vaisala HMP240 User Manual

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: [phone]

Email: [e-mail]

Fax: [phone]

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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