Specifications

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HMP 243 Dewpoint Transmitter for
Condensing Environments and Challenging
Outdoor Applications
UNIQUE COMPOSITE SENSOR
PROVIDES EXCELLENT STABILITY UNDER
EXTREME CONDITIONS
The HMP 243 provides fast and reliable dewpoint
measurement even under extreme conditions where
a combination of high humidity and rapidly changing
temperature can present unwanted dew formation on
the sensor head. Because the temperature of the HMP
243's sensor head is constantly higher than ambient,
the possibility of dew formation is eliminated. The
result is uninterrupted, accurate and stable dewpoint
measurement that is unmatched by more common
chilled mirror and psychrometric instruments.
FEATURES/BENEFITS
 Versatile and easy to use
 Wide temperature range from -40 to +356 °F
(-40° to +180°C)
 Configuration and parameters can be set by the user
 Electronic, on-site, one-point calibration
 Typically requires calibration/maintenance only
every one to two years
 Aluminum housing protects against dust/sprayed
water and electromagnetic interference
 Optional sensor re-gaining function for resistance
to interfering chemicals
 Optional temperature sensor head for ambient
temperature reference and calculation of relative
humidity, dewpoint difference, mixing ratio,
absolute humidity, wet bulb temperature
 Supplied with NIST certificate of calibration
CUSTOMIZE YOUR INSTRUMENT
Vaisala's unique microprocessor design and modular-
ity allow you to customize the HMP 243 at time of
purchase. You can select:
 Local display or no display
 Sensor head cable length (2, 5 or 10 meters)
 Serial bus (RS 232C, RS 485/422, digital current
loop)
 Choice of filter
 Choice of analog output signals
 Various temperature measurement ranges
 Metric or non-metric units
 Installation kit for duct mounting
 Re-Gaining option for extra protection against
interference from rare chemicals
 Optional temperature sensor
Note: The temperature probe should be kept at least 1 meter
apart from the heated probe. For outdoor installations, ask for
the meteorological installation kit. (MIK)
MEASURE DEWPOINT AND CALCULATE
OTHER VARIABLES
With the addition of an optional temperature sensor
to measure ambient temperatures, the HMP 243 can
calculate relative humidity or absolute humidity; the
difference between ambient and dewpoint tempera-
ture; and the mixing ratio and wet bulb temperature
of ambient air. Small and light, the temperature
sensor reacts quickly to changes in ambient tempera-
ture, providing very fast response time even for the
calculated variables.
NEW RE-GAINING OPTION
For 25 years, Vaisalas HUMICAP
®
sensor has proven
its resistance to dust and most chemicals time and
time again. When there is the risk of certain rare
chemicals accumulating in the humidity sensor,
thereby decreasing the accuracy, Vaisalas new
re-gaining option is recommended. With this option,
contaminants are evaporated from the sensor and
performance is returned to normal. Re-gaining can be
activated using a software command or it can be
programmed to occur at set intervals.
HMP 243