Specifications

73
INTRODUCING THE CARBOCAP
®
Vaisalas duct mounted GMD 20 and wall mounted
GMW 20 series transmitters use the new silicon based
CARBOCAP sensor. The simple structure and refer-
ence measurement capabilities make this Single-
Beam Dual-Wavelength NDIR sensor extremely
stable and reliable. The GMD/W series transmitters
are specially designed for Indoor Air Quality (IAQ)
and Demand Controlled Ventilation (DCV) applica-
tions. They are easy to install and require almost no
maintenance.
CARBOCAP
®
TECHNOLOGY
The structure of the diffusion aspirated Single-Beam
Dual-Wavelength sensor is remarkably simple: it
consists of an infrared source, a sample cell, a
tunable solid state interference filter and an IR
detector.
The tunable interference filter enables measurements
at two wavelengths. As a result, the reference
measurements can be made without the typical
weaknesses of Dual-Beam sensors.
The use of the new CARBOCAP sensor and the
GMD/W 20 series has several advantages:
 high accuracy
 excellent stability
 negligible temperature dependence
 reliable operation
 ease of installation
 five year recommended calibration interval
The measurement accuracy of the sensor is not
affected by dust, water vapor or most chemicals.
Use of the GMD/W 20 series transmitters results in
considerable savings in installation, operation,
maintenance and recalibration costs. In addition, it
ensures the best possible control of air quality.
VERSATILE TRANSMITTERS
The GMD/W 20 series transmitters can be used
independently or they can be incorporated into
building energy management systems. The series
GMD 20 and GMW 20 Series
CO
2
Transmitters for Indoor Air Quality
and Demand Controlled Ventilation
consists of a duct mount unit and wall mount units
with display (D), or without display. The duct units
compact sensor head design requires only a small
hole in a ventilation duct, thereby minimizing the risk
of leaking gaskets and measurement errors. In
addition to the standard 0...20 mA, 4...20 mA and
0...10 V outputs, there are also two options:
a LonWorks
®
interface and a relay output. The relay
output is standard with the display units.
TEMPERATURE OPTION
The GMA 20T temperature module, an option with
the GMW 21 wall mount unit, combines both CO
2
and temperature measurement into one transmitter.
The GMA 20T has a temperature range of 32°122°F
(050°C), an accuracy @ 25°C of ±0.9°F (±0.5°C),
and an output of 010V.
The versatile GMD/W 20 transmitters are easy to
install and provide superior stability, accuracy, and
temperature dependence over a broad temperature
range. The self-compensating CARBOCAP® sensor
technology ensures long term measurement stability
(better than ±100ppm) over a 5-year period 
without calibration.
CARBOCAP
®
s breakthrough self compensating
sensor technology provides superior stability,
accuracy, and temperature dependence over a
broader temperature range. Theres no add-on
software fix or external software compensation.
Just excellent sensor stability - for five years!
GMD/W Series
IR-SOURCE
SAMPLE CELL
TUNABLE
INTERFERENCE FILTER
IR-DETECTOR
SIGNAL
PROCESSING
DIFFUSION MEMBRANE