Net Safety™ ST3
XChem Electrochemical Sensors
Reference Manual
00809-0100-4303, Rev AB
November 2020
Important instructions
Emerson designs, manufactures, and tests products to function within specific conditions. Because these products are
sophisticated technical instruments, the owner and operation personnel must strictly adhere to both the information printed on
the product nameplate and all instructions provided in this manual prior to installation, operation, and maintenance.
WARNING
Explosions and hazardous substances
Installing, operating, or maintaining this product improperly could lead to serious injury or death from explosion or exposure to
dangerous substances.
Comply with all information on the product, in this manual, and in any local and national codes that apply to this product.
Use parts and work procedures specified in this manual.
WARNING
Physical access
Unauthorized personnel may potentially cause significant damage to and/or misconfiguration of end users’ equipment. This could
be intentional or unintentional and needs to be protected against.
Physical security is an important part of any security program and fundamental to protecting your system. Restrict physical access
by unauthorized personnel to protect end users’ assets. This is true for all systems used within the facility.
Notice
The contents of this publication are presented for informational purposes only, and while every effort has been made to ensure
their accuracy, they are not to be construed as warranties or guarantees, expressed or implied, regarding the products or services
described herein or their use or applicability. All sales are governed by Emerson's terms and conditions, which are available upon
request.
Emerson does not assume responsibility for the selection, use, or maintenance of this product. Responsibility for proper selection,
use, and maintenance of any Net Safety product remains solely with the purchaser and end user.
To the best of Emerson's knowledge, the information herein is complete and accurate. Emerson makes no warranties, expressed
or implied, including implied warranties of merchantability and fitness for a particular purpose, with respect to this manual, and in
no event, shall Emerson be liable for any incidental, punitive, special, or consequential damages, including, but not limited to, loss
of production, loss of profits, loss of revenue, or use and costs incurred including without limitation for capital, fuel and power,
and claims of third parties.
Product names used herein are for manufacturer or supplier identification only and may be trademarks/registered trademarks of
these companies.
All rights reserved. No part of this work may be reproduced or copied in any form or by any means (graphic, electronic, or
mechanical) without first receiving written permission from Emerson.
Warranty
1. Limited Warranty. Subject to the limitations contained in Section 2 (Limitation of Remedy and Liability) herein, Seller
warrants that (a) the licensed firmware embodied in the Goods will execute the programming instructions provided by
Seller; (b) that the Goods manufactured by Seller will be free from defects in materials or workmanship under normal use
and care; and (c) Services will be performed by trained personnel using proper equipment and instrumentation for the
particular Service provided. The foregoing warranties will apply until the expiration of the applicable warranty period.
Sensors and detectors are warranted against defective part and workmanship as per warranty. Products purchased by
Seller from a third party for resale to Buyer (Resale Products) shall carry only the warranty extended by the original
manufacturer. Buyer agrees that Seller has no liability for Resale Products beyond making a reasonable commercial effort
to arrange for procurement and shipping of the Resale Products. If Buyer discovers any warranty defects and notifies Seller
thereof in writing during the applicable warranty period, Seller shall, at its option, (i) correct any errors that are found by
Seller in the firmware or Services; (ii) repair or replace FOB point of manufacture that portion of the Goods found by Seller
to be defective; or (iii) refund the purchase price of the defective portion of the Goods/Services. All replacements or
repairs necessitated by inadequate maintenance; normal wear and usage; unsuitable power sources or environmental
conditions; accident; misuse; improper installation; modification; repair; use of unauthorized replacement parts; storage
or handling; or any other cause not the fault of Seller, are not covered by this limited warranty and shall be replaced or
repaired at Buyer’s sole expense and Seller shall not be obligated to pay any costs or charges incurred by Buyer or any
other party except as may be agreed upon in writing in advance by Seller. All costs of dismantling, reinstallation, freight
and the time and expenses of Seller’s personnel and representatives for site travel and diagnosis under this limited
2
warranty clause shall be borne by Buyer unless accepted in writing by Seller. Goods repaired and parts replaced by Seller
during the warranty period shall be in warranty for the remainder of the original warranty period or 90 days, whichever is
longer. This limited warranty is the only warranty made by Seller and can be amended only in a writing signed by an
authorized representative of Seller. The limited warranty herein ceases to be effective if Buyer fails to operate and use the
Goods sold hereunder in a safe and reasonable manner and in accordance with any written instructions from the
manufacturers. THE WARRANTIES AND REMEDIES SET FORTH ABOVE ARE EXCLUSIVE. THERE ARE NO REPRESENTATIONS
OR WARRANTIES OF ANY KIND, EXPRESSED OR IMPLIED, AS TO MERCHANTABILITY, FITNESS FOR PARTICULAR PURPOSE
OR ANY OTHER MATTER WITH RESPECT TO ANY OF THE GOODS OR SERVICES.
