Teledyne 3000TA User Manual

OPERATING INSTRUCTIONS FOR

MODEL 3000TA

Trace Oxygen Analyzer

P/N M66316

3/09/11

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

3000TA- EU

Copyright © 2011 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 91749-1580.

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

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-C: In addition to all standard features, this model

also has separate ports for zero and span gases,
and built-in control valves. The internal valves
are entirely under the control of the 3000TA
electronics to automatically switch between
gases in synchronization with the analyzer’s
operations

 19" Rack Mnt: The 19" Relay Rack Mount units are available

with either one or two 3000 series analyzers
installed in a standard 19" panel and ready to
mount in a standard instrument rack.

Sensor Options Available for the Instrument with the Above Serial
Number:

 Insta-Trace B2C (Default)
 A2C
 L2C
 L2CL
 Insta-Trace A2C

Teledyne Analytical Instruments iii

3000TA- EU

Important Notice

Model 3000TA-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 iv

Trace Oxygen Analyzer

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 v

3000TA- EU

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 vi

Trace Oxygen Analyzer

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 vii

3000TA- EU

Table of Contents

Safety Messages ........................................................................... v

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 Recognizing Difference Between LCD & VFD 4

1.7 Rear Panel (Equipment Interface) 5

Operational Theory ....................................................................... 7 

2.1 Introduction 7

2.2 Micro-Fuel Cell 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 11

2.4 Electronics and Signal Processing 13

Installation ................................................................................... 17

3.1 Unpacking the Analyzer 17

3.2 Mounting the Analyzer 17

3.3 Rear Panel Connections 19

3.3.1 Gas Connections 19

3.3.2 Electrical Connections 21

3.3.2.1 Primary Input Power 21

3.3.2.2 50-Pin Equipment Interface Connector 22

3.3.2.3 RS-232 Port 27

Teledyne Analytical Instruments viii

Trace Oxygen Analyzer

3.4 Installing the Micro-Fuel Cell 29

3.5 Testing the System 29

Operation ..................................................................................... 31

4.1 Introduction 31

4.2 Using the Data Entry and Function Buttons 31

4.3 The System Function 33

4.3.1 Tracking Oxygen Readings During Calibration and
Alarm Delay 34

4.3.2 Setting up an Auto-Cal 36

4.3.3 Password Protection 37

4.3.3.1 Entering the Password 37

4.3.3.2 Installing or Changing the Password 38

4.3.4 Logout 40

4.3.5 System Self-Diagnostic Test 41

4.3.6 Version Screen 42

4.3.7 Showing Negative Oxygen Readings 42

4.4 The Zero and Span Functions 43

4.4.1 Zero Cal 44

4.4.1.1Auto Mode Zeroing 44

4.4.1.2 Manual Mode Zeroing 45

4.4.1.3Cell Failure 45

4.4.2 Span Cal 46

4.4.2.1 Auto Mode Spanning 46

4.4.2.2 Manual Mode Spanning 47

4.4.3 Span Failure 49

4.5 The Alarms Function 49

4.6 The Range Function 51

4.6.1 Setting the Analog Output Ranges 52

4.6.2 Fixed Range Analysis 53

4.7 The Analyze Function 54

4.8 Signal Output 54

Maintenance ................................................................................. 57

5.1 Routine Maintenance 57

5.2.1 Storing and Handling Replacement Cells 57

Teledyne Analytical Instruments ix

3000TA- EU

5.2.2 When to Replace a Cell 58

5.2.3 Removing the Micro-Fuel Cell 58

5.2.4 Installing a New Micro-Fuel Cell 59

5.2.5 Cell Warranty 61

5.3 Fuse Replacement 61

5.4 System Self Diagnostic Test 62

5.5 Major Internal Components 63

5.6 Cleaning 64

5.7 Troubleshooting 64

Appendix ...................................................................................... 67

A-1 Model 3000TA Specifications 67
A-2 Recommended 2-Year Spare Parts List 68
A-3 Drawing List 70
A-4 19-inch Relay Rack Panel Mount 70
A.5 Application notes 71
A-5 Material Safety Data Sheet 75

Teledyne Analytical Instruments x

Trace Oxygen Analyzer

List of Figures

Figure 1-1: Model 3000TA Front Panel ........................................... 3

Figure 1-2: Model 3000 TA Rear Panel ........................................... 5

Figure 2-1: Micro-Fuel Cell .............................................................. 8

Figure 2-2. Cross Section of a Micro-Fuel Cell (not to scale) .......... 8

Figure 2-3. Characteristic Input/Output Curve for a Micro-Fuel

Cell ............................................................................. 11

Figure 2-4: Piping Layout and Flow Diagram for Standard Model . 12

Figure 2-5: Flow Diagram .............................................................. 13

