DETCON, Inc.
May 29. 2014 • Document # 4429 • Revision 1.3
Model CX-DM
CX-DM Toxic Gas Sensors
CX-DM O2 Deficiency Sensors
Operator’s Installation and Instruction Manual
Covers all Model CX-DM Sensors
4055 Technology Forest Blvd, Suite 100
The Woodlands, Texas 77381
Phone: 713.559.9200 • Fax: 281.292.2860
www.detcon.com
Model CX-DM
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Model CX-DM ii
Model CX-DM
Table of Contents
1. Introduction ..................................................................................................................................................1
1.1 Description .......................................................................................................................................... 1
1.2 Modular Design .................................................................................................................................. 2
2. Installation ....................................................................................................................................................3
2.1 Hazardous Locations Installation Guidelines for Safe Use ................................................................. 3
2.2 Sensor Placement ................................................................................................................................ 4
2.3 Sensor Contaminants and Interference ............................................................................................... 5
2.4 Sensor Mounting ................................................................................................................................. 5
2.5 Electrical Installation .......................................................................................................................... 6
2.6 Field Wiring ........................................................................................................................................ 7
2.6.1 Terminal Connections 3-Wire 4-20mA .......................................................................................... 7
2.6.2 Terminal Connections 4-20mA and RS-485 .................................................................................. 8
2.7 Initial Start Up..................................................................................................................................... 9
2.7.1 O
3. Operation ....................................................................................................................................................11
3.1 Operator Interface ............................................................................................................................. 12
3.2 Normal Operation ............................................................................................................................. 13
3.3 Calibration Mode .............................................................................................................................. 13
3.3.1 AutoZero ....................................................................................................................................... 14
3.3.2 AutoSpan ...................................................................................................................................... 15
3.4 Program Mode .................................................................................................................................. 17
3.4.1 View Sensor Status ....................................................................................................................... 17
3.4.2 Set Detection Range ..................................................................................................................... 18
3.4.3 Set AutoSpan Level ...................................................................................................................... 18
3.4.4 Bump Test .................................................................................................................................... 18
3.4.5 Restore Defaults ........................................................................................................................... 19
3.4.6 Set Modbus ID .............................................................................................................................. 19
3.5 Fault Diagnostic/Failsafe Feature ..................................................................................................... 20
4. Modbus™ Communications .......................................................................................................................21
4.1 General Modbus™ Description ........................................................................................................ 21
4.2 Modbus™ Register Map & Description ........................................................................................... 21
4.2.1 Sensor Faults – Register 40005 .................................................................................................... 22
4.2.2 Temperature Compensation – Register 40012 ............................................................................. 23
5. Service and Maintenanc e ............................................................................................................................24
5.1 Replacement of Plug-in Sensor ......................................................................................................... 24
5.2 Replacement of ITM – Aluminum J-Box ......................................................................................... 25
5.3 Replacement of ITM – Stainless Steel Mini Condulet
6. Troubleshooting Guide ...............................................................................................................................27
6.1 Under-Range problems ..................................................................................................................... 27
6.2 Stability problems ............................................................................................................................. 27
6.3 Clearing problem .............................................................................................................................. 27
6.4 Poor Calibration Repeatability .......................................................................................................... 28
6.5 Unstable Output/ sudden spiking ...................................................................................................... 28
6.6 Nuisance Alarms ............................................................................................................................... 28
6.7 Intelligent Transmitter Module (ITM) not responding ..................................................................... 28
