instruction
manual
Model 8800T
TRACE MOISTURE ANALYZER
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
8800T User’s Manual
i
8800T User’s Manual
8800T User’s Manual Table of Contents
1.0 Overview of the 8800T .................................................1
2.1 Precautions using the sensor .........................................3
2.2 Sensor Technical Specifications ...................................4
2.3 Sensor Installation & Sampling Techniques .................4
2.3.1 In-situ Installation ......................................................5
2.3.2 Extractive Installation ................................................7
2.4 Troubleshooting unexpected readings ..........................9
3.1 Precautions using the 8800T .......................................13
3.1.1 Electromagnetic Compatibility Considerations .......13
3.2 Instrument Technical Specifications ...........................14
3.3 Installation ..................................................................15
3.3.1 Mechanical Installation ............................................15
3.3.2 Electrical Installation ...............................................16
3.4 Operating the Instrument ............................................17
3.4.1 Starting up ................................................................17
3.4.2 Display Conventions ................................................17
3.4.3 Push Buttons ............................................................19
3.4.4 Operating State ........................................................19
3.4.4.1 Viewing Dewpoint Mode ......................................20
3.4.4.2 Viewing Temperature at the Sensor ......................20
3.4.4.3 Start Calibration (SpanCheck™) Mode ................21
3.4.4.4 Viewing Serial Number Mode ..............................24
3.4.5 SetUp State ..............................................................24
3.5 Troubleshooting the Instrument ..................................28
Appendix A: Operating State User Interface flowchart ....31
Appendix B: Set-Up State User Interface flowchart .........32
Appendix C: 8800T Mechanical Drawing ........................34
Appendix D: 8800T Electrical Connections .....................35
Appendix E: Sensor/SpanCheck™ Theory of Operation .36
Appendix F: Pressure Correction ......................................39
Appendix G: Current vs. Dewpoint ..................................40
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8800T User’s Manual
Appendix H: Uncertainty in LBS & ppmV calculations ..43
Appendix I: Sensor Response Time ..................................44
Appendix J: Return Authorization Request ......................45
iii
Section 1: Introduction
1.0 Overview of the 8800T
The 8800T is a microprocessor based 4-20mA loop powered
(2 wire) hygrometer, for measuring moisture content in
gases in the range from -100°C to +20°C. The measurement
is displayed on the instrument’s custom LCD, and is transmitted by varying the current drawn (4-20mA) from the
power supply. The current varies linearly proportional to the
selected measurement units. An optional digital output is
available which modulates/demodulates the 4-20mA loop
line without interfering with its operation. With this option
the 8800T is capable of communicating with properly
equipped Personal Computers or other RS-232 capable controllers. Three front panel buttons provide the user with a
wide variety of features. The 8800T’s advanced design
allows it to be housed in a small stainless steel enclosure
behind the sensor probe, thus the instrument and sensor are
a single integrated unit.
The 8800T uses the Teledyne HTF™ sensor which is encapsulated in sintered stainless steel, thus it is capable of coming into contact with a wide variety of environments.
However one should keep in mind that the sensor is a sensitive device and it should be handled accordingly.
page 1
8800T User’s Manual
page 2
Section 2: Sensor and Sampling Techniques
2.1 Precautions using the sensor
The Teledyne HTF™ Al2O3 sensor is designed and field
proven to be highly reliable, rugged and maintenance free.
However the user should consider the following precautions:
• To avoid the need for prolonged dry-down (when
expecting to measure dewpoints dryer than -65ºC), do
not expose the sensor to room air longer than necessary
(1 - 2 minutes). Thus, do not open the sensor container
before you are ready to install the sensor.
• The sensor container has desiccant to keep the sensor
dry during shipping and to avoid damage due to condensation. Close the container immediately after removing
the sensor to avoid degradation of the desiccant.
• Do not throw away the sensor container, you may use it
again to transport the sensor between locations, to store
it between uses or to ship it back to the factory for certification. The container can be attached to the loop cable,
by trapping the cable with the lid strap.
• Do not expose the sensor to corrosive gases such as
gases containing chlorine, ammonia or HCl. (SO2 can
be monitored when the moisture content is low).
• Except for the XTR65W sensor:
1. Do not expose the sensor to liquid water, as it may get
damaged.
2. Do not breathe directly onto the sensor, as condensation may form which could damage the sensor element.
• Do not install the sensor near heat sources such as radiators or air ducts.
• Do not install the sensor in places subject to extreme
mechanical vibration or shock. If this is not avoidable,
use resilient mounting. If in doubt, call your representa-
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8800T User’s Manual
tive.
• Do not disassemble the porous metal filter encapsulation, as this will damage the sensor and void your factory warranty.
• Prior to installation of the probe, ensure that no contaminants are present in the system (e.g. oil, liquid water).
2.2 Sensor Technical Specifications
Type: .................................Hyper Thin Film high capacitance Al2O3.
Dewpoint range:
XTR-100........................-148°F to +68°F (-100°C to +20°C)
XTR-65..........................-85°F to +68°F (-65°C to +20°C).
Capacitance:......................15nF to 200nF.
Accuracy:..........................±5.5°F (±3°C).
Repeatability:....................±0.9°F (±0.5°C).
Response time:..................see graph in Appendix I.
Temperature range:...........-10°C to +70°C.
Sample Flow range:
(linear velocity @ 1ATM):Static to 100m/s.
Storage temperature:. ........-40°F to+176°F (-40°C to +80°C).
Mechanical:.......................encapsulated in 100µ sintered stainless steel.
Calibration method: ..........SpanCheck™, sensor saturates at dewpoint above
+68°F (+20°C). NIST/NPL traceable multi-point
factory calibration available optionally.
2.3 Sensor Installation & Sampling Techniques
Keep in mind that the moisture content at the sensor is not
only due to the moisture of the gas being measured, but also
due to desorption of water from tubing, trapped moisture (at
the interconnection points, valves, filters and other hygroscopic materials in the system), leaks in the system, and others. Thus the measurement may vary from the expectation,
and therefore care should be taken in choosing the sampling
technique utilized in the measurement. Factors such as gas
pressure, flow rate, materials of construction, length and
page 4
Section 2: Sensor and Sampling Techniques
diameter of tubing, number of interconnecting fittings, dead
space in tubing and manifolds; will influence the measurement value and response time.
The high capacitance HTF™ sensors can be installed either
directly in the line to be sampled (in-situ), or in a slip stream
of a sample system (extractive).
To assure a long and accurate performance of the sensor, it
should be protected from contaminants such as liquids
(water, oil etc.), and particulates. The sintered stainless steel
sensor encapsulation protects from particulates larger than
100 microns, finer particulates (e.g. from degraded desiccant or rust) should be filtered with a particulate filter with
suitable capability, do not use hygroscopic filter materials.