2. Limitation of Remedy and Liability. SELLER SHALL NOT BE LIABLE FOR DAMAGES CAUSED BY DELAY IN PERFORMANCE.
THE REMEDIES OF BUYER SET FORTH IN THE AGREEMENT ARE EXCLUSIVE. IN NO EVENT, REGARDLESS OF THE FORM OF
THE CLAIM OR CAUSE OF ACTION (WHETHER BASED IN CONTRACT, INFRINGEMENT, NEGLIGENCE, STRICT LIABILITY,
OTHER TORT OR OTHERWISE), SHALL SELLER’S LIABILITY TO BUYER AND/OR BUYER’S CUSTOMERS EXCEED THE PRICE TO
BUYER OF THE SPECIFIC GOODS MANUFACTURED OR SERVICES PROVIDED BY SELLER GIVING RISE TO THE CLAIM OR
CAUSE OF ACTION. BUYER AGREES THAT IN NO EVENT SHALL SELLER’S LIABILITY TO BUYER AND/OR BUYER’S
CUSTOMERS EXTEND TO INCLUDE INCIDENTAL, CONSEQUENTIAL OR PUNITIVE DAMAGES. THE TERM “CONSEQUENTIAL
DAMAGES” SHALL INCLUDE, BUT NOT BE LIMITED TO, LOSS OF ANTICIPATED PROFITS, REVENUE OR USE AND COSTS
INCURRED INCLUDING WITHOUT LIMITATION FOR CAPITAL, FUEL AND POWER, AND CLAIMS OF BUYER’S CUSTOMERS.
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Reference Manual Contents
00809-0100-4303 November 2020
Contents
Chapter 1 Introduction.............................................................................................................. 7
1.1 Models covered........................................................................................................................... 7
1.2 Service support............................................................................................................................7
1.3 Return of material........................................................................................................................7
1.4 Product recycling/disposal...........................................................................................................8
Chapter 2 Install.........................................................................................................................9
2.1 Unpack and inspect..................................................................................................................... 9
2.2 Locate sensor...............................................................................................................................9
2.3 Mount sensor...............................................................................................................................9
2.4 Mounting...................................................................................................................................10
2.5 Dimensional drawings............................................................................................................... 13
2.6 Wiring........................................................................................................................................15
2.7 Calibration.................................................................................................................................18
Chapter 3 Operate....................................................................................................................19
3.1 Access sensor configuration settings......................................................................................... 19
3.2 Power up sensor........................................................................................................................ 19
3.3 Sensor end of life diagnostic...................................................................................................... 20
3.4 Sensor communication..............................................................................................................20
3.5 Configure Net Safety Millennium II Basic Transmitter.................................................................21
3.6 Fault conditions......................................................................................................................... 22
Chapter 4 Maintenance............................................................................................................23
4.1 Cross sensitivities.......................................................................................................................23
4.2 Bump testing.............................................................................................................................24
4.3 Replace sensor module..............................................................................................................24
4.4 Troubleshooting........................................................................................................................25
4.5 Storage......................................................................................................................................25
4.6 Spare parts and accessories....................................................................................................... 25
Chapter 5 Electrostatic sensitive device....................................................................................27
Chapter 6 Wire resistance table............................................................................................... 29
Chapter 7 Product certifications...............................................................................................31
7.1 Installing in North America.........................................................................................................31
7.2 North America........................................................................................................................... 31
7.3 IECEx..........................................................................................................................................31
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Introduction
1 Introduction
1.1 Models covered
Emerson has designed the ST3 XChem electrochemical toxic gas sensors for use with the
Net Safety Millennium II Transmitter (models M21, M22, or M2B). This sensor is both
versatile and reliable, for fast, accurate, and continuous monitoring of gases in extreme
environments.
The sensor assembly consists of a factory sealed explosion proof enclosure (housing) rated
for hazardous locations and a replaceable sensor module. Only use this sensor with a Net
Safety Millennium II series transmitter. If you connect the sensor to any other model of
transmitter, it will not function, and the sensor or transmitter may be damaged.
1.2 Service support
For technical support, contact your local Emerson representative or the Technical Support
department at +1 866 347 3427 (toll free) or Safety.CSC@Emerson.com.
1.3 Return of material
To expedite the repair and return of this product, proper communication between the
customer and the factory is important.
Prerequisites
Before returning a product for repair, call +1 866 347 3427 (toll free) or email
Safety.CSC@emerson.com for a Return Material Authorization (RMA) number.
On the return of the equipment, include the following information:
1. RMA number provided to you by Emerson
2. Company name and contact information
3. Purchase order, from your company, authorizing repairs or request for quote
Procedure
1. Ship all equipment, prepaid to:
Emerson Automation Solutions
6021 Innovation Blvd
Shakopee, MN 55379
2. Mark all packages with Return for Repair and include RMA number and type of return
(e.g., return for evaluation).
