| ±2%| 9 secs| >2 years
CO| STX3241.01.250.250| CARBON MONO XIDE| 0 to 250 ppm| ±2% FS| 2%
month| ±2%| 9 secs| >2 years
CO| STX3241.01.250.500| CARBON MONOXIDE| 0 to 500 ppm| ±2% FS|
2% month| ±2%| 9 secs| >2 years
NO2| STX3241.01.254.20| NITROGEN OXIDE| 0 to 20 ppm| ±2%| 2% month|
±2%| 15 secs| >2 years
NO| STX3241.01.259.100| NITRIC OXIDE| 0 to 100 ppm| ±5%| 2% month|
±2%| 9 secs| >2 years
H2S| STX3241.01.251.50| HYDROGEN SULPHIDE| 0 to 50 ppm| ±2%| 2%
month| ±2%| 14 secs| >2 years
H| STX3241.01.261.1000| HYDROGEN| 0 to 1000 pp| m ±2%| 2% month|
±2%| 14 secs| >2 years
SO2| STX3241.01.252.20| SULPHUR DIOXIDE| 0 to 20 ppm| ±2%| 2%
month| ±2%| 7 secs| >2 years
Cl2| STX3241.01.255.10| CHLORINE| 0 to 10 ppm| ±2%| 2% month| ±2%|
7 secs| >2 years
O2| STX3241.01.257.25| OXYGEN| 0 to 25%| ±2%| 2% month| ±2%| 7
secs| >2 years
| *IN CLEAN AIR
Electrical Details
STX3241.01 GROUP I APPLICATIONS (12 V dc)
| Output: | 0.4 to 2 V dc |
|---|---|
| Min Load | 10 k ohms |
| Supply | 6.5 to 14.4 V dc |
| Max Supply Current | 10 mA (@12 V) |
| Output: | 4 to 20 mA |
|---|---|
| Max Load @12 V | 250 ohms @ 12 V |
| Supply | 6.5 to 14.4 V dc |
| Max Supply Current | 30 mA (@12 V) |
INSTALLATION
Conformity Check
(Refer to Test Certificate provided with the sensor).
Does the output signal of the sensor concur with the input requirement of the monitoring equipment being used?
12 V dc
Is the correct supply voltage available for the sensor?
Is the type of gas and its anticipated maximum level of concentration, within the operating parameters of the sensor?
Is the temperature variation range, at the installation, within the stated temperature range of the sensor?
Is the hazardous area classification correct?
STANDARD OPTIONS AVAILABLE
STX3241.01 TOXIC GAS SENSOR/ TRANSMITTER
TYPE OF GAS
| OUTPUT SIGNAL | 0.4 to 2 V | (11) |
|---|---|---|
| 4 to 20 mA | (12) |
TX3241.01.84 TOXIC GAS SENSOR/ TRANSMITTER with Remote Gas Sensing Module.
| OUTPUT SIGNAL | 0.4 to 2 V | (11) |
|---|---|---|
| 4 to 20 mA | (12) |
Location
Each installation needs to be considered in its own right, with reference to safety authorities and in compliance with mandatory local safety regulations. The sensor must be operated in accordance with the Installation and Operating Data to maintain safety, reliability and to preserve Intrinsic Safety integrity where applicable.
It is important that sensors are located in positions determined in consultation with those who have specialised knowledge of the plant or installation and of the principles of gas dispersion. Reference should also be made to those responsible for the engineering layout and topology of the plant as they will be most familiar with the nature of the potential dangers and the most likely sources of gas release.
It is also important to recognise that the characteristics of the gas source can be influenced by many factors; including the relative density or buoyancy of the gas, the pressure at the point of release, the ambient temperature and the ventilation of the site.
Sensor coverage cannot be simply expressed in terms of ‘number per unit area’. Sensors need to be sited where they are capable of monitoring those parts of a plant where gas may accumulate or when a source of gas release is expected to occur. This way the earliest possible warning of a gas release can be given to initiate shutdown functions, alarm functions or safe evacuation of the premises.
System Integrity
If a gas monitoring system should fail for any reason, it is important that
the system is capable of immediately alerting operational staff to this fact.
The sensor will indicate a system failure or mechanical defect and this
information can be utilised to initiate a warning alarm. It is good practice
to provide emergency facilities to protect against the loss of the mains power
supply.
Standby batteries can be incorporated with automatic changeover facilities, so
guaranteeing continued operation of the sensing system even in the event of a
plant breakdown as a result of a power supply failure. Certainly, in critical
plants, duplication or triplication of sensors is recommended.
