Specifications

47
HMW 21/31 Series
FEATURES/BENEFITS
 Full 0 to 100%RH measurement
 4 to 20 mA output (HMW 21)
 Selectable voltage output (HMW 31)
 Temperature compensation
 ±2% accuracy
 Optional temperature measurement
 NEMA 4 housing
 Electronic, on-site, one-point calibration
NEMA 4 PROTECTIVE ENCLOSURE
The HMW 21 and HMW 31 series is configured for
measuring relative humidity and temperature in
systems in more demanding environments, where
condensation and dust will commonly be encoun-
tered. A fully gasketed NEMA 4 enclosure, locking
strain relief connector and membrane filter protect
the electronics and sensors from environmental or
mechanical damage. These transmitters are available
as relative humidity only (UB), and as relative
humidity and temperature (YB).
OUTPUT SIGNALS
The HMW 21 series features 2-wire, 4-20 mA output
signals proportional to 0 to 100 %RH and -4 to +176°F
(-20 to 80°C). It can be powered by AC or DC
voltage. The HMW 31 series features output signals
of 0-1V, 0-5V, 0-10V and 0-20 mA and can be pow-
ered by either AC or DC voltage.
FAST, ON-SITE CALIBRATION
The accuracy of the transmitters is simple to check
using the HMI 41 humidity calibrator. The calibration
can be done in seconds with a single potentiometer
without disturbing operation. This saves hours of
maintenance time and ensures high system accuracy.
THE UNIQUE HUMICAP
®
SENSOR
These relative humidity transmitters feature Vaisala's
patented HUMICAP sensor. It is based on the capaci-
tance change in a one-micron-thin polymer as it
absorbs water vapor. The sensor exhibits fast re-
sponse and has excellent long term stability, allowing
the transmitters to achieve ±2 % accuracy. It is
unaffected by dust and most chemicals.
HMW 21/31 Series
Humidity and Temperature Transmitters