Ametek Thermox WDG-V UOP User manual

Thermox® IECEx/ATEX
WDG-V UOP Combustion Analyzer
User Manual
Thermox
150 Freeport Road
Pittsburgh, PA 15238
PN 9000-280-VE Rev. B

© 2019 AMETEK
This manual is a guide for the use of the Thermox WDG-V UOP. Data herein has been veried and validated and is believed adequate for the
intended use of this instrument. If the instrument or procedures are used for purposes over and above the capabilities specied herein, conrma-
tion of their validity and suitability should be obtained; otherwise, AMETEK does not guarantee results and assumes no obligation or liability. This
publication is not a license to operate under, or a recommendation to infringe upon, any process patents.
O󰀩ces
USA - Pittsburgh
150 Freeport Road
Pittsburgh, PA 15238
Ph. 412-828-9040
Fax [phone]
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Contents | iii
Contents
Offices ............................................................................................................................ ii
Safety Notes ................................................................................................................ vii
Electrical Safety...........................................................................................................vii
Grounding...................................................................................................................vii
Special Conditions for Safe Use..............................................................................viii
HAZARDOUS LOCATION LIMITATIONS ...................................................viii
Warning Labels............................................................................................................ ix
Environmental Information (WEEE) ....................................................................... ix
General Safety Summary ............................................................................................ x
Use Proper Wiring ................................................................................................ x
Avoid Electrical Overload .................................................................................... x
Ground the Product.............................................................................................. x
Do Not Operate without Covers ........................................................................ x
Use Proper Fuse..................................................................................................... x
Product Damage Precautions.................................................................................... xi
Use Proper Power Source.................................................................................... xi
Do Not Operate with Suspected Failures......................................................... xi
Use Caution When Lifting .................................................................................. xi
Use Proper Attire .................................................................................................. xi
Chapter 1 System Overview ........................................................................................1-1
UOP CCR Platforming Process............................................................................... 1-1
History.................................................................................................................. 1-1
CCR - Continuous Catalyst Regeneration.....................................................1-1
Thermox and WDG UOP Series....................................................................1-3
Analyzer Operations ................................................................................................ 1-4
Basic Elements of the Analyzer.............................................................................. 1-5
Analyzer I/O...................................................................................................1-5
Analyzer Communications.............................................................................1-5
How the Oxygen Measuring Cell Works........................................................ 1-6
Measuring Non-Combustible Gases...............................................................1-7
Hydrocarbons in the Gas Sample ...................................................................1-7
Sensor Operations - WDG-V UOP .................................................................. 1-8
RTD Flow Sensor ................................................................................................ 1-9
Temperature Zones and Heaters.................................................................... 1-10
Flame Arrestors................................................................................................. 1-10
Electronics ................................................................................................................ 1-11
I/O ...................................................................................................................... 1-11
Current Output Connections......................................................................... 1-11
Standard Current Outputs ..........................................................................1-11
Standard Alarm Connections.......................................................................1-12

iv | Thermox WDG-V UOP IECEx/ATEX
Remote Calibration Unit Connections.......................................................... 1-13
Oxygen-Only Remote Calibration Unit Connections .................................1-13
Digital Input to Initiate Remote Calibration Unit ......................................1-14
Terminal Block Connections ........................................................................... 1-14
Technical Support.................................................................................................... 1-16
Chapter 2 Specications..............................................................................................2-1
Sensor : WDG-V UOP .............................................................................................. 2-1
Approvals and Certifications for WDG-V UOP ................................................... 2-2
Remote Calibration Unit (RCU).............................................................................. 2-3
WDG-V UOP Series Analyzer Rating Labels........................................................ 2-4
WDG-V UOP Series Analyzer Markings............................................................... 2-5
Chapter 3 Installation Guide........................................................................................3-1
Analyzer Location ..................................................................................................... 3-2
Inspect Shipping Contents ...................................................................................... 3-2
Mechanical Installation ............................................................................................ 3-3
Sample Inlet Probe Installation ........................................................................ 3-3
Standard 1/4"NPT probe installation............................................................3-4
Exhaust Tube Installation .................................................................................. 3-5
Sensor Mounting ................................................................................................ 3-5
Calibration/Aspirator Air................................................................................... 3-7
Required Calibration Gases and Tubing.........................................................3-7
Rapid Exchange Purge System......................................................................... 3-8
Connections....................................................................................................3-8
Purging Operation .........................................................................................3-8
Purging Instructions....................................................................................3-10
Aspirator and Manual Calibration Connections ......................................... 3-11
Aspirator N2Connections ............................................................................3-11
Manual Calibration .......................................................................................... 3-11
Standard RCU Mechanical Installation ........................................................ 3-12
AMEVision Display User Interface Mounting.................................................... 3-14
Wiring........................................................................................................................ 3-14
General Wiring and Conduit Requirements................................................ 3-15
WDG-V UOP Mains Supply Connections ................................................... 3-16
EMC Grounding, Shielding and Noise Protection ......................................3-17
EMC Grounding Method.............................................................................3-17
Transient and RFI interference.....................................................................3-19
Current Output Connections......................................................................... 3-20
Standard current outputs.............................................................................3-20
Alarm Contact Connections............................................................................ 3-21
Standard alarm connections.........................................................................3-21
Remote Calibration Unit Connections.......................................................... 3-23
Digital Input to Initiate Remote Calibration Unit ......................................3-23

