Teledyne BDS-3000 User Manual

Oxygen Analyzer

OPERATING INSTRUCTIONS FOR

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Oxygen Analyzer

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P/N M71903
11/30/01
ECO # 01-

DANGER

Tox ic g a se s a nd o r fla mma ble liq uids ma y be pr es e nt in this mon itor ing s y stem.

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.

Teledyne Analytical Instruments i

BDS 3000

Before conducting any maintenance or servicing, consult with authorized
supervisor/manager.

Teledyne Analytical Instruments ii

Oxygen Analyzer

Copyright © 2000 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

T hi s in str ument p ro v id es measur ement read in g s to it s user, an d serv es as a to o l b y w h i c h
v al uabl e d at a can b e g at h er ed . The i n fo rmat i on p r ov id ed by t h e in st r umen t may assi st th e user
i n el imi nati n g po ten ti al hazard s cau sed b y his p r ocess; ho wev er , it is essent ial t hat all
p er so nn el in v ol ved in th e u se o f t he in st ru men t or it s int er f ace, wi th t h e pr ocess b ein g
measu red , be pr op er l y tr ain ed i n t he pr ocess i tself , as well as all in s t r u m e n t a t io n rel at ed to i t .

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 iii

BDS 3000

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:

• BDS 3000-V: Instrument configured for Vacuum Service

• 19" Rack Mnt: The 19" Relay Rack Mount units are

available with one BDS 3000 series
analyzers installed in a standard 19" panel
and ready to mount in a standard rack.

Teledyne Analytical Instruments iv

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.

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.

CAUTION: THE ANALYZER SHOULD ONLY BE USED FOR THE

PURPOSE AND IN THE MANNER DESCRIBED IN
THIS MANUAL.

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BDS 3000

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

Oxygen Analyzer

Table of Contents

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

Table of Contents ........................................................................ vii

List of Figures................................................................................ x

List of Tables ............................................................................... xii

Introduction ...................................................................................1

1.1 Overview 1

1.2 Typical Applications 1

1.3 Main Features of the Analyzer 1

1.4 Front Panel (Operator Interface) 2

1.5 Rear Panel (Equipment Interface) 5

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

2.1 Introduction 7

2.2 BDS Sensor 7

2.2.1 Principles of Operation 7

2.2.2 Gas Flow Rate 10

2.2.3 Gas Pressure 11

2.2.4 Temperature effect 11

2.2.5 Recovery from High Level Oxygen Exposure 11

2.2.6 Background gas compatibility 12

2.2.7 Stability 13

2.2.8 Maintenance 13

2.3 Sample System 14

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

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BDS 3000

3.3.1 Gas Connections 21

3.3.2 Electrical Connections 22

3.3.2.1 Primary Input Power 22

3.3.2.2 50-Pin Equipment Interface Connector 23

3.4 Electrolyte Refill of BDS Sensor 28

3.5 Testing the System 30

3.6 Sensor Protection Mode 30

Operation ..................................................................................... 33

4.1 Introduction 33

4.2 Using Data Entry and Function Buttons 34

4.3 The System Function 36

4.3.1 Tracking Oxygen During Cal and Alarm Delay 37

4.3.2 Setting up an Auto-Cal 38

4.3.3 Password Protection 39

4.3.3.1 Entering the Password 40

4.3.3.2 Installing or Changing the Password 41

4.3.4 Logout 43

4.3.5 System Self-Diagnostic Test 43

4.3.6 Version Screen 44

4.3.7 Filter Function 44

4.3.8 Negative Value Display 45

4.3.9 The Gas Correction Factor 45

4.3.10 Troubleshooting Screen 46

4.3.11 Temperature 47

4.3.12 Extended Analog Output Function 47

4.3.13 Zero Baseline Temperature Compensation 48

4.4 Calibration of the Analyzer 49

4.4.1 Zero Cal 50

4.4.1.1 Auto Mode Zeroing 50

4.4.1.2 Manual Mode Zeroing 51

4.4.2 Span Cal 52

4.4.2.1 Auto Mode Spanning 52

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Oxygen Analyzer

4.4.2.2 Manual Mode Spanning 53

4.4.3 Span Failure 54

4.5 The Alarms Function 54

4.6 The Range Function 57

4.6.1 Setting the Analog Output Ranges 58

4.6.2 Fixed Range Analysis 58

4.7 The Analyze Function 59

4.8 Signal Output 59

Maintenance................................................................................. 65