7. Customer Support and Service Policy ........................................................................................................29
7.1 Warranty Notice ................................................................................................................................ 29
7.2 CX-DM Sensor Warranty ................................................................................................................. 30
8. Appendix ....................................................................................................................................................31
Deficiency Sensors .................................................................................................................. 10
2
...................................................................... 25
Model CX-DM iii
Model CX-DM
Shipping Address: 4055 Technology Forest, Suite 100, The Woodlands, Texas 77381
Phone: 713.559.9200 • Fax: 281.292.2860 •www.detcon.com • sales@detcon.com
8.1 Specifications .................................................................................................................................... 31
8.2 Sensor Specific Data ......................................................................................................................... 32
8.3 Interfer ence Tabl e ............................................................................................................................. 34
8.4 Spare Parts, Sensor Accessories, Calibration Equipment ................................................................. 40
8.5 Revision Log ..................................................................................................................................... 40
Table of Figures
Figure 1 Construction of Electrochemical Toxic Sensor ...................................................................................... 1
Figure 2 Construction of Galvanic Cell ................................................................................................................ 1
Figure 3 Sensor Assembly Breakaway ................................................................................................................. 2
Figure 4 Functional Block Diagram ..................................................................................................................... 2
Figure 5 Plug-in Sensor ........................................................................................................................................ 3
Figure 6 Approval Label ...................................................................................................................................... 3
Figure 7 CX-DM Sensor with Mini-Condulet ...................................................................................................... 6
Figure 8 Sensor Wire Connections ....................................................................................................................... 8
Figure 9 Terminal Interconnect ............................................................................................................................ 9
Figure 10 Magnetic Programming Tool ............................................................................................................. 11
Figure 11 Magnetic Programming Switches ...................................................................................................... 12
Figure 12 Software flow chart ............................................................................................................................ 13
Figure 13 Modbus™ Frame Format ................................................................................................................... 21
Figure 14 Sensor Cell and ITM Mating ............................................................................................................. 24
List of Tables
Table 1 Protection vs. Wire Gauge....................................................................................................................... 7
Table 2 CX-DM Register Map ........................................................................................................................... 22
Table 3 Sensor Specific Data ............................................................................................................................. 32
Table 4 Interfering Gases ................................................................................................................................... 34
Table 5 Cross Interference Table ....................................................................................................................... 35
Mailing Address: P.O. Box 8067, The Woodlands Texas 77387-8067
Model CX-DM iv
Model CX-DM
1. Introduction
1.1 Description
Detconꞌs CX-DM sensor for toxic gas and O
monitor a wide range of toxic gases in air. Detection ranges for toxic gases are 0-1ppm up to 0-10,000ppm
(typical ranges of detection are 0-10ppm, 0-25ppm, 0-50ppm and 0-100ppm). Ranges for O
1% up to 0-25% by volume. The basic sensor assembly consists of an electrochemical sensor mounted in an
intrinsically safe stainless steel housing and includes a Splash Guard Cal Adapter.
Electrochemical Sensor Technology
The toxic gas sensors are based on electrochemical cells. Each cell consists of three electrodes embedded in an
electrolyte solution and housed beneath a diffusion membrane. Sensitivity to target gases is achieved by
varying composition of any combination of the sensor components. The cells are diffusion limited by way of
small capillary barriers resulting in a long service life of three or more years. The electrochemical cell is
packaged as a field replaceable plug -in sensor.
deficiency are non-intrusive sensors designed to detect and
2
deficiency are 0-
2
Figure 1 Construction of Electrochemical Toxic Sensor
Principle of Ope r at io n
The O
deficiency sensor technology is a two electrode galvanic metal air battery type cell housed as a field
2
replaceable intelligent plug-in sensor. The cell is diffusion limited and functions as a direct current generator
proportional to the amount of oxygen adsorption. The sensors are temperature compensated and show good
accuracy and stability over the operating temperature range of -20°C to 50°C (-4°F to +122°F). The sensor is
warranted for two years with an expected service life of up to 2.5 years in ambient air at 20.9% oxygen.
Figure 2 Construction of Galvanic Cell
CX-DM Instruction Manual Rev. 1.3 Page 1 of 40
Model CX-DM
CX-DM Bottom
Housing Assembly
Plug-in Replaceable
Sensor
Intelligent Transmitter Module (ITM)
Micro-processor controlled circuit
encapsulated in an Explosion proof
housing.