Pack items to protect them from damage and use anti-static bags or aluminumbacked cardboard as protection from electrostatic damage.
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Important
Ship all equipment prepaid. Emerson will not accept collect shipments.
1.4 Product recycling/disposal
Consider recycling equipment and packaging. Dispose of the product and packaging in
accordance with local and national legislations and regulations.
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Install
2 Install
2.1 Unpack and inspect
Procedure
1. Carefully remove all the components from the packaging and check them against
the enclosed packing list.
2. Inspect all components for any obvious damage, such as broken or loose parts. If
you find any components missing or damaged, notify your local Net Safety
representative or the factory immediately.
2.2 Locate sensor
Prior to the installation process, develop a plan. Although there are no absolute rules
determining the quantity of detectors or location of a sensor, consider the following
points when planning the installation.
• Carefully locate the sensor in an area where gases may potentially accumulate.
(Remember, light gases tend to rise, and heavy gases tend to accumulate in low areas).
• Use redundant systems to enhance protection and reliability.
• Consider the air movement patterns within the facility.
• Consider the construction of the facility, such as trenches where heavy gases or peaks
where light gases may accumulate.
• Seek advice from experts knowledgeable about the primary gas to be detected.
• Use common sense and refer to the regulatory publications that discuss guidelines for
your industry.
2.3 Mount sensor
You can either mount the sensor directly attached to a Net Safety Millennium II
transmitter or remotely, away from the transmitter.
Make sure the sensor is accessible for calibration and maintenance purposes. Also, make
sure the transmitter is accessible and visible.
2.3.1
Mount sensor remotely
If mounting the sensor remotely, connect it to a certified junction box. Make sure the
transmitter is located near eye level for easy access and the sensor is mounted where the
gas is likely to accumulate.
In order to ease the calibration process, you can attach a calibration cup (CCS-1) to the
bottom of the sensor housing and run calibration tubing from the calibration cup to a
convenient place for applying the calibration gas, eliminating the need to access the
sensor directly. In this case, to compensate for the effect of distance, consider decreasing
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the calibration tubing length to some length where the end of the tubing to the gas
canister is still accessible or increase the calibration gas flow rate between the calibration
gas cylinder and sensor.
Refer to Figure 2-1 for an example of the sensor separation. For tubing lengths less than 10
ft. (3 m), use a 0.5 LPM regulator, and for lengths greater than 10 ft. (3 m) use a 1.0 LPM
regulator. On initial install, always confirm readings directly at the transmitter by applying
a known gas concentration to the sensor and compare the output from the transmitter.
Readings should be accurate to the gas concentration applied, taking into account the
sensor accuracy specifications in Specifications.
Figure 2-1: Sensor Separation Example
Reference Manual
A. Controller
B. Apply calibration gas.
C. Tubing for calibration gas
D. Sensor
E. Calibration cup
F. Conduit
G. Junction box
H. Approximately knee level
2.4 Mounting
Prior to mounting the sensor to the transmitter or junction box enclosure apply suitable
grease (jet lube, etc.) to the threading of the ¾-in. female national pipe thread (FNPT)
conduit entry of the enclosure as well as the threading on the sensor ¾-in. male national
pipe thread (MNPT) fitting. This aids in protecting the enclosures from water. After
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applying the grease, use the appropriate tools to fit and tighten the sensor to the
transmitter or junction box enclosure.
The transmitter and junction box have mounting holes to allow mounting to a flat surface
or pole as desired. Mounting kit accessories are available to aid in mounting the detector
to a flat surface or a pole. Contact your local Net Safety representative for detailed
information.
Note
Always mount the sensor vertically such that its mouth is pointed in the downward
position as shown in Figure 2-2 and Figure 2-3.
