COSA Xentaur XPDM Operating Manual
1. Introduction
The XPDM is a portable, hand-held, microprocessor controlled, battery operated dewpoint meter with built in dry-storage for the sensor. The instrument is ideally suited for all
applications, where quick and precise measur ements are required.
Standard Equipment:
1. XPDM Portable Instrument with
sensor, desiccant cartridge and
lithium battery.
2. 2 VCO to Swagelok fittings and 2
Swagelok to barbed hose fittings.
3. Calibration bulb.
4. Shoulder strap.
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Optional Equipment:
5. VCO to VCO Fittings.
6. Pig tail.
7. Flexible stainless steel hose.
8. Pressure regulator, all stainless
steel, (preset at 1.5 atm) with
mounting bracket.
9. Coalescing filter, all stainless steel
with mounting bracket.(not shown)
10.Wall transformer (with factory
installed I/O option).
11.Replacement desiccant cartridge.
12.Padded transport case.
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2. Precautions
• Warranty limitation: The XPDM’s sample cell/piston assembly should not be disassembled except by factory trained personnel. The warranty is voided, if the sample
cell piston assembly is disassembled by the customer.
• Avoid contaminated sample streams: The XPDM has been designed to allow for fast
and precise measurements of dewpoints as low as -100 °C. Therefore, all surfaces in
contact with the sample stream are made from electropolished stainless steel. This
minimizes the time for the instrument to reach equilibrium with the sample stream,
thus speeding up the measurement. The introduction of corrosive gases or gases
contaminated with oils, solvents etc. may damage or coat the electropolished surfaces and slow down the measurement. Surfaces contaminated with oils etc. can be
cleaned by factory trained personnel (please contact your sales representative). Surfaces damaged by corrosive gases are damaged permanently, causing longer
response times. Gases containing chlorine, ammonia, HCl or SO2 may also cause
damage to the sensor. SO2 can be monitored when the moisture content is low.
• Avoid liquid water: Avoid the introduction of liquid water into the sample cell, as this
may damage the sensor. Do not breathe directly into the instruments sample ports,
as condensation may form which could damage the sensor element. If liquid water
can not be av oided, or der the XTR-65W senso r which is w ater proof , b ut has a limit ed
range, and a slower dry down response.
• Avoid high pressure: The XPDM has been designed for operation at pressures
slightly above atmospher i c, however each sample cell/sensor piston/dry-storage
assembly has been tes ted for pressures up to 120 PSI. Do not introduce sample
streams, whi ch could cau se pressure rises ab ov e 100 PSI. Mak e your m easurements
at atmospheric pressures, and use the pressure calculation feature to calculate dewpoints at higher pressures. Ask your representative for a regulator installation kit.
• Exercise Caution with Hazardous Gases: Please use appropriate precautions if the
sample you are about to measure is hazardous. Place the unit in a safe area, if it is to
be used with hazardous gases. Please be aware that the possibility of a small leak
always exists. Such a leak will not influence the accuracy of the measurement, but
may represent a risk if the sample gas is of hazardous nature.
• Avoid Extreme temperatures: Do not install the unit near heat sources such as radiators or air ducts. The instruments’ operating temperature range is -10°C to 50°C.
• Avoid Mechanical Vibration: Do not install the unit in places subject to extreme
mechanical vibration or shock. Use resilient mounting, if shock and vibration are not
avoidable. Call your representative if in doubt.
• Avoid long exposures of sensor element to room air: For reasons explained later in
this manual (section 7), do not expose the senso r to room air for longer then necessary (1 - 2 Minutes). The sensor is exposed to room air, when the sensor actuator is
in the out position and no sample line is connected, or the sample gas is shut off. It is
best to push the sensor bac k into d ry-storage , after a measu rement is co mplete d and
whenever the instrument is not in use.
• Do not force the Actuator: Remove any port obstructions (such as shipping caps)
before operating the Actuator.
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3. Principle of Operation
Dewpoint sensors, like all hygroscopic materials, adsorb much faster than they desorb.
Therefore, an accurate measurement will be obtained much faster, if at the beginning of
the measurement, the sensor is at a dewpoint drier than the gas to be measured. The
XPDM design allows the sensor to be moved directly between dry-storage and the sample
cell, without any exposure to ambient air.
Sensor in Sensor In
dry-storage position measuring position
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1. Sample Ga s In 7. Sensor Actuator
2. Sample Gas Out 8. Desiccant Chamber
3. Piston 9. Filter Mesh
4. Sample Cell 10.Electronic Board
5. Sensor 11.Instrument Case
6. Spring loaded PTFE seals
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The drawin g on the left sho ws the XPDM with th e sensor in dry-storage position . The sensor is enclosed in a gas-tight container and surrounded by desiccant. The sample gas
passes through the sample chamber and prepares the environment for measurement.
Blocking of the outlet port will pressurize the sample chamber and move the piston into
the position sho wn on the right. The sensor is no w exposed to the sam ple gas without ev er
having b een exposed to ambient air. Af ter t he measurement is ta ken, pushin g in the sensor actuator will return the sensor into dry-storage, where it will dry down and ready itself
for another fast measurement.
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A note about dry-storage
The dry-storage consist of a stainless steel container filled with desiccant. The electropolished st ainless steel sensor guard slides between the dry-storage and the sample
cell through a spring energized PTFE seal, assuring maximum possible gas tightness
and minimum gas transport between the two chambers when the sensor is moved. When
in dry-storage, the sen sor guar d is separ ated from the de siccant b y a stai nless stee l wire
mesh with a thic kness of 127µ (0. 005”) and a me sh size of 100µ . This k eeps the distance
between the sensor and the desiccant to a minimum, which is critical for fast and low drydowns, while protectin g the sensor from contamination with desiccant particles.
