New Flexibility in Demanding HVAC Applications

Timo Ranta-aho, Product Line Manager
Harri Lehtonen, Project Manager
Vaisala
Helsinki, Finland
Introducing Vaisala HUMICAP® Humidity and
Temperature Transmitter Series HMT100
New Flexibility in Demanding
HVAC Applications
Several different applications require reliable humidity measurement.
Stability rooms and chambers come in many sizes, all of which
require vigilant monitoring of temperature and humidity. The trend
in greenhouses is towards room-specific humidity sensors. Fruit
and vegetables are stored and ripened in specially built rooms that
contain systems for controlling humidity. Outside air measurements
are needed in weather reporting and forecasting but also in many
other applications, such as building automation.
T
he Vaisala HUMICAP®
Humidity and Temperature Transmitter Series
HMT100 has been introduced
for humidity and temperature
monitoring, especially in demanding HVAC (heating, ventilation and air conditioning) applications. Several optional features make it a flexible solution for the user, who can order
a transmitter that optimally fits
their specific application.
Reliable performance
in dusty and humid
environments
Alternative output
parameters and output
signals
The HMT100 can measure relative humidity or dewpoint alone,
or either one of these together
with temperature. Relative humidity is the most commonly
measured parameter, for example, when the effects of humidity
on storage, use and consistency
of materials and products need
to be monitored. On the other
hand, dewpoint provides a temperature-independent humidity
parameter such as when incoming air is supplied into an air conditioning network or the temperature where condensation would
occur needs to be known.
Different controllers and
peripherals work using various types of input signals. The
HMT100 outputs the measurement results as either a loop pow-
169/2005
to re-adjust the HMT100 transmitter at the measurement site.
The probe can easily be changed
to another HMP100 probe,
which is either supplied directly from the factory or calibrated elsewhere. Alternatively, the
transmitter can be adjusted using
a system such as the Vaisala HUMICAP® Hand-Held Humidity
and Temperature Meter HM70
and a suitable connection cable.
The HM70’s indicator shows the
readings of both the HMT100
and the reference probe simultaneously, and the adjustment can
be made quickly and easily.
The HMT100 can also be
calibrated in a conventional way
using the Vaisala Humidity Calibrator HMK15, or by sending the unit to a Vaisala service
center.
ered 4...20 mA signal or as a linear voltage signal.
Choice of probes and
displays
The HMT100 comes with either a fixed humidity probe for
mounting the unit on a wall or
with a cable probe that enables
the probe to be installed at a distance from the transmitter body.
A separate duct installation kit
enables the probe to be installed
in an air channel, where the exact
installation depth of the probe
can be adjusted. Three different
cable lengths are available and a
separate extension cable allows a
maximum 20 m distance between
the probe and the transmitter.
The HMT100 can also be or-
dered with a local LCD display
which instantly shows the user
the observed humidity and temperature levels.
Interchangeable probe flexibility in calibration
As a new feature, the HMT100
series incorporates a model with
an interchangeable probe. This
probe can also be bought separately as a spare unit for the
HMT100 transmitter. When adjusting the transmitter, the adjustment result is stored in the
HMP100 probe. The probe can
therefore be adjusted in a calibration laboratory using another HMT100 body.
The interchangeable probe
provides the user with a new way
The transmitter cover is dust
and water spray resistant and
meets the IP65 requirements.
This makes the HMT100 particularly suitable for wet and humid environments that are regularly cleaned with sprayed water. A separate weather shield
and a radiation shield are available for installing the HMT100
outdoors. In addition, the sensor
elements can be protected either
with a plastic grid, with a membrane filter, or with a durable sintered filter.
The HMT100 incorporates
the Vaisala HUMICAP® sensor,
which has excellent stability and
is insensitive to dust, particulate
dirt and most chemicals. ●

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