Trace Oxygen Analyzer
Model 356WA
Trace Oxygen Analyzer
Instruction Manual
DANGER
HIGHLYTOXICANDORFLAMMABLELIQUIDSORGASESMAYBEPRESENTINTHISMONITORINGSYSTEM.
PERSONALPROTECTIVEEQUIPMENTMAYBEREQUIREDWHENSERVICINGTHISSYSTEM.
HAZARDOUSVOLTAGESEXISTONCERTAINCOMPONENTSINTERNALLYWHICHMAYPERSISTFORA
TIMEEVENAFTERTHEPOWERISTURNEDOFFANDDISCONNECTED.
P/NM356WA
09/14/99
ECO#99-0373
ONLYAUTHORIZEDPERSONNELSHOULDCONDUCTMAINTENANCEAND/ORSERVICING. BEFORE
CONDUCTINGANYMAINTENANCEORSERVICINGCONSULTWITHAUTHORIZEDSUPERVISOR/MANAGER.
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Table of Contents
1 Introduction
1.1 Method of Operation................................................. 1-1
1.2 Required Equipment................................................. 1-2
1.2.1 Sample Conditioning ................................... 1-2
1.2.2 Recorder /Meter Readout ........................... 1-2
2 Operational Theory
2.1 Sensor ..................................................................... 2-1
2.2 Humidifier ................................................................ 2-1
2.3 Flow System ............................................................ 2-2
3 Installation
3.1 Location .................................................................... 3-1
3.2 Electrical Connections ............................................. 3-1
3.3 Sample Connections ............................................... 3-2
4 Operations
4.1 Filling the Reservoir.................................................. 4-1
4.2 Detector Cell............................................................. 4-1
4.2.1 Cell Packaging ............................................ 4-1
4.2.2 Electrolyte ................................................... 4-1
4.2.3 Cell Installation............................................ 4-3
4.3 Throttle Valve ........................................................... 4-5
4.4 Humidity Control ....................................................... 4-5
4.5 Power ....................................................................... 4-7
4.6 Warm-Up and Stabilization....................................... 4-7
4.7 Calibration ................................................................ 4-7
5 Maintenance & Troubleshooting
5.1 Flowmeter and Humidifier ....................................... 5-1
5.2 Cell Electrolyte Level ............................................... 5-1
5.3 Reservoir ................................................................. 5-1
5.4 Calibration ............................................................... 5-1
5.5 Cell .......................................................................... 5-2
5.5.1 Electrolyte Replacement.............................. 5-2
5.5.2 Lead Electrode............................................. 5-2
5.6 Screen Assembly..................................................... 5-4
iii
Teledyne Analytical Instruments
Model 356WA
5.7 Reservoir and Humidifier Column ........................... 5-4
5.8 Leak Detection ........................................................ 5-6
5.8.1 Leak Detection Procedure ........................... 5-6
5.8.2 Cell Leak...................................................... 5-7
Appendix
Specifications ................................................................. A-1
Spare Parts List .............................................................. A-2
Drawing List.................................................................... A-3
Calibration Data.............................................................. A-4
Material Safety Data Sheets........................................... A-9
iv
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Introduction 1
Introduction
The Teledyne Analytical Instruments Model 356WA Trace Oxygen
Analyzer is designed to detect oxygen concentrations in process streams. It
utilizesTeledyne’spatentedelectrochemicalsensorwhichrequiresminimal
maintenance and exhibits a 90% response in less than one minute. Cell
output is insensitive to flow rate changes within the operating range of the
analyzer’sflowmeter.
The Model 356WA features a welded stainless sampling system for
long-term,leak-freeoperation.
While the analyzer is offered in several configurations, they are virtually
identical with the exception of housing or options such as special meters. For
purposes of clarity, this manual will discuss the unit in general. The differ-
ences between the configurations are minor and will be obvious to the user.
1.1
Method of Operation
Gas from the process stream is fed through a sample line to the sample
inlet port of the analyzer. The sample is directed through the analyzer’s
sample system, where oxygen concentration is detected by the sensor. The
sensor generates an output signal which is read out on a suitable recorder or
meter.
The analyzer components include:
•
•
•
•
A throttle valve and flowmeter to control sample flow
A humidifier to condition the sample
The measuring cell where catalytic conversion occurs
An electronic amplifier circuit for converting the output of the
cell to a DC signal.
•
•
A thermostatic assembly for temperature control in the cell
compartment
A reservoir for providing make-up water to the humidifier.
Teledyne Analytical Instruments
1-1
1 Introduction
Model 356WA
1.2
Required Equipment
For proper operation, the analyzer may require accessory equipment,
particularly in the area of sample conditioning. The need for additional
equipment is dictated by the conditions of each application.
1.2.1 Sample Conditioning
The sample must be free of entrained solids and condensable vapors,
and be at a relatively constant pressure between 1 and 100 psig. However,
more efficient operation is obtained with pressures in the range of 5 to 10
psig. Pressure surges can carry fluid from the humidifier into the cell and
impair cell operation. Filters, scrubbers, or pressure regulators are often
necessary, depending on local conditions.
1. Filters. If filters are necessary, they should be conveniently
located near the analyzer, and installed in a fashion which permits
easy removal for periodic cleaning or replacement.
2. Scrubbers. If the sample contains small quantities of acidic
anhydrides (SO2, etc.) or mercaptans (H2S, etc.) they will react
with the electrolyte or the cathode, and must be removed. A
causticscrubberisusuallyeffective.
3. Pressureregulators. While the analyzer will accept pressures to
100 psig, a range of 5 to 10 psig is recommended. In addition,
pressure surges can affect instrument operation. In either case, the
use of a pressure regulator is advisable. Install the regulator as
close to the sample point as possible to reduce sample travel time
to a minimium. The regulator should incorporate a metallic
diaphragm to prevent the diffusion of atmospheric oxygen into
thesample.
1.2.2 Recorder /Meter Readout
The meter installed on the 356WA is either analog or digital. The
recorder used for analyzer signal readout is usually of the self-balancing
potentiometric type. It should have an input inpedance of 10 Ω or higher.
