Figure 1: Sensor Cell Construction - Teledyne 700 IR Series Instruction Manual

Infrared gas detector for combustible and co2 gases

Hide thumbs

Table Of Contents

Table of Contents

700 IR Series

INFRARED GAS DETECTOR FOR COMBUSTIBLE AND CO

GASES

USER MANUAL

1.1.1

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 an infrared lamp source, two pyro

electric detectors, and an 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 pyro electric detectors at the completion

of the optical path. The "active" pyro electric detector is covered by a filter specific to the part of

the IR spectrum where the target gas absorbs light. The "reference" pyro electric 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. The technique for CO

response to CO

. Unlike catalytic bead type sensors, Teledyne Oldham Simtronics IR sensors are

completely resistant to poisoning from corrosive gases and they 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.

1.1.2

Principle of Operation

The target gas diffuses through a sintered stainless steel flame arrestor and into the volume of the

sample gas optical chamber. An alternating miniature lamp provides a cyclical IR radiation

source, which reflects through the optical gas sample chamber and terminates at two pyro electric

detectors. The active and reference pyro electric detectors each give an output which measures

the intensity of the radiation contacting their surface. The active detector is covered by an optical

filter specific to the part of the IR spectrum where the target gas absorbs light. The reference

detector is covered by a filter specific to the non-absorbing part of the IR spectrum.

is similar except that the sensor provides a selective