Teledyne 3000PB User Manual
Percent Oxygen Analyzer
OPERATING INSTRUCTIONS FOR
Model 3000PB
Percent Oxygen Analyzer
DANGER
HIGHLY TOXIC AND OR FLAMMABLE LIQUIDS OR GASES MAY BE PRESENT IN THIS MONITORING
SYSTEM.
PERSONAL PROTECTIVE EQUIPMENT MAY BE REQUIRED WHEN SERVICING THIS SYSTEM.
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
P/N M66682
03/29/2006
ECO # 06-0059
i
Model 3000PB
Copyright © 1999 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
acknowledgments 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.
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Teledyne Analytical Instruments
Percent Oxygen Analyzer
Table of Contents
1 Introduction
1.1 Overview........................................................................ 1-1
1.2 Typical Applications ....................................................... 1-1
1.3 Main Features of the Analyzer....................................... 1-1
1.4 Model Designations ....................................................... 1-2
1.5 Operator Interface.......................................................... 1-3
1.5.1 Displays ................................................................. 1-6
1.5.2 Function Keys ........................................................ 1-6
1.5.3 Data Entry Keys..................................................... 1-6
1.5.4 I/O Power Button.................................................... 1-7
1.5.5 Access Door .......................................................... 1-7
1.6 Recognizing Difference Between LCD & VFD ............... 1-7
1.7 Equipment Interface....................................................... 1-7
1.7.1 Electrical Connector Panel..................................... 1-7
1.7.2 Gas Connector Panel............................................. 1-9
2 Operational Theory
2.1 Introduction .................................................................... 2-1
2.2 Micro-Fuel Cell Sensor .................................................. 2-1
2.2.1 Principles of Operation............................................ 2-1
2.2.2 Anatomy of a Micro-Fuel Cell.................................. 2-2
2.2.3 Electrochemical Reactions...................................... 2-3
2.2.4 The Effect of Pressure............................................. 2-4
2.2.5 Calibration Characteristics ...................................... 2-4
2.2.6 Micro-Fuel Cell “Class”............................................ 2-5
2.3 Sample System.............................................................. 2-6
2.4 Electronics and Signal Processing ................................ 2-7
3 Installation
3.1 Unpacking the Analyzer................................................. 3-1
3.2 Mounting the Analyzer ................................................... 3-1
3.3 Electrical Connections ................................................... 3-3
3.3.1 Primar y Input Power .............................................. 3-4
3.3.2 Fuse Installation..................................................... 3-4
3.3.3 Analog Outputs...................................................... 3-4
3.3.4 Alarm Relays ......................................................... 3-6
3.3.5 Digital Remote Cal Inputs ...................................... 3-7
3.3.6 Range ID Relays.................................................... 3-9
3.3.7 Network I/O............................................................ 3-9
3.3.8 RS-232 PorT.......................................................... 3-9
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Model 3000PB
3.3.9 Remote Sensor and Solenoid Valves..................... 3-10
3.4 Installing the Micro-Fuel Cell.......................................... 3-12
3.5 Gas Connections ........................................................... 3-12
3.6 Testing the System ........................................................ 3-14
4 Operation
4.1 Introduction .................................................................... 4-1
4.2 Using the Data Entry and Function Buttons................... 4-2
4.3 The System Function..................................................... 4-3
4.3.1 Setting the Display................................................. 4-4
4.3.2 Setting up an Auto-Cal........................................... 4-5
4.3.3 Password Protection .............................................. 4-5
4.3.4 Logout.................................................................... 4-8
4.3.5 System Self-Diagnostic Test .................................. 4-9
4.3.6 Version Screen ...................................................... 4-9
4.4 The Span Functions....................................................... 4-10
4.4.1 Cell Failure............................................................. 4-10
4.4.2 Span Cal ................................................................ 4-11
4.5 The Alarms Function...................................................... 4-12
4.6 The Range Function ...................................................... 4-15
4.6.1 Setting the Analog Output Ranges ........................ 4-15
4.6.2 Autoranging Analysis ............................................. 4-16