5.1 Routine Maintenance 65

5.2 Adding Water to the BDS Sensor 65

5.3 Fuse Replacement 66

5.4 System Self Diagnostic Test 67

5.5 Major Internal Components 68

5.6 Cleaning 70

5.7 Troubleshooting 70

Appendix...................................................................................... 73

A-1 Specifications 73

A-2 Recommended 2-Year Spare Parts List 75

A-3 Drawing List 76

A-4 19-inch Relay Rack Panel Mount 76

A-5 Application notes 77

A-6 Material Safety Data Sheet 79

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BDS 3000

List of Figures

Figure 1-1: BDS-3000 Front Panel.................................................. 3

Figure 1-2: Model BDS 3000 Rear Panel........................................ 5

Figure 2.1: Cross Section of the BDS Oxygen Sensor................... 9

Figure 2.2: BDS sensor output at different gas flow rate............... 10

Figure 2-3: BDS Sample System .................................................. 11

Figure 2.4 Typical Purge-down Curve After Air Saturation............ 12

Figure 2.5: Adding DI Water to the BDS Sensor .......................... 13

Figure 2-6: Flow Diagram.............................................................. 14

Figure 2-7: Electronic Component Location .................................. 16

Figure 2-8: BDS 3000 Electronics Block Diagram......................... 17

Figure 3-1: Model BDS 3000 Front Panel ..................................... 20

Figure 3-2: Required Front Door Clearance................................. 20

Figure 3-3: Rear Panel of the Model Ultra Trace 3000................. 21

Figure 3-4: Equipment Interface Connector Pin Arrangement ...... 23

Figure 3-5: Remote Probe Connections........................................ 28

Figure 3-6: FET Series Resistance ............................................... 29

Figure 3.7: Adding Electrolyte to the BDS Sensor......................... 29

Figure 4-2: Analyzer Power-up Sequence .................................... 62

Figure 4-3: Analyzer Span Sequence ........................................... 63

Figure 4-4: Analyzer Zero Sequence ............................................ 64

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Oxygen Analyzer

Figure 5.1 Adding water into the BDS sensor................................ 66

Figure 5-2: Removing Fuse Block from Housing ........................... 67

Figure 5-3: Installing Fuses ........................................................... 67

Figure 5-4: Rear Panel Screws .....................................................69

Figure 5-5: Vacuum Degassing for the BDS Oxygen Sensor........ 71

Figure A-1: Single 19" Rack Mount (dimensions in mm) ............... 76

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BDS 3000

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....................................... 27

Table 4-1: Characters Available for Password Definition: ............ 42

Table 4-2: Linear Output for a 0-100 ppm O2 Range................... 59

Table 4-3: Range ID Output .......................................................... 61

Table 5-1: Self-Test Failure Codes ............................................... 68

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Oxygen Analyzer

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.

Teledyne Analytical Instruments xiii

Oxygen Analyzer Introduction

Introduction

1.1 Overview

The Teledyne Analytical Instruments Model BDS 3000 Trace
Oxygen Analyzer is a versatile microprocessor-based instrument for
detecting oxygen at the parts-per-billion (ppb) level in a variety of gases.
This manual covers the Model BDS 3000 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 BDS 3000 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 BDS 3000 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. The screen
continuously prompts and informs the operator.

• High resolution, accurate readings of oxygen content from

low ppb levels through 100 ppm. Large, bright, meter
readout.

• New BDS Sensing technology, Patent pending.

Teledyne Analytical Instruments 1

Introduction BDS 3000

• 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 0-100 ppb through

0-100 ppm) allow best match to users process and
equipment, plus a fixed 100 ppm over range.