Figure 2-2: Sensor Mounted to a Net Safety Millennium II Transmitter
A. ¾-in. national pipe thread (NPT)
B. ATEX locking collar
C. Sensor pointing downwards
D. Sensor mouth
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Figure 2-3: Sensor Mounted to Net Safety Millennium II Basic Transmitter and
Junction Box
A. ¾-in. NPT
B. ATEX locking collar
C. Sensor mouth
D. Sensor pointing downwards
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2.5 Dimensional drawings
Figure 2-4: Net Safety Millennium II (M21 or M22) Enclosure and Sensor
Dimensions
(1)
1. Aluminum shown
Table 2-1: Dimensions in Inches (Millimeters)
Letter Aluminum housings Stainless steel housings
A 6.3 (160) 5.9 (150)
B 5.6 (142) 5.1 (130)
C 5.4 (137) 4.6 (117)
D 9.7 (246) 8.9 (226)
E 6.0 (152) 6.0 (152)
F 5.7 (145) 5.8 (147)
G 2.6 (66) 2.6 (66)
H 2.9 (74) 2.9 (74)
I 4.1 (103) 3.9 (100)
J 0.157 (4) 0.157 (4)
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Figure 2-5: Net Safety Millennium II Basic (M2B) or Junction Box (JB) Enclosure and
Sensor Dimensions
Table 2-2: Net Safety Millennium II Basic (M2B) or Junction Box (JB) Enclosure and
Sensor Dimensions in Inches (Millimeters)
Stainless steel Aluminum
A 4.7 (119) 4.8 (122)
B 3.6 (91) 3.6 (91)
C 3.6 (91) 3.6 (91)
D 4.7 (119) 4.8 (122)
E 5.1 (130) 5.1 (130)
F 0.3 (7,6) 0.3 (7,6)
G 2.6 (66) 2.6 (66)
H 2.9 (74) 2.9 (74)
I 2.8 (71) 3.0 (76)
J 8.9 (226) 9.0 (229)
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Install
2.6 Wiring
2.6.1 Field installation
WARNING
Electrical shock
Failure to follow these installation guidelines could result in death or serious injury.
Ensure that only qualified personnel perform the installation.
Electrical shock could cause death or serious injury.
Use extreme caution when making contact with the leads and terminals.
Do not open the transmitter, sensor, or junction box enclosure when in a classified area
or where an explosive atmosphere may be present unless the power to the transmitter
and sensor has been removed.
2.6.2
2.6.3
Note
Wiring codes and regulations may vary. Wiring must comply with all applicable regulations
relating to the installation of electrical equipment in a hazardous area and is the
responsibility of the installer. If in doubt, consult a qualified official before wiring the
system.
When separating the sensor from the transmitter, Emerson highly recommends using
shielded cable to protect against interference caused by extraneous electrical or
electromagnetic noise. To meet EN50270:2006 requirements, follow the
recommendations on cable choice and guidelines as outlined in the Net Safety Millennium
II Transmitter Reference Manual or Net Safety Millennium II Basic Reference Manual. In
applications where the wiring is installed in conduit, do not use the conduit for wiring to
other equipment.
Sensor separation distance
The resistance of the connecting wiring, a function of the gauge of wire being used, limits
the maximum separation distance between the sensor and transmitter.
Net Safety recommends that sensor separation does not exceed 2000 ft. (610 m) while
using 16AWG (1.31 mm2) wire. Refer to Wire resistance table for wire gauges and
resistance values.
Install to transmitter or junction box
Emerson supplies the Net Safety ST3 with a ¾-in. national pipe thread (NPT) male conduit
connection. Mount the sensor directly to an available ¾-in. NPT conduit entry on a Net
Safety Millennium II Transmitter or remotely using a certified junction box.
Net Safety has an available offering of certified junction boxes designed specifically to
work with this sensor. Please contact your local Net Safety representative for further
information.
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2.6.4 Wire sensor
WARNING
Do not open the transmitter, sensor, or junction box enclosure when in a classified area or
when an explosive atmosphere may be present unless power to the sensor has been
removed.
Procedure
1. When connecting cable wires, use a small flathead screwdriver to gently press down
and hold the spring connector open.
2. Insert the appropriate wire into the open connector hole, releasing the screwdriver
to secure the wire.
Refer to Figure 2-6.
Figure 2-6: Terminal Connection
3. Connect the sensor wires to the Net Safety Millennium II Transmitter or junction
box as per the appropriate transmitter or junction box manual.
Figure 2-7 outlines the connections to a Net Safety M21 Millennium II Transmitter.
Table 2-3 outlines the wire colors and their purpose.
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Figure 2-7: Net Safety Millennium II M21 Sensor Wiring
A. Modbus® terminals
B. Power and output terminals
C. Channel #1 4-20 mA signal
D. Channel #2 4-20 mA signal
E. Earth ground
F. White wire
G. Red wire
H. Blue wire
I. Black wire
J. M2 transmitter terminal board
K. Channel 2 sensor terminals
L. Channel 1 sensor terminals
M. Sensor
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Table 2-3: Sensor Wire Colors and Terminal Definitions
Wire color Marking Function
White +Vdc 10.5 to 32 Vdc connection
Red Signal A Signal A
Blue Signal B Signal B
Black COM Common/supply ground
Green N/A Earth ground
2.6.5 External ground
In order to ensure proper operation of the sensor, Net Safety recommends connecting an
external ground screw to the grounding point on the enclosure.
2.7 Calibration
Note
Power up the Net Safety ST3 sensor for at least 24 hours before completing the first
calibration.