2.3.1 In-situ Installation
In-situ installation is recommended only for measurements
where the gas pressure is expected to vary little, the gas is
expected to be free of contaminants, the gas temperature is
wit hin the oper a ting s pec if ic at ions of the se nsor , a nd th e re is
no chance of liquids coalescing. Examples of applications
suited for in-situ installations are: pure gases, output of desiccant dryers (for instrument air), glove boxes, etc. For most
other applications in-situ installation should be avoided for
the following reasons:
• Sample conditioning is almost always necessary to
avoid exposure of the sensor to liquid water and other
contaminants, such as hydrocarbons, which may damage the sensor or affect accuracy over time.
• Variations in line pressure affect the reading of the sen-
sor because dewpoint varies with pressure.
• If the gas line is under pressure, it is more likely that
water condensation occurs which may damage the sensor.
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8800T User’s Manual
• Under a pressurized system removal of the sensor with-
out the installation of isolation valves can be dangerous.
If in-situ installation is required, bypass mounting is preferable; make sure to install the sensor at the upper surface of
the gas line to minimize its exposure to liquid water, should
condensation occur, the XTR65W sensor is best suited for
these applications. Also consider the need to isolate (depressurize) before installing or removing the sensor.
4-20mA loop cable
Main
Gas Line
8800T
oint Transmitter
Think
Read
Safety
www.xentaur.com
Mo
In-Line Installation, Sensor
Se
Manual
Measuring at Line Pressure
Ma
NOT RECOMMENDED
4-20mA loop cable
8800T
oint Transmitter
Think
Read
Safety
www.xentaur.com
Mo
Se
Bypass Installation, Sensor
Manual
Ma
Measuring at Line Pressure
Safety shut-off Valve
Safety shut-off Valve
Sample Cell
Bypass
Main
Gas Line
Control
Valve *
* maintain differential pressure to provide adequate flow through sample cell
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Section 2: Sensor and Sampling Techniques
2.3.2 Extractive Installation
For extractive installations we recommend our sample system ESS, which may be equipped with a variety of features,
such as: isolation valve, coalescing or particulate filter,
pressure regulator , calibration sample injection or ext raction
port, pressure gauge, flow meter, weatherproof enclosure.
Refer to the ESS literature for more information.
If the resources to make your own sample system are available, the following two diagrams may be used as a guideline
to configure a simple system.
4-20mA loop cable
Safety shut-off Valve
oint Transmitter
Think
Safety
8800T
Read
Manual
www.xentaur.com
Exhaust
Mo
Se
Ma
Regulator or
Needle Valv e
Main
Gas Line
4-20mA loop cable
Regulator or
Needle Valv e
Main
Gas Line
Sample Cell
Extractive Installation, Sensor
Measuring at Line Pressure
8800T
oint Transmitter
Mo
Se
Think
Read
Manual
Safety
Ma
www.xentaur.com
Exhaust
Sample Cell
Extractive Installation, Sensor
Measuring at Ambient Pressure
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8800T User’s Manual
It is generally recommended to measure at ambient pressure
for the following reasons:
• The readings will not be affected by variations in line
pressure.
• The risk of exposing the sensor to liquid water is signif-
icantly reduced.
• ppm readings are computed for a pressure of one atmo-
sphere (1 bar); and have to be corrected using software
in the instrument, or a pressure nomograph, or calcula-
tor if the sensor is measuring at different pressures.
If readings at line pressure are necessary, it is recommended
to measure at ambient pressure and to use the instrument’s
pressure compensation feature to calculate the dewpoint at
line pressure. See appendix F.
Please make sure that:
• The sample is taken from the upper surface of the main
gas line. This avoids problems with contamination. The
sample should be taken away from pipe line walls where
flow rates may be low, and dewpoint changes may lag.
• For dewpoints dryer than -40°F, use stainless steel tub-
ing only. Copper tubing is acceptable for dewpoints wet-
ter than -40°F. Do not use plastic, rubber or tygon tubing
under any circumstances, as measurements would be
incorrect and/or response time slow due to water reten-
tion inside these materials.
• Try to run pipes to the sensor upwards, so that contami-
nants tend to fall back into the main line.
• Keep the length of the sample line to the sensor as short
as possible.
• Use small diameter pipes (1/4” or 1/8” OD).
• Use sufficient flow rates (e.g. 1 l/min with 6 feet of 1/8”
piping is adequate). The flow rate will influence the sys-
tems’ response time.
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Section 2: Sensor and Sampling Techniques
• Do not install any devices upstream of the sensor, such
as other measuring systems, flow meters etc., which are
not absolutely necessary as these are potential leak
sources.
• Installation of a coalescing and / or particulate filter
ahead of the sensor is desirable to prevent any liquid or
particulate contamination of the sensor.
• If filters are used upstream of the sensor, make sure
these contain non-hygroscopic filter materials only.
• If pressure regulators, shut off valves etc. are used
upstream of the sensor, make sure these do not contain
rubber or other hygroscopic materials.
2.4 Troubleshooting unexpected readings
If erroneous readings are suspected on a newly acquired
instrument, compare the serial number engraved on the sensor sintered filter, to the one stored in the instrument memory. The two should be the same; if they are not, the
instrument may not be calibrated with the installed sensor.
To troubleshoot other problems, identify the unexpected
reading category in the following table, and consider the
possible causes and appropriate diagnostic action and remedy.
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8800T User’s Manual
Troubleshooting unexpected readings (table spans 2 pages)
Symptom Possible Cause
Reading is not
changing
Slow Response
Dry Reading SpanCheck™ wrongly set, or faulty sensor.
We t Read ing
Display Shows
Condensation in sample system.
1. Water vapor in the system.
2. Flow rate too low.
3. Sample pipe too large and/or too long.
4. Unsuitable sample pipe material.
5. Leaks
6. Hygroscopic materials in sample system
Leak in system or use of unsuitable pipe.
Comparison of readings with manual cooledmirror instrument.
Prolonged exposure to wet gas.
6$7
Display Shows
1. In st ru men t F a i lu re
6+5
2.Short circuited sensor.
Display Shows
231
1. In st ru men t fai lu re.
2. Open circuit on sensor.
For non-sensor related problems (e.g. no reading on instrument) refer to section 3.5
page 10
Section 2: Sensor and Sampling Techniques
Troubleshooting unexpected readings (continued from previous page)
Symptom Diagnostic/Remedy
Reading is not
changing
Slow Response
Dry Reading Veri fy SpanCheck™, or return sensor for full calibration to your representative.
We t Read ing
Display Shows
6$7
Display Shows
6+5
Display Shows
Condensation will occur if the temperature of the sample system, at any point is below
(colder) the dewpoint temperature of the sample gas. Once having formed, the sample
reaching the sensor will have a dewpoint equal to the temperature of the condensation,
regardless of the dewpoint of the sample at the sample point.
It is usually more satisfactory to bleed a sample gas at atmospheric pressure through
the sensor sampling chamber, and to use 1/8” (3mm) o.d. sample pipe.