• 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 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 Front Panel (Operator Interface)

The standard BDS 3000 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.

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.

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Oxygen Analyzer Introduction

Figure 1-1: BDS-3000 Front Panel

• 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:

• Left & Right Arrows
Select between functions currently
displayed on the VFD screen.

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Introduction BDS 3000

• 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 Light Emitting Diode
(LED) device that produces large, bright, 7-segment numbers that are
legible in any lighting. It produces a continuous readout from 0-999.9
ppb and then switches to a continuous ppm readout from 0-100.00 ppm.
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 0.1 to

2.0 standard liters per minute (SLPM) of nitrogen
Standby Button: The Standby 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 t o the BDS S ensor , the front panel swi ngs open
when the l at ch in t he upper r ight corner of t he panel i s pressed al l the way
i n wi th a nar row gauge t ool . Accessi ng the mai n cir cuit boar d requir es
unf astening rear panel screws and sl i di ng t he uni t out of the case.

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Oxygen Analyzer Introduction

1.5 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.

Figure 1-2: Model BDS 3000 Rear Panel

• 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.

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Introduction BDS 3000

• 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 BDS 3000 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.

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

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

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Oxygen Analyzer Operational Theory

Operational Theory

2.1 Introduction

The analyzer is composed of three subsystems:

• BDS Sensor

• Sample System

• 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 BDS Sensor is an electrochemical 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 BDS Sensor

2.2.1 Principles of Operation

The BDS oxygen sensor technology developed at Teledyne
Analytical Instruments is a result of TAI’s heavy investment on R&D
and expertise established during the half-century’s manufacturing of
electrochemical oxygen sensor. It stands for Bipotentiostat Driven
Sensor. A BDS oxygen sensor accurately translates the oxygen level in
the sample gas into to an electrical current signal.

A potentiostat contains three electrodes: a working electrode, a
reference electrode and a counter electrode. A Bipotentiostat is a
combination of two potentiostats that share the reference electrode and
the counter electrode. The potential at the working electrode is precisely
controlled with respect to the
is used to carry the current that flow through the sensor. A potentiostat is
typically constructed with several operational amplifiers. The three
electrodes in an electrochemical cell and the operational amplifiers in

Teledyne Analytical Instruments 7

reference electrode. The counter electrode

Operational Theory BDS 3000

the potentiostat constitute a feedback-control loop. The potentiostat
technology has been well accepted in the field of electrochemistry, and
proven effective in eliminating polarization of the reference electrode
and automatic compensating electric resistance in the cell.

In a BDS oxygen sensor, the sensing electrode is a working
electrode that is under precise potential control as discussed above. A
stable sensing electrode potential is very critical for an oxygen sensor to
achieve high stability, low noise and large dynamic range. The reference
electrode in a BDS sensor is a Ag/Ag

O electrode which is well known

2

for its stable electrode potential and compatibility with the KOH
electrolyte in an oxygen sensor. The counter electrode is made of a
Platinum wire.

The sensing process involves electrochemical reactions inside the
sensor. At the sensing electrode, oxygen is reduced at the controlled
potential:

+ 2H2O + 4e

O

2

-

— > 4OH

-

(1)

There is no net electrochemical reaction at the reference electrode
since it is connected to the high impedance input of the operation
amplifier.

The electrochemical reaction at the counter electrode is:

4OH- — > O2 + 2H2 O + 4e

-

It is noteworthy that reaction (2) is reverse of the reaction (1). It is
indicative of a net change of zero inside a BDS sensor throughout the
sensing process. This feature produces a long-term stability for the BDS
sensor.

There are two resources of oxygen being reduced at the sensing
electrode: from the sample gas and dissolved oxygen within the
electrolyte. The oxygen molecules in the sample gas diffuse to the
sensing electrode through a diffusion barrier (controlled diffusion) to
produce a current signal which is proportional to the oxygen level in the
sample gas. However, the dissolved oxygen in the electrolyte also
diffuses through the electrolyte. It is reduced at the sensing electrode and
produces a background current. This background current represents the
detection limit of an oxygen sensor.