4.6.3 Fixed Range Analysis ............................................ 4-16
4.7 The Analyze Function .................................................... 4-17
4.8 Signal Output ................................................................. 4-17
4.3.3.1 Entering the Password................................... 4-6
4.3.3.2 Installing or Changing the Password ............. 4-7
4.4.2.1 Auto Mode Spanning ..................................... 4-11
4.4.2.2 Manual Mode Spanning................................. 4-12
Maintenance
5.1 Routine Maintenance..................................................... 5-1
5.2 Major Internal Components ........................................... 5-1
5.3 Cell Replacement .......................................................... 5-2
5.4 Fuse Replacement......................................................... 5-7
5.5 System Self Diagnostic Test........................................... 5-7
5.6 LCD Display................................................................... 5-8
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5.3.1 Storing and Handling Replacement Cells ............... 5-3
5.3.2 When to Replace a Cell ........................................... 5-3
5.3.3 Removing the Micro-Fuel Cell ................................. 5-4
5.3.4 Installing a New Micro-Fuel Cell.............................. 5-6
5.3.5 Cell Warranty........................................................... 5-6
Teledyne Analytical Instruments
Percent Oxygen Analyzer
5.7 Troubleshooting.............................................................. 5-9
Appendix
A-1 Specifications................................................................. A-1
A-2 Recommended 2-Year Spare Parts List......................... A-3
A-3 Drawing List ................................................................... A-4
A-5 Applicatiopn Notes on Restrictors, Pressures & Flow.... A-5
A-6 The Zero Functions........................................................ A-8
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Model 3000PB
DANGER
COMBUSTIBLE GAS USAGE WARNING
This is a general purpose instrument designed for usage 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 operating of
this equipment is 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.
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Teledyne Analytical Instruments
Percent Oxygen Analyzer Introduction 1
Introduction
1.1 Overview
The Teledyne Analytical Instruments Model 3000PB Percent Oxygen
Analyzer is a versatile microprocessor-based instrument for detecting oxygen
in a variety of gases. This manual covers the Model 3000PB, percent oxygen, general purpose, bulkhead-mount units only.
1.2 Typical Applications
A few typical applications of the Model 3000PB 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 3000PB Percent 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 %
levels through 100%. Large, bright, meter readout.
• Advanced Micro-Fuel Cell for percent analysis. Standard cell has
a six month warranty and an expected lifetime of eight months.
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1 Introduction Model 3000PB
• 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 % through
0-100 %) 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.
• RS-232 serial digital port for use with a computer or other digital
communication device.
• Analog outputs for concentration and range identification.
(0-1 V dc standard, and isolated 4–20 mA dc optional.)
1.4 Model Designations
3000PB: Standard model.
3000PB-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 3000PB electronics, to automatically switch between
gases in synchronization with the analyzer’s operations
3000PB-S: Stainless steel cell block and sampling system.
3000PB-M: 4-20 mA dc Signal and Range ID outputs, in addition
to the standard voltage outputs.
All of the above options are available in combination. For example, the
-C and -V options are combined as Model 3000PB-C-V.
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Percent Oxygen Analyzer Introduction 1
1.5 Operator Interface
Figure 1-1 is an illustration of the front of the Model 3000PB Oxygen
Analyzer with the outer door open showing the control panel (which is also
the inner door).
All displays on the standard 3000PB are visible from outside the housing. The instrument has a digital meter and an alphanumeric display, which
are viewed through a glass viewing window in the outer door of the main
housing, and a sample flowmeter on the gas control panel attached to the
main housing. They give the operator constant feedback from the instrument.
The operator controls are pushbutton membrane switches located
behind the outer door of the housing. All of them are reached by unlatching
and swinging open the outer door of the enclosure. They are described
briefly here and in greater detail in chapter 4, Operation.
Figure 1-2 shows the 3000PB with the outer door and inner door both
open. The inner door is opened for access to the electrical connections and to
the cell block which houses the Micro-Fuel Cell. Door-mounted components
are shown in chapter 5, Maintenance.
