Teledyne 3000TA-XLEU User Manual
Trace Oxygen Analyzer
OPERATING INSTRUCTIONS FOR
MODEL 3000TA-XL-EU
Trace Oxygen Analyzer
P/N M69603
12/02/13
DANGER
Toxic gases and or flammable liquids may be present in this monitoring system.
Personal protective equipment may be required when servicing this instrument.
Hazardous voltages exist on certain components internally which may persist
for a time even after the power is turned off and disconnected.
Only authorized personnel should conduct maintenance and/or servicing.
Before conducting any maintenance or servicing, consult with authorized
supervisor/manager.
Teledyne Analytical Instruments i
3000TA-XL-EU
Copyright © 2013 Teledyne Analytical Instruments
All Rights Reserved. No part of this manual may be reproduced, transmitted, transcribed,
stored in a retrieval system, or translated into any other language or computer language in
whole or in part, in any form or by any means, whether it be electronic, mechanical,
magnetic, optical, manual, or otherwise, without the prior written consent of Teledyne
Analytical Instruments, 16830 Chestnut Street, City of Industry, CA 91748.
Warranty
This equipment is sold subject to the mutual agreement that it is warranted by us free
from defects of material and of construction, and that our liability shall be limited to
replacing or repairing at our factory (without charge, except for transportation), or at
customer plant at our option, any material or construction in which defects become
apparent within one year from the date of shipment, except in cases where quotations
or acknowledgements provide for a shorter period. Components manufactured by
others bear the warranty of their manufacturer. This warranty does not cover defects
caused by wear, accident, misuse, neglect or repairs other than those performed by
Teledyne or an authorized service center. We assume no liability for direct or indirect
damages of any kind and the purchaser by the acceptance of the equipment will
assume all liability for any damage which may result from its use or misuse.
We reserve the right to employ any suitable material in the manufacture of our
apparatus, and to make any alterations in the dimensions, shape or weight of any
parts, in so far as such alterations do not adversely affect our warranty.
Important Notice
This instrument provides measurement readings to its user, and serves as a tool by
which valuable data can be gathered. The information provided by the instrument may
assist the user in eliminating potential hazards caused by his process; however, it is
essential that all personnel involved in the use of the instrument or its interface, with the
process being measured, be properly trained in the process itself, as well as all
instrumentation related to it.
The safety of personnel is ultimately the responsibility of those who control process
conditions. While this instrument may be able to provide early warning of imminent
danger, it has no control over process conditions, and it can be misused. In particular,
any alarm or control systems installed must be tested and understood, both as to how
they operate and as to how they can be defeated. Any safeguards required such as
locks, labels, or redundancy, must be provided by the user or specifically requested of
Teledyne at the time the order is placed.
Therefore, the purchaser must be aware of the hazardous process conditions. The
purchaser is responsible for the training of personnel, for providing hazard warning
methods and instrumentation per the appropriate standards, and for ensuring that
hazard warning devices and instrumentation are maintained and operated properly.
Teledyne Analytical Instruments, the manufacturer of this instrument, cannot accept
responsibility for conditions beyond its knowledge and control. No statement
expressed or implied by this document or any information disseminated by the
manufacturer or its agents, is to be construed as a warranty of adequate safety control
under the user’s process conditions.
Teledyne Analytical Instruments ii
Trace Oxygen Analyzer
Teledyne Analytical Instruments iii
3000TA-XL-EU
Specific Model Information
The instrument for which this manual was supplied may
incorporate one or more options not supplied in the standard instrument.
Commonly available options are listed below, with check boxes. Any
that are incorporated in the instrument for which this manual is supplied
are indicated by a check mark in the box.
Instrument Serial Number: _______________________
Options Included in the Instrument with the Above Serial Number:
3000TA-XL -VS: Instrument configured for Vacuum Service
3000TA-XL-CV: Instrument with calibration valves
19" Rack Mnt: The 19" Relay Rack Mount units are available
with either one or two 3000TA-XL series
analyzers installed in a standard 19" panel and
ready to mount in a standard rack.
3000TA-XL-I Web enabled version.
Sensor Options Available for the Instrument with the Above Serial
Number:
Insta-Trace B2CXL (Default)
L2CXL
Teledyne Analytical Instruments iv
Trace Oxygen Analyzer
Important Notice
Model 3000TA-XL-EU complies with all of the requirements of
the Commonwealth of Europe (CE) for Radio Frequency Interference,
Electromagnetic Interference (RFI/EMI), and Low Voltage Directive
(LVD).