Output is 0 to 1VDC or less (optional: 1 to 5, 4 to 20, or 10 to 50 mADC).
Teledyne Analytical Instruments
1-2
Trace Oxygen Analyzer
Operational Theory 2
Operational Theory
2.1 Sensor
The sensor is an open-cathode cell, an electrochemical transducer
specific to oxygen. The cathode of the cell is composed of silver screen
elements with a large surface area. The screen assembly is mounted in an
acrylic block, with the lower edges of the screens immersed in potassium
hydroxide electrolyte. A thin layer of electrolyte is maintained on the sur-
faces of the screens by capillary action. A lead disk is positioned under the
screens and serves as the anode. An exploded view of the cell is showm in
Figure 5-1.
The sample gas stream is passed directly over the cathode screens,
initiating an electrochemical reaction. Four electrons are generated by the
oxidation of the lead anode, and are then used to reduce oxygen at the
cathode. The flow of electrons between the anode and cathode creates an
electric current which is directly proportional to the oxygen concentration in
the sample stream. In the absence of oxygen, no oxidation or reduction
takes place, and no current is produced.
In simplified form, the reaction may be described as follows: oxygen is
reduced at the cathode by the mechanism
-
-
4e +O2 + 2H2O → 4OH
This cathodic half-reaction occurs simultaneously with the anodic half-
reaction
-
-
Pb + 2OH → PbO + H2O + 2e
The overall reaction is
O2+ 2Pb → 2PbO
2.2 Humidifier
It is necessary to maintain a film of electrolyte on the screens of the
electrode assembly. This means that the humidity of the sample as it flows
through the cell must be such that the water vapor pressure of the electro-
Teledyne Analytical Instruments
2-1
2 Operational Theory
Model 356WA
lyte is equal to the water vapor pressure in the sample gas. If the humidity
of the sample is too low, water will evaporate from the electrolyte, drying
the cell. If the sample humidity is too high, water will condense out into the
electrolyte, flooding the cell.
The sample is humidified by bubbling it through water in the humidifier
column just before it enters the cell. The humidifier column is in the same
heated compartment as the cell and so is held at the same temperature. The
water in the column, however, is cooled by evaporation into the sample gas.
Thus, the sample gas will normally have a humidity that is too low for
equilibrium with the cell. It is assumed here, of course, that since the cell
component is heated above ambient temperature, the sample gas is less than
saturated at the compartment temperature when it enters the analyzer.
The humidity of the sample is increased to be in equilibrium with the
cell electrolyte by heating the water in the humidifier column. The humidifer
heater is in the base of the column, and the amount of heating is adjusted
with the humidity control that is located on the panel of the control unit.
The amount of heating required depends on the sample flow rate, the
sample humidity, and the specific heat of the sample. The correct adjust-
ment for the operating conditions of any particular installation is obtained by
checking the cell electrolyte level periodically and replenished when neces-
sary according to the instructions in Section 4.2.3: Cell Installation.
The humidifier column also contains baffles to stop water from splas-
hing up into the line to the sample cell at high flow rates.
2.3 Flow System
The analyzer flow system is shown schematically in Figure 2-1. It
includes a needle valve for adjusting the sample flow rate, a flowmeter to
indicate the sample flow required for calibration, the humidifier, the measur-
ing cell, and an automatic level control system for the water in the humidi-
fier.
As can be seen from Figure 2-1, the sample enters the humidifier
column against the pressure of a water column from the base of the humidi-
fier to the water level in the reservoir, which is approximately 4 inches.
This determines the minimum sample pressure at which any sample can flow
through the analyzer. In practice, the sample pressure must be somewhat
greater than this in order to have an adequate flow rate.
The automatic level control in the humidifier column is accomplished
by connecting the sample outflow from the cell to the bottom of the reser-
2-2
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Operational Theory 2
Cell
Pressure
ATM + (b - a)
Flowmeter
Sample In
Throttle
Valve
Vent
b - a
b
a
Reservoir
Drain
Water
Humidifier
Column
Cell Compartment
Figure 2-1: Flow System Schematic
Teledyne Analytical Instruments
2-3
2 Operational Theory
Model 356WA
voir. This places a back pressure on the sample in the cell and upper portion
of the humidifier column equal to the water column from the bottom of the
reservoir to the water level in the reservoir. Thus, the water level in the
humidifier column is held even with the sample connection at the bottom of
the reservoir. There will be a slight additional pressure in the top of the
humidifier column depending on the flow rate (the pressure needed to push
the sample through the cell and associated tubing), but at normal flow rates
this merely slightly lowers the level in the humidifier column.
The sample bubbles through the water in the reservoir on its way to the
outlet port. Some of the water vapor will re-condense, so that the sample
flows out of the outlet port saturated at the reservoir temperature, which is
slightly above ambient. The sample bubbling through the make-up water
will scrub out any oxygen which may be dissolved in it. This assures that the
sample will not pick up any oxygen as it passes through the humidifier
column.
2-4
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Installation 3
Installation
3.1 Location
With proper shielding of the leads, the analyzer and the readout device
can be separated by as much as 1,000 feet. However, they should be placed
as close together as possible. For the most convenient operation, the read-
out recorder or meter should be within view of the controls, particularly
when the unit is being calibrated. Figure 2-1 depicts a typical system layout.
Other location considerations:
1) The analyzer should be sheltered from the elements.
2) Ambient temperature must be within 30 to 120 °F.
3) The unit should not be subject to excessive shock or vibration.
4) It should be as close as possible to the sample point.
5) There must be access to the back and side of the unit for
connection or maintenance of sample lines and power.
NOTE: Since the level of the electrolyte in the measuring cell is critical and
the water level control system for the humidifier is gravity sensitive,
THE ANALYZER MUST BE MOUNTED SO THAT THE BOTTOM OF
THE CASE IS LEVEL.
3.2 Electrical Connections
A diagram of the necessary electrical connections is shown in Figure 2-2.