Although Emerson calibrated the sensor at the factory, this calibration may have been
disrupted after shipment, and calibration after installation is necessary to ensure
performance.
To ensure proper operation of Net Safety ST3, Emerson recommends calibrating hydrogen
sulfide sensors every six months and calibrating carbon monoxide or oxygen sensors every
three months.
Refer to the Net Safety Millennium II Multi-Channel Transmitter Reference Manual or to
the Net Safety Millennium II Basic Transmitter Reference Manual for the calibration
procedure.
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3 Operate
3.1 Access sensor configuration settings
Use the Net Safety Millennium II series of transmitters to access configuration settings for
the Net Safety ST3.
Select Menu options from the main display.
Tip
Refer to the relevant transmitter manual prior to calibrating.
3.2 Power up sensor
When the transmitter applies power to the sensor, a warm-up routine begins during which
the sensor is automatically tested to ensure its proper operation.
The warm-up time for the Net Safety ST3 sensor is typically between 30 and 90 seconds
depending on the sensor type; the Net Safety ST341 oxygen sensor could take up to an
hour to warm up. During the warm-up period, the sensor may not provide accurate results
and gas concentration levels may fluctuate. Refer to the Net Safety Millennium II
Transmitter Reference Manual or the Net Safety Millennium II Basic Transmitter Reference
Manual for status indicators during this period. Confirm that the Net Safety Millennium II
transmitter display properly shows ppm on the display as shown in Figure 3-1. If the
display reads xxx, then the sensor cell is not seated properly in the sensor housing. Refer to
Replace sensor module for more information.
Figure 3-1: Net Safety Millennium II Display Examples
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3.3 Sensor end of life diagnostic
The sensor performs an automatic test daily to ensure its integrity. It performs this test
one hour after initial power-up and then every 24 hours after that.
Note that sensor end of life indication is not available on the oxygen (Net Safety ST340 or
ST341) sensors.
During the test cycle, a period of 10 seconds, the sensor response time should increase to
less than 60 seconds.
If a sensor end of life indication fault is generated, the analog output of the associated
transmitter will be 2.5 mA (fault condition) for a period of 10 seconds. The analog output
will then return to its operational state (4 mA with no gas present) for a period of 50
seconds. This cycle will continue until the sensor has been replaced. When using the Net
Safety M21 or M22 transmitter, the display will read "Sensor Reached Life End" on the
respective channel, and the gas concentration will not be shown.
If used with a Net Safety Millennium II transmitter with relay capabilities, the sensor end of
life diagnostic will be indicated through the fault relay. The fault relay will change states
(de-energize, indicating a fault condition,) upon the detection of the end of life condition.
The fault relay will stay de-energized as long as the fault condition is present. When the
sensor has detected an end of life condition, the alarm relay will not provide an alarm
condition if gas is present; therefore, Emerson recommends replacing the sensor as soon
as possible. For further information on the operation of the relays, please refer to the
associated transmitter manual (Net Safety Millennium II Multi-Channel Transmitter
Reference Manual or Net Safety Millennium II Basic Transmitter Reference Manual).
Note
Net Safety recommends monitoring the fault signal (2.5 mA) and fault relay (if available)
to indicate sensor faults if using a fire and gas system or other control system.
Due to the electrochemical sensor technology used in the Net Safety ST3 sensors, the
sensor end of life diagnostic may indicate a sensor with decaying response or a nonresponding sensor.
Contact Net Safety for replacement sensor modules.
3.4 Sensor communication
The Net Safety ST3 sensor uses a proprietary protocol to communicate with the Net Safety
Millennium II series of transmitters.
Never connect this sensor to any device other than the Net Safety Millennium II series of
transmitters. Selected DIP switches and menu options allow communication between the
transmitter and sensor. The sensor's memory stores confituration settings. Incorrect
settings will cause the sensor to not communicate properly with the transmitter. If any
problems develop, please refer to Troubleshooting.
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3.5 Configure Net Safety Millennium II Basic Transmitter
When using the Net Safety ST3 sensor with the Net Safety Millennium II Basic Digital
transmitter model (M2B-D), you can change the sensor's range by accessing a specific
Modbus® register.
Write to register 40027 using the preset single register command 0x06. Then enter the
desired range in the register. Refer to Detection range for the available ranges.
When using the Net Safety ST3 sensor with the Net Safety Millennium II Basic Analog
(M2B-A), Analog/HART® (M2B-AH), and Relay (M2B-R) transmitter models you can change
the sensor’s range to facilitate the need to accurately detect different gas concentrations.
To do this, use the transmitter’s DIP Switch 2 positions as seen in Hydrogen sulfide sensor
(Net Safety ST320) DIP switch settings and Carbon monoxide sensor (Net Safety ST360)
DIP switch positions. Select the transmitter’s DIP Switch 2 position that gives the range of
gas to be detected.