Magnetic
Programming Switches
Splash Guard
3
4
" NPT Locking
Nut
All metal components are constructed from electro polished 316 Stainless Steel to
maximize corrosion resistance in harsh environments.
mA Output
Power In
Power
Intrinsically
Safe Barrier
Modbus Output
1.2 Modular Design
The CX-DM sensor assembly is completely modular and is composed of four parts (Figure 3).
1. CX-DM Intelligent Transmitter Modu le (I TM)
2. Plug-in Electrochemical Sensor (varies by gas type and range)
3. CX Series Bottom Housing
4. Splash Guard
Figure 3 Sensor Assembly Breakaway
NOTE
CX-DM Intelligent Transmitter Module
The transmitter module is microprocessor-based and attached to the explosion proof junction box. Circuit
functions include an intr insi cal ly s af e b arri er , on-board power supply, microprocessor, magnetic programming
switches, and a linear 4-20mA DC output. Magnetic program switches (located on either side of the ITM) are
activated by a hand-held magnetic programming tool, allowing non-intrusive operator interface with the
transmitter module. Electrical classifications are Class I, Div 1, Groups B, C, and D.
Plug-In
Sensor
Micro-
Processor
I/O
Circuit
Protection
supplies
Figure 4 Functional Bloc k Diagram
Field Replaceable Sensor
Detconꞌs electrochemical gas sensors are field proven, plug-in sensors with over-sized gold-plated connections
that eliminate corrosion problems. The sensor can be easily accessed and replaced in the field by releasi ng the
locking screw and unthreading the splashguard adapter assembly. Detconꞌs toxic sensors have a long shelf life
and supported by an industry-leading warranty.
CX-DM Instruction Manual Rev. 1.3 Page 2 of 40
Model CX-DM
Figure 5 Plug-in Sens or
2. Installation
2.1 Hazardous Location s Installation Guidelines for Safe Use
1. Install the sensor only in areas with classifications matching the approval label. Follow all warnings
listed on the label.
Figure 6 Approval Label
2. Do not remove the junction box cover while in the classified are unless it is conformed the there is no
explosive gas levels in the area.
3. A good ground connection should be verified between the sensor’s metal enclosure and the junction
box. If a good ground connection is not made, the sensor can be grounded to the junction box using
the sensor’s external ground lug. Verify a good ground connection between the junction box and earth
ground.
4. Proper precautions should be taken during installing and maintenance to avoid the build-up of static
charge on the plastic components of the sensor (Splash Guard) Wipe with damp cloth on plastic
components to avoid static discharge.
5. Do not substitute components. Substitution of components may impair the intrinsic safety rating.
6. Do not operate the sensor outside of the stated operating temperature limits.
7. Do not operate the sensor outside the stated operating limits for voltage supply.
8. These sensors meet ATEX standards EN60079-0:2012. EN60079-1:2007 and EN60079-11:2012.
9. These sensors have a maximum safe location voltage of Um=30V.
10. The CX-DM apparatus is not capable of withstanding the 500V insulation test required by clause
6.3.12 of IEC/EN 60079-11:2007 (and by clause 6.8.1 of CSA Std. 142); thus, the enclosure must be
grounded.
CX-DM Instruction Manual Rev. 1.3 Page 3 of 40
Model CX-DM
In all installations, the gas sensor should point straight down. Improper sensor orientation
may result in false readings and permanent sensor damage.
11. The CXT-DM may be used as an oxygen deficiency sensor; the CXT-DM must not be used for
detecting oxygen concentrations expected to be greater than 21%
12. The CXT-DM must only use gas sensor cell model 371-xxxx00-yyy. No other gas sensor shall be
used.
2.2 Sensor Placement
Sensor location is critical to the overall safe performance of the product. Confirm that the following five
factors are verified during sensor placement.
