Teledyne Oxygen Equipment 356WA User Manual

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.  
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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  
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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  
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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.  
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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 or higher.  
Output is 0 to 1VDC or less (optional: 1 to 5, 4 to 20, or 10 to 50 mADC).  
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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-  
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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  
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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  
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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  
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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.  
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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  
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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.  
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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  
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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.  
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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  
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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.  
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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  
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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.  
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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  
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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.  
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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  
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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.  
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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  
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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  
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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  
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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  
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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  
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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.  
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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  
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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.  
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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  
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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.  
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5 Maintenance & Troubleshooting  
Model 356WA  
5-12  
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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  
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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  
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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  
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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  
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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  
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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.  
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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.  
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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  
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