3.5.1
Detection range
Hydrogen sulfide (ST320) Carbon monoxide
(ST360)
20 ppm, 50 ppm, 100 ppm 500 ppm, 1000 ppm 25% volume
Oxygen (ST341)
3.5.2 Hydrogen sulfide sensor (Net Safety ST320) DIP switch settings
Position 1 Position 2 Position 3 Position 4 Range (Setting)
ON OFF OFF OFF Range 1 (20 ppm)
OFF ON OFF OFF Range 2 (50 ppm)
OFF OFF ON OFF Range 3 (100
ppm)
3.5.3 Carbon monoxide sensor (Net Safety ST360) DIP switch positions
Position 1 Position 2 Position 3 Position 4 Range(Setting)
ON OFF OFF OFF Range 1 (500
ppm)
OFF ON OFF OFF Range 2 (1000
ppm)
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3.6 Fault conditions
The Net Safety ST3 sensor provides a number of fault conditions that the Net Safety
Millennium II transmitter translates into an analog or fault relay output. These fault
conditions are outlined in Table 3-1.
Table 3-1: Fault Conditions
Fault condition Analog output Fault relay output
Sensor zero drift 2.5 mA Fault
Memory fault 2.5 mA Fault
Sensor nearing end of life Alternating 2.5 mA for 10
seconds and normal level for 50
seconds
Calibrate sensor 2.5 mA Fault
Alternating 2.5 mA for 10
seconds and normal level for 50
seconds
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4 Maintenance
4.1 Cross sensitivities
Certain compounds and or gases can cause a reaction and hence some effects or response
from the sensor.
See Cross sensitive gases for hydrogen sulfide sensor (Net Safety ST320) and Cross
sensitive gases for carbon monoxide sensor (Net Safety ST360) for a list of these cross
sensitive gases/compounds. For more information, please contact Net Safety.
Note
The values listed below are typical values and should not be used as a basis for cross
calibration. Cross sensitivities may not be linear and should not be scaled either. The data
provided is based on gassing for a minimum of five minutes using the gas sensor
manufacturer's test equipment. Some cross interference break through will occur if gas is
applied for a longer period of time.
4.1.1
Cross sensitive gases for hydrogen sulfide sensor (Net Safety ST320)
Table 4-1: Cross-Sensitive Gases/Compounds
Cross sensitive gas
Carbon monoxide 300 ppm < 3 ppm
Sulfur dioxide 5 ppm < 1 ppm
Nitrogen dioxide 5 ppm < ±0.5 ppm
Nitric oxide 50 ppm < 1 ppm
Hydrogen 100 ppm < 1 ppm
Chlorine 1 ppm 0 ppm
Ethylene 100 ppm 0 ppm
Carbon dioxide 5000 ppm 0 ppm
Cross sensitive gas
concentration
Reading
4.1.2 Cross sensitive gases for carbon monoxide sensor (Net Safety ST360)
Table 4-2: Cross Sensitive Gases/Compounds
Cross sensitive gas
Hydrogen sulfide 15 ppm < 0.1 ppm
Sulfur dioxide 5 ppm 0 ppm
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concentration
Reading
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Table 4-2: Cross Sensitive Gases/Compounds (continued)
Reference Manual
Cross sensitive gas
Nitrogen dioxide 5 ppm -0.5 ppm
Nitric oxide 35 ppm < 7 ppm
Hydrogen 100 ppm < 60 ppm
Chlorine 1 ppm 0 ppm
Ethylene 100 ppm < 90 ppm
Cross sensitive gas
concentration
4.2 Bump testing
As part of the site preventative maintenance program Net Safety recommends bump
testing the sensor every three months. Bump testing consists of a visual inspection of the
sensor, application of a known gas concentration to the sensor to verify the accuracy of
the response to the specifications of the sensor, and alarm system simulation. If the
response is outside of the specifications of the sensor, calibrate the sensor.
Refer to Calibration for more information. After calibrating, Net Safety recommends bump
testing to verify accuracy and response of the sensor.
4.3 Replace sensor module
Reading
Emerson pre-calibrates the sensors at the factory; however, you must perform field
calibration as a part of commissioning. When the sensor end of life diagnostic indicates a
fault condition, you can no longer calibrate, or the sensor is not working properly, you may
need to replace the sensor module.
WARNING
Do not open the transmitter, sensor, or junction box enclosure when in a classified area or
when an explosive atmosphere may be present unless the power to the sensor has been
removed.
CAUTION
Avoid touching any electronic components, as they may be susceptible to electrostatic
discharge (ESD).
Refer to Electrostatic sensitive device for further information and instructions on
properly handling electronic components.