1. Density of the gas to be detected
2. Most probable leak sources within the industrial process
3. Ventilation or prevailing wind conditions
4. Personnel exposure
5. Maintenance access
Density
Sensor placement should be relative to the density of the target gas. For the detection of heavier than air gases,
sensors should be located within 4 feet of grade since heavy gases typically settle in low lying areas. For gases
lighter than air, sensor placement should be 4 to 8 feet above grade in open areas or in pitched areas of
enclosed spaces.
Leak Sources
The most leak sources in an industrial process are flanges, valves, and tubing connections where seals may
either fail or wear. Other leak sources are best determined by facility engineers with experience in similar
processes.
Ventilation
Normal ventilation or prevailing wind conditions can dictate efficient location of gas sensors in a manner
where the movement of gas clouds is quickly detected.
Personnel Exposure
The undetected migration of gas clouds should not be allowed to approach concentrated personnel areas such
as control rooms, maintenance or warehouse buildings. Selecting sensor location should combine leak so urce
and perimeter protection in the best possible configuration.
Maintenance Access
Consideration should be given to providing easy access for maintenance personnel and the consequences of
close proximity to contaminants that may cause the sensor to wear prematurely.
NOTE
CX-DM Instruction Manual Rev. 1.3 Page 4 of 40
Model CX-DM
If wall mounting without a mounting plate, make sure to use at least 1/2" spacers underneath
the wall and to allow access to the sensor assem bly .
Metal-on-metal contact must be maintained to provide a solid electrical ground path. Only
be externally
grounded using a ground strap.
Additional Placement Considerations
The sensor should not be positioned where it might be sprayed or coated with surface contaminating
substances. Painting sensor assemblies is prohibited.
Although the sensor is designed to be RFI resistant, it should not be mounted in close proximity to highpowered radio transmitters or sim ilar RFI generati ng equipment.
When possible mount in an area void of high wind, accumulating dust, rain, splashing from hose spray, direct
steam releases, and continuous vibration. If the sensor cannot be mounted away from potentially damaging
conditions then use the Detconꞌs Harsh Location Dust Guard accessory.
Do not mount in locations where temperatures will exceed the operating temperature limits of the sensor. Use
a sunshade to maintain correct operating temperature if mounted in direct sun light.
2.3 Sensor Cont aminants and Interferen ce
Electrochemical toxic gas may be adversely affected by exposure to other airborne gases. Depending on the
cross-sensitivity relationship, there may be a false high or false low reading. The most common gases that may
cause interference are referenced in Section 8.3 (Table 4 and Table 5).
Cross-Interference Data T ab le
Gases typically found in industrial environments that may cause interference with Detconꞌs toxic gas sensors
are listed in Section 8.3, Table 5. To effectively reference the table; locate the chosen gas, scan across the row
for possible interference gases, and then determine the magnitude of cross-interference that may occur.
2.4 Sensor Mounting
Vertically position the CX-DM so the sensor points straight down. The explosion-proof enclosure or junction
box is typically mounted on a wall or pole. Detcon provides a selection of standard junction boxes in
aluminum and stainless steel.
NOTE
NOTE
When mounting on a pole, secure the junction box to a suitable mounting plate and attach the mounting plate
to the pole using U-Bolts. (Pole-Mounting brackets for Detcon junction boxes are available separately .)
the aluminum junction boxes 1/4" mounting holes to move the sensor assembly away from
use Teflon Tape or other pipe thread material on the 3/4" threads if the sensor is mounted in
a severe or harsh environment. If Teflon Tape is used the Sensor must
CX-DM Instruction Manual Rev. 1.3 Page 5 of 40
Model CX-DM
6-32 tapped
ground point
3.45
3
4
NPT Port
4.2
Ø0.4 X 0.475"
mounting
holes
Splash Guard Adapter
Splash Guard
ITM Assembly
Typ.
3.47
A conduit seal is required to be located within 18" of the J-Box and sensor assembly.
Crouse Hinds type EYS2, EYD2 or equivalent are suitable for this purpose.
NOTE
Water damage from water leaking into the enclosure is not covered by the Detcon warranty.