The following International Symbols are used throughout the
Instruction Manual. These symbols are visual indicators of important
and immediate warnings and when you must exercise CAUTION while
operating the instrument. See also the Safety Information on the next
page.
STAND-BY: Instrument is on Stand-by, but circuit is
active
GROUND: Protective Earth
CAUTION: The operator needs to refer to the manual
for further information. Failure to do so may
compromise the safe operation of the equipment.
CAUTION: Risk of Electrical Shock
Teledyne Analytical Instruments v
3000TA-XL-EU
Safety Messages
Your safety and the safety of others is very important. We have
provided many important safety messages in this manual. Please read
these messages carefully.
A safety message alerts you to potential hazards that could hurt you
or others. Each safety message is associated with a safety alert symbol.
These symbols are found in the manual and inside the instrument. The
definition of these symbols is described below:
GENERAL WARNING/CAUTION: Refer to the
instructions for details on the specific danger. These cautions
warn of specific procedures which if not followed could
cause bodily Injury and/or damage the instrument.
No
Symbol
CAUTION: HOT SURFACE WARNING: This warning is
specific to heated components within the instrument. Failure
to heed the warning could result in serious burns to skin and
underlying tissue.
WARNING: ELECTRICAL SHOCK HAZARD: Dangerous
voltages appear within this instrument. This warning is
specific to an electrical hazard existing at or nearby the
component or procedure under discussion. Failure to heed
this warning could result in injury and/or death from
electrocution.
Technician Symbol: All operations marked with this
symbol are to be performed by qualified maintenance
personnel only.
NOTE: Additional information and comments regarding a
specific component or procedure are highlighted in the form
of a note.
Teledyne Analytical Instruments vi
Trace Oxygen Analyzer
CAUTION: THE ANALYZER SHOULD ONLY BE USED FOR THE
PURPOSE AND IN THE MANNER DESCRIBED IN
THIS MANUAL.
IF YOU USE THE ANALYZER IN A MANNER OTHER
THAN THAT FOR WHICH IT WAS INTENDED,
UNPREDICTABLE BEHAVIOR COULD RESULT
POSSIBLY ACCOMPANIED WITH HAZARDOUS
CONSEQUENCES.
This manual provides information designed to guide you through
the installation, calibration and operation of your new analyzer. Please
read this manual and keep it available.
Occasionally, some instruments are customized for a particular
application or features and/or options added per customer requests.
Please check the front of this manual for any additional information in
the form of an Addendum which discusses specific information,
procedures, cautions and warnings that may be peculiar to your
instrument.
Manuals do get lost. Additional manuals can be obtained from
Teledyne at the address given in the Appendix. Some of our manuals are
available in electronic form via the internet. Please visit our website at:
www.teledyne-ai.com.
Teledyne Analytical Instruments vii
3000TA-XL-EU
This is a general purpose instrument designed for use in a nonhazardous
area. It is the customer's responsibility to ensure safety especially when
combustible gases are being analyzed since the potential of gas leaks
always exist.
The customer should ensure that the principles of operation of this
equipment are well understood by the user. Misuse of this product in
any manner, tampering with its components, or unauthorized
substitution of any component may adversely affect the safety of this
instrument.
Since the use of this instrument is beyond the control of Teledyne, no
responsibility by Teledyne, its affiliates, and agents for damage or injury
from misuse or neglect of this equipment is implied or assumed.