See below re: sample pipe material, also see section 2.3
Cure the leak, or replace unsuitable pipe with copper or stainless steel. Flexible connections should be made with PTFE pipe. NEVER use rubber or plastic pipe.
This type of indicator reads about 10°C dry at about -50°C dewpoint due to temperature gradi ent s wit hin the de vi ce. Th e error in cr ease s at drier levels.
Dry the sensor, install sensor in either a known dry gas stream i.e. instrument quality
air or dry nitroge n, or place sensor in a dry can or bottle of desiccan t an d seal the container from outside air (the shipping container is designed for this purpose)
Remove (unscrew) sensor, if the instrument still reads
instrum ent. Howeve r , if the instrument rea ds
Remove (unscrew) sensor and note that the meter reading returns to
sensor, or apply approximately 20V DC, between the center pin & the filter body of
the sensor, MOMEN T AR ILY with the s ensor in a known dry condition. Pola rit y is not
important, but the contact MUST be very brief or the sensor may be damaged.
Remove (unscrew) the sensor. Short the center contact of the 8800T sensor connection
to the case, if the ins trumen t read s
the instrument for service.
231
the problem is in the sensor, otherwise return
6+5
the problem is with the
6+5
then check possible cause #2
. Use a new
231
231
Check sensor connection or replace sensor.
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8800T User’s Manual
page 12
Section 3: Instrument
3.1 Precautions using the 8800T
The 8800T uses state-of-the-art microelectronics to provide
a miniature full functioning instrument. The user should
consider the following precautions when using any sensitive
electronic device.
• Do not install the unit near heat sources such as radia-
tors or air ducts.
• Do not install the unit in places subject to extreme
mechanical vibration or shock. If this is not avoidable,
use resilient mounting. If in doubt, call your representa-
tive.
• Observe the appropriate electrical safety codes and reg-
ulations
• If weather proofing is required consult your representa-
tive for an optional cover.
3.1.1 Electromagnetic Compatibility Considerations
The 8800T has been designed and verified by testing to
meet the requirements of the EC Council EMC Directive
89/336/EEC, for Industrial, Scientific & Medical equipment. The sensor ground (8800T housing) is isolated from
the 4-20mA loop, however they are also shunted with a
2000pF capacitor and a 33V Transient Voltage Suppressor;
this prevents electrostatic buildup, noise pick-up, and in
conjunction with the internal fuse protects the instrument
from over-voltage inputs. Please consider the following
electromagnetic interference issues during installation:
• In order to provide an acceptable noise environment for
the 8800T or any other digital equipment in the proxim-
ity of inductive loads, it is recommended that there be
varistors placed across the inductors to keep down the
high voltage spikes during transitions.
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8800T User’s Manual
• Any circuitry which is activated by relay contacts
should account for the contact bounce, one simple
debouncing method is placing a capacitor across the
relay contacts.
• AC power wiring should be routed as far away from the
8800T and its wiring as practical.
3.2 Instrument Technical Specifications
Enclosure:.........................Stainless Steel, optional weather proof cover is avail-
able.
Dimensions & Weight:......~2”Dia. x ~4.75” long including sensor & connector
(see appendix C) 0.5lbs.
Pressure operating range:..Standard:.....500 PSI (34 bar).
Optional:.....5,000 PSI (340 bar).
Mechanical connections:...14mm x 1.25mm threads, and ¾”-16 threads.
Electrical connections:......2.1mm x 5.5mm (12mm minimum barrel length)
power jack, with retainer.
Cable:................................Two conductor cable, 12’ (~4m) provided.
Power Requirements:........10 to 33 VDC polarity independent, the instrument
draws 4-20mA depending on measured dewpoint.
Input resolution:................0.1°C dewpoint.
Indicators:.........................3.5 digit LCD with custom legends.
Engineering units:. ............°C,°F, PPM, LBS H
Controls:............................3 push buttons, user’s selections are stored in
EEPROM.
Outputs:.............................Analog and digital outputs are available from the
8800T.
A. 4-20mA drawn by the instrument from the power
supply. The 4-20mA is linear to the selected engi-
neering units, the range is programmable. Output
resolution is 0.1°C dewpoint.
B. The instrument can supply digital output by
modulating the 4-20mA loop line. The timing and
format of the data conforms to RS-232, however to
interface to a PC or other RS-232 device an optional
adapter is required.
In the digital mode the 8800T can be remotely
operated and the dewpoint as well as temperature
O/mm scf,gm H2O/M3.
2
page 14
Section 3: Instrument
(and pressure if installed) can be read.
In the digital mode multiple units can operate on
the same loop cable as a multi-channel instrument.
Alarms:..............................The 4-20mA signal or the digital output may be used
by an external device to operate relays.
Isolation:...........................Sensor and case are isolated from the current loop
but are shunted with a 33V transorb and 2000pF
capacitor.
3.3 Installation
3.3.1 Mechanical Installation
The 8800T has two thread sizes for mounting to the sample
cavity (consult the sensor installation section) where the
dewpoint will be measured. Various adapters are available
for direct connection into existing system openings. Ask
your representative for a Sample Cell, if you do not have the
ability to provide an appropriate sample cavity mounting. If
the ¾”x16 thread is used then the 8800T will seal against the
wall of the sample cell with the provided Viton A O-ring. If
the 14mm x 1.25 spark plug thread is used then an additional Viton gasket must be installed to provide the proper
seal. Ask your representative for this gasket, it is available
free of charge. The 8800T is light enough such that either
thread will mechanically support the whole instrument. To
prevent any leaks, tighten the 8800T into the sample cavity,
with a
metal-to-metal contact.
Since the tightened positioning of the 8800T is unpredictable, its front panel may be rotated (360°) to allow easy
reading of the display. Press down gently on the spring
loaded face plate and turn it to the desired position.
The sensor can be removed from the 8800T by unscrewing
it. Make sure that the sensor is securely fastened to the
” wrench, 1/8 turn past finger-tight to assure
17/
8
page 15
8800T User’s Manual
8800T (the tension washer should be compressed), so that it
does not come loose during use.
3.3.2 Electrical Installation
The 8800T will operate properly with 10VDC to 33VDC at
its input, if this voltage is exceeded the internal fuse may
blow. When selecting the power supply voltage do not
neglect the drop across any current measurement resistor
and wiring in the loop. The connector is a standard 2.1mm x
5.5mm (12mm minimum barrel length) DC power jack, an
internal diode bridge accommodates either polarity. The
8800T may be powered using an off-the-shelf wall transformer with 2.1mm connector, or from a power supply
using the provided connectorized cable. The provided cable
is terminated with a connector which has a retainer, the
retainer may be used to secure the connector to the 8800T
thus avoiding accidental disconnection.
The 8800T will draw 4mA to 20mA from the power supply
depending on the dewpoint being measured. The dewpoints
corresponding to 4mA and to 20mA are user selectable, in
between the current will vary linearly to the selected engineering units, see appendix G.
