Detcon IR-642 - Manual (Page 3)

3.0 D ESCRIPTION
Detcon MicroSafe™ Model IR-640, carbon dioxide gas sensors are non-intrusive “Smart” sensors designed to detect
and monitor CO2 gas in air over the 0-5% range. The Detcon MicroSafe™ Model IR-642 CO2 gas sensor measures
in the 10-100% Range. One of the primary features of the sensor is its method of automatic calibration which
guides the user through each step via instructions displayed on the backlit LCD. The sensor features f ield
adjustable, fully programmable alarms and provides relays for two alarms plus fault as standard. The sensor comes
with two different outputs: analog 4-20 mA, and serial RS-485. These outputs allow for greater f lexibility in system
integration and installation. The microprocessor supervised electronics are packaged as a plug-in module that mates
to a standard connector board. Both are housed in an explosion proof condulet that includes a glass lens window
which allows for the display of sensor readings as well as access to the sensor’s menu driven features via a hand-held
programming magnet.
The sensor technology is a f ield proven “plug-in replaceable” non-dispersive infrared (NDIR) optical type. NDIR
optical sensors show an excellent response to CO2. The NDIR type sensor is characteristically stable for both span
and zero and is capable of providing reliable performance with low maintenance requirements for periods approach-
ing 5 years in most industrial environments.
Typical ranges of detection are 0-0.30%, 0-0.50%, 0-1.00%, 0-2.00%, 0-3.00% and 0-5% with the IR640. Typical
Ranges with the IR642 are 0-10%, 0-25%, 0-50%, 0-100%. Other ranges may be accommodated and all ranges are
covered by this manual. To determine the range of detection, refer to the instructions found in section 3.8.
3.0.1 Non-dispersive Infrared (NDIR) Optical Sensor
The Detcon NDIR sensor is designed as a miniature single piece “plug-in replaceable” component, which can easily be
changed out in the field. The NDIR sensor consists of an infrared lamp source, two pyroelectric detectors, and an
optical gas sample cavity. The lamp source produces infrared radiation which interacts with CO2 as it travels through
the optical gas sample cavity. The infrared radiation contacts each of two pyroelectric detectors at the completion of
the optical path. The “active” pyroelectric detector is covered by a filter specific to the part of the IR spectrum where
CO2 absorbs light. The “reference” pyroelectric detector is covered by a filter specific to the non-absorbing part of the
IR spectrum. When CO2 is present, it absorbs IR radiation and the signal output from the “active” pyroelectric detec-
tor decreases accordingly while the “reference” detector output remains unchanged. The ratio of the “active” and “ref-
erence” detector outputs is then used to compute CO2 concentration.
Detcon Model IR-640/IR-642 Carbon Dioxide Sensor PG.3