Teledyne Analytical Instruments viii
Trace Oxygen Analyzer
Table of Contents
Safety Messages .......................................................................... vi
Introduction ................................................................................... 1
1.1 Overview 1
1.2 Typical Applications 1
1.3 Main Features of the Analyzer 1
1.4 Model Designations 2
1.5 Front Panel (Operator Interface) 3
1.6 Rear Panel (Equipment Interface) 5
Operational Theory ....................................................................... 7
2.1 Introduction 7
2.2 Micro-Fuel Sensor 7
2.2.1 Principles of Operation 7
2.2.2 Anatomy of a Micro-Fuel Cell 8
2.2.3 Electrochemical Reactions 9
2.2.4 The Effect of Pressure 10
2.2.5 Calibration Characteristics 10
2.3 Sample System 12
2.4 Electronics and Signal Processing 15
Installation ................................................................................... 19
3.1 Unpacking the Analyzer 19
3.2 Mounting the Analyzer 19
3.3 Rear Panel Connections 21
3.3.1 Gas Connections 21
3.3.2 Electrical Connections 22
3.3.2.1 Primary Input Power 23
3.3.2.2 50-Pin Equipment Interface Connector 23
Teledyne Analytical Instruments ix
3000TA-XL-EU
3.3.2.2.1 Analog Outputs 23
3.3.2.2.2 Alarm Relays 24
3.3.2.2.3 Digital Remote Cal Inputs 26
3.3.2.2.4 Cal Contact 26
3.3.2.2.5 Remote Calibration Protocol 27
3.3.2.2.6 Range ID Relays 27
3.3.2.2.7 Network I/O 28
3.3.2.2.8 Remote Valve Connections 28
3.3.2.3 RS-232 Port 30
3.4 Installing the Micro-fuel Cell 31
3.4.1 B-2CXL Micro-fuel Cell 31
3.4.2 Insta-Trace Micro-fuel Cell 32
3.5 Testing the System 34
Operation ..................................................................................... 37
4.1 Introduction 37
4.2 Using the Data Entry and Function Buttons 38
4.3 The System Function 40
4.3.1 Tracking the Oxygen Readings During Calibration and
Alarm Delay 41
4.3.2 Setting up an Auto-Cal 42
4.3.3 Password Protection 43
4.3.3.1 Entering the Password 43
4.3.3.2 Installing or Changing the Password 44
4.3.4 Logout 46
4.3.5 System Self-Diagnostic Test 47
4.3.6 Version Screen 48
4.4 Calibration of the Analyzer 48
4.4.1 Zero Cal 49
4.4.1.1 Auto Mode Zeroing 49
4.4.1.2 Manual Mode Zeroing 50
4.4.1.3 Cell Failure 51
4.4.2 Span Cal 51
Teledyne Analytical Instruments x
Trace Oxygen Analyzer
4.4.2.1 Auto Mode Spanning 51
4.4.2.2 Manual Mode Spanning 52
4.4.3 Span Failure 53
4.5 Switching of Sample Streams 54
4.5.1 Special Notes on Hydrogen Gas Stream 55
4.6 The Alarms Function 55
4.7 The Range Function 57
4.7.1 Setting the Analog Output Ranges 58
4.7.2 Fixed Range Analysis 59
4.8 The Analyze Function 59
4.9 Signal Output 60
4.10 The IP Address Function 61
4.11 Cold Boot to Return to Default Settings 62
Web Implementation ................................................................... 63
5.1 The Embedded Browser 63
5.2 Remote Calibration 65
5.2.1 Remote Span 65
5.2.2 Remote Zero 67
5.3 Set the Alarms Remotely 68
5.4 Set the Ranges Remotely 69
5.5 System Menu 70
5.6 The Self-Test function 71
Maintenance ................................................................................. 73
6.1 Routine Maintenance 73
6.2 Cell Replacement 73
6.2.1 Storing and Handling Replacement Cells 73
6.2.2 When to Replace a Cell 74
6.2.3 Removing the Micro-Fuel Cell 75
6.2.4 Installing a New Micro-Fuel Cell 75
6.2.5 Cell Warranty 77
6.3 Fuse Replacement 78
6.4 System Self Diagnostic Test 79
Teledyne Analytical Instruments xi
3000TA-XL-EU
6.5 Major Internal Components 80
6.6 Cleaning 81
6.7 Troubleshooting 81
Appendix ...................................................................................... 83
A-1 Specifications 83
A-2 Recommended 2-Year Spare Parts List 85
A-3 Drawing List 86
A-4 19-inch Relay Rack Panel Mount 86
A.5 Application notes 87
Material Safety Data Sheet 89
Teledyne Analytical Instruments xii
Trace Oxygen Analyzer
List of Figures
Figure 1-1: Model 3000TA-XL-EU Front Panel 3
Figure 1-2: Model 3000TA-XL Rear Panel 6
Figure 2-1: Micro-Fuel Cell 8