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1 Introduction Model 3000PB
(Pressing the latch button
will open the Inner Door)
Figure 1-1: Model 3000PB—Outer Door Open—Showing Control Panel
1-4
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Percent Oxygen Analyzer Introduction 1
Figure 1-2: Model 3000PB—Inner Door Open—Showing Internal Components
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1 Introduction Model 3000PB
1.5.1 Displays
Digital Meter Display: The meter display is a LED device that
produces large, bright, 7-segment numbers that are legible in any lighting
environment. It produces a continuous readout from 0-100 %. It is accurate
across all ranges without the discontinuity of 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).
1.5.2 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.
1.5.3 Data Entry Keys
Six touch-sensitive membrane switches are used to input data and
commands 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 Moves VFD display on to the next screen in a series. If
none remains, returns to the Analyze screen.
1-6
• Escape Moves VFD display back to the previous screen in a
series. If none remains, returns to the Analyze screen.
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Percent Oxygen Analyzer Introduction 1
1.5.4 I/O Power Button
The red I/O button switches the instrument power between I (ON) and
O (a Keep-Alive state). In the O state, the instrument’s circuitry is operating,
but there are no displays or outputs.
CAUTION: The power cable must be unplugged to fully
disconnect power from the instrument. When
chassis is exposed or when inner door is open and
power cable is connected, use extra care to avoid
contact with live electrical circuits.
1.5.5 Access Door
To access the electrical connector panel, or the cell block, the control
panel doubles as a door that can be unlatched and swung open (after unlatching and swinging open the outer access door). See Figure 1-2.
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.
1.7 Equipment Interface
1.7.1 Electrical Connector Panel
The electrical connector panel, shown in Figure 1-3, contains the
electrical connections for external inputs and outputs. The connectors are
described briefly here and in detail in the Installation chapter of this manual.
CAUTION: The power cable must be disconnected to fully
remove power from the instrument.
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1 Introduction Model 3000PB
3.0 AMAX
Figure 1-3: Electrical Connector Panel
Electrical Connections: The electrical connections on the electrical
connector panel are described briefly here, and in more detail in chapter 3
Installation.
• Power Connection 115 or 230 V ac, 50 or 60 Hz.
• Analog Outputs 0-1 V dc concentration plus 0-1 V dc
range ID, and isolated 4-20 mA dc plus
4-20 mA dc range ID.
• Alarm Connections 2 concentration alarms and 1 system
alarm.
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Percent Oxygen Analyzer Introduction 1
• RS-232 Port Serial digital concentration signal output
and control input.
• Remote Valves Used for controlling external solenoid
valves, if desired.
• Remote Sensor Used for external sensor and thermistor
• 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.
1.7.2 Gas Connector Panel
The gas connector panel, shown in Figure 1-4, contains the gas connections 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.
Note:
For Additional information,
please, see page 1-4
Figure 1-4: Model 3000PB Gas Connector Panel
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1 Introduction Model 3000PB
• Gas Inlet and Outlet One inlet (must be externally valved)
and one exhaust out.
Optional:
• Calibration Gas Ports Separate fittings for zero, span and
sample gas input, plus internal valves for
automatically switching the gases in
sync with the 3000PB electronics.
Note: If you require highly accurate Auto-Cal timing, use external
Auto-Cal control where possible. The internal clock in the
Model 3000PB is accurate to 2-3 %. Accordingly, internally
scheduled calibrations can vary 2-3 % per day.
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Percent Oxygen Analyzer Operational Theory 2
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 3000PB 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
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2 Operational Theory Model 3000PB
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.)
2.2.2 Anatomy of a Micro-Fuel Cell
The Micro-Fuel Cell is a cylinder only 1¼ inches in diameter and 1
inch thick. It is made of 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
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Percent Oxygen Analyzer Operational Theory 2
the oxygen sensing element—the cathode—with a surface area almost 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.
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:
O2 + 2H2O + 4e– → 4OH
–
(cathode)
(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 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
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2 Operational Theory Model 3000PB
(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 as 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 constant
between calibrations.
2.2.5 Calibration Characteristics
Given that the total pressure of the sample gas at 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. In the percent ranges, the cell
itself does not need to be zeroed. In practical application zeroing is still used
to compensate for zero offsets in the electronics. (The electronics is zeroed
automatically when the instrument power is turned on.)