Note: See the Interconnection Diagram (drawing A-37526) included in the
back of this manual, as well as any Addenda that may be included
with this manual for information specific to your instrument.
Teledyne Analytical Instruments
3-1
3 Installation
Model 356WA
Percent Oxygen
Analyzer
Sample Line
(1/4" or 1/8" Metal Tubing)
Signal Leads
(22 ga. Twisted
Pair Shielded
Cable)
Recorder
Vent
Sample
In
Shut Off
Valve
Pressure
Regulator
(5-10 psig Output)
1/4"
Tubing
Vent
Sample
Line
115 VAC Power and Ground
2 Power Leads
1 Ground Wire
(16 ga. Insulated)
Condensate Trap
Figure 2-1 Typical System Layout
The connections include a terminal for grounding the analyzer case and
chassis in accordance with accepted industrial practices. The maximum
power requirement is less than 1½ amperes at 115 VAC.
3.3 Sample Connections
The sample line is connected at the back of the analyzer case as de-
picted in Figure 2-3. Use care in assembling any part of the sampling system
to avoid leaks. Oxygen can diffuse into the system through small leaks even
when sample pressure is much greater than atmospheric pressure. A 1/8
"
female NPT fitting is installed on the back of the instrument for making
sample and vent line connections. Thepurge line is fitted with a 1/4" tube
fitting.
1. Connectors. Use straight tube connectors where possible.
This facilitates removal of the analyzer section from the case
during maintenance or service.
2. Lines. Lines should consist of metallic tubing, since oxygen can
diffuse through plastic. Use continuous tubing where possible.
3. Vent. The analyzed sample is vented through the back of the
unit as shown in Figure 2-3.
3-2
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Installation 3
TS 1
1
2
3
4
5
6
7
8
9 10 11 12 13 14
HOT
AC Power In
150 Watt Max
Load
mV
Output
NEUT
GND
NO
C
GND
Current
Output
Alarm 2
Alarm 1
NC
NO
C
NC
Figure 2-2: General Connection Diagram
See the specific Interconnection Diagram for your instrument in the drawing
package located at the back of the manual. See also any Addenda that may be
included with this manual.
The analyzer should have a vent line of ¼" diameter tubing at least two
feet long, running downward from the vent connection. This is to prevent
air from diffusing into the reservoir and dissolving into the humidifier make-
up water.
If it is not desirable to vent the sample into the atmosphere, a vent line
to carry the sample to a suitable venting area will be required. The sample
leaves the vent connection of the analyzer saturated with water vapor at a
temperature somewhat above ambient, so a suitable trap to remove conden-
sate without plugging the vent line will be required. The vent line should
also be arranged so that it cannot become plugged by dirt or dust.
Teledyne Analytical Instruments
3-3
3 Installation
Model 356WA
9"
15"
2"
5/16"
17"
7-15/16"
17-9/16"
18-1/4"
Sample
Purge
Vent
1/4" Female NPT
115 V 50/60 Hz
Power In
7/8" dia. holes
for 1/2" conduit
Signal Out
FIGURE 5 ANALYZER OUTLINE DIAGRAM
Figure 5: Gas Connections to Back of Analyzer
3-4
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Operations 4
Operations
4.1
Filling the Reservoir
The reservoir is located on the right side of the analyzer case.
1) Insure that the cap on the drain spout is securely tightened.
2) Remove cap from fill port on top of reservoir.
3) Pour distilled water into reservoir until it is half full (about one
quart). The water will automatically flow into the humidifier
column.
4) Replace cap on fill port and securely tighten. A missing or loose
cap will permit the sample to vent into the analyzer case.
4.2
Detector Cell
The cell is located in the heated compartment on the left side of the
analyzer case, as shown in Figure 4-1. To open the compartment, unscrew
the captive knurled knobs at the top and bottom of the compartment and
remove the plastic window.
4.2.1 Cell Packaging
The cell is packaged separately from the analyzer. It is filled with
distilled water to prevent oxidation of the electrodes from exposure to the
atmosphere. The cell should be left filled with the distilled water until the
analyzer is installed and ready for operation. The cell should not be exposed
to the atmosphere for any prolonged duration.
4.2.2 Electrolyte
The cell electrolyte is Teledyne Type A, used in applications where
there is a complete absence of acidic anhydrides (CO2, SO2) in the sample
gas. Type A electrolyte is a 10% solution (w/v) of reagent-grade potassium
hydroxide (KOH) in distilled water.
Teledyne Analytical Instruments
4-1
4 Operations
Model 356WA
Heater
Cell Compartment Terminal Strip
Control Assembly
20
2
30
3
10
1
Interconnect
Terminal Strip
Humidifier
Control
Range
Span
1
2
3
4
5
Current Adj
2 Amp
Alarm 1
Alarm 2
Cell
Assembly
Heater
Flowmeter
Throttle
Valve
Sample
System
Assembly
with
Humidifier
Column
Assembly
Reservoir
Sample
System
Assembly
Figure 4-1: Typical Model 306WA With 2 Alarm Option
WARNING: Type A electrolyte is caustic. Use extreme care in
handling. Protective equipment including but not
limited to gloves and safety glasses should be worn
while handling electrolyte. Refer to the Material Safety
Data Sheet in the Appendix regarding potential hazards
and corrective action in case of accident.
Type B electrolyte is a 20 % solution (w/v) of potassium carbonate and
should be used when the CO2 level in the background gas is between 500
ppm and 1 %. This narrow range is rarely encountered. It is, however
available from the factory. Safety related information for this electrolyte can
be found in the Appendix.
Type C electrolyte is a 20 % solution (w/v) of potassium bicarbonate
and should be used when the CO2 level in the background gas is between 1
and 100 %. Safety related information for this electrolyte can be found in
the Appendix.
4-2
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Operations 4
Sufficient electrolyte is provided for initial servicing of the cell. Elec-
trolyte for future service should be ordered from Teledyne. When ordering,
specify type and quantity.