The Trolex TX9042 Programmable Sensor Controller can be programmed to operate with sensors in the multiple voting mode.
Sensor Management
A very important part of an efficient gas monitoring system is the training of plant personnel in operation and maintenance of the sensors and the complete monitoring system. Training facilities can be provided by qualified Trolex application engineers.
Once a sensor installation is complete, the sensor locations and types should be formally recorded and a planned test and maintenance procedure instituted.
Relative Density
The relative density or buoyancy of the gas or vapour with respect to air is a
very
important consideration. This determines its propensity to rise or fall when
released into the atmosphere.
Gases or vapours with a buoyancy less than air will tend to rise from the source of release.
Conversely, gases or vapours heavier than air will tend to fall and accumulate in concentrations for long periods of time.
This is a particular problem in pits, trenches, machine rooms, etc. Normal air movements in and around such gas concentrations will have the inevitable effect of producing zones of of highly toxic mixtures.
This knowledge of the characteristics of the gas assists when positioning the gas sensor.
The behaviour of the gas accumulation will also be affected by the velocity and location of the gas release and by ambient air movement caused by ventilation systems or draughts.
Pockets of gas can be trapped in trenches or ceiling cavities, all of which adds to the unpredictability of critical gas concentrations.
| Hydrogen | LIGHTER THAN AIR |
|---|
Carbon Monoxide
Nitric Oxide| HEAVIER THAN AIR
Oxyg en
Sulphur Dioxide
Chlorine
Nitrogen Dioxide
Hazardous Areas
Do not disassemble the sensor whilst in the hazardous area or use a sensor that has a damaged housing in the hazardous area.
Evacuation
If a dangerous level of gas concentration is detected by the instrument, leave the area immediately.
Operating Life
Electrochemical cells contain an electrolyte that is gradually consumed during
use. The average life is about two years, dependent upon the duty cycle.
The response should be checked at regular intervals.
Sensitivity
Electrochemical cells for toxic gases can be affected by other interfering gases which may displace the subject gas being monitored. Steam laden atmospheres and condensation can also reduce the sensitivity.
Flammable
Be aware that some toxic gases are also ‘flammable’ at high percentage
concentrations.
Biased Sensors
Some gas sensors must be continuously powered to maintain the calibration.
If the gas head is removed from any supply voltage for greater than 10
minutes, it could take 24–48 hours to restore its calibration.
CONNECTIONS
OUTPUT SIGNALOPTIONS
STX3241.01 TOXIC GAS SENSOR/ TRANSMITTER
0.4 to 2 V Output Signal
3 WIRE CONNECTION
A low impedance two-wire voltage output signal requiring a separate power
supply to the sensor. This can be derived from a Trip Amplifier or
Programmable Sensor Controller, when one of those is used as the monitoring
instrument.
This connection configuration works well up to about 10 m distance between the
sensor and the monitoring equipment.
4 WIRE CONNECTION
Both the signal and the power supply to the sensor are being carried in the
common 0 V conductor so at some point – influenced by the length of the cable
and the resistance of the cable cores – the current flowing in the 0 V
conductor will impose an unacceptable voltage error onto the signal.
This effect can be reduced on long distance connections by increasing the size
of the cable cores, or even better, running a separate 0 V conductor to power
the sensor enabling operating distances up to 1000 m.
4 to 20 mA Output Signal
The sensor may be connected the 3 or 4 wire connection mode.
The power supply for the sensor may be sourced from the monitoring equipment (eg. TX9131 Trip Amplifier or a TX9042 Programmable Sensor Controller) or from a separate power supply.
Using Gas Sensors in Hazardous Areas
GROUP I HAZARDOUS AREAS (MINING)
STX3241.01 TOXIC GAS SENSOR/ TRANSMITTER
Both options of the STX3241.01 sensor (0.4 to 2 V, 4 to 20 mA) are certified Intrinsically Safe for use in Group I hazardous areas (Mining) when used with approved equipment – eg. TX9131 Trip Amplifier or a TX9042 Programmable Sensor Controller.
THE COMPLETE SYSTEM, BOTH SENSOR AND MONITORING DEVICE, CAN BE MOUNTED IN THE HAZARDOUS AREA.
The interconnecting cable between the sensor and the monitoring device must have steel wire armoured protection or a braided earth screen.
The cross sectional area of the conductors must be a minimum of 1 mm2.