The main advantage of the BDS technology lies in the unique
second potentiostat. It is designed to remove dissolved oxygen and other

( 2)

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Oxygen Analyzer Operational Theory

impurities in the electrolyte. It eliminates the internal background
current which previously limited the detection process.

The second potentiostat is located adjacent to the sensing electrode.
It uses a novel material, Reticulated Vitreous Carbon (RVC) and precise
control of the potential to remove the dissolved oxygen and impurities in
the electrolyte efficiently. As the result, the BDS sensor achieves an
outstanding feature of absolute zero output in the absence of oxygen.

Figure 2.1: Cross Section of the BDS Oxygen Sensor

Figure 2.1 shows the schematic of a BDS oxygen sensor. The
sample gas enters the sensor through the gas inlet port and exits at the
gas outlet. A portion of oxygen in the sample gas diffuses through the
diffusion barrier to be reduced at the sensing electrode to form OH- in
the electrolyte. OH- can move freely through the porous 2nd working
electrode. At the Counter Electrode, OH- is oxidized back to oxygen.
While the 2nd working electrode allows OH- to move through, it
prevents the dissolved oxygen from the top portion of the sensor to reach

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Operational Theory BDS 3000

the sensing electrode. The reference electrode provides a potential
reference for both the sensing electrode and the 2nd working electrode.

NOTE: BDS technology and sensor is a patent pending

technology of Teledyne Analytical Instruments in the
United State of America as well as many foreign countries.

To learn more about BDS technology, please visit TAI’s web page at
http://www.Teledyne-AI.com

To learn more about potentiostat, visit Electochemical Society’s web
page at http://www.electrochem.org

2.2.2 Gas Flow Rate

The output from a BDS oxygen sensor is relatively insensitive to
change of gas flow rate if operated in the range of 1 - 3 SCFH (in
nitrogen). The output drops when the flow rate is below 1 SCFH. Figure

2.2 is a typical curve showing the sensor outputs at different flow rate.

Figure 2.2: BDS sensor output at different gas flow rate

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Oxygen Analyzer Operational Theory

2.2.3 Gas Pressure

The analyzer is equipped with a flow restriction tube (from the
back panel of the analyzer to the left side of the BDS sensor) as shown
in Figure 2-3. The sensor is not affected by pressure as long as the
analyzer vents to atmosphere. If the analyzer is not vented to
atmosphere, the downstream pressure must not exceed 10 inch of water.
A clogged or restricted vent or excessive pressure will force gas into the
electrolyte and cause damage to the BDS sensor.

Figure 2-3: BDS Sample System

2.2.4 Temperature effect

The raw output from a BDS oxygen sensor has a temperature
coefficient about 0.25% / °C. This temperature effect is compensated by
the software throughout the operation temperature range (5 – 40°C).

2.2.5 Recovery from High Level Oxygen Exposure

The ambient air contains about 210,000,000 ppb (2.1 x 108)
oxygen. Figure 2.4 is a typical purge-down curve for a new BDS sensor
which had been air saturated. It is normal to take several hours, even
days for an air saturated BDS to purge down to a low ppb level.

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Operational Theory BDS 3000

Figure 2.4 Typical Purge-down Curve After Air Saturation

S h or t e n i ng t h e ai r exp o s u r e wi l l al l o w a f a s t e r se ns o r r ec o v e r y.
A ty p i c a l BD S se n s o r wi l l re c o v e r t o 1 pp m i n ap p r ox i m a t el y 25
m i nu t e s , t o 10 0 pp b af t e r 80 m i n , an d 10 pp b i n ab ou t 8 ho u r s , af t e r
s u f f e r i n g a t e n m i n u t e ex p os u r e to ai r .