Contents | v
Standard Connection using PC Configurator Software ................................... 3-25
Overview ........................................................................................................... 3-25
Connecting to the WDG-V UOP.................................................................... 3-25
Setting the Address using the Dip Switch...................................................3-25
Connecting the PC to the Analyzer..............................................................3-26
Chapter 4 AMEVision Display Installation Guide ......................................................4-1
The AMEVision Display Unit ........................................................................... 4-1
Communication Options ...............................................................................4-1
Setting the Analyzer Address ........................................................................... 4-2
Connecting the Analyzers................................................................................. 4-3
Single Analyzer Connection...........................................................................4-3
Multiple Analyzer Connections .....................................................................4-3
Final Daisy Chain Connection Configuration Setting ..................................4-4
Troubleshooting.................................................................................................. 4-4
No Communications: .....................................................................................4-4
Intermittent Communications: ......................................................................4-4
Customer I/O Connections...................................................................................... 4-5
Retrofitting the WDG-V UOP to WDG-IV UOP.................................................. 4-6
Chapter 5 Troubleshooting..........................................................................................5-1
General Troubleshooting ......................................................................................... 5-2
Leak Check .......................................................................................................... 5-2
Sniffing for Leaks ...........................................................................................5-2
Pressurizing for Leaks....................................................................................5-2
Plugged Plumbing Check ................................................................................. 5-3
Diagnostics Checks ................................................................................................... 5-4
Thermocouple Checks....................................................................................... 5-5
Calibration/Aspirator Setup Checks................................................................ 5-6
AC Power Checks ............................................................................................... 5-7
Furnace Checks................................................................................................... 5-7
Process Pressure Checks (Only if above 2 psig) ............................................ 5-8
Cell Checks .......................................................................................................... 5-8
Alarm and Warning Messages ................................................................................ 5-9
ALARMS .............................................................................................................. 5-9
WARNINGS....................................................................................................... 5-11
Chapter 6 Service and Parts........................................................................................6-1
Warnings ................................................................................................................... 6-2
Cautions...................................................................................................................... 6-2
Cell Replacement/Cleaning ..................................................................................... 6-4
Thermocouple Replacement ................................................................................... 6-6
Flow Sensor Replacement........................................................................................ 6-8
Furnace Replacement............................................................................................... 6-9
Box Heater Replacement........................................................................................ 6-10

vi | Thermox WDG-V UOP IECEx/ATEX
Electronics Replacement........................................................................................ 6-13
Recommended Maintenance Schedule............................................................... 6-14
Calibration ......................................................................................................... 6-14
Replacement Parts List ........................................................................................... 6-15
Sensor ................................................................................................................. 6-15
Remote Calibration Unit (RCU) ..................................................................... 6-15

| vii
Safety Notes
WARNINGS, CAUTIONS, and NOTES contained in this manual emphasize
critical instructions as follows:
An operating procedure which, if not strictly observed, may result in
personal injury or environmental contamination.
An operating procedure which, if not strictly observed, may result in dam-
age to the equipment.
Important information that should not be overlooked.
Burn hazard. Hot surface. Do not touch, allow to cool before servicing.
Electrical Safety
Up to 5 kV may be present in the analyzer housings. Always shut down
power source(s) before performing maintenance or troubleshooting. Only a
qualified electrician should make electrical connections and ground checks.
Any use of the equipment in a manner not specified by the manufacturer may
impair the safety protection originally provided by the equipment.
Grounding
Instrument grounding is mandatory. Performance specifications and safety
protection are void if instrument is operated from an improperly grounded
power source.
Verify ground continuity of all equipment before applying power.