Figure 2-6: 3000TA Internal Electronic Component Location ........ 14

Figure 2-7: Block Diagram of the Model 3000TA-EU Electronics . 15

Figure 3-1: Front Panel of the Model 3000TA ............................... 18

Figure 3-2: Required Front Door Clearance .................................. 18

Figure 3-3: Rear Panel of the Model 3000TA ................................ 19

Figure 3-4: Equipment Interface Connector Pin Arrangement ....... 22

Figure 3-5: Remote Probe Connections ........................................ 27



Figure 3-6: FET Series Resistance ............................................... 27

Figure 5-1: Removing the Micro-Fuel ............................................ 59

Figure 5-2: Removing Fuse Block from Housing ........................... 61

Figure 5-3: Installing Fuses ........................................................... 62

Figure 5-4: Rear-Panel Screws ..................................................... 64

Figure A-1: Single and Dual 19" Rack Mounts .............................. 70

Teledyne Analytical Instruments xi

3000TA- EU

List of Tables

Table 3-1: Analog Output Connections Pin Function .................... 23

Table 3-2: Alarm Relay Contact Pins ............................................ 24

Table 3-3: Remote Calibration Connections .................................. 25

Table 3-4: Range ID Relay Connections ....................................... 26

Table 3-5: Commands via RS-232 Input ....................................... 28

Table 5-1: Self Test Failure Codes ................................................ 62



Teledyne Analytical Instruments xii

Trace Oxygen Analyzer Introduction

Introduction

1.1 Overview

The Teledyne Analytical Instruments Model 3000TA 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 General Purpose flush­panel 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 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 Trace Oxygen Analyzer is sophisticated yet
simple to use. The main features of the analyzer include:

 A 2-line alphanumeric display 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.

 Nylon cell block. (Stainless steel optional)

Teledyne Analytical Instruments 1

Introduction 3000TA- EU

 Advanced Micro-Fuel Cell, designed for trace analysis,

has a one year warranty and an expected lifetime of two
years.

 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 0-10 ppm

through 0- 250,000 ppm) allow best match to users
process and equipment.

 Air-calibration range for convenient spanning at 20.9 %.

 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.

 CE Compliance.

 RS-232 serial digital port for use with a computer or

other digital communication device.

 Four analog outputs: two for measurement (0–1 VDC 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: Standard model.

3000TA-C: In addition to all standard features, this model

also has separate ports for zero and span gases,
and built-in control valves. The internal valves are
entirely under the control of the 3000TA
electronics, to automatically switch between gases
in synchronization with the analyzer’s operations.

Teledyne Analytical Instruments 2

Trace Oxygen Analyzer Introduction

1.5 Front Panel (Operator Interface)

The standard 3000TA 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 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.

Data Entry Keys: Six touch-sensitive membrane switches are used to
input data to the instrument via the alphanumeric VFD display:

Teledyne Analytical Instruments 3

Introduction 3000TA- EU

 Left & Right Arrows Select between functions currently

displayed on the VFD screen.

 Up & Down Arrows Increment or decrement values of

functions currently displayed.

 Enter Moves VFD display on to the next screen in a series.

If none remains, returns to the Analyze screen.

 Escape Moves VFD display back to the previous screen in a

series. If none remains, returns to the Analyze screen.

Digital Meter Display: The meter display is a 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.

Flowmeter: Monitors the flow of gas past the sensor. Readout is 0.2 to

2.4 standard liters per minute (SLPM).

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 CHASSIS IS EXPOSED OR
WHEN ACCESS DOOR IS OPEN AND 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
requires unfastening rear panel screws and sliding the unit out of the
case.

1.6 Recognizing Difference Between LCD & VFD

LCD has GREEN background with BLACK characters. VFD has
DARK background with GREEN characters. In the case of VFD - NO
CONTRAST ADJUSTMENT IS NEEDED.

Teledyne Analytical Instruments 4

Trace Oxygen Analyzer Introduction

1.7 Rear Panel (Equipment Interface)

The rear panel, shown in Figure 1-2, contains the gas and electrical
connectors for external inlets and outlets. Those that are optional are
shown shaded in the figure. The connectors are described briefly here

and in detail in the Installation chapter of this manual.

Figure 1-2: Model 3000 TA Rear Panel

 Power Connection Universal AC power source.

 Gas Inlet and Outlet One inlet (must be externally valved)

and one exhaust out. Three inlet when “C” option ordered.

 RS-232 Port Serial digital concentration signal output and

control input.

 Remote Valves Used in the 3000TA for controlling external

solenoid valves only.

 50-Pin Equipment Interface Port:

 Analog Outputs 0–1 VDC concentration plus 0-1 VDC

range ID, and isolated 4–20 mA DC plus 4-20 mA DC
range ID.

 Alarm Connections 2 concentration alarms and 1 system

alarm.

Teledyne Analytical Instruments 5

Introduction 3000TA- EU

 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.