4.2.3 Cell Installation
Prior to servicing and installing the cell, inspect the lead electrode in
the acrylic base for signs of oxidation, indicated by a reddish-brown or
yellow discoloration. If discoloration is noted, clean the cell as directed in
section 5.5.2 before placing it in service.
WARNING: Type A electrolyte is caustic. Use extreme care in
handling. Protective equipment including but not
limited to gloves and safety glasses should be worn
while handling electrolyte. Refer to the Material Safety
Data Sheet in the Appendix regarding potential hazards
and corrective action in case of accident.
1) Remove the four cell mounting bolts which secure the plastic
cover. Pour out the distilled water.
2) Pour about half the furnished electrolyte into the cell and slosh
until all components within the cell are wetted by the solution.
Drain and dispose of the solution.
3) Wipe the top of the cell and the O-ring with a clean, disposable
tissue to remove solution from the exterior. DO NOT touch the
interior of the cell.
4) Carefully pour in electrolyte until it just touches the bottom edge
of the silver screen assembly at all points. This is indicated by a
definite wicking of electrolyte onto the screen assembly at every
point along ithe bottom edge. It is essential at this point that the
bottom edge of the screen assembly be wetted at all points (as
seen by the wicking action), but not over-immersed (as large a
surface area as possible of the screen assembly must remain
above the electrolyte, while every point of the bottom edge must
be wetted). The level is correct when the bottom edge of the
sensor screen is wetted but not immersed; approximately 3/32 "of
the silver electrode extends into the pool of eelectrolyte.
NOTE:The electrolyte level in the cell is critically related to its sensitivity
due to the change in the cathode surface area exposed to the
eledctrolyte.
5) Carefully place the cell under the cell mounting plate with the
outer terminal toward the front. Secure in place with four bolts
supplied with the cell. Refer to Figure 4-2.
Teledyne Analytical Instruments
4-3
4 Operations
Model 356WA
Cell Mounting
Bolts
Terminal Strip
No. 4
Flowmeter
O-Ring
Sample Flow
Control Valve
Cell Block
Humidifier Column Heater
Humidifier Column
Figure 4-2: Cell Compartment Components
4-4
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Operations 4
6) Connect the red lead to the center terminal and the black lead to
the outer terminal.
NOTE:The silver screens in the cell have been specially treated to pro-
vide proper detection characteristics. They must be kept clean and
MUST NOT be touched. Even clean fingers secrete natural oils
which contaminate the screens. If the screens need straightening,
wash a small pair of tweezers thoroughly to remove any grease,
rinse them in distilled water, and use them to carefully bend the
screens back into place.
4.3
Throttle Valve
The throttle valve is located at the top of the reservoir tank. Refer to
Figure 4-1.
1) Gently turn the valve counterclockwise. A stream of bubbles
should appear at the base of the humidifier column, and the float
of the flowmeter should rise in its tube.
2) Adjust the valve so that the flowmeter float is centered in the
flow rate reference indicator.
CAUTION:
Open the throttle valve carefully. Excessive flow rate
may cause water in the humidifier column to be carried
into the detector cell. This can cause erratic readings
and may require disassembly, cleaning, and refilling of
the sensor.
3) The flowmeter indicator has been factory set to a flow rate of
150 cc/min. for the specified sample gas.
CAUTION:
Excessive flow rate may cause water in the humidifier
to be carried to the flowmeter causing moisture to
accumulate. This can cause the ball to stick in the
flowmeter. To remove moisture, remove the flowmeter
and allow to air or blow dry. Refer to the detailed in-
structions in Figure 5-2 for removal and installation of
the column.
4.4
Humidity Control
The humidity control is located on the front panel of the control unit,
and is adjusted to maintain a constant electrolyte level in the detector cell.
In effect, the control governs the humidity of the sample which is directed
to the cell.
Teledyne Analytical Instruments
4-5
4 Operations
Model 356WA
Outside Electrode Connected to
"Y" Terminal Post (+)
Oxygen Generated Here
Electrical Terminal Board
Sub-Assembly
Wick Saturated With KOH
Electrolyte Solution
O-Ring
Inside Electrode Connected
to "B" Terminal Post (-)
Hydrogen Generated Here
Figure 8: Calibrator Assembly
4-6
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Operations 4
1) At start-up, the humidity control knob should be set to 30. Note
the cell electrolyte level as a reference. Approximately 3/32" of
the bottom edge of the screen assembly should be immersed in
the electrolyte.
2) Operate the analyzer for 24 hours and compare the electrolyte
level with the “reference” established in Step 1. If the level is
lower than the reference, adjust the knob a few divisions
clockwise; if higher, adjust a few divisions counterclockwise.
3) Operate another 24 hours and repeat Step 2.
4) Continue adjustments at ever-increasing intervals until a constant
electrolyte level is attained in the cell.
Once the analyzer is suitably located, all components serviced and
installed, and sample and electrical connections made, the instrument is
ready for operation.
4.5
Power
When power is turned on, power is applied to the cell compartment
heater. The cell operates without applied power, but its output will vary
with changes in ambient temperature.
4.6
Warm-Up and Stabilization
When the analyzer is initially put into operation, the air in the lines and
sample passages will drive the output indication to the top of the scale. The
time required to sweep out this residual air may be several hours before an
on-scale indication is reached. During this time the cell compartment is
heating and reaching its controlled temperature.
4.7
Calibration
The analyzer is calibrated by adding a known amount of oxygen into
the analyzer by means of a calibrated span gas. The sensitivity of the ana-
lyzer is adjusted until the change indicated by the analyzer is equal to the
amount of oxygen known to be present in the span gas. The span gas must
be composed of the same elements as the specified sample gas if the
analyzer's calibrated flowmeter is to be used. TBE/AI recommends that the
oxygen content of the span gas be between 70–90% of full scale on the
range of interest.
Teledyne Analytical Instruments
4-7
4 Operations
Model 356WA
To calibrate the analyzer:
1. Shut the sample gas off, disconnect the sample in line and
connect the the span gas to the sample inlet. Allow the span gas
to flow through the system. Adjust the span gas flow rate until
the flowmeter float is centered in the flowmeter reference
indicator. Note the reading of the external recorder or meter.