viii | Thermox WDG-V UOP IECEx/ATEX
Special Conditions for Safe Use
The WDG-V UOP is designed to be used in Category 3 hazardous locations
where explosive gases may be present. Protection against explosion is provid-
ed by purge technique. There are four rules that must always be followed:
1. Do not open the enclosure unless the power is removed from both sensor
and control unit for 90 minutes while maintaining pressurization, or the
area is demonstrated to be non-hazardous.
2. Perform purge system maintenance as described in Chapter 3 of the user
manual.
3. Use only appropriate approved conduit fittings or cable glands for cable
entry (IIC, IP40 minimum). No holes shall be left unplugged.
4. Internal temperature rises above the rated T-class. The end user must take
immediate action on the loss of pressure to reinstate purge.
HAZARDOUS LOCATION LIMITATIONS
The WDG-V UOP is a Category 3 analyzer specifically designed and certified
for use in ATEX II 3 G and IECEx hazardous locations. It can be safely oper-
ated in a location in which:
• No gases are present with a higher probability of ignition than hydrogen
(e.g., acetylene).
• The ambient temperature does not exceed 60°C.
• Voltages are 104-127 VAC or 207-253 VAC, 740 VA.
Make sure the location in which the WDG is installed meets all of the
Hazardous Location Limitation criteria for a Category 3 analyzer de-
scribed above.

| ix
Warning Labels
These symbols may appear on the instrument in order to alert you of existing
conditions.
PROTECTIVE CONDUCTOR TERMINAL
(BORNIER DE L’ECRAN DE PROTECTION)
Schutzerde
CAUTION - Risk of electric shock
(ATTENTION-RISQUE DE DÉCHARGE ÉLECTRIQUE)
Achtung - Hochspannung Lebensgefahr
CAUTION - (Refer to accompanying documents)
(ATTENTION-SE RÉFERER AUX DOCUMENTS JOINTS)
Achtung (Beachten Sie beiliegende Dokumente)
CAUTION - Hot Surface
(ATTENTION-SURFACE CHAUDE)
Achtung - Heiße Oberäche
Environmental Information (WEEE)
This AMETEK product contains materials that can be reclaimed and recycled.
In some cases the product may contain materials known to be hazardous to
the environment or human health. In order to prevent the release of harmful
substances into the environment and to conserve our natural resources,
AMETEK recommends that you arrange to recycle this product when it
reached its “end of life”.
Waste Electrical and Electronic Equipment (WEEE) should never be disposed
of in a municipal waste system (residential trash). The Wheelie Bin marking
on this product is a reminder to dispose of the product properly after it has
completed its useful life and been removed from service. Metals, plastics, and
other components are recyclable and you can do your part by doing one of
the following steps:
•When the equipment is ready to be disposed of, take it to your local or
regional waste collection administration for recycling.
•In some cases, your “end of life” product may be traded in for credit to-
wards the purchase of new AMETEK instruments. Contact your dealer to
see if this program is available in your area.
•If you need further assistance in recycling your AMETEK product, contact
our o󰀩ce listed in the front of the instruction manual.

x | Thermox WDG-V UOP IECEx/ATEX
General Safety Summary
Review the following safety precautions to avoid injury and prevent damage
to this product or any products connected to it.
Use Proper Wiring
To avoid fire hazards, use only the wiring specified in the Installation chapter
of this user’s manual.
Avoid Electrical Overload
To avoid electrical shock or fire hazard, do not apply a voltage to a terminal
that is outside the range specified for that terminal.
Ground the Product
Follow the grounding instructions provided in the Installation chapter of this
user manual. Before making connections to the input or output terminals of
this product, ensure that the product is properly grounded.
Do Not Operate without Covers
To avoid electric shock or fire hazard, do not operate this product with covers
or panels removed.
Use Proper Fuse
To avoid fire hazard, use only the fuse type and rating specified for this prod-
uct.

