Detcon CX-IR - Manual (Page 5)

Model CX-IR
1. Introduction
1.1 Description
Detcon Model CX-IR combustible gas sensors are non-intrusive “Smart” sensors designed to detect and
monitor combustible hydrocarbon gases in the air with a detection range of 0-100% LEL (Lower Explosive
Limit). The sensor features an LED display of current reading, fault and calibration status. A primary feature
of the sensor is its method of automatic calibration, which guides the user through each step via fully scripted
instructions illustrated on the LED display.
The microprocessor-supervised electronics are enclosed in an encapsulated module and housed in an explosion
proof casting. The infrared detector is mounted in an intrinsically safe stainless steel housing and includes a
Splash Guard Cal Adapter.
Non-Dispersive Infrared (NDIR) Optical Sensor Technology
The sensor technology is designed as a miniature plug-in replaceable component, which can easily be changed
out in the field.
The NDIR sensor consists of (Figure 1);
• one infrared lamp source,
• two pyroelectric detectors (active and reference),
• and one optical gas sample chamber.
The lamp source produces infrared radiation, which interacts with the target gas as it is reflected through the
optical gas sample chamber. The infrared radiation contacts each of the 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 the target gas absorbs light. The reference pyroelectric detector is covered by a filter
specific to the non-absorbing part of the IR spectrum. When the target gas is present, it absorbs IR radiation
and the signal output from the active detective decreases accordingly. The reference detector output remains
unchanged. The ratio of the active and reference detector outputs are then used to compute the target gas
concentration.
The technique is referred to as non-selective and may be used to monitor most any combustible hydrocarbon
gas. Unlike catalytic bead type sensors, Detcon IR sensors are completely resistant to poisoning from corrosive
gases and can operate in the absence of an oxygen background. The sensors are characteristically stable and
capable of providing reliable performance for periods exceeding 5 years in most industrial environments.
Figure 1 Sensor Cell Construction
CX-IR Instruction Manual Rev. 1.2 Page 1 of 34