Procedure
1. Remove power from the sensor.
2. Remove the locking ring by loosening the set screws with 1.5 mm Allen Key tool.
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3. Remove the bottom part of the sensor enclosure by turning it in a counter clockwise
rotation to expose the sensor module.
4. Carefully remove the sensor module from the sensor housing by pulling the module
straight out of the housing.
CAUTION
Do not twist the sensor module.
5. Properly dispose of the old sensor module as per local guidelines and regulations.
6. Remove the replacement sensor module from its packaging, taking care not to
touch any electronic components.
7. Rotate replacement sensor module until it aligns with the guide posts. Once
aligned, press firmly into place.
8. Install and hand-tighten the bottom part of the sensor enclosure by turning it in a
clockwise direction.
9. Install the locking ring by tightening the set screws with 1.5 mm Allen Key tool.
10. Restore power to sensor via the transmitter.
11. Verify that the display shows ppm and not xxx as shown in Figure 3-1.
If the display is showing xxx, then the sensor module is not seated properly. In this
case, repeat all steps within this procedure.
4.4 Troubleshooting
Emerson did not design these sensors and transmitters to be repaired in the field. If
problems should develop, first check for faulty wiring, confirm proper voltage to the
sensor, and try to calibrate.
If problems persist, please contact Net Safety’s technical support department first by
phone to try and resolve any issues. If issues cannot be resolved, please follow the
procedure in Return of material.
4.5 Storage
Store the sensor and its electronic parts in locations free from dust, liquid spills,
contaminants, and moisture.
Ensure the storage temperature is well within within the limits of the certified
temperatures of the equipment. See Specifications for certified temperatures.
4.6 Spare parts and accessories
Description Part number
Calibration cup/splash guard CCS-1
Calibration kit CAL-KIT-1
Net Safety ST3 25
Maintenance Reference Manual
November 2020 00809-0100-4303
Description Part number
Calibration gas CAL-CYL-AIR (27.2 gal. [103 L] air)
CAL-CYL-H2S-10 (15.3 gal. [58 L], 10 ppm, H2S,
nitrogen balanced)
CAL-CYL-H2S-25 (20.1 gal. [76 L], 25 ppm, H2S,
nitrogen balanced)
CAL-CYL-H2S-50 (20.1 gal. [76 L], 50 ppm, H2S,
nitrogen balanced)
CAL-CYL-H2S-A-10 (15.3 gal. [58 L], 10 ppm,
H2S, oxygen balanced)
CAL-CYL-H2S-A-25 (15.3 gal. [58 L], 25 ppm,
H2S, oxygen balanced)
CAL-CYL-H2S-A-50 (15.3 gal. [58 L], 50 ppm,
H2S, oxygen balanced)
CAL-CYL-SO2-10 (15.3 gal. [58 L],10 ppm, SO2)
CAL-CYL-CO-250 (27.2 gal. [103 L], CO)
Calibration cup
Separation kit JB-MPD-A - aluminum
Replacement sensor module ST320: 100 (H2S)
Ingress protection filter IPF-001
2-in. (50.8 mm) pole mounting kit UN-MK-32
Duct mounting kit UDM-001 (3.3 ft. [1 m] sampling pipe)
CCS-1
JB-MPD-S - stainless steel
ST330: 100 (SO2)
ST341: 25 (O2)
ST360: 1000 (CO)
UDM-002 (4.9 ft. [1.5 m] sampling pipe)
UDM-003 (direct mount to duct)
26 Emerson.com/FlameGasDetection
Reference Manual Electrostatic sensitive device
00809-0100-4303 November 2020
5 Electrostatic sensitive device
Electrostatic discharge (ESD) is the transfer, between bodies, of an electrostatic charge
caused by direct contact or induced by an electrostatic field.
The most common cause of ESD is physical contact. Touching an object can cause a
discharge of electrostatic energy. If the charge is sufficient and occurs near electronic
components, it can damage or destroy those components. In some cases, damage is
instantaneous and an immediate malfunction occurs. However, symptoms are not always
immediate; performance may be marginal or seemingly normal for an indefinite period of
time, followed by a sudden failure.
To eliminate potential ESD damage, review the following guidelines:
• Handle boards by metal shields, taking care not to touch electronic components.
• Wear grounded wrist or foot straps, ESD shoes, or heel grounders to dissipate
unwanted static energy.
• Prior to handling boards, dispel any charge in your body or equipment by touching a
grounded metal surface.
• Ensure all components are transported and stored in static safe packaging.
• When returning boards, carefully package in the original carton and static protective
wrapping.
• Ensure ALL personnel are educated and trained in ESD control procedures.
In general, exercise accepted and proven precautions normally observed when handling
electrostatic sensitive devices. A warning label is placed on the packaging, identifying
products using electrostatic sensitive semiconductor devices.