Various strategies for interfacing with the 8800T are shown
in Appendix D.
Please observe good electrical safety and grounding practices when connecting any electrical equipment; connecting
one end (e.g. negative) of the power supply to earth ground
is advisable.
After the installation is complete, proper detection by the
user’s equipment of the 4-20mA out put, may be tested using
the Analog Output test feature of the 8800T, see section
3.4.5.6.
page 16
Section 3: Instrument
3.4 Operating the Instrument
3.4.1 Starting up
The instrument is ready for use as soon as the power cable is
installed. When power is applied the instrument will initialize its program and for a moment display
enter the Operating State. If the MODE button is held
pressed while the instrument is performing its power-up initialization, it will enter the Set-Up State, which allows the
user to select operating variables of the instrument.
To accommodate a variety of installation possibilities, the
8800T front panel may be rotated (360°) by gently pressing
down on the spring loaded face plate and turning it to the
desired position.
3.4.2 Display Conventions
1. To display characters with the 7 segment numeric dis-
play, the following pseudo-alphanumerics are used:
Numbers:
0 123456789
, then it will
;(1
Letters:
ABCDEFGH IJ LNOPQRSTUXYZ
$%&'( ) *+, -/12345678;<=
Symbols:
?-.
"
2. The instrument will indicate whether a particular mode
lets you change a parameter by showing the word
“SET” in the upper left corner of the display. Be careful
page 17
8800T User’s Manual
+20°C
-100°C
+68°F
-148°F
23,612 ppmV
0.013,849
ppmV
2,000,000
0.000,000,1
1104.2
lbs H
2
O/mmSCF
0.000,921,15
lbs H
2
O/mmSCF
17.688
grams H
2
O/meters
3
0.000,014,75
grams H
2
O/meters
3
not to change any parameter inadvertently.
3. °C°F appear simultaneously, to indicate the sensors’
attenuation in decibels.
4. Values larger than ±1999 or smaller than ±0.01 are dis-
±3
played in powers of 10
-3
“10
” will appear above and to the right of the dis-
. As required, either a “10 3” or
played value, the value will be rounded off to 3½ digits.
The display will show
(out of ranGe), if the num-
51*
ber to be displayed is larger than 1,999,000. Twelve
examples follow; for each the number and units desired
to be displayed are shown in
italics,
depicted immedi-
ately below them is the resultant 3½ digit LCD display:
3
DEWPOINT
x10
˚C
DEWPOINT
˚F
DEWPOINT
PPM
DEWPOINT
LBS
DEWPOINT G/M
DEWPOINT
3
-3
x10
PPM
DEWPOINT
x10
LBS
-3
page 18
DEWPOINT
DEWPOINT G/M
˚C
x10
3
˚F
DEWPOINT
-3
Section 3: Instrument
3.4.3 Push Buttons
Three push buttons are located on the front panel.
Teledyne 8800T
SET %
HILO
TEMP
DEWPOINT PSI G/M³ LBS
MODE button UP button DOWN button
x10¯³
PPM
˚C˚F
Each button is marked with an icon engraved above it.
In general the MODE button navigates through the different
user options “Modes”; the UP and DOWN buttons modify
the units, values or choices in the selected mode. Refer to
the flow diagrams in Appendix A for detailed overview of
button functionality. A button may be held down for a prolonged time, for accelerated incrementing or decrementing
of numeric values.
3.4.4 Operating State
Upon power up, the unit performs certain initialization tests
(see table in section 3.5), and enters the ‘Operating State’, in
the Viewing Dewpoint mode. Depressing the ‘MODE’ button will change modes (see appendix A) in the following
order: nViewing Dewpoint ‹ oViewing Temperature ‹
Start Calibration ‹ qViewing Serial Number ‹ (back to)
p
Viewing Dewpoint. The unit will return to Viewing Dew-
n
point mode if no buttons are pressed for 30 seconds, unless
it is performing a calibration.
page 19
8800T User’s Manual
3.4.4.1 Viewing Dewpoint Mode
In this mode the user can view the dewpoint, this is indicated by the presence of the ‘DEWPOINT’ legend on the
lower left of the display. The available engineering units in
which to view the moisture content are °C, °F, PPM, LBS
3
and G/M
; the UP and DOWN buttons scroll back and forth
through these units in respective order. The °C and °F are
dewpoint readings. The PPM is parts per million by volume
computed at the sensor pressure (more about pressure in
3
appendix F). The LBS and G/M
are pounds of water per
million standard cubic feet and grams of water per standard
cubic meters, both in Natural Gas, they are computed
according to data derived by IGT Research Bulletin 8, taking into account sensor pressure.
Note that the analog output is linear to the selected engineering units, therefore be mindful that while scrolling
through various units the analog output may change even
though the measured dewpoint is stable.
The PSI legend flashes at the bottom of the display, when
there is pressure correction in the computation of the displayed values, refer to appendix F.
3.4.4.2 Viewing Temperature at the Sensor
In this mode the user can view the thermodynamic temperature at the dewpoint sensor inside the sampling chamber,
this is indicated by the flashing ‘TEMP’ legend on the lower
left of the display. The available units in which to view the
temperature are °C and °F. The UP and DOWN buttons
switch back and forth between these units.
Pressing the MODE button changes to the Start Calibration
Mode.
page 20
Section 3: Instrument
3.4.4.3 Start Calibration (SpanCheck™) Mode
The instrument is calibrated at the factory with the sensor it
is shipped with and does not need to be re-calibrated prior
to installation.
Instrument calibration is recommended in approximately 12
month intervals, and the XTR65W sensor should be re-calibrated after prolonged exposure to liquid water. Simply follow steps 1 - 7 of the procedure below, removing the sensor
from the sample gas stream. Make sure the gas stream is
depressurized before removing the sensor to avoid injury.
It is recommended to keep the sensor exposure to room air
as short as possible to avoid super saturation of the sensor.
While super saturation is not damaging to the sensor, it will
prolong the initial dry-down time after you install the sensor
in the sample stream. Therefore, remove the sensor from the
packaging container only after you are ready to proceed
with the calibration procedure and install the sensor in the
sample stream immediately after the calibration procedure
is completed. If you are not ready to use the sensor right
away after calibration, put the sensor back in the shipping
container for dry storage.
The instrument must be calibrated with the sensor it will be
used with. The calibration procedure takes advantage of the
designed saturation level (DSL) feature of the sensor and is
executed by the instrument computer, by performing the following steps:
1. If the instrument is locked and a calibration is
attempted; it will display
and will not perform the
/2&
calibration. To unlock the instrument consult section
3.4.5.9.
page 21
8800T User’s Manual
2. Push the MODE key a few times until the display shows
.
&$/
3. Press the UP button. The display will show
, prompt-
&1)
ing you to confirm that you want to start the calibration
procedure. You can abort the calibration procedure by
pressing the MODE key.