Unused ports should be blocked with suitable 3/4" male NPT plug. Detcon supplies one 3/4"
appropriate male plug of like construction material.
2.5 Electrica l Installation
Figure 7 CX-DM Sensor with Mini-Condulet
The sensor assembly wiring should be installed in accordance with local electrical codes. Proper electrical
installation of the gas sensor is critical for conformance to electrical codes and to avoid damage due to water
leakage.
If a conduit run exists, a drain should be incorporated. The drain allows condensation inside the conduit run to
drain safely away from the sensor assembly. Electrical seals act as a secondary seal to prevent water from
entering the wiring enclosure. However, electrical seals are not designed to provide an absolute watertight seal,
especially when used in the vertical orientation. The electrical seal fitting is required to meet the National
Electrical Code per NEC Article 500-3d (or Canadian Electrical Code Handbook Part 1 Section 18-154).
Requirements for locations of electrical seals are covered under NEC Article 501-5.
NOTE
NOTE
NPT male plug with each J-box enclosure. If connections are other than 3/4" NPT, use an
CX-DM Instruction Manual Rev. 1.3 Page 6 of 40
Model CX-DM
CAUTION
Over-Current
Protection
22
0.723mm
3A
20
0.812mm
5A
18
1.024mm
7A
16
1.291mm
10A
14
1.628mm
20A
NOTE 1: Wiring table is based on stranded tinned copper wire and is designed to serve as a
reference only.
NOTE 2: Shielded cable is required for installations where cable trays or conduit runs include
high voltage lines or other possible sources of induced interference. Separate conduit runs are
highly recommended in these cases.
NOTE 3: The supply of power should be from an isolated source with over-current pr ot ect i on
as stipulated in ta b le.
Do not apply system power to the sensor until all wiring is properly terminated
(Section 2.7).
2.6 Field Wiring
Detcon Model CX-IR se nsor assemblies require three conductor connections between power supplies and host
electronic controller’s 4-20mA output. Wiring designations are + (DC), – (DC), and mA (sensor signal.
Maximum wire ohmic resistance between sensor and 24VDC source is defined below. Maximum wire size for
termination in the De tc o n J-Box accessory is 14 gauge.
Max Resistance drop on red and black wire is 10 ohms. This considers wire diameter, wire length and
maximum operation temperature.
Max loop load resistance between green and black wire is 500 ohms. Minimum loop load resistance between
green and black wire is 100 ohms. This is considers wire diameter, wire length, max operating temperature
and selected termination resistor.
AWG Wire Dia.
Table 1 Protection vs. Wire Gauge
2.6.1 Terminal Connections 3-Wire 4-20mA
CAUTION: Do not apply System power to the sensor until all wiring is properly terminated. Refer to
Section 2.5 Initial Start Up
CX-DM Instruction Manual Rev. 1.3 Page 7 of 40
Model CX-DM
mA
(+)
(-)
Wiring to
Sensor Assembly
Red
Green
Black
Explosion
Proof
Junction Box
(+)
mA
(-)
Wiring to
Controller
Red
Green
Black
Detcon Inc.
Rev. 1
440-005208-000
MODULE
PROTECTION
TRANSIENT
Figure 8 Sensor Wire Connecti ons
a) Remove the junction box cover. Identify the terminal blocks for customer wire connections.
b) Observing correct polarity, terminate the 3-conductor 4-20mA field wiring (+, -, mA) to the sensor
assembly wiring in accordance with the detail shown in Figure 8.
c) Replace the junction box cover.
2.6.2 Terminal Connections 4-20mA and RS-485
1. Remove the junction box cover.
2. Connect the incoming 24V to the terminal labeled "+" and 24V return to the terminal labeled "–". Connect
the mA output to the “mA” terminal and the Modbus signals (if used) to the “A” and “B” terminals. Note:
the “Y” terminal is not used.