Figure 2-2: Cross Section of a Micro-fuel Cell (not to scale) 9
Figure 2-3: Characteristic Input/Output Curve for a Micro-Fuel
Cell 11
Figure 2-4: Piping Layout 13
Figure 2-5A: Flow Diagram—Sample Under Pressure-Standard 14
Figure 2-5B: Flow Diagram—Low Pressure-Model 3000TA-XL-VS14
Figure 2-5C: Flow Diagram—Sample Under Pressure-Model
3000TA-XL-CV 14
Figure 2-6: Power supply and PCB Location 15
Figure 2-7: Block Diagram of the Model 3000TA-XL-EU
Electronics 16
Figure 3-1: Front Panel of the Model 3000TA-XL-EU 20
Figure 3-2: Required Front Door Clearance 20
Figure 3-3: Rear Panel of the Model 3000TA-XL-EU 21
Figure 3-4: Equipment Interface Connector Pin Arrangement 23
Figure 3-5: Remote Probe Connections 29
Figure 3-6: FET Series Resistance 29
Figure 3-7: Installing the B-2CXL MFC (other cells similar) 32
Figure 3-8: Installing the Insta-Trace Micro-fuel Cell 34
Figure 4-1: Hierarchy of Available Functions 39
Figure 5-1: Analyzer Status Window—Running 64
Figure 5-2: Span Calibration Window 66
Figure 5-3: Zero Calibration Window 67
Figure 5-4: Set Alarms Window 68
Teledyne Analytical Instruments xiii
3000TA-XL-EU
Figure 5-5: Set Range Window 69
Figure 5-6: System Window 70
Figure 5-7: Self-Test Window 71
Figure 6-1: Removing the Micro-Fuel 76
Figure 6-2: Installing the Insta-Trace Cell 77
Figure 6-3: Removing Fuse Block from Housing 78
Figure 6-4: Installing Fuses 79
Figure 6-5: Rear Panel Removal 80
Figure A-1: Single and Dual 19" Rack Mounts 86
Teledyne Analytical Instruments xiv
Trace Oxygen Analyzer
List of Tables
Table 3-1: Analog Output Connections 24
Table 3-2: Alarm Relay Contact Pins 25
Table 3-3: Remote Calibration Connections 26
Table 3-4: Range ID Relay Connections 28
Table 3-5: Commands via RS-232 Input 30
Table 3-6: Required RS-232 Options 30
Table 4-1: Output Signals 60
Table 4-2: Range ID Output Voltage 61
Table 6-1: Self Test Failure Codes 79
Teledyne Analytical Instruments xv
Trace Oxygen Analyzer Introduction
Introduction
1.1 Overview
The Teledyne Analytical Instruments Model 3000TA-XL-EU Trace
Oxygen Analyzer is a versatile microprocessor-based instrument for
detecting oxygen at the parts-per-million (ppm) level in a variety of
gases. This manual covers the Model 3000TA-XL-EU General Purpose
flush-panel and/or rack-mount units only. These units are for indoor use
in a nonhazardous environment.
1.2 Typical Applications
A few typical applications of the Model 3000TA-XL-EU are:
Monitoring inert gas blanketing
Air separation and liquefaction
Chemical reaction monitoring
Semiconductor manufacturing
Petrochemical process control
Quality assurance
Gas analysis certification.
1.3 Main Features of the Analyzer
The Model 3000TA-XL-EU Trace Oxygen Analyzer is
sophisticated yet simple to use. The main features of the analyzer
include:
A 2-line alphanumeric vacuum fluorescent display (VFD)
screen, driven by microprocessor electronics, that
continuously prompts and informs the operator.
High resolution, accurate readings of oxygen content from
low ppm levels through 25%. Large, bright, meter readout.
Stainless steel cell block.
Teledyne Analytical Instruments 1
Introduction 3000TA-XL-EU
Advanced Micro-Fuel Cell, designed for trace analysis, has a
0-1 ppm low range with less than a 0.2 ppm offset and six
months warranty and an expected lifetime of one year.
Versatile analysis over a wide range of applications.
Microprocessor based electronics: 8-bit CMOS
microprocessor with 32 kB RAM and 128 kB ROM.
Three user definable output ranges (from 0-1 ppm through 0-
250,000 ppm) allow best match to users process and
equipment.
Air-calibration range for spanning at 20.9 % (209,000 ppm)
available.
Auto Ranging allows analyzer to automatically select the
proper preset range for a given measurement. Manual
override allows the user to lock onto a specific range of
interest.
Two adjustable concentration alarms and a system failure
alarm.
Extensive self-diagnostic testing, at startup and on demand,
with continuous power-supply monitoring.