The factory supplied desiccant provides dry-storage dewpoints as low as -80°C when
fresh. When the sensor is pushed into dry-storage it will take some time to dry down
completely and reach equilibrium with the dewpoint in the dry-storage. The dry-down
time to equilibrium depends on how wet the sensor was before it was returned to drystorage, and in case that it was completely wet, how long it had remained in wet condition.
To take full advantage of the dry-storage, make sure, that the dry-storage dewpoint is
below the expected dewpoint of the sample gas by periodically checking the indicated
dewpoint afte r the senso r has remain ed in dry-storag e f or an e x tended period of time , f or
example o ver night. Rep lace the d esiccant cartridge, if th e dry-storag e de w point is m uch
higher than -80°C and above your expected sample dewpoints.
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4. Operating the XPDM
4.1. Sample Hook-up
4.1.1. Fittings
The XPDM can be hooked up to the sampl e ga s usi n g a variety of fitting s , d ep end i ng o n
the application. The instruments’ sample ports are 1/4” VCO female, to assure proper
seals for even the lowest dewpoint measurements.
Depending on the application and needs, we recommend the use of one of the following
methods of attachment:
•VCO
stainless steel hoses, available optionally.
•VCO
nections are acceptable.
•VCO
above -65°C and should in all cases be used only with PTFE tubing.
4.1.2 Recommended Pipes
Stainless steel pipes should be used exclusively, for dewpoints below -65°C. You r representative ha s a fle xible s tainless steel ho se av ailab le. The length of the sam ple line to the
instrument should be kept as short as possible, to assure fast equilibrium. We recommend
the attachment of at lea st 12" long stainless stee l pipe at the outlet port to avoid bac k flow
of ambient air when sampling at low flow rates, ask your representative for the optional
pigtail.
PTFE tubes are perfectly acceptable, and offer advantages due to their flexibility, for dewpoints above -65°C. However, PTFE tubes should be kept as short as possible.
Under no circumstance s use rubber or plastic tube s, which are both, hygrosco pic and permeable. No valid measurements can be expected when such materials are used.
VCO: This method is ideal for all applications, including the use of flexible
➜
Swagelok: This method is suitable for all applications where rigid pipe con-
➜
Swagelok ➜ Barbed Hose Fitting: This method is acceptable for dewpoints
➜
4.1.3. Sample condition ing
• Pre-filters: Do not use any pre-filters for oil, particles or liquid water when measuring
dewpoints below -65°C. Pre-filters store and release water vapor, and slow down and
distort the measurement at low dewpoints.
• Pressur e re gulators: Do not use a pressure regulator containing any materials other
than stainless steel, for dewpoints below -65°C. To ensure the use of the right product, use regulators provided by your sales representative.
4.2. Measuring
• Turn the unit on by pushing the Power button.
• Select the desired engineering units, using the up or down buttons.
• Take note of the indicated dewpoint while the sensor is still in dry-storage.
• Introduce the sample gas into the unit while the output port is unobstructed. Wait one
minute, for ev ery 10°C below 0°C of expected dewpoint, to allow the sample chamber
to adapt to the sample dewpoint.
• Block the outlet po rt. The smal l pressure build-up in the sam ple chamber should be
sufficient to push out the piston and move the sensor into the sample chamber. If not
sufficient, assist by gently pulling on the sensor actuator located on the front of the
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instrument, while still blocking the sample outlet port.
• Observe the change in dewpoint indication. The reading will be stable within about 3
minutes, if the dewpoint is increasing. A longer stabilization period will be required, if
the dewpoint is decreasing. Make sure the reading has completely stabilized before
taking the final reading. After the reading is taken, push the sensor actuator back into
the dry-down position.
Note that when the instrumen t is being op er ated on a batte ry it will shut off aut omatica lly
if no buttons are pressed for: 6 minutes when sensor is in the sample chamber (the out
position), or 3 minutes when sensor is in the desiccant.
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5.0 The User Interface
The user interface consists of a custom LCD display, an audio indicator, 5 push buttons
and a sensor actuator.
5.1 Display Conventions
1. To display letters with the 7 segment numeric display, the following pseudo-alpha-
numerics are used:
Numbers:
0123456789
Letters:
ABCDEFGHI JLNOPQRSTUXYZ
$%&'( ) *+, -/12345678;<=
Symbols:
?- .
"
2. The instrument will indicate whether a particular mode lets you change a parame-
ter by showing the word “SET” in the upper left corner of the display. Be careful
not to change any parameter inadvertently.
3. °C°F appear simultaneously, to indicate the sensors’ attenuation in decibels.
4. Values higher than ±1999 and lower than ±0.01 are displayed in powers of 10±3.
Either a “10 3” or “10-3” will appear above and to the right of the displayed value, if
this is required, and the value will be rounded off to 3½ digits. Examples follow:
actual
value +20°C+68
DEWPOINT
˚C
DEWPOINT
F 23612 1104.2 17.688
°
ppmV lbs H20/mmSCF grams H20/meters
3
x10
˚F
DEWPOINT
PPM
DEWPOINT
LBS
DEWPOINT G/M
actual
value -100°C -148°F 0.013849 0.00092115 0.00001475
ppmV lbs H20/mmSCF grams H20/meters
DEWPOINT
-3
x10
˚C
DEWPOINT
˚F
DEWPOINT
PPM
DEWPOINT
x10
LBS
-3
DEWPOINT G/M
3
3
x10
3
3
-3
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