4. Remove the sensor from its packaging container so that
the porous metal filter is visible and the sensor is
exposed to in-hand micro-climate. Close the packaging
container as soon as you have removed the sensor to
avoid degradation of the desiccant inside of the container. You may want to re-use the container at a later
date.
5. Push the UP button again to confirm that you want to
start the calibration procedure. The display will flash
$&
for 60 seconds, while the sensor is saturating. Make sure
you keep the sensor exposed to in-hand micro-climate
until the display shows
(1'
.
6. After 60 seconds, the display will flash the selected sen-
sor type (see “
Selecting a sensor type 3.4.5.2
”) and then
the instrument will calculate the slope and offset of the
sensor curve while displaying the calculations and then
will display
for a few seconds, after which the
(1'
instrument will automatically go into measuring mode.
The sensor calibration is completed. (The display may
flash
, indicating that the sensor has super-saturated.
6$7
As soon as the sensor is exposed to an atmosphere with
a dewpoint lower than the saturation dewpoint, the display will indicate the dewpoint measured by the sensor.)
The display may show alternating
6(1
and
/2
as an
in dica tion t h at the mea sure d capa cit ance is too low to be
from a saturated sensor, in this case make sure that the
sensor is fully engaged into the 8800T, and repeat the
page 22
Section 3: Instrument
calibration procedure.
7. Install the sensor in the sample cell or adapter fitting or
put it back into the packaging container for later use.
The instrument will retain the calibration even if the power
is turned off.
Under certain conditions, an over (super) saturated sensor
may need to be completely dried out before a calibration is
performed. Symptoms of these conditions are a sensor that
will not go through the SpanCheck™ function to the
(1'
display, or a sensor that will not dry down after calibration.
To dry, install sensor in either a known dry gas stream i.e.
instrument quality air or dry nitrogen, or place sensor in a
dry can or bottle of desiccant and seal the container from
outside air (the shipping container is designed for this purpose). After a minimum dry out period of 24 hours, proceed
with the calibration procedure of your choice.
SpanCheck™ calibrates sensors by using micro climates.
Please contact your representative if you have any questions
about how to create such micro climates.
A perfectly acceptable and accurate for calibration microclimate may be created for the XTR100 and XTR65 sensors
by cupping the sensor in the palm of one’s hand during the
SpanCheck™ procedure. Remember that the micro-climate
does not have to be accurate, it just has to be higher than the
designed saturation level. The dewpoint of the micro-climate within the fingers is usually higher than the dewpoint
of the room air and probably well above the +20°C upper
range of the sensor. On a dry day one may need to exhale in
the hand before cupping the sensor to guarantee a high dewpoint. The sensor should be warmed up close to body temperature before performing this procedure. Care must be
page 23
8800T User’s Manual
12
345
XSN
taken that the sensor temperature is not below the temperature of the hand, as in such case condensation could occur
and super saturate the sensor. For the same reason, avoid
exhaling directly onto the sensor.
3.4.4.4 Viewing Serial Number Mode
In this mode the user can view the serial number of the sensor calibrated and shipped with the instrument. This number
is also engraved on the stainless steel sintered filter of the
sensor element. The display shows the serial number by
alternately displaying
and the number. If the number is
;61
larger than 1999 then it is displayed in 2 parts, first part is
3
the thousands signified by the x10
legend in the upper right
corner of the display and the second part is the units. For
example serial number 12345 will be shown as:
3
x10
Pressing the UP and DOWN buttons simultaneously resets
the instrument, this is useful for restarting in the set-up state
(by holding the MODE button), in installations where
power can not be turned on and off easily.
Pressing the MODE button changes the unit to the Viewing
Dewpoint Mode.
3.4.5 SetUp State
To enter the Setup State power-up the unit (or reset it from
the serial number Mode), and hold the MODE key pressed
while the unit is initializing. Refer to Appendix B for a flow
page 24
Section 3: Instrument
diagram of the SetUp State.
The setup state provides nine capabilities, each one controlled from its own mode. Depressing the MODE button
navigates through the modes in the following order: nSelect Alternate Display Units ‹ oSelect Sensor Type ‹ pSet
Measured Attenuation of Sensor at a Low Dewpoint ‹ qSet
the Low Dewpoint at which the Attenuation was measured ‹
Set the Calibration Mid-range Adjust ‹ sPerform a Test
r
and Verification of the Analog Output ‹ tSet dewpoint corresponding to 4mA of Analog Output ‹ uSet dewpoint corresponding to 20mA of Analog Output ‹ vLock/Unlock the
instrument ‹ (back to) nSelect Alternate Display Units.
These nine functions are explained in their respective sections which follow.
unlocked instrument
Changes can be made only to an
, the changes are stored (when the
MODE button is pressed) and retained even if the unit is
turned off.
1.
Display of alternate units
: In this mode, a second engineering unit can be chosen to be displayed alternating
with the engineering unit selected in the operating state,
for example, a dewpoint can be displayed alternating
with the sample temperature, or dewpoint can be alternately shown in °C and in PPM.
2.
Selecting the sensor type
: In this mode the user can
select the software matching the type of sensor installed
in the instrument;
3&4
Adjusting low end sensor attenuation and dewpoint
: XTR-100 (-100°C to +20°C);
;7
: XTR-65 (-65°C to +20°C).
;7
These modes are used to enter a data pair representing a
low dewpoint and the sensor attenuation measured at
this low dewpoint. (see Sensor Theory of Operation
appendix E). This data pair should not be modified
unless the sensor is replaced. The sensor shipping con-
:
page 25
8800T User’s Manual
tainer is labeled with the proper values.
5.
Calibration Adjustment
: In this mode the user can
enter a sensor specific Adjustment Value to improve the
instruments’ accuracy in the range of -50°C to -10°C,
this adjustment has very little or no effect outside this
range. The Calibration Adjustment Value is printed on
the shipping container supplied with the sensor, or may
be derived if the sensor can be exposed to a known reference.
Deriving an Adjustment Value
①
: If the adjustment
value for your sensor is not known, contact your representative and follow the instructions in paragraph B on
the next page. If the value is not available, then it may
be derived using a manual method, provided that a
moisture calibration lab is available.
The calibration must be done in the range of -25°C to
-20°C (attempting to calibrate outside this range may
cause inaccuracies), the dewpoint must be kept stable
during calibration and it must be measured accurately
by a reference instrument such as a chilled mirror. One
must also note the state of pressure compensation and
turn it on or off as applicable to the reference.