Two way RFI protection.
RS-232 serial digital port for use with a computer or other
digital communication device.
Four analog outputs: two for measurement (0–1 V dc and
Isolated 4–20 mA dc) and two for range identification.
Convenient and versatile, steel, flush-panel or rack-
mountable case with slide-out electronics drawer.
1.4 Model Designations
3000TA-XL:
3000TA-XL-VS:
3000TA-XL-CV:
3000TA-XL-I:
Standard model for sample under pressure
Instrument configured for Vacuum Service
Instrument with calibration valves
Web enabled version
Teledyne Analytical Instruments 2
Trace Oxygen Analyzer Introduction
1.5 Front Panel (Operator Interface)
The standard 3000TA-XL-EU is housed in a rugged metal case
with all controls and displays accessible from the front panel. See Figure
1-1. The front panel has thirteen buttons for operating the analyzer, a
digital meter, an alphanumeric display, and a window for viewing the
sample flowmeter.
Figure 1-1: Model 3000TA-XL-EU Front Panel
Function Keys: Six touch-sensitive membrane switches are used to
change the specific function performed by the analyzer:
Analyze Perform analysis for oxygen content of a sample
gas.
System Perform system-related tasks (described in detail
in Chapter 4, Operation.).
Span Span calibrate the analyzer.
Zero Zero calibrate the analyzer.
Alarms Set the alarm setpoints and attributes.
Range Set up the 3 user definable ranges for the
instrument.
Teledyne Analytical Instruments 3
Introduction 3000TA-XL-EU
Data Entry Keys: Six touch-sensitive membrane switches are used to
input data to the instrument via the alphanumeric VFD display:
Left & Right Arrows Select between functions currently
displayed on the VFD screen.
Up & Down Arrows Increment or decrement values of
functions currently displayed.
Enter Advances VFD display to the next screen in a series
or returns to the Analyze screen if none remain.
Escape Backs VFD display to the previous screen in a series
or returns to the Analyze screen if none remain.
Digital Meter Display: The meter display is a Light Emitting Diode
(LED) device that produces large, bright, 7-segment numbers that are
legible in any lighting. It produces a continuous readout from 0-10,000
ppm and then switches to a continuous percent readout from 1-25%. It is
accurate across all analysis ranges without the discontinuity inherent in
analog range switching.
Alphanumeric Interface Screen: The VFD screen is an easy-to-use
interface from operator to analyzer. It displays values, options, and
messages that give the operator immediate feedback.
Needle Valve: Needle valve used to adjust flow of gas sample.
Flowmeter: Monitors the flow of gas past the sensor. Readout is 0.2 to
2.4 standard liters per minute (SLPM) of nitrogen.
Standby Button: The Standby button
turns off the display and
outputs, but circuitry is still operating.
CAUTION:
THE POWER CABLE MUST BE UNPLUGGED TO
FULLY DISCONNECT POWER FROM THE
INSTRUMENT. WHEN THE CHASSIS IS EXPOSED
OR WHEN THE ACCESS DOOR IS OPEN WHILE THE
POWER CABLE IS CONNECTED, USE EXTRA CARE
TO AVOID CONTACT WITH LIVE ELECTRICAL
CIRCUITS.
Access Door: For access to the Micro-Fuel Cell, the front panel
swings open when the latch in the upper right corner of the panel is
pressed all the way in with a narrow gauge tool. Accessing the main
circuit board
Teledyne Analytical Instruments 4
Trace Oxygen Analyzer Introduction
requires unfastening rear panel screws and sliding the unit out of the
case.
1.6 Rear Panel (Equipment Interface)
The rear panel, shown in Figure 1-2, contains the gas and electrical
connectors for external inlets and outlets. Some of those depicted are
optional and may not appear on your instrument. The connectors are
described briefly here and in detail in Chapter 3 Installation.
Power Connection Universal AC power source.
Gas Inlet and Outlet One inlet and one exhaust out.
Analog Outputs 0–1 VDC oxygen concentration plus 0-
1 VDC range ID, and isolated 4–20 mA
DC oxygen concentration plus 4-20
mA DC range ID.
Alarm Connections 2 concentration alarms and 1 system
alarm.
RS-232 Port Serial digital concentration signal
output and control input.
Remote Probe Used in the 3000TA-XL-EU for
controlling external solenoid valves
only.