2. Turn the range selector switch to the range which encompases
the oxygen concentration of the span gas. The meter or recorder
should move upscale and indicate the exact concentration of
oxygen in the span gas.
3. If the external recorder/meter does not indicate the proper
amount of oxygen, adjust the span dial until it does.
4. After the recorder or meter has stabilized on the proper readout,
turn off the span gas flow, disconnect the span gas, reconnect
the sample gas and establish the proper flow.
4-8
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Maintenance & Troubleshooting 5
Maintenance & Troubleshooting
After the analyzer has been put into operation and calibration has been
accomplished, routine inspection will be required for normal operation.
5.1 Flowmeter and Humidifier
The flowmeter and humidifier column must be checked daily to insure
proper flow, and corrected as necessary. Refer to Section 2.2: Humidifier
and 4.4: Throttle Valve.
5.2 Cell Electrolyte Level
The level of electrolyte in the cell must be checked daily and adjusted
as necessary. Refer to Section 4.2.3: Cell Installation. The proper level for
the electrolyte is when the bottom edge of the sensor screen is wetted but not
immersed. Approximately 3/32 " of the silver electrode should extend into the
poolofelectrolyte.
5.3 Reservoir
The water level in the reservoir should be checked at least every two
weeks. Follow this procedure:
a) Remove the cap from the filler spout.
b) Obtain a clean glass tube about 4 to 5 inches long and about ¼ "
outerdiameter.
c) Lower the tube into the tank through the filler spout until it
touchesbottom.
d) Place a finger over the end of the tube, and withdraw the tube
from the tank. The height of water in the tube is the height
of the water level in the tank.
e) If the water level in the reservoir is below 1 ", add a quart of
distilledwater.
f) Replace the filler spout cap securely after verifying that the O-
ring seal is in good condition.
Teledyne Analytical Instruments
5-1
5 Maintenance & Troubleshooting
Model 356WA
5.4 Calibration
The sensitivity of the unit should be checked at two to four week
intervals. Calibration procedures are described in Section 4.7:Calibration.
5.5 Cell
The electrochemical reaction in the analytical process results in the
accumulation of lead ions in the electrolyte, making the replacement of the
lead electrode or the electrolyte necessary.
5.5.1 Electrolyte Replacement
Replace the electrolyte at least every two months, or even more fre-
quently if foreign matter is accumulating in the cell. Remove the cell from is
compartment, and drain, clean, rinse, and refill as described in Section 4.2.3:
Cell Installation. After the cell is serviced or replaced, calibrate the analyzer
as outlined in Section 4.7: Calibration.
5.5.2 Lead Electrode
If electrode is discolored when new, or has obviously deteriorated from
use, it may be necessary to clean or replace the electrode. Use the following
procedure while referring to Figure 5-1.
If the lead electrode is simply discolored, clean the entire cell according
to the following procedure:
a) Heat a quart of Teledyne cleaning solution to slightly below the
boiling point, and completely fill the cell cavity with the heated
solution.
b) Let the solution stand for approximately five minutes. Drain and
dispose of solution in an approved manner.
c) Repeat steps a) and b).
d) Rinse the cell with distilled water and then fill with electrolyte.
Let stand for approximately two minutes and then drain and
dispose of electrolyte in an approved manner.
e) Refill the cell with electrolyte, immersing the lower edge of the
silver screens to about a 3/32 " depth.
If the lead electrode is obviously beyond repair, it must be replaced.
a) Remove the terminal nuts by removing them from the mounting
screws.
b) Carefully remove the screw which holds the screen assembly in
place. Remove the screen assembly. Use clean tweezers and do
5-2
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Maintenance & Troubleshooting 5
Cell Mounting
Nuts (4)
Cell Block
Terminal seal
O-rings (2)
Mounting Bolts (4)
Lead Electrode
Cathode Screen
Assembly
O-Ring
Cover
Figure 5-1: Cell Assembly
Teledyne Analytical Instruments
5-3
5 Maintenance & Troubleshooting
Model 356WA
not touch it with your fingers. Avoid any possible
contamination of the screen.
c) Cleanse the cell thoroughly in electrolyte solution.
d) Insert the new lead electrode in place in the cell body and secure
with lock washers and screws.
e) Carefully install screen assembly and secure with mounting
screw.
f) Immerse the cell assembly in hot cleaning solution and then rinse
indistilledwater.
g) Install prepared cell assembly as described in Section 4.2.3:Cell
Installation.
5.6 Screen Assembly
The screen assembly will become discolored after prolonged use due to
contamination. When this occurs, and if the cell no longer displays adequate
sensitivity, the entire cell assembly must be replaced. Refer to Section 4.2.3:
CellInstallationforcellinstallationinstructions.
5.7 Reservoir and Humidifier Column
Approximately once each year the reservoir and humidifier column
should be drained and cleaned. Use the following procedure:
a) Reduce sample flow to approximately 50 cc/min.
b) Refer to Figure 4-1. Place a small funnel with attached tubing
beneath the drain spout which is located on the underside of the
reservoir. Remove the drain spout cap and allow the reservoir
and humidifier column to drain thoroughly.
c) Replace the drain spout cap, turn the sample flow off, and
remove the fill cap on the top of the reservoir.
d) Add a small amount of electrolyte to a pint of warm distilled
water. Pour the solution into the reservoir and replace the fill cap.
e) Gently open the throttle valve and permit the sample to flow for
five to ten minutes.
f) Reduce the sample flow to 50 cc/min. and drain the solution
from the reservoir. When drained, replace the drain cap and turn
off the sample flow.
g) Rinse by filling with distilled water and draining several times.
h) If the humidifier column still retains deposits on its walls, it should
be removed and cleaned with a brush and suitable cleaner. See
5-4
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Maintenance & Troubleshooting 5
Figure 5-2. After cleaning,
thoroughly rinse the column in
distilledwaterbefore
reinstalling.