2.2.6 Background gas compatibility

T he BDS oxygen sensor wi l l work in i ner t gas backgr ounds,
i ncludi ng ni t rogen, hydr ogen, ar gon, heli um and ethane. The sensor
out put, however, i s dif fer ent in di ff erent backgr ound gases. For exam pl e,
t he sensor output i n a hydr ogen background is twi ce as much as it woul d
be in a ni tr ogen background. Therefor e, i t is recom mended to cali br ate t he
analyzer wit h an oxygen standar d that has a sim il ar background as the
sam pl e gas. If an oxygen st andar d is unavai l able for a par ti cul ar
background, a Gas F act or which is det er mi ned at TAI coul d be used t o
cor rect the sensor out put in dif f er ent backgr ound (see sect ion 4.3.9) .

Note: the gas flow meter in the analyzer is calibrated for air. The

error for measuring nitrogen is usually negligible. But for

hydrogen, it reads 100% lower. For example, when the

float ball in the flow meter is at 0.5 SLPM, the actual flow

rate of hydrogen is about 1 SLPM.

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Oxygen Analyzer Operational Theory

The BDS oxygen sensor can tolerate exposure to acidic gases. Up

to 0.2% CO

has no effect to ppb level oxygen measurement.

2

2.2.7 Stability

The BDS sensor is essentially drift free. Typically a BDS sensor
requires no re-calibration over an entire year period. However, there
may be some intrusion to the zero during the maintenance. See next
section for details.

2.2.8 Maintenance

The only maintenance required on the BDS sensor is to replenish
distilled or de-ionized water every three to four months. It is not
necessary to take the analyzer out of service while adding water to the
sensor but caution should be taken to avoid spilling water on the PC
boards or other area inside the analyzer.

Figure 2.5: Adding DI Water to the BDS Sensor

There is a Max line and Min Line clearly marked on the BDS
sensor body. It is a good practice to check the electrolyte level every
month and add de-ionized water into the sensor whenever it is
convenient.

When running dry gas through the sensor, the gas carries out
moisture from the sensor. Therefore, the electrolyte (10% KOH in

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Operational Theory BDS 3000

water) inside the sensor is gradually concentrated during the sensor
operation. It typically takes about four months for the electrolyte level to
drop from the Max line to Min line. When adding water to increase the
electrolyte level from the Min line to the Max line, it is typical that the
oxygen reading will drift down about 10 ppb in an hour. If the oxygen
content in the sample gas is very close to zero, the analyzer may display
a negative reading during this period. The sensor will recover by itself
during the following week. This drift-down then recover-back
phenomenon is caused by the quick dilution of the electrolyte and re­establishment of a new equilibrium inside the sensor. To minimize this
effect, add a small amount of water each time and do this before the
electrolyte level reaches the Min line.

2.3 Sample System

The sample system delivers gases to the BDS sensor from the
analyzer rear panel inlet. Depending on the mode of operation either
sample or calibration gas is delivered.

The Model BDS 3000 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 sampl e syst em for the standar d inst rument incor porates 1/4" VCR
fit tings for sample inl et and swagelock fittings for outl et tube connections at
the rear panel. The sample or cal ibrati on gas that flows through the system
is monitored by a flowmeter downstream from the sensor .

Figure 2-6 represents the flow diagram of the sampling system. In
the standard instrument, calibration gases can be connected directly to
the Sample In port by teeing to the port with appropriate valves.

Figure 2-6: Flow Diagram

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Oxygen Analyzer Operational Theory

2.4 Electronics and Signal Processing

T he Model BDS 3000 Oxygen Analyzer uses an 8031
m icrocontr ol l er wi th 32 kB of RAM and 128 kB of ROM to cont rol all
signal processi ng, i nput / output, and di splay functi ons f or the analyzer .
S ystem power is suppli ed fr om a universal power suppl y module desi gned
t o be compat i bl e wi t h any i nt er nat ional power source. F i gure 2- 7 shows
t he l ocati on of t he power suppl y and the mai n el ect roni c P C 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 2-8 is a block
diagram of the Analyzer electronics.

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

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 4-20 mA DC and the 0-1 VDC analog
concentration signal outputs, and the analog range ID outputs.

Signals from the power supply are also monitored, and through the
microprocessor, the system failure alarm is activated if a malfunction is
detected.

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Operational Theory BDS 3000

Figure 2-7: Electronic Component Location

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