CONTROLS AND INDICATORS
STX3241.01 TOXIC GAS SENSOR/ TRANSMITTER
STX3241.01.84 TOXIC GAS SENSOR/ TRANSMITTER with REMOTE GAS SENSING MODULE
This version uses the same gas sensing module as the STX3241.01.
The module is fitted into a robust metal housing which can be mounted at a
remote location where space is constricted or the operating conditions are
extremely harsh.
Connections:| 2 m, flexible cable in a flexible armoured conduit.
(other lengths available to specification. Max 10 m).
---|---
Protection Classification:| Dust & waterproof to IP66.
Gas inlet port to IP54.
Housing Material:| Brass.
CALIBRATION
The gas sensing module will gradually change its response characteristics, by a small amount, during normal use. The output signal is standardi sed so the module can be quickly changed when necessary.
The gas sensing module may be re-calibrated when required, using a Trolex TX6520 Gas Test Kit equipped with both Air and T est Gas canisters.
Prepare to Calibrate
The sensor should be powered for a minimum of 30 minute prior to commencing calibration.
Connect the application tube of the gas test kit to the inlet aperture of the gas sensing module using the bayonet fixing gas test hood provided.
Calibrate Zero
Apply purge air, at a flow rate of 0.3 to 1.0 l/min.
Allow the display reading to stabilise.
If necessary, adjust the ZERO potentiometer until display reads 0.00.
Remove the purge air.
Calibrate Span
Apply calibration gas, at a flow rate of 0.3 to 1.0 l/min.
Allow the reading to stabilise.
Adjust the SPAN potentiometer until display reads the same value as calibration gas being used.
Remove the SPAN gas.
The test gas used must be a minimum concentration of 25% of the full scale measuring value of the sensor.
MAINTENANCE
It is good safety practice to carry out regular preventative maintenance to confirm correct operation.
Output Signal
Check the response of the sensor at pre-determined intervals by injecting a test gas using a Trolex TX6520.32 Gas Test Kit.
Compare the value of the display with the value marked on the test gas canister.
Insert an approved test meter into the signal line and compare the value of the display with the measured value.
Change the gas sensing module if necessary.
Recalibrate if necessary.
Annual Safety Check
The main transmitter itself will not normally require maintenance or calibration but it is advisable to return it to the Trolex Product Support Department for an annual safety check.
Damaged Sensors
A Sensor that has been dropped or damaged in any way should be taken out of service immediately for inspection, repair and re-calibration.
Record Keeping
Institute a regular calibration and maintenance procedure and keep a record.
Incorrect use of the Sensor or inadequate maintenance may not necessarily be self evident in the Sensor and consequently it must be regularly checked and maintained.
Maintenance and Calibration Log
| ORDER REF STX3241.01 | DATE SUPPLIED |
|---|---|
| SERIAL No. | USER |
| GAS TYPE | LOCATION |
| DATE | SCHEDULED |
| MANUFACTURER | COMMENTS |
| --- | --- |
| DD/MM/YY |
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APPROVALS AND CERTIFICATION
Intrinsically Safe
ATEX
The instrument is certified Intrinsically Safe Group I apparatus for use in potentially explosive atmospheres when used with an approved power supply or safety barriers.
The sensor is designed to comply with the ATEX directive (94/9/EC).
STX3241.01
TOXIC GAS SENSOR/TRANSMITTER
GROUP I: I M1
Ex ia I Ma
Sira 07ATEX2170
(Ta = –20 to +55°C)
ANZEx
The instrument is certified Intrinsically Safe Group I apparatus for use in potentially explosive atmospheres when used with an approved power supply or safety barriers.
STX3241.01.11 and STX3241.01.12
TOXIC GAS SENSOR/TRANSMITTER
GROUP I: Ex ia I Ma
ANZEx 08.3038X
(Ta = +55°C)
MASC
The instrument is certified Intrinsically Safe Group I apparatus for use in potentially explosive atmospheres when used with an approved power supply or safety barriers.
STX3241.01
TOXIC GAS SENSOR/TRANSMITTER
GROUP I: Ex ia I Ma
MASC M/11-360X
(Ta = -20 to +55°C)
General Conditions for Safe Use
Prior to installation, it is essential that the user refers to the relevant
certificate to ensure that the termination and cable parameters are fully
complied with and are compatible with the application.
Copies of certificates are available from
www.trolex.com.
TROLEX LIMITED
NEWBY ROAD, HAZEL GROVE, STOCKPORT,
CHESHIRE SK7 5DY, UK
+44 (0)161 483 1435
sales@trolex.com
www.trolex.com