NOTE: If electrolyte has severely etched the
column, it should be replaced.
i) After the reservoir and column
have been cleaned, refill the
reservoir as outlined in Section
4.1: Filling the Reservoir.
Removing the Humidifier
Column:
1) Grasp the tube, and with a
twisting motion, work it up into
the top humidifier block until it
clears the bottom block
completely.
2) Angle the bottom of the tube
towards you and twist it free of
the top block.
3) The top and bottom O-rings will
remain captive in their blocks.
To Reinstall:
1) Engage the top of the tube in the
top block at an angle and twist
up into the cavity of the top
block unit the bottom of the tube
clears the bottom block.
2) Swing the tube into line, and
twist down into the bottom
block until the tube seats.
NOTE: The flowmeter is similarly constructed
and can be removed and reinstalled
followingthesameprocedureoutlined
above.
Figure 5-2: Removing/Replacing the
Humidifier
Refer to the Spare Parts List in the Appen-
dix for replacement part numbers for the
Teledyne Analytical Instruments
5-5
5 Maintenance & Troubleshooting
Model 356WA
flowmetercolumnorhumidifiercolumn.
5.9 Leak Detection
The most frequent cause of trouble in trace measurement is leakage.
Tiny leaks which may be unnoticeable can cause serious errors in trace
measurements. One of the principal problems is that air can diffuse into a gas
line through a small leak, even though the gas pressure in the line may
greatlyexceedatmosphericpressure.
When a leak occurs in a system where the mass flow velocity is less
than the molecular velocity, gas molecules move in both directions through
the leak. The net flow of a particular gas, e.g. oxygen, will depend on the
relative partial pressure of that gas on each side of the leak. In a sample
having only a few parts-per-million oxygen, there will be a net flow of
oxygen inward unless the sample pressure is many thousands of pounds.
5.9.1 Leak Detection Procedure
The procedure outlined here is based on the premise that the leak rate is
independent of sample flow rate.
a) Stop the sample flow to permit oxygen to accumulate at the point
of the leak.
b) After approximately one minute, restart the sample flow. It is
advisable to practice establishing the flow rate to 150 cc/min., the
reference flow indication on the flowmeter, with one quick turn
of the throttle valve.
c) Simultaneous to restarting the flow, start a stopwatch to measure
the time required for the recorder/meter to respond to the
accumulatedoxygen.
d) The following are approximate times for the accumulated oxygen
to reach the cell from various points in the sample path through
the analyzer at 150 cc/min.
1.5 to 2 seconds
3.5 to 3.75 seconds
5.5 seconds
Calibrator
Base of humidifier column*
Flowmeter
6.5 seconds
Metering valve
7.5 seconds
> than 7.5 seconds
Gas connection at rear of analyzer
Sample connection lines leading to
analyzer
* A leak at this location may indicate a leak in the column or in the
reservoirsystem.
5.9.2 Cell Leak
5-6
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Maintenance & Troubleshooting 5
If there is no rise in oxygen reading when the sample flow is restarted in
step 5.9.1.b, the measuring cell should be checked for leaks. The two most
likely leaks locations are at the two terminal seal O-rings, or at the large O-
ring in the cell block mounting base.
Check that the terminals are screwed tightly into place. Frequently,
when a leak occurs at a terminal connection, a greenish crystalline deposit
will be found inside the cell around the terminal mounting screw. This is lead
carbonate, which is formed by carbon dioxide in the air reacting with lead
ions in the electrolyte.
If the large O-ring at the mounting plate is leaking, the oxygen indica-
tion will begin rising almost immediately after the sample flow is stopped. It
will continue to rise until sample flow is restarted, at which time it will begin
to gradually decrease.
Teledyne Analytical Instruments
5-7
5 Maintenance & Troubleshooting
Model 356WA
What To Do
Symptom
Cause
No analyzer response to
oxygen.
a) Poor electrical connection,
or F1 fuse (a standard 2
amp Slo-Blo fuse) has
blown.
a) Verify proper connection
from the cell through the
control unit to the external
recorder or meter; check for
blown fuse. Replace as
necessary.
b) Cell electrolyte level too
low.
b) Inspect electrolyte level and
add as necessary. See
Section 4.2.3, item 4.
c) Dirty cell.
c) Remove cell and clean
thoroughly. See Section
4.2.3.
d) Short between cell cathode
and anode (the screen to
lead [the base material] is
shorted.)
d) Correct short. Refill with
fresh electrolyte as needed.
e) If d) above corrects the
problem, the cell has
e) Check for excessive flow-
rate.
probably been poisoned,
probably by fluid flowing into
the cell humidifier column.
Check for excessive foam-
ing in the humidifier column.
Drain and clean reservoir as
necessary. Refer to Section
5.8.
f) Cell has been poisoned by a
component in the sample.
f) If there has been no change
in the normal sample
composition, a scrubber
may be required to remove
the offending component.
Cell lacks sensitivity.
a) Cell electrolyte level too low
due to misadjusted or faulty
humidity control.
a) Add electrolyte as neces-
sary. Adjust humidity
control. See Section 4.5.
b) Cell electrolyte too high,
due to misadjusted or faulty
humidity control.
b) Drain electrolyte and refill.
Adjust humidity control. See
Section 4.5.
c) Faulty humidity control.
c) • Shut off main power.
• Disconnect orange wire
from TS1 terminal 5,
place a voltmeter (set to
AC current, range 0–100
mA) in series with TS1-5
and the disconnected
orange wire.
CAUTION: High voltage AC
present.
5-8
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Symptom
Maintenance & Troubleshooting 5
What To Do
Cause
Cell lacks sensitivity (contin-
ued.)
Faulty humidity control (contin-
ued.)
• Turn humidifier control
completely counter-
clockwise.
• Turn on main power.
• While watching the
voltmeter, turn the
humidifier control clock-
wise; the meter reading
should go from 0–50
milliamps. If not, replace
the humidifier heater
element or the humidifier
heater control. To deter-
mine which should be
replaced, see paragraph
below.