Contents | xi
Product Damage Precautions
Use Proper Power Source
Do not operate this product from a power source that applies more than the
voltage specified.
Do Not Operate with Suspected Failures
If you suspect there is damage to this product, have it inspected by qualified
service personnel.
Use Caution When Lifting
Use caution when lifting the analyzer from its crate.
Use Proper Attire
Equipment is hot, user should wear protective groves while handling the
equipment.

xii | Thermox WDG-V UOP IECEx/ATEX
WARRANTY AND CLAIMS
We warrant that any equipment of our own manufacture or manufactured for us pursuant to our
specications which shall not be, at the time of shipment thereof by or for us, free from defects
in material or workmanship under normal use and service will be repaired or replaced (at our
option) by us free of charge, provided that written notice of such defect is received by us within
twelve (12) months from date of shipment of portable analyzers or within eighteen (18) months
from date of shipment or twelve (12) months from date of installation of permanent equipment,
whichever period is shorter. All equipment requiring repair or replacement under the warranty
shall be returned to us at our factory, or at such other location as we may designate, transporta-
tion prepaid. We shall examine such returned equipment, and if it is found to be defective as a
result of defective materials or workmanship, it shall be repaired or replaced as aforesaid. Our
obligation does not include the cost of furnishing any labor in connection with the installation
of such repaired or replaced equipment or parts thereof, nor does it include the responsibility
or cost of transportation. In addition, instead of repairing or replacing the equipment returned
to us as aforesaid, we may, at our option, take back the defective equipment, and refund in full
settlement the purchase price thereof paid by Buyer.
The warranty shall not apply to any equipment (or part thereof) which has been tampered with
or altered after leaving our control or which has been replaced by anyone except us, or which
has been subject to misuse, neglect, abuse or improper use. Misuse or abuse of the equip-
ment, or any part thereof, shall be construed to include, but shall not be limited to, damage by
negligence, accident, re or force of the elements. Improper use or misapplications shall be
construed to include improper or inadequate protection against shock, vibration, high or low
temperature, overpressure, excess voltage and the like, or operating the equipment with or in a
corrosive, explosive or combustible medium, unless the equipment is specically designed for
such service, or exposure to any other service or environment of greater severity than that for
which the equipment was designed.
The warranty does not apply to used or secondhand equipment nor extend to anyone other than
the original purchaser from us.
THIS WARRANTY IS GIVEN AND ACCEPTED IN LIEU OF ALL OTHER WARRANTIES, WHETHER
EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION AND WARRANTIES OF FITNESS OR
OF MERCHANTABILITY OTHER THAN AS EXPRESSLY SET FORTH HEREIN, AND OF ALL OTHER
OBLIGATIONS OR LIABILITIES ON OUR PART. IN NO EVENT SHALL WE BE LIABLE UNDER THIS
WARRANTY OR ANY OTHER PROVISION OF THIS AGREEMENT FOR ANY ANTICIPATED OR LOST
PROFITS, INCIDENTAL DAMAGES, CONSEQUENTIAL DAMAGES, TIME CHANGES OR ANY OTHER
LOSSES INCURRED BY THE ORIGINAL PURCHASER OR ANY THIRD PARTY IN CONNECTION WITH
THE PURCHASE, INSTALLATION, REPAIR OR OPERATION OF EQUIPMENT, OR ANY PART THEREOF
COVERED BYTHIS WARRANTY OR OTHERWISE. WE MAKE NO WARRANTY, EXPRESS OR IMPLIED,
INCLUDING WITHOUT LIMITATION ANYWARRANTIES OF FITNESS OR OF MERCHANTABILITY, AS
TO ANY OTHER MANUFACTURER’S EQUIPMENT, WHETHER SOLD SEPARATELY OR IN CONJUNC-
TION WITH EQUIPMENT OF OUR MANUFACTURE. WE DO NOTAUTHORIZEANY REPRESENTATIVE
OR OTHER PERSON TO ASSUME FOR US ANY LIABILITY IN CONNECTION WITH EQUIPMENT, OR
ANY PART THEREOF, COVERED BY THIS WARRANTY.

System Overview |1-1
SYSTEM OVERVIEW
UOP CCR Platforming Process
“The CCR Platforming process uses naphtha boiling in the range of
180-400°F to produce high-octane gasoline or petrochemical precursors.
This technology is the world’s leading reforming process. It is also the
technology of choice for new reforming applications, providing refiners
with proven, ultra-low-pressure (50 psig reactor pressure) operation and
producing the highest reforming yields.
In gasoline applications, the Platforming process produces high-octane
reformate for unleaded gasoline blending to make higher-octane grades
of gasoline. In reformulated gasoline applications, the low-pressure, low-
severity Platforming process restores a refinery’s hydrogen balance by
maximizing the yield of hydrogen, even at the required low-octane severi-
ties. With appropriate prefractionation, the process produces the low-ben-
zene, low-vapor-pressure material mandated by reformulated gasoline.”
World Wide Web page (no author)
CCR Platforming Process [Online], Available:
http://www.uop.com/framesets/rening.html [2002, April 19].
History
The semi-regenerative Platforming process, introduced by UOP in 1949,
was the first catalytic reforming process to use platinum-coated catalysts.
Advances continuously improved the process, and in 1972, UOP introduced
the Platforming process with CCR (Continuous Catalyst Regeneration).
CCR - Continuous Catalyst Regeneration
CCR Platforming incorporates a moving catalyst bed that allows catalyst
to be added or removed from the reactor while the unit is operating.
Spent catalyst from the reactor flows to the regeneration tower where the
carbon is burned off and the catalyst is reconditioned. Regenerated cata-
lyst is returned to the top of the reactor stack.