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Percent Oxygen Analyzer Operational Theory 2
Figure 2-3. Characteristic Input/Output Curve for a Micro-Fuel Cell
2.2.6 Micro-Fuel Cell “Class”
TBE manufactures Micro-Fuel Cells with a variety of characteristics to
give the best possible performance for any given sample conditions. A few
typical Micro-Fuel Cells are listed below with their typical use and electrical
specifications.
2.2.6.1 Class A-3 Cell
The class A-3 cell is for use in applications where it is exposed continuously to carbon dioxide concentrations between 1 % and 100 % in the
sample gas.
Nominal output in air is 0.20 mA, and 90 % response time is 45 s.
Expected life in flue gas is 8 months.
2.2.6.2 Class A-5 Cell
The class A-5 cell is for use in applications where it is exposed intermittently to carbon dioxide concentrations up to 100 % in the sample gas.
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2 Operational Theory Model 3000PB
Nominal output in air is 0.19 mA, and 90 % response time is 45 s.
Expected life in flue gas is 8 months.
2.2.6.3 Class B-1 Cell
The class B-1 cell is for use in applications where it is exposed to less
than 0.1 % of carbon dioxide, and where fast response is important.
Nominal output in air is 0.50 mA, and 90 % response time is 7 s.
Expected life in air is 8 months.
2.2.6.4 Class B-3 Cell
The class B-3 cell is for use in applications where a slightly longer
response time is acceptable in order to have a longer cell life.
Nominal output in air is 0.30 mA, and 90 % response time is 13 s.
Expected life in air is 12 months.
2.2.6.5 Class C-3 Cell
The class B-1 cell is for use in applications where it is exposed to less
than 0.1 % of carbon dioxide, and where a longer response time is acceptable in order to have a longer cell life.
Nominal output in air is 0.20 mA, and 90 % response time is 30 s.
Expected life in air is 18 months.
2.2.6.6 Hydrogen and/or Helium Service
If the sample gas contains 10 % or more hydrogen and/or helium,
“clamp” cells are used. These Micro-Fuel cells are identified by the suffix -C
added to the cell class number.
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 3000PB 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 mini-
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Percent Oxygen Analyzer Operational Theory 2
mizes residual gas pockets that can interfere with very low level oxygen
analysis.
The sample system for the standard instrument incorporates ¼ 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. The
sample or calibration gas flow through the system is monitored by a flowmeter downstream from the cell.
Figure 2-4 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 valves, when supplied, are installed inside the NEMA enclosure and are regulated by the instrument's internal electronics.
Span In
Zero In
Sample In
In va c u u m service th e
restrictor should be
placed here.
Exhaust Out
Restrictor
In normal service the
restricto r s h o u ld b e
placed here.
Solenoid
Valves
Components in the shaded area are in
the -C option (internal control valves)
only and are not shown in the piping
diagram above.
Cell
Flowmeter
Figure 2-4: Flow Diagram
2.4 Electronics and Signal Processing
The signal processing and display electronics PCBs are mounted on the
back of the inner door. See Major Internal Components in chapter 5, for
illustration. The power supply module is mounted underneath the bottom end
of the Electrical Connector Panel.
The Model 3000PB Percent 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 most international power sources. CE approved units for the European
market also contain an EMI filter. Figure 2-5 is a simplified block diagram of
the Analyzer electronics.
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2 Operational Theory Model 3000PB
Figure 2-5: Block Diagram of the Model 3000PB Electronics
In the presence of oxygen the cell generates a current. A current to
voltage amplifier converts this current to a voltage, and then the voltage 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
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Percent Oxygen Analyzer Operational Theory 2
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.
The digital concentration signal along with input from the control panel
is processed by the microprocessor, and appropriate control signals are
directed to the display, alarms and communications port. The same digital
information is also sent to a 12 bit digital to analog converter that produces
the 0-1 V dc analog percent-of-range signal output and the analog range ID
output. Models with the –M option also have a 4-20 mA dc percent-of-range
signal output and analog range ID output.
Signals from the power supply are also monitored by the microprocessor, and the system failure alarm is activated if a malfunction is detected.
Teledyne Analytical Instruments
2-9
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