If there is no current, either
the humidifier element or
control is defective. To
determine which it is:
• Turn the humidifier control
knob fully ccw.
• Disconnect the voltmeter
from TS1-5 and orange
wire. Reconnect the
orange wire.
• Change the voltmeter
function to 200V AC.
• Place the voltmeter
across TS1-5 and termi-
nal TS1-4.
• Watching the meter, turn
the humidifier control
knob cw and watch the
voltmeter read 0–110 to
120V AC.
• If not, replace R2 (behind
the control knob); see
paragraph below.
• If there is voltage, replace
the heater element; see
paragraph below.
Teledyne Analytical Instruments
5-9
5 Maintenance & Troubleshooting
Model 356WA
What To Do
Symptom
Cause
To replace humidifier
control:
• Shut off all power and
remove the AC power
cord from the power
source.
Faulty humidity control (contin-
ued.)
Cell lacks sensitivity (contin-
ued.)
• Refer to wiring diagram D-
18633 (upper right-hand
corner of the control unit.)
Remove the wiring and
controls. Replace R2 with
appropriate part, P/N P31.
To replace humidifier
heater element:
• Shut off all power and
remove the AC power
cord from the power
source.
• Refer to wiring diagram C-
18593 (left-hand side,
bottom of the cell com-
partment.)
• Pull out the block assem-
bly from the bottom of the
humidifier column; pull out
the heater element, and
unsolder the wires.
• Replace with new heater
element (P/N R139.)
Solder wires, turn the
terminals down into the
holder, and replace the
holder.
d) Verify that the power switch
is ON.
d) Cell compartment not at
proper temperature
(120 °F).
Check condition of 2A fuse.
e) • Remove the cell compart-
ment cover. Refer to
Interconnection diagram
A-18594 (upper left-hand
corner.)
e) Faulty triac (Q6) in heater
control or faulty triac driver
(A4).
• Connect voltmeter (set to
high AC) to terminals 1
and 2 of terminal strip
TS4 (Schematic diagram
D-18632, lower right-hand
corner; Wiring diagram C-
18593, upper left-hand
corner.)
5-10
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Symptom
Maintenance & Troubleshooting 5
Cause
What To Do
Cell lacks sensitivity (contin-
ued.)
Faulty triac (Q6) in heater
control or faulty triac driver (A4)
(continued.)
• Disconnect the thermo-
switch by removing one of
the wires from TS4
terminal 3. Meter should
show voltage.
• If voltage shows, short
terminals 3 and 4 with a
test jumper. Meter reading
should drop to about zero
(less than 10 VAC.)
• If power fails to go on and
off as jumper is alter-
nately installed and
removed between termi-
nals 3 and 4, the triac or
triac driver is probably at
fault and should be
replaced.
• If power does go on and
off, the thermoswitch (P/N
T22) is faulty and should
be replaced.
• If none of the above
improve the sensitivity,
replace the cell.
Teledyne Analytical Instruments
5-11
5 Maintenance & Troubleshooting
Model 356WA
5-12
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Appendix
Appendix
Specifications
Standard Ranges: Three ranges between 0-10 PPM and
0-5000 PPM O2 (0-2 PPM O2 avail-
able as an option).
SamplingSystem:
Wetted parts: 304 welded stainless
steel.
Sensitivity: 1% of low range.
Accuracy: +2% of low range.
Response and Recovery Time: 90% in less than 1 minute (for lowest
range).
Operating Temperature Range:
SampleRequirement:
+40 °F to +120 °F (+5 °C to +49 °C).
Flow: 150cc/min.*
Pressure: 1 to 150 psig.
Temperature: +60 °F to +100 °F
(+15 °C to +38 °C)
Power Requirement:
Alarms:
115 VAC, 50/60 Hz, 150 W (other
voltagesavailable.)
Adjustable single or dual alarm (op-
tional)setpoints.
Recorder Signal Output:
Voltage: 0-1 VDC or less.
Current: 1-5, 4-20, 10-50 mADC
(optional.)
Local Readout: Digital or analog meter.
* Specified flow rate required only during calibration. Measuring
cell is not sensitive to changes in flow rate.
A-1
Teledyne Analytical Instruments
Appendix
Model 356WA
Spare Parts List
QTY.
PART NO.
DESCRIPTION
1
1
B1473
C1372
Leadelectrode
Cellassembly
NOTE: Specify cell class and range of analyzer when ordering.
2
1
1
2
2
2
1
1
1
1*
1
5
5
2
1
1
O5
O25
O26
O9
O-ring,cellterminal
O-ring, cell seal
O-ring, calibratorcoverplate
O-ring,humidifiercolumn
O-ring, reservoir cap
O-ring,flowmeter
Thermistorassembly
Humidifiercolumnassembly
Humidifier column heater (110V)
Humidifier column heater (220V)
Reservoir cap
Fuse, 3AG-2A
Fuse, 3AG-1/4A, Slo-Blo
Heater
Flowmeter asm. (specify background gas)
PC Board, Proportional temp. control
(For applications 10 PPM or higher)
O8
O204
A33748
A3042
R2454
R2453
A5267
F10
F6
H2
B6274
B30868
1*
1
B36026
C14449
PC Board, Proportional temp. control (220V)
PC Board, Proportional temp. control
(For applications less than 10 PPM)
1*
1*
1*
C41274
B29600
A9309
PC Board, Proportional temp. control (220V)
PC Board, E/I converter, isolated (O option)
PC Board, Alarm comparator, dual (-2 opt.)
* optional
A minimum charge is applicable to spare parts orders.
IMPORTANT: Orders for replacement parts should include the model num-
ber, serial number, and range of the analyzer for which the
partsareintended.
