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P.O. Box 26, FIN-00421 Helsinki, FINLAND
HMP240 Series Dewpoint Transmitters
for High Humidity Measurements
Features/Benefits
• Wide temperature range from
-40 to +180 °C
• Designed for use in high humidity
• Incorporates the HUMICAP
for excellent accuracy and long-term
stability, neglible hysteresis and
resistance to dust and most chemicals
• Optional temperature sensor
• Probe cable lengths: 2, 5 or 10 meters
• Choise of local display, filter, serial bus
(RS232C, RS485/422, digital current
loop), analog output signal and
temperature ranges
• NIST traceable (certificate included)
Tel: +358 9 894 91
Email: industrialsales@vaisala.com
Fax: +358 9 8949 2485
www.vaisala.com
®
Sensor
The HMP243 (on the left) and HMP247 Transmitters with the optional temperature sensor.
The HMP240 Series provides fast and
reliable dewpoint measurement
especially under high humidity
conditions where dew would normally
form on the humidity sensor head and
thereby cause errors in measurements.
Warmed probe head
The temperature of the probe head is
constantly kept higher than the ambient
temperature thus eliminating the
possibility of dew formation on the
sensor. The result is uninterrupted,
accurate and stable dewpoint
measurement. The measurement is
fully temperature independent so the
warming does not affect the
measurement. This patented techology
has proven its functionality in a wide
variety of applications.
The measurement with the HMP240
Series Tranmitters is fast because the
response time of dewpoint is
proportional only to the diffusion time
of water molecules inside the sensor
head.
Two models
The HMP240 Series includes two
models: HMP243 and HMP247. Both
work from lower humidities up to
saturating conditions, and from stable
to rapidly changing environments. The
HMP243 Transmitter with plastic probe
is the most suitable for outdoor
measurements, and the HMP247 with
pressure tight steel probe more for
industrial applications.
Optional temperature
sensor
The basic version of HMP240 Series
Transmitters has one sensor head; the
output variables are dewpoint
temperature and mixing ratio.
Optionally the transmitter can be
equipped with an additional
temperature sensor head that measures
the ambient temperature, which is used
in the calculation of relative humidity,
absolute humidity, wet bulb
temperature and dewpoint difference
to ambient temperature.
Note: The temperature probe should
be located at least 1 meter from the
heated probe.
Fast, reliable and easy to
use
Due to the modular construction,
HMP240 series transmitters can be
adapted for various applications. The
transmitters have two analog output
channels and any two of the available
variables can be selected as output
signals. Transmitters are configured to
selected requirements already in the
production line.
Typically the user will not need to
change any transmitter settings when
installing the instrument. If necessary,
the transmitter settings can be easily
altered in the field. Selecting, scaling and
calibrating the analog output signals and
parameters can be carried out in a few
minutes using software commands.
HUMICAP® performance
The HMP240 Series Transmitters are
fitted with the latest version of the
HUMICAP®, a polymer sensor known
for its accuracy, reliability and long-term
stability. The sensor has a high tolerance
to particulate abrasion and chemical
contamination.
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VAISALA HMP240 SERIES
Technical Data
DEWPOINT
Dewpoint temperature
Measurement range -40...+100 °C
Accuracy: find the intersection of the dewpoint temperature curve
and the dewpoint difference reading (process temperature dewpoint temperature) on the x-axis and read the accuracy in
dewpoint measurement at the y-axis
Response time (90%) at +20 °C in still air 15 s
(with sintered filter)
Sensor HUMICAP® KC sensor
Temperature (option)
Measurement range -40...+180 °C
Typical accuracy at +20 °C ±0.1 °C
Typical temperature dependence of electronics 0.005 °C/°C
Sensor Pt 100 IEC 751, class 1/4 B
Outputs
Two analog outputs, 0...20 mA, 4...20 mA,
selectable and scaleable 0...1 V, 0...5 V, 0...10 V
Typical accuracy of analog ±0.05 % full scale
output at +20 °C
Typical temperature dependence 0.005 % full scale/°C
of analog output
Serial output available RS 232C
0...5 & 0...10 V outputs > 10 kohm (to ground)
Operating temperature range for -40...+60 °C
electronics
with display cover 0...+50 °C
Storage temperature range -40...+70 °C
Housing material G-AlSi12 (DIN 1725)
Housing classification IP 65 (NEMA 4)
Bushing for 7...10 mm diameter cables
(8 x 0.5 mm2 shielded cable)
Probe cable lengths 2, 5 or 10 metres
Humidity sensor protection sintered filter of
(Ø 13.5 mm) stainless steel
PPS grid with steel netting
Complies with EMC standard EN61329-1:1997 + Am1:1998;
Industrial Environment.
Serial interface modules
Module types RS 485/422
digital current loop
Assembly plug-in module
Connections screw terminals for 0.5 mm2
wires (AWG 20), stranded
wires recommended
Number of devices on line
RS 485/422 32
digital current loop 6 (single loop)
9 (dual loop)
Network cable type twisted pair
Network line length 1000 m max.
Network data speed
RS 485/RS422 9600 baud max.
digital current loop 4800 baud max.
Dimensions
Dimensions in mm.