Remote Span/Zero Digital inputs allow external control of
analyzer calibration.
Calibration Contact To notify external equipment that
instrument is being calibrated and
readings are not monitoring sample.
Range ID Contacts Four separate, dedicated, range relay
contacts. Low, Medium, High, Cal.
Network I/O Serial digital communications for local
network access. For future expansion.
Not implemented at this printing.
Teledyne Analytical Instruments 5
Introduction 3000TA-XL-EU
Note: If you require highly accurate Auto-Cal timing, use external
Auto-Cal control where possible. The internal clock in the
Model 3000TA-XL is accurate to 2-3 %. Accordingly,
internally scheduled calibrations can vary 2-3 % per day.
Figure 1-2: Model 3000TA-XL Rear Panel
Teledyne Analytical Instruments 6
Trace Oxygen Analyzer Operational Theory
Operational Theory
2.1 Introduction
The analyzer is composed of three subsystems:
1. Micro-fuel Cell Sensor
2. Sample System
3. Electronic Signal Processing, Display and Control
The sample system is designed to accept the sample gas and
transport it through the analyzer without contaminating or altering the
sample prior to analysis. The Micro-Fuel Cell is an electrochemical
galvanic device that translates the amount of oxygen present in the
sample into an electrical current. The electronic signal processing,
display and control subsystem simplifies operation of the analyzer and
accurately processes the sampled data. The microprocessor controls all
signal processing, input/output and display functions for the analyzer.
2.2 Micro-Fuel Sensor
2.2.1 Principles of Operation
The oxygen sensor used in the Model 3000TA-XL series is a
Micro-Fuel Cell, Model B-2CXL designed and manufactured by
Analytical Instruments. It is a sealed plastic disposable electrochemical
transducer.
The active components of the Micro-Fuel Cell are a cathode, an
anode, and the aqueous KOH electrolyte in which they are immersed.
The cell converts the energy from a chemical reaction into an electrical
current in an external electrical circuit. Its action is similar to that of a
battery.
There is, however, an important difference in the operation of a
battery as compared to the Micro-Fuel Cell: In the battery, all reactants
are stored within the cell, whereas in the Micro-Fuel Cell, one of the
reactants (oxygen) comes from outside the device as a constituent of the
sample gas being analyzed. The Micro-Fuel Cell is therefore a hybrid
Teledyne Analytical Instruments 7
Operational Theory 3000TA-XL-EU
between a battery and a true fuel cell. (All of the reactants are stored
externally in a true fuel cell.)
2.2.2 Anatomy of a Micro-Fuel Cell
The Micro-Fuel Cell is a cylinder only 1¼ inches in diameter and
1¼ inches thick. It is made of an extremely inert plastic, which can be
placed confidently in practically any environment or sample stream. It is
effectively sealed, although one end is permeable to oxygen in the
sample gas. The other end of the cell is a contact plate consisting of two
concentric foil rings. The rings mate with spring-loaded contacts in the
sensor block assembly and provide the electrical connection to the rest
of the analyzer. Figure 2-1 illustrates the external features.
Figure 2-1: Micro-Fuel Cell
Refer to Figure 2-2, Cross Section of a Micro-Fuel Cell, which
illustrates the following internal description.
At the top end of the cell is a diffusion membrane of Teflon,
whose thickness is very accurately controlled. Beneath the diffusion
membrane lies the oxygen sensing element—the cathode—with a
surface area approximately 4 cm2. The cathode has many perforations to
ensure sufficient wetting of the upper surface with electrolyte, and it is
plated with an inert metal.
Teledyne Analytical Instruments 8
Trace Oxygen Analyzer Operational Theory
Figure 2-2: Cross Section of a Micro-fuel Cell (not to scale)
The anode structure is below the cathode. It is made of lead and has
a proprietary design which is meant to maximize the amount of metal
available for chemical reaction.
At the rear of the cell, just below the anode structure, is a flexible
membrane designed to accommodate the internal volume changes that
occur throughout the life of the cell. This flexibility assures that the
sensing membrane remains in its proper position, keeping the electrical
output constant.
The entire space between the diffusion membrane, above the
cathode, and the flexible rear membrane, beneath the anode, is filled
with electrolyte. Cathode and anode are submerged in this common
pool. They each have a conductor connecting them to one of the external
contact rings on the contact plate, which is on the bottom of the cell.