 Optional:

 Calibration Gas Ports (Auto Cal Option) Separate

fittings for zero, span and sample gas input, and internal
valves for automatically switching the gases.

Note: If you require highly ac curate Auto-Cal timing, use external

Auto-Cal control where possible. The internal clock in the
Model 3000TA is accurate to 2-3 %. Accordingly, internally
scheduled calibrations can vary 2-3 % per day.

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 Cell Sensor

2.2.1 Principles of Operation

The oxygen sensor used in the Model 3000T series is a Micro-Fuel
Cell 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 15% 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
between a battery and a true fuel cell. (All of the reactants are stored
externally in a true fuel cell.)

Teledyne Analytical Instruments 7

Operational Theory 3000TA- EU

2.2.2 Anatomy of a Micro-Fuel Cell

The Micro-Fuel Cell is a cylinder only 11/4 inches in diameter and
11/4 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.

Figure 2-2. Cross Section of a Micro-Fuel Cell (not to scale)

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 almost 4 cm2. The cathode has many perforations to ensure

Teledyne Analytical Instruments 8

Trace Oxygen Analyzer Operational Theory

sufficient wetting of the upper surface with electrolyte, and it is plated
with an inert metal.

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.)

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

Teledyne Analytical Instruments 9

Operational Theory 3000TA- EU

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 + O

→2PbO

2

(These reactions will hold as long as no gaseous components
capable of oxidizing lead—such as iodine, bromine, chlorine and
fluorine—are present in the sample.)

The output of the fuel cell is limited by (1) the amount of oxygen in
the cell at the time and (2) the amount of stored anode material.

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
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 oxygen, the
characteristic curve has close to an absolute zero (within ± 1 ppm
oxygen). In practical application, zeroing may still used to compensate
for the combined zero offsets of the cell and the electronics. (The

Teledyne Analytical Instruments 10

Trace Oxygen Analyzer Operational Theory

electronics is zeroed automatically when the instrument power is turned
on.)

Figure 2-3. Characteristic Input/Output Curve for a Micro-Fuel

Cell

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 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 encounters almost no dead
space. This minimizes residual gas pockets that can interfere with trace
analysis.

The sample system for the standard instrument incorporates 1/4
inch tube fittings for sample inlet and outlet connections at the rear
panel. For metric system installations, 6 mm adapters are supplied with
each instrument to be used if needed. The sample or calibration gas
flows through the system is monitored by a flowmeter downstream from

Teledyne Analytical Instruments 11

Operational Theory 3000TA- EU

the cell. Figure 2-4 shows the piping layout and flow diagram for the
standard model.

Figure 2-4: Piping Layout and Flow Diagram for Standard Model

Figure 2-5 is the flow diagram for the sampling system. In the stan­dard instrument, calibration gases (zero and span) can be connected di­rectly to the Sample In port by teeing to the port with appropriate valves.
The shaded portion of the diagram shows the components added when
the –C option is ordered. The valving is installed inside the 3000TA-C
enclosure and is regulated by the instruments internal electronics.

Teledyne Analytical Instruments 12

Trace Oxygen Analyzer Operational Theory

Figure 2-5: Flow Diagram

2.4 Electronics and Signal Processing

The Model 3000TA Trace Oxygen Analyzer uses an 8031
microcontroller with 32 kB of RAM and 128 kB of ROM to control all
signal processing, input/output, and display functions for the analyzer.
System power is supplied from a universal power supply module
designed to be compatible with any international power source. Figure
2-6 shows the location of the power supply and the main electronic PC
boards.

The signal processing electronics including the microprocessor,
analog to digital, and digital to analog converters are located on the
motherboard at the bottom of the case. The preamplifier board is
mounted on top of the motherboard as shown in the figure. These boards
are accessible after removing the back panel. Figure 2-7 is a block
diagram of the Analyzer electronics.

Teledyne Analytical Instruments 13

Operational Theory 3000TA- EU

Figure 2-6: 3000TA Internal Electronic Component Location

In the presence of oxygen the cell generates a current. A current to
voltage amplifier converts this current to a voltage, which is amplified in
the second stage amplifier.

The second stage amplifier also supplies temperature compensation
for the oxygen sensor output. This amplifier circuit incorporates a ther­mistor, which is physically located in the cell block. The thermistor is a
temperature dependent resistance that changes the gain of the amplifier
in proportion to the temperature changes in the block. This change is in­versely proportional to the change in the cell output due to the same
temperature changes. The result is a signal that is temperature
independent. The output from the second stage amplifier is sent to an 18
bit analog to digital converter controlled by the microprocessor.

Teledyne Analytical Instruments 14

Trace Oxygen Analyzer Operational Theory

Figure 2-7: Block Diagram of the Model 3000TA-EU Electronics

Teledyne Analytical Instruments 15