Electronics housing
Calculated variables
Available only when temperature sensor head in use
Typical ranges
relative humidity 0...100 %RH
dewpoint difference 0...+50 °C
mixing ratio 0...500 g/kg d.a.
absolute humidity 0...600 g/m
wet bulb temperature 0...+100 °C
Accuracy of relative humidity ±(0.5 %RH + 2.5% of reading)
measurement
General
Connections screw terminals for 0.5 mm
wires (AWG 20), stranded
wires recommended
Operating voltage 24 VDC/VAC (20...28 V)
Power consumption 200 mA max. (24 VDC)
during re-gaining 270 mA max. (24 VDC)
Recommended external load for
current outputs < 500 ohm
0...1 V output > 2 kohm (to ground)
3
2
Optional temperature probe for HMP243 and HMP247
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P.O. Box 26, FIN-00421 Helsinki, FINLAND
Tel: +358 9 894 91
Fax: +358 9 8949 2485
Email: industrialsales@vaisala.com
HMP243 and HMP247 Dewpoint Transmitters
for Condensing Environments
www.vaisala.com
The HMP243 Transmitter is suitable for
outdoor applications.
HMP243 for Condensing
Environments and
Outdoor Applications
The HMP243 probe is suitable for use
in outdoor/meteorological applications
where sudden temperature changes
and windy conditions can occur.
HMP243 can be installed using
HMP243FA installation kit. The kit
consists of a flange and a supporting bar
for the sensor head cable; using this kit
the distance between the sensor head
and the channel or duct wall can be
easily adjusted.
HMP243 is available also with a
meteorolocal installation kit.
Technical Data
Sensor head material PPS
Installation kit for duct mounting
HMP243FA
Meteorological installation kit
HMP243MIK
Dimensions
Dimension in mm.
HMP243 humidity probe
The HMP247 Transmitter is designed for
demanding industrial applications.
HMP247 for Pressurized
Spaces and High Humidity/
Condensing Environments
HMP247 is intended for demanding
industrial humidity measurement
applications with a risk of
condensation.The stainless steel probe
head is mechanically very durable and
preferred for most industrial
applications. The HMP247 probe head
is leak-proof up to 1 MPa.
The HMP247 probe head can be
installed also using the M3 threaded
holes on the back of the probe.
Technical Data
Pressure range
Humidity probe 0...1 MPa
(the entire sensor head in pressurized
space 0...10 bar, 0...145 psi)
Temperature probe 0...0.7 MPa
(the entire sensor head in pressurized
space 0...7 bar, 0...100 psi)
Sensor head material
stainless steel (AISI 316L)
Dimensions
Dimension in mm.
HMP247 humidity probe
(pressure tight)
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VAISALA HMP240 SERIES
Options
Technical Data
DEWPOINT
Calibration
Fast one-point calibration for HMP240
Series Transmitters can be done with
Vaisala's hand-held humidity meter
without disturbing the operation. A twopoint calibration can be performed in a
controlled environment using Vaisala's
HMK15 Salt Bath Calibrator. The
transmitters can also be sent to Vaisala
Service Centers for multi-point
calibration and adjustment against
standards traceable to national
standards.
The recommended calibration interval
for the HMP240 Series Transmitters is
one year.
Sensor re-gaining option
minimizes the effect of
contaminants
The HUMICAP® Sensor used in the
HMP240 Series is ideal for the
condensing applications, both in
industry and meteorology. However,
where chemicals or other agents could
contaminate the sensor a sensor regaining option is available.
The sensor re-gaining option helps to
maintain the accuracy and stability of
the HMP240 Transmitters in
environments with high concentrations
of chemicals and cleaning agents
During sensor re-gaining the
performance of the sensor in returned
to normal by evaporating harmful
chemicals from the sensor. The sensor
re-gainig can be initiated using a
software command or it can be
programmed to occur at set intervals.
HMP243MIK
Meteorological
Installation Kit
In weather observations dew formation
makes reliable humidity measurement
difficult or even impossible. At a
weather station high humidity
combined with rapidly changing
outdoor temperature can cause dew
formation onto the sensor head. It is
impossible to obtain a true reading until
this dew evaporates or dries.
Obtaining a true humidity reading is
particularly important e.g. in traffic
safety: at airports and at sea as well as
on the roads. It is essential, for example,
in fog and frost prediction.
Vaisala's HMP243 dewpoint transmitter
is optimized for measurement in high
humidities, i.e. when ambient
temperature is near dewpoint
temperature.
The probe head of the HMP243 is
mounted in a specially designed
radiation shield. This shield is open at
the bottom, which ensures steady air
circulation to the sensor even in calm
weather.
In traditional radiation shields sleet or
snow can accumulate on the shield and
prevent the proper air circulation
through the shield, and so create a
microclimate which has a very high
humidity until the snow melts away.
The open structure of the Vaisala
radiation shield prevents this as the
snow can not block the air circulation in
the shield. The open structure can be
used when the measurement is not
temperature dependent.
All these characteristics combined
make the HMP243 Transmitter the right
choice for accurate and reliable
measurement in extreme weather
conditions.
HMP243MIK provides radiation shields for
dewpoint and temperature probes.
Dewpoint Measurement
with Relative Humidity
Sensor
The HMP240 Series use the HUMICAP
relative humidity polymer sensor. As the
sensor head is warmed, the relative
humidity inside the sensor head stays
below that of the ambient: with accurate
temperature control the dewpoint of
the ambient can be measured directly.
To achieve the true ambient relative
humidity, an additional temperature
sensor head can be used. The
measured ambient temperature
provides the needed temperature
compensation for calculating relative
humidity and other humidity
parameters.
®
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