A-2
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Appendix
Orders should be sent to:
Teledyne Analytical Instruments
16830 Chestnut Street
City of Industry, CA 91749-1580
Phone (626) 934-1500
FAX (626) 961-2538
TWX (910) 584-1887 TDYANLY COID
or your local representative
Drawing List
A-5855
Outline
A-47143
D-47142
B-30364
B-14718
B-15016
D-22297
D-47139
B-21916
Piping
Schematic
Schematic
Schematic
Schematic
Wiring
Wiring
Interconnection
A-3
Teledyne Analytical Instruments
Appendix
Model 356WA
Calibration Data
Range
The ranges of this analyzer are:
Range Switch Position No. 1
Range Switch Position No. 2
Range Switch Position No. 3
PPM O2
PPM O2
PPM O2
Output Signal
The output signal is
D.C.
Background Gas
This analyzer is intended to measure oxygen in a background of:
The flowmeter has been set to indicate a flow of 150 cc/min. of this gas.
If any other type of gas is to be analyzed, the flowmeter must be reset for that
gas, using a displacement type flowmeter, when the flow is set to 150 cc/
min.
Cell Class:
Electrolyte Type
Type A: 10% potassium hydroxide in distilled water
Type B: 10% potassium carbonate in distilled water
Type C: 20% potassium bicarbonate in distilled water
Calibration Considerations
In order to calibrate the Model 356, all that is required is to center the
float of the flow tube in the target, add a known quantity of oxygen (0–100
PPM) via a calibrated span gas and adjust the span potentiometer to match
the known oxygen concentration of the span gas. It should not be necessary
to compensate for changes in altitude or ambient temperature.
The flow tube is a mass flow device and therefore automatically com-
pensates for altitude changes should the instrument be moved to a higher
elevation (in this instance a higher span setting will be required since the
sensing element is sensitive to the partial pressure of oxygen).
The ambient temperature does not affect the flow rate through the
analyzer since the flow tube is located in the same temperature controlled
compartment as the cell assembly.
A-4
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Appendix
When span gases are used or when sample gas is being analyzed the
flow can vary ±10–20% and more without changing the reading. It is best,
however, to keep the sample flow so that the float in the flow tube is at or
near the center of the target. Otherwise, a different humidifier setting may be
required.
If positioning the float in the center of the target is in error by plus or
minus one-quarter of the float’s diameter, an error of approximately ±1.5%
*
of reading will be produced.
There are instances when it will be necessary to reset or check the exit
flow of sample gas and set or reset the position of the target on the flow tube:
•
•
When a different background gas is being analyzed.
When the target has been accidently repositioned on the flow tube.
The vent flow should be measured either with a volume displacement
flow device (e.g. a “bubble-o-meter”) or a calibrated rotometer with correc-
tion factors for ambient temperature and pressure, and sample gas density
and viscosity. When using a volume displacement flow device it will be
necessary to correct the 150 cc/min flow rate for ambient temperature and
pressure. It will also be necessary, using either type of flow measuring
device, to compensate for the increase in flowrate due to humidifying the
sample gas. (The flow tube inside the analyzer is measuring the dry gas
flowrate.)
To determine the corrected vent flow rate it will be necessary to know
the ambient temperature (in °K), the ambient pressure (in mm Hg) and the
vapor pressure of water at ambient temperature.
Ambient temperature can be measured in °Centigrade or °F and con-
verted to °K.
Degrees C = 5 (°F -32)
9
Degrees K = °C + 273
Ambient pressure can be measured with an accurate barometer.
P
= P(in Hg) x 760
30.00
(mm Hg)
*
If the actual oxygen concentration were, for example, 8.0 ppm, the
resultant reading would be 7.9 (float high) or 8.1 (float low).
A-5
Teledyne Analytical Instruments
Appendix
Model 356WA
or by knowing the altitude
P(mm-Hg) = 760 - (2.50 per 100 ft. of altitude)*
The vapor pressure of water at ambient temperature can be obtained
from Table 1.
To determine the corrected flow (Fcorrected), substitute the ambient tem-
perature, pressure and vapor pressure of water in the following formula:
T
760 mm Hg
P
P + Pwater
F
=150cc
×
×
×
min
corrected
294° K **
P
Where:
T = ambient temperature (in °K)
P = ambient pressure (in mm Hg)
Pwater = vapor pressure of water at ambient temp. (in mm Hg)
By way of example, suppose that the target’s position on the flow tube
is in question and it has been determined that the ambient temperature is 77
°F and the altitude where the instrument is being used is 5000 ft. above sea
level.
5
Ambient Temp: ° K = 77 −32 +273 =298° K
(
)
9
Ambient Pressure: P(mm Hg) = 760 - 2.50×50 = 635 mm Hg
(
)
Vapor Pressure of Water (at 298° K): 23.9 mm Hg
298 760 635+ 23.9
Corrected Flow:
F
= 150×
×
×
= 189 cc
min
corr
294 635
635
*
This approximation is within ±0.5% of the ICAO Standard Atmo-
sphere over the range 0-7500 ft. above sea level. Ref: “Fluid Mechanics for
Engineering Technology” by Irving Granet, Prentice Hall, pp 83–84.
**
Reference ambient temperature : 294 °K (21 °C) was the ambient
temperature used in the Faradaic calculations.
A-6
Teledyne Analytical Instruments
Trace Oxygen Analyzer
Appendix
From these computations, the exit flow rate should be set to 189 cc/min.
using an appropriate flow measuring device and the target respositioned if
necessary so that the float is centered within the target opening.
Subsequently, it should not be necessary to measure the exit flow unless
another circumstance, of the type listed above, occurs.
A-7
Teledyne Analytical Instruments
Appendix
Model 356WA
Table 1:
Vapor Pressure of Water
(From 288–308°K)
Ambient Temperature (°K)
Vapor Pressure of Water (mm Hg)
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
12.9
13.7
14.6
15.6
16.6
17.7
18.8
20.0
21.2
23.9
23.9
25.4
26.9
28.6
30.7
32.1
34.0
35.9
38.0
40.2
42.5
NOTE: The MSDS on this material is available upon request
through the Teledyne Environmental, Health and
Safety Coordinator. Contact at (626) 934-1592
A-8
Teledyne Analytical Instruments
|