The necessary steps are described below (also refer to
the Set-Up State flow diagram in Appendix B):
a. Make sure that the low attenuation and low dewpoint
are correctly entered for this sensor.
b. SpanCheck™ the sensor.
c. Dry-down the sensor for at least 12 hrs.
d. Expose the sensor to the known dewpoint (-25°C to
-20°C), for a sufficient time (at least 30 min.)
e. Go to t he
&$/$'-
mode and press the UP button, the
display will show the current value, in the range of -1.99
to +1.99 followed by blinking horizontal lines.
page 26
Section 3: Instrument
f. Observe the display, if the buttons are not being
pressed; the display will every few seconds show for a
short duration the dewpoint as being computed at the
moment (utilizing the current cal-adjust value in the
computation).
g. Use the UP or DOWN buttons to modify the caladjust value and observe the alternately displayed dewpoint. Perform this adjustment until the dewpoint
matches the value shown by the reference instrument.
h. Press the MODE button to go to the next mode, this
will save the new cal-adjust value, and it will be retained
even if power is turned off.
Entering a known Adjustment Value
②
: If the sensor is
being replaced an adjustment value should be supplied
with the sensor, to enter it into the instrument:
a. Go to t he
&$/$'-
mode and press the UP button, the
display will show the current value, in the range of -1.99
to +1.99 followed by blinking horizontal lines, ignore
the alternately displayed dewpoint.
b. Use the UP or DOWN buttons to modify the caladjust value as necessary.
c. Press the MODE button to go to the next mode, this
will save the new cal-adjust value, and it will be retained
even if power is turned off.
2), 3), 4) and 5) are set at the factory and need only be
modified when a sensor is changed.
6.
Testing the analog output
: By pushing the UP or
DOWN buttons, the user forces the analog output to its
low and high values, respectively. This facilitates the
hook-up and testing of the user’s monitoring equipment.
7&8
Output range setting
: These modes are used to set
dewpoints corresponding to the low and/or high end of
page 27
8800T User’s Manual
the current loop output, refer to appendix G.
9.
Lock/Unlock the instrument
: This mode is used to
block access to parameter settings, protecting the instrument from unauthorized or inadvertent changes of
parameters. Attempting to change settings while instrument is locked will display
/2&
To unlock the instrument press the UP button, to lock
the instrument press the DOWN button. Pressing the
MODE button will navigate back to the Select Alternate
Display Units mode.
Pressing and holding either the UP or DOWN button,
will save the lock or unlock setting depending on the
button, and reset the instrument. This feature is useful if
it is difficult to power off the instrument.
Note: It is imperative that one returns the instrument to
the locked mode to avoid unauthorized changes.
3.5 Troubleshooting the Instrument
This instrument performs diagnostic tests on power up as
well as once every two minutes. The table that follows,
depicts all possible error/unexpected messages that may be
displayed on the instrument. For each message the table has
explanations for the reason, and if necessary a suggested
action to remedy it.
page 28
Section 3: Instrument
DISPLAY EXPLANATION REQUIRED ACTION
LO
(55
HI
(55
%
(55
&6)
(55$'
(555()
/2%$7
LO
51*
TEMP
HI
51*
TEMP
231
6$7
6+5
'%
6(1/2
(55((3
/2&
51*
°C(
w/flashing
DEWPOINT
flashing
PSI
when
dew
;(1
Legend:
PROM check sum failed.
RAM write/read te st failed. cycle power
Unidentified power-up failure. if problem persists,
EEPROM Check Sum Failed. return to your representative
power on tests
converter failure.
A/D
erence voltage for A/D out of spec.
Ref
Low supply
Instrument low
has been excee ded . make sure that th e unit is at a
Instrument high
has been excee ded .
Sensor circuit is
Sensor is
Sensor circuit is
Trying to calculate dewpoint for
voltage.
erature
temp
eratur e
temp
open
urated. sensor troubleshooting
sat
shor
undefined sensor.
e
rang
system tests once per 2 min.
e
rang
.
ted. section
dewpoint display tests
Trying to calibrate an undefined
fo r s erv ice.
check input voltage 10-33VDC
temperature of -10°C to +70°C.
see table in
select sensor and
SpanCheck.
see Calibration instructions.
sensor.
sor reading is ‘
Sen
rated sensor, for SpanCheck.
ROM write cycle not completed.
EEP
Attempting to modify a
number can not be displayed in 3.5 digits.
°F)
An XTR-65 sensor is measuring less
w to be a satu-
too’ lo
Calibration. tests
if this persists, return for service.
ked unit. unlock unit, see set-up mode.
loc
than -70°C or -94°F dewpoint.
miscellaneous
Pressure correction is enabled.
Turn on message,
denotes alternately flashing messages.
Xen
taur (
Greek Ξ
=X)
page 29
8800T User’s Manual
The instrument contains a fuse which may open if the
instrument is subjected to voltages exceeding the specifications. Under these circumstances the unit display will be
blank and the instrument will not draw any current when
powered up. The fuse is not user replaceable, therefore the
8800T must be sent to your representative for servicing.
page 30
Appendices
SEN/2LO
AC/_AC
CNF/AC?
CAN
/
Appendix A: Operating State User Interface flowchart
Power ON initialization
and sign on message
30 seconds anywhere
other than calibration
without a key press
Viewing
Dewpoint
Viewing
Sensor
Temperature
Calibration
Menu
Viewing
Serial
Number
Teledyne 8800T
DEWPOINT
PSI
select
units
Teledyne 8800T
TEMP
select
units
Teledyne 8800T
SET
Teledyne 8800T
a flashing
PSI legend
means pressure
correction is
being applied,
see appendix F
˚C
˚F
Press together to
RESET the Instrument.
Then quickly press and hold
MODE to go to Set-Up State.
1sec.
Confirm
SpanCheck™
1 minute
Sensor
Reading
OK
Teledyne 8800T
SET
numbers calculating
calibration
Teledyne 8800T
Teledyne 8800T
SET
Teledyne 8800T
SET
Too Low
few
seconds
Teledyne 8800T
SET
Teledyne 8800T
SET
1 sec.
Cancel Calibration (calibration values are not changed)
2 sec.
Values Stored
New Calibration
LEGEND: 1. Arrows leading out from below a button depict the flow as a result of
pressing the button.
2. Arrows leading out of other locations depict flow as a result of
completing a function or a time-out.
3. A slash '
' in the display area, is used to depict two alternately
shown (flashing back and forth) messages.
page 31
8800T User’s Manual
LOC
ALT/DSP
SEN/XT1
DB/
CAL/ADJ
A.0./TST LO/BAT
A.O./RNG/
XT1 XT6 DB
Appendix B: Set-Up State User Interface flowchart
CAUTION! These parameters are set
properly at the factory, to correspond to
the shipped sensor. Do not modify them
unless you are replacing the sensor.
appears when changing
settings of a locked instrument
XTR-100 XTR-65 attenuation
+/- 0.01 units
If no buttons pressed
for 3 seconds the dew
is shown for a moment.
SET
Power-Up with
MODE key pressed
blank ˚F ˚C ppm LBS G/M3 Temp˚F Temp˚C%PSI ˚C˚F
Choose alternate units to show when displaying dewpoint
SET
Factory default is blank (there is no alternate display).