1-2 | Thermox WDG-V UOP IECEx/ATEX
Fresh
Catalyst
Catalyst
Regenerator
Stacked
Reactor
Combined Feed
Exchanger
Naphtha Feed
from Treating
Fired Heaters
Recovery
Station
Fuel Gas
Light Ends
Stabilizer
C
6
Aromatics
Net H
2
Rich Gas
Net Gas
Compressor
Separator
Naphtha Feed
from Treating
CCR Platforming Process.
Catalytic reaction causes coke to be deposited on the catalyst as it moves
through the reactors, degrading its performance. Once in the regenerator,
the coke is burned off the catalyst. However, the resulting high tempera-
ture greatly increases the risk of permanent damage to the catalyst and so
the combustion must be controlled. This is done by controlling the oxygen
content. The catalyst is the key ingredient used in the catalytic reforming
process and oxygen measurement is critical to this process. It is essential
that the oxygen analyzer function accurately and be easy to service and
maintain.
A major benefit of the of the UOP CCR process is that the catalytic reform-
ing process can run uninterrupted. Other catalyst regeneration methods
require a shutdown of the process which is costly and defeats the pur-
pose of the UOP-type system. The oxygen analyzer is critical to the UOP-
patented CCR process and designed specifically to monitor oxygen levels
during catalyst regeneration.

System Overview |1-3
Thermox and WDG UOP Series
1980 Thermox, in conjunction with the UOP Process Division, de-
veloped the WDG-III UOP to monitor the gaseous atmosphere
during a regeneration cycle of UOP’s Licensed Continuous
Catalyst Regeneration process. With their technical guidance
this analyzer evolved to the current model WDG-IV UOP/RP.
1999 UOP and Thermox addressed plugging and corrosion issues
with the external sample return line which is outside the scope
of our supply. The revised UOP Project Specification 630 allows
the close-coupled, nitrogen-aspirated, return-to-process design
of the Thermox model WDG-IV UOP/RP (or an in-situ probe
design) to be used to measure oxygen content of the process.
This eliminated the need for the external sample return line
and the sample flow sensor used to check for plugging in the
return line that were part of the WDG-III and WDG-IV UOP
analyzer designs. Since the process piping of the CCR is 316
stainless steel, and the process was adjusted to include nitro-
gen blanketing at shutdown, UOP decided that Hastelloy C
was no longer mandatory for the process-wetted parts. The
standard analyzer is now constructed of 316 SS, but Hastelloy
C is still available as an option.
2007 Thermox added an option to the WDG-IV UOP to include iso-
lation valves on the inlet and outlet process connections. This
option allows for maintenance of the WDG-IV UOP analyzer
without shutting down the process.
2019 Thermox updated the instrument’s electronics package and re-
named the product WDG-V UOP. The new electronics package
includes additional diagnostics and meets the ROHS compli-
ance directive. The AMEVision Controller replaces the Series
2000 Controller for the instrument as well. It includes a color
LED display and additional communications options.

1-4 | Thermox WDG-V UOP IECEx/ATEX
Analyzer Operations
Designed for fast response in a wide range of flue gas applications, the
sensor mounts directly on the combustion process to provide continuous
measurement of oxygen.
A sample is drawn from the process stream by means of an air-operated
aspirator and is immediately returned to the process. A portion of this gas
rises past the oxygen measuring cell and returns to the primary loop. All
sample wetted parts are heated to 200°C maintain the sample above the
dewpoint of the gas.
Follow these cautions when working on the sensor:
Do not turn on the aspirator until the analyzer has been turned on
and is hot - preferably 24 hours. Also, if you turn off the analyzer or
the process is shut down, turn off the aspirator air to avoid plugging
problems!
Remove AC power from the sensor and allow the sensor to cool for at
least one hour before performing any maintenance or troubleshooting
activities.
The outside of the sensor cover and all sensor assembly components
are hot during normal operation (up to 500°F, 260°C inside the cover).
Allow sensor components to cool for at least 90 minutes before work-
ing inside the sensor. Use caution and wear appropriate gloves when
handling components or when touching the sensor cover!