2.2.3 Electrochemical Reactions
The sample gas diffuses through the Teflon membrane. Any
oxygen in the sample gas is reduced on the surface of the cathode by the
following HALF REACTION:
O
+ 2H2O + 4e–→ 4OH– (cathode)
2
(Four electrons combine with one oxygen molecule—in the
presence of water from the electrolyte—to produce four hydroxyl ions.)
Teledyne Analytical Instruments 9
Operational Theory 3000TA-XL-EU
When the oxygen is reduced at the cathode, lead is simultaneously
oxidized at the anode by the following HALF REACTION:
Pb + 2OH
–
→ Pb+2 + H2O + 2e– (anode)
(Two electrons are transferred for each atom of lead that is
oxidized. Therefore it takes two of the above anode reactions to balance
one cathode reaction and transfer four electrons.)
The electrons released at the surface of the anode flow to the
cathode surface when an external electrical path is provided. The current
is proportional to the amount of oxygen reaching the cathode. It is
measured and used to determine the oxygen concentration in the gas
mixture.
The overall reaction for the fuel cell is the SUM of the half
reactions above, or:
2Pb + O2 → 2PbO
(These reactions are specific to oxygen as long as no gaseous
components capable of oxidizing lead—such as iodine, bromine,
chlorine and fluorine—are present in the sample.)
In the absence of oxygen, no current is generated.
2.2.4 The Effect of Pressure
In order to state the amount of oxygen present in the sample in
parts-per-million or a percentage of the gas mixture, it is necessary that
the sample diffuse into the cell under constant pressure.
If the total pressure increases, the rate that oxygen reaches the
cathode through the diffusing membrane will also increase. The electron
transfer, and therefore the external current, will increase, even though
the oxygen concentration of the sample has not changed. It is therefore
important that the sample pressure at the fuel cell (usually vent pressure)
remain relatively constant between calibrations.
2.2.5 Calibration Characteristics
Given that the total pressure of the sample gas on the surface of the
Micro-fuel Cell input is constant, a convenient characteristic of the cell
is that the current produced in an external circuit is directly proportional
to the rate at which oxygen molecules reach the cathode, and this rate is
Teledyne Analytical Instruments 10
Trace Oxygen Analyzer Operational Theory
directly proportional to the concentration of oxygen in the gaseous
mixture. In other words it has a linear characteristic curve, as shown in
Figure 2-3. Measuring circuits do not have to compensate for
nonlinearities.
In addition, since there is zero output in the absence of oxygen, the
characteristic curve has close to an absolute zero (less than ± 0.2 ppm
oxygen). This means there is usually no need to zero calibrate the
instrument. Depending upon the application, zeroing may still be used
to compensate for the combined zero offsets of the cell and the
electronics.
Figure 2-3: Characteristic Input/Output Curve for a Micro-Fuel Cell
Teledyne Analytical Instruments 11
Operational Theory 3000TA-XL-EU
If, however, a low range accuracy better than 100 ppb is required,
then a zero calibration is recommended. See Section 4.4.1.
2.3 Sample System
The sample system delivers gases to the Micro-fuel Cell sensor
from the analyzer rear panel inlet. Depending on the mode of operation
either sample or calibration gas is delivered.
The Model 3000TA-XL-EU sample system is designed and
fabricated to ensure that the oxygen concentration of the gas is not
altered as it travels through the sample system.
The sample system for the standard instrument incorporates VCR
tube fittings for sample inlet and 1/4” outlet tube connections at the rear
panel. The sample or calibration gas that flows through the system is
monitored by a flowmeter downstream from the cell. Figure 2-4 shows
the piping layout for the standard model.
Figure 2-5 shows the flow diagram for sampling systems used for
the three configurations offered as options for this instrument. In the
standard instrument, calibration gases can be connected directly to the
Sample In port by teeing to the port with appropriate valves.
Teledyne Analytical Instruments 12
Trace Oxygen Analyzer Operational Theory
Figure 2-4: Piping Layout
Teledyne Analytical Instruments 13
Operational Theory 3000TA-XL-EU
Figure 2-5A: Flow Diagram—Sample Under Pressure-Standard
Figure 2-5B: Flow Diagram—Low Pressure-Model 3000TA-XL-VS
Figure 2-5C: Flow Diagram—Sample Under Pressure-Model 3000TA-
XL-CV
Teledyne Analytical Instruments 14
Loading...