Choose Sensor type
SET
page 32
Set measured attenuation at a known low dewpoint
˚C˚F
SET
LO
+/- 0.01dB
Set low dewpoint for the above set attenuation
˚C
SET
LO
DEWPOINT
+/- 0.1˚C
Calibration Midrange Adjust
SET
Appendices
/
A.0./TST LO/BAT
A.O./RNG/
A.O./RNG/
UN/LOC
User Interface Flow Diagram - Set-Up State (continued from previous page
Ensure minimum voltage at LPDT
to be 10VDC, when drawing 20mA
Too
Low
Test
Voltage
Current Loop
OK
Test Analog Output
4mA
20mA
HILO
+/- 0.1˚C
Set dewpoint corresponding to low end of analog output
Factory default is -100˚C
˚C
SET
LO
SET
+/- 0.1˚C
Lock or unlock the instrument
Set dewpoint corresponding to high end of analog output
Factory default is 20˚C
˚C
When locked instrument parameters can not be changed.
Prolonged press of either button will reset the unit
Factory default is locked.
Lock
Unlock
HI
SET
)
' in the display area, is used to depict two alternately
page 33
LEGEND: 1. Arrows leading out from below a button depict the flow as a result of
pressing the button.
2. A slash '
shown (flashing back and forth) messages.
8800T User’s Manual
m
Appendix C: 8800T Mechanical Drawing
˚
0
6
3
y
l
e
e
r
f
s
e
t
a
t
o
r
l
e
n
a
p
t
n
o
r
f
DC Power Jack
oint Transmitter
Think
Safety
Power Jack screw-on retainer
1.750"
x10¯³
PPM
˚C˚F
SET %
HILO
TEMP
DEWPOINT PSI G/M³ LBS
Teledyne 8800T
Read
Manual
www.teledyne-ai.com
Mo
Se
Ma
8
/
7
flats for 1 " wrench
5/16"-24
tension washer
3/4"-16
sintered stainless steel,
unscrew to remove.
Removable Sensor encapsulated
in 100
Viton A O-ring
14mm x 12.5mm
2.230" 1.850" 0.600"
page 34
Appendix D: 8800T Electrical Connections
W
Methods of Using and Interfacing the 8800T
Operation with Wall Transformer
Dewpoint viewed on Instrument Display
10-33VDC
120V
or
220V
Wall Transformer
Operation with DC Power Supply
Dewpoint viewed on Instrument Display
and available as 4-20mA output
maintain
10-33VDC here
VDC
4-20mA
oint Transmitter
Think
Read
Safety
www.xentaur.com
oint Transmitter
Think
Read
Safety
www.xentaur.com
Mo
Se
Manual
Ma
Mo
Se
Manual
Ma
Operation with Relay Option Board
Dewpoint viewed on Instrument Display
and available as 4-20mA output
Relay Option Board
Provides two
independent Relays
with programmable
trip point and
hysteresis
DC or AC supply
Operation with Remote Option Board
Dewpoint viewed on Instrument Display
and available on remote
Display
Buttons
Relays
Voltage or Current
Output
RS-232 Output
Power Supply
4-20mA
Appendices
oint Transmitter
Mo
Se
Think
Read
Manual
Safety
Ma
www.xentaur.com
oint Transmitter
Mo
Se
Think
Read
Manual
Safety
Ma
www.xentaur.com
Operation with DC Power Supply
Dewpoint viewed on Instrument Display
and available as Voltage output
12-33VDC
0.4 - 2V output
100
oint Transmitter
Think
Read
Safety
www.xentaur.com
85 - 265VAC
Operation with Multichannel Option Board
Dewpoint viewed on each Instrument Display
and available on remote interface
Multichannel
Option Board
Mo
Se
Manual
Ma
multiple units connected on the same two wires
oint Transmitter
oint Transmitter
Think
Think
Safety
Safety
www.xentaur.com
Read
Read
www.xentaur.com
Manual
Manual
Mo
Se
Ma
Ma
page 35
RS-232C
to Computer
DC or AC supply
Mo
Se
oint Transmitter
Think
Safety
Read
www.xentaur.com
Manual
Mo
Se
Ma
8800T User’s Manual
Appendix E: Sensor/SpanCheck™ Theory of Operation
The Sensor is constructed as a capacitor whose dielectric
consists of porous Aluminum Oxide as well as the gas that
has entered in the pores of the Aluminum Oxide. The plates
(electrodes) of this capacitor are an aluminum substrate and
a porous gold layer deposited on top of the Aluminum
Oxide, the porous gold electrode allows transfer of gases
into or out of the Aluminum Oxide pores.
The capacitance due to the Aluminum Oxide is always constant, while the capacitance due to the gas varies according
to the gas content and pressure. Since the dielectric constant
of water is orders of magnitude larger than that of any gases
being measured, the quantity of water vapor present in the
pores changes the capacitance of the sensor to a much
greater extent than any other system variable. For the same
reason (the extremely large dielectric constant of the water
molecule), any capacitance variations arising from the Aluminum Oxide, such as changes due to temperature, are
insignificant in relation to the capacitance due to the water
content. Thus the sensor capacitance varies greatly in proportion to the water content in the surrounding gas. The sensor is designed such that the relationship of the quantity of
water and the resultant capacitance has an "S" shaped curve.
At the extremely dry end the curve is asymptotic to the
capacitance due to the Aluminum Oxide and the gas, while
at the very wet end the curve is asymptotic to the capacitance due to water molecules packed extremely tightly (saturated) in the pores of the Aluminum Oxide. This upper end
is an excellent indication of the total pore volume; while the
lower end of the curve is an indication of the distance
between, and area of the capacitor plates (electrodes), this is
the intrinsic capacitance of the sensor. Therefore knowing
these two points, a sensor can be calibrated with compensa-
page 36
Appendices
tion for small manufacturing deviations.
As the sensor is used in real world applications, it is
exposed to various elements and stress; like any other sensor it may over time drift from calibration. However one
must note that the intrinsic capacitance will not change with
use because it is based simply on the dielectric constant of
Al
and the distance between, & area of the plates (elec-
2O3
trodes), thus the original factory measured values will
always be valid. What may change is the pore volume, due
to clogging with contaminants, residual oxidation, metal
migration, etc. Thus to re-calibrate the sensor the instrument
needs only to "know" the capacitance at the wet end of the
curve. As discussed previously the capacitance at the wet
end approaches asymptotically a saturated pore capacitance,
therefore if the sensor is saturated (the exact water content
will not be important since the curve is asymptotic), then the
instrument can measure the capacitance and re-calibrate the
sensor. This is refered to as SpanCheck™. The advantages
of this unique capability of Teledyne sensors and instruments
are obvious in time and cost savings for re-calibration, as
well as ease of sensor replacement.