System Overview |1-5
Basic Elements of the Analyzer
The WDG-V UOP analyzer is a complete standalone unit; no separate
controller is required. The unit consists of three basic systems:
1. Plumbing
Includes all inlet and outlet tubing, O2cell housing, the calibration gas
inlet and aspirator assembly, flow sensor, and the aspirator used to
pull the sample into the analyzer.
2. Measuring System
Includes the oxygen cell and flow sensor.
3. Temperature System
Includes the electrical cell heater (furnace), sensor case heaters, the
type “K” thermocouple (maintains cell operating temperature). The
sensing cell operates at a constant temperature. The WDG-V is a com-
plete standalone unit. No separate controller is required.
Analyzer I/O
All required I/O comes with the analyzer. See the “Electronics” section for
descriptions.
Analyzer Communications
The analyzer is configured, calibrated and monitored using the MODBUS
RTU interface. AMETEK/Thermox provides two options for communicat-
ing with the analyzer:
• AMEVision Display User Interface
• WDG-V UOP Congurator Software via PC (standard with each unit)
The interface is industry standard MODBUS which allows custom-
ized user-software. Contact the factory for the MODBUS register
definitions.

1-6 | Thermox WDG-V UOP IECEx/ATEX
How the Oxygen Measuring Cell Works
The sensing element is a closed-end tube made from ceramic zirconium
oxide stabilized with an oxide of yttrium or calcium. Porous platinum
coatings on the inside and outside serve as both a catalyst and as elec-
trodes. At high temperatures (generally above 1200 °F/650 °C), oxygen
molecules coming in contact with the platinum electrodes near the sensor
become ionic.
• As long as the oxygen partial pressures on either side of the cell are
equal, the movement is random and no net ow of ions occurs.
• If, however, gases having dierent oxygen partial pressures are on ei-
ther side of the cell, a potentiometric voltage is produced. The magni-
tude of this voltage is a function of the ratio of the two oxygen partial
pressures.
• If the oxygen partial pressure of one gas is known, the voltage pro-
duced by the cell indicates the oxygen content of the other gas. A refer-
ence gas, usually air (20.9% O2), is used for one of the gases.
Figure 1-1. Zirconium oxide cell principle of operation.

System Overview |1-7
The voltage of the cell depends on temperature, and so the cell is main-
tained at a constant temperature. The oxygen content is then determined
from the Nernst equation:
E = In
RT
4F
O1
O2
where R and F are constants, T is absolute temperature, and O1and O2are
the oxygen partial pressures on either side of the cell.
Measuring Non-Combustible Gases
For measuring oxygen in non-combustibles gases, the calibration of an
analyzer is obtained using the formula:
AT = 48.0 at 680°C
E = A*T*Log 20.9%
O2Unk%
Where A is a constant, T is the cell temperature on an absolute scale (°C +
273) and O2Unk% is the unknown oxygen concentration of the gas to be
analyzed, and which is calculated by the analyzer.
The cell produces zero voltage when the same amount of oxygen is on
both sides. Voltage increases as the oxygen concentration of the sample
decreases. The voltage created by the difference in the sample gas and the
reference air is transmitted to the microprocessor control unit and linear-
ized to an output signal.
Hydrocarbons in the Gas Sample
When hydrocarbons are present in a gas sample, a combustion process oc-
curs when the sample is exposed to the high temperature of the zirconia
cell. If the oxygen reading is lower than expected, it may be an indication
that hydrocarbons are present.
The amount of oxygen reduction is dependent on the type of hydrocar-
bons present in the sample gas.

1-8 | Thermox WDG-V UOP IECEx/ATEX
Sensor Operations - WDG-V UOP
The WDG-V UOP was designed for meeting the purpose of low level
oxygen measurement during the regeneration cycle in which coke depos-
its are removed from the catalyst by oxidation. The WDG-V UOP analyzer
has a specially treated Zirconium Oxide cell which is used to survive the
destructive effects of halogen-oxidation.
The sensor uses a nitrogen-operated aspirator to draw a sample of gas
from the catalyst regenerator. A portion of this gas passes over the zirco-
nia sensor. Because the aspirator gas contains no oxygen, the sample can
simply be returned to the process.
Figure 1-2. Typical WDG-V UOP sensor conguration.