3. Replace the junction box cover after Initial Start Up (Section 2.7).
CX-DM Instruction Manual Rev. 1.3 Page 8 of 40
Model CX-DM
B
A
mA
VV+
Black
Red
Green
Blue
White
White
Blue
Green
Red
Black
To Sensor
Wiring
Ferrite
Bead
A 6-32 or 8-32 threaded exterior ground point is provided on most junction boxes for an
strap must be used to ensure that the sensor is electrically grounded.
Figure 9 Terminal Interconnect
NOTE
external ground. If the sensor assembly is not mechanically grounded, an external ground
2.7 Initial Start Up
Toxic Gas Sensors
Upon completion of all mechanical mounting, apply power to the sensor. Observe the following normal
conditions:
1. Upon power up, the sensor will scroll "CX-DM V##.##" and will then display the current reading for
about 5 seconds. A temporary upscale reading may occur as the sensor stabilizes. This upscale reading
will decrease to "0" ppm within 1 to 2 minutes of power-up, assuming there is no gas in the area of the
sensor. Sensors cells that use a bias voltage require a longer time to stabilize. This can vary between 1
and 24 hours depending on the sensor type and range. Biased sensors include NH
VOC gases (ethylene oxide, ethylene, methanol, formaldehyde….etc.).
2. After the initial power up, the sensor display will turn off . T hereafter the display will come on once
every 10 seconds, display the current reading for 2 seconds, and then return to a blank display.
, NO, HCl, and
3
Initial Operational Tests
After a warm up period of 1 hour (or when zero has stabilized), verify that the sensor has sensitivity to the
target gas.
CX-DM Instruction Manual Rev. 1.3 Page 9 of 40
Model CX-DM
Calibration gas generators using perm tubes or electrochemical sources may be used in
place of span gas cylinders.
The wind guard must be used during calibration with the integral cal port to ensure proper
calibration.
Material Requirements
• Splash Guard with integral Cal Port and with Wind Guard (Detcon PN 613-120000-700) -or-
• Threaded Calibration Adapter (Detcon PN 943-000006-132) - or -
• Teflon Calibration Adapter for highly reactive gases (Detcon PN 943-01747-T05)
• Detcon Span Gas; 50% of range target gas in balance N
500cc/min (500cc/min is preferred)
NOTE
13. Attach the calibration adapter to the splashguard adapter assembly or connect tubing to integral cal
port. It is recommended that the wind guard is installed over the splash guard during calibration.
14. Apply the test gas at a controlled flow rate of 200 - 500cc/min (500cc/min is the recommended flow).
Observe that the ITM display increases to a level near that of the applied calibration gas value.
NOTE
15. Remove the test gas and ensure that the display decreases to "0".
16. If a calibration adapter was used during these tests, remove them from the unit, and re-install the
Splash Guard. If used, remove the wind guard.
Initial operational tests are complete. CX-DM toxic gas sensors are factory calibrated prior to shipment, and
should not require significant adjustment upon start up. However, it is recommended that a complete
calibration test and adjustment be performed 16 to 24 hours after power-up. Refer to zero and span calibration
instructions in Section 3.3.
or Air at fixed flow rate between 200-
2
2.7.1 O2 Deficiency Sensors
1. When first powered up, the CX-DM display should read close to 20.9%.
2. The reading should stabilize within 1 to 2 minutes of power-up (assuming a normal ambient O
concentration).
Initial Operational Tests
2
After a warm-up period of 5 minutes, verify that the sensor responded to the O
deficiency.
2
Material Requirements
• 700 Series Splash Guard with integral Cal Port and with Wind Guard (Detcon PN 613-120000-700 )
-or-
• Threaded Calibration Adapter (Detcon PN 943-000006-132)
• Detcon Zero Gas: 100% N2 at fixed flow rate of 200-500cc/min
1. Attach the calibration adapter to the threaded sensor housing or connect tubing to the integral cal port.
Apply the test gas at a controlled flow rate of 200-500cc/min (500cc/min is the recommended flow).
Observe that the ITM display decreases to a level near z ero .
CX-DM Instruction Manual Rev. 1.3 Page 10 of 40
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