Net Safety ST3 27
Electrostatic sensitive device Reference Manual
November 2020 00809-0100-4303
28 Emerson.com/FlameGasDetection
Reference Manual Wire resistance table
00809-0100-4303 November 2020
6 Wire resistance table
Resistance shown is one way. Double this figure when determining closed loop resistance.
Distance: feet
(meters)
100 (30.5) 1.02 0.64 0.40 0.25
200 (61) 2.03 1.28 0.80 0.51
300 (91.4) 3.05 1.92 1.20 0.76
400 (121.9) 4.06 2.55 1.61 1.01
500 (152.4) 5.08 3.20 2.01 1.26
600 (182.9) 6.09 3.83 2.41 1.52
700 (213.4) 7.11 4.47 2.81 1.77
800 (243.8) 8.12 5.11 3.21 2.02
900 (274.3) 9.14 5.75 3.61 2.27
1000 (304.8) 10.20 6.39 4.02 2.53
1250 (381) 12.70 7.99 5.03 3.16
1500 (457.2) 15.20 9.58 6.02 3.79
1750 (533,4) 17.80 11.20 7.03 4.42
2000 (609.6) 20.30 12.80 8.03 5.05
2250 (685.8) 22.80 14.40 9.03 5.68
2500 (762) 25.40 16.00 10.00 6.31
AWG #200.5mm
2
AWG #180.8mm
2
AWG #161.0mm
2
AWG #142.0mm
2
3000 (914.4) 30.50 19.20 12.00 7.58
3500 (1066.8) 35.50 22.40 14.10 8.84
4000 (1219.2) 40.60 25.50 16.10 10.00
4500 (1371.6) 45.70 28.70 18.10 11.40
5000 (1524) 50.10 32.00 20.10 12.60
5500 (1676.4) 55.80 35.10 22.10 13.91
6000 (1828.8) 61.00 38.30 24.10 15.20
6500 (1981.2) 66.00 41.50 26.10 16.40
7000 (2133.6) 71.10 44.70 28.10 17.70
7500 (2286) 76.10 47.90 30.10 19.00
8000 (2438.4) 81.20 51.10 23.10 20.20
9000 (2743.2) 91.40 57.50 36.10 22.70
10,000 (3048) 102.00 63.90 40.20 25.30
Net Safety ST3 29
Wire resistance table Reference Manual
November 2020 00809-0100-4303
30 Emerson.com/FlameGasDetection
Reference Manual Product certifications
00809-0100-4303 November 2020
7 Product certifications
7.1 Installing in North America
The US National Electrical Code® (NEC) and the Canadian Electrical Code (CEC) permit the
use of Division-marked equipment in Zones and Zone-marked equipment in Divisions. The
markings must be suitable for the area classification, gas, and temperature class. This
information is clearly defined in the respective codes.
7.2 North America
Markings
7.3 IECEx
Markings
Special Condition of Use:
Flameproof joints are not intended to be repaired.
Class 1, Division 1, Groups BCD T5
Ex d IIB+H2 T5
Class 1, Zone 1, AEx d IIB+H2 T5 Gb
Type 4X, IP64
Ex db IIB+H2 T5 Gb
-40 °C ≤ Tamb ≤ +75 °C
Net Safety ST3 31
00809-0100-4303
Rev. AB
2020
EMERSON AUTOMATION SOLUTIONS
6021 Innovation Blvd.
Shakopee, MN 55379
+1 866 347 3427
+1 952 949 7001
safety.csc@emerson.com
EUROPE
Emerson Automation Solutions
Neuhofstrasse 19a PO Box 1046
CH-6340 Baar
Switzerland
+41 (0) 41 768 6111
+41 (0) 41 768 6300
safety.csc@emerson.com
Linkedin.com/company/Emerson-Automation-Solutions
Twitter.com/Rosemount_News
Facebook.com/Rosemount
Youtube.com/user/RosemountMeasurement
MIDDLE EAST AND AFRICA
Emerson Automation Solutions
Emerson FZE
Jebel Ali Free Zone
Dubai, United Arab Emirates, P.O. Box 17033
+971 4 811 8100
+971 4 886 5465
safety.csc@emerson.com
©
2020 Emerson. All rights reserved.
Emerson Terms and Conditions of Sale are available upon request. The Emerson logo is a
trademark and service mark of Emerson Electric Co. Rosemount is a mark of one of the
Emerson family of companies. All other marks are the property of their respective owners.
The Emerson logo is a trademark and service mark of Emerson Electric Co. Net Safety is a
mark of one of the Emerson family of companies. All other marks are the property of their
respective owners.
ASIA-PACIFIC
Emerson Automation Solutions
1 Pandan Crescent
Singapore 128461
Republic of Singapore
+65 6 777 8211
+65 6 777 0947
safety.csc@emerson.com
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