Teledyne HTF™ Sensor: Dewpoint vs. Capacitance Response Curve
200
Saturated Capacitance Asymtote of New Sensor
Saturated Capacitance Asymtote of Aged Sensor
160
rCurve
nsor Curve
120
Aged Se
New Senso
80
Capacitance (nF)
40
0
Dry Capacitance Asymtote of New & Aged Sensor
-80
-60
-40
Dewpoint Reference ˚C
-20
0
20
page 37
8800T User’s Manual
page 38
Appendix F: Pressure Correction
Appendices
Sensor Pressure
is used in the context that this is the pressure inside the sampling chamber when performing the
measurement, i.e. it is the operating pressure of the sensor.
Gas Pressure
is use d in th e c ontex t that this is the pr essur e at
which the dewpoint is to be calculated.
Pressure Correction
is used in the context that the values
displayed signify the moisture content at some pressure (we
refer to this as the ‘Gas Pressure’) different from the pres-
3
sure at the sensor. Note that PPM, LBS and G/M
readings
are by definition unaffected by pressure correction because
only the pressure at the sensor affects their value. While °C
and °F are affected by pressure correction by reporting what
the dewpoint would be at the Gas Pressure when the dewpoint is what is measured at the pressure at the sensor. However, this also implies that whether pressure correction is
3
applied or not the PPM, LBS and G/M
readings are
affected by the setting of the sensor pressure.
The factory default settings are: 14.7psi for both sensor and
gas pressure and pressure correction disabled.
When Pressure correction is disabled all dewpoints are
computed by assuming that both Sensor and Gas Pressures
are 14.7psi.
As all Teledyne dewpoint meters, the 8800T is equipped with
the necessary software to perform pressure correction.
However, for the lack of space, the 8800T does not have a
Pressure Correct button. Therefore the user can not set or
enable Pressure Correction, this must be done at the factory .
Consult with your representative.
page 39
8800T User’s Manual
Appendix G: Current vs. Dewpoint
The current being pulled by the 8800T, varies with the dewpoint being measured by the 8800T. To use the current to
calculate the value of the dewpoint measurement, one must
know the settings of the low and high ends of the analog
output range, then:
4
–
()
I
----------------------------------------L+=
D
where:I = current drawn by 8800T loop in mA.
= value of High end of Analog Output range
H
converted to sele cted engineering units
= value of Low end of Analog Output range
L
converted to sele cted engineering units
= dewpoint measured by instrument in selected
D
engineering units.
()×
HL
16
–
Consult section 3.4.5.7&8 and/or appendix B, to check and
set the Analog Output low and high ranges; the factory
default settings are -100°C and +20°C respectively.
For example a unit with factory default settings, drawing
12mA is computed to be measuring a dewpoint of -40°C:
12 4
–
()
----------------------------------------------------------- -
20 100
–
–
()
()×
16
100
–
+
()
40
–=
Note that the computation is such that the current is linear to
the selected engineering units. Hence, selecting ppmV or
LBS or G/M3 units, will cause the analog output to be linearly proportional to those units (approximately logarithmically proportional to dewpoint), refer to the graph that
follows. Naturally selecting °C or °F will cause the analog
output to be linearly proportional to dewpoint.
When monitoring in ppmV or LBS or G/M3, the analog
output low & high ranges may have to be adjusted to pro-
page 40
Appendices
vide a useful output. Consider an example where the area of
interest to be monitored is 10 to 100 ppmV, and the analog
output is set up with the factory defaults of -100°C to +20°C
(which is 0.014 to 23612 ppmV); then the current loop output will vary only from ~4.1 to ~4.2 mA in the area of interest (consult with the graph on the following page). In most
instances this would be an unacceptable output for proper
monitoring of the measurement. In this example the user
should adjust the analog output low & high ranges such that
the output range is better suited to the measurement of 10 to
100 ppmV. It may be useful to select the low and high
ranges to be 5 and 150 ppmV respectively, thus out of range
conditions will be detected properly. Then the low range
will be set to 5ppmV which is -65.5°C dewpoint, and the
high range will be set to 150ppmV which is -38.5°C dewpoint. Now the current loop output will be 4.55 to 14.48 mA
in the range of 10 to 100 ppmV, the ~10mA variation is
more than sufficient for a good measurement by the user’s
equipment. One may carry out similar calculations for LBS
or G/M3 and choose the appropriate settings. While making
these computations it may be useful to obtain a copy of
Teledyne’s dewpoint calculator, this is a Microsoft Windows™ program which simplifies the process of converting
dewpoint measurement units. It is available at www.Tel-
edyne-ai.com. If you are not certain how to carry out such calculations send, by e-mail to Teledyne@Teledyne-ai.com or by fax to
(626) 961-2538, your system specifics, and some one will
get back to you with appropriate analog output settings.
In general, if the dewpoint is monitored in °C or °F, there is
no need to change the factory default -100°C to +20°C settings, because the 4-20mA provides sufficient resolution to
measure the output better than the specified accuracy of the
sensor.
page 41
8800T User’s Manual
Relationship of 4-20mA output and instrument reading in ppmV or LBS
289.1 LBS = 0˚C = 6063.8 ppmV
49.3 LBS = -20˚C = 1019.3 ppmV
Low AO range = -100˚C High AO range = +20˚C
Instrument reading in ppmV
0.56 LBS = -60˚C = 10.66 ppmV
10 100 1000 10000
8mA
12mA
20mA
4/20 mA output
1.97 LBS = -50˚C = 38.83 ppmV
High AO range = -38.5˚C
5mA
4.5mA
page 42
Instrument reading in LBS of H2O / million cubic feet
Low AO range = -65.5˚C
0.1 1 10 100 1000
4.1mA
Appendices
Appendix H: Uncertainty in LBS & ppmV calculations
48
44
38
34
29
24
19
15
900
800
700
600
500
400
300
1000
10
5
2.5
O / mmscf
2
1
Calculated LBS H
0.5
0.25
0.1
Uncertainty of LBS & ppmV calculations due to +/-3˚C measurment accuracy
0.05
-65
-60
-55
-50
-45
-40
-35
-30
-25
-20
Dewpoint +3˚C
Dewpoint -3˚C
-75
-70
200
100
90
80
70
60
50
40
30
20
10
9
8
7
6
5
4
3
2
1
0.9
0.8
0.7
0.6
0.5
-80
Measured Dewpoint ˚C
Calculated ppmV
page 43
8800T User’s Manual
Appendix I: Sensor Response Time
100
95
90
85
80
after 48hrs of equilibrium
(dp)
Sensors to a Step-change (DOWN)
3
O
2
at time 0, to -62.2 ˚C
(dp)
from -39.4 ˚C
Response Time of TAI Al
0
5
1015202530354045505560657075808590
65% of step change
% of step change
75
70
65
60
55
50
45
Time (minutes)
40
35
30
25
20
15
10
5
95% of step change
0
95
100
105
page 44
Teledyne, 16830 Chestnut St., City of Industry, CA 91748 Tel: (626) 934-1500
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