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Go to Specific Information that
interests you; Principle of Operation | Gases
Measured by Open Path Infra Red Gas Detectors | Calibration
of Open Path Infra Red Gas Detectors | Advantages and
Disadvantages of Open Path Infra Red Gas Detectors |Infra
Red Point Gas Detection | Infra Red Gas Detection Technical
Engineering References | Fire
and Gas Technical Information |
Infra-red (IR) gas detection is based on the absorption of energy by hydrocarbons.
bond between hydrogen and carbon absorbs proton energy at a wavelength of 3.3
The wavelength is carefully selected to accurately measure
the concentration of methane and other hydrocarbon gases in air, ensuring that
the measurement is not effected by water vapour or other gases.
Infra-Red (IR) Line of Sight (LOS) Open Path Gas Detectors
measure the amount of hydrocarbon gas in an Infrared beam by determining the
amount of Infrared Absorption of the air or air-gas mixture in the line of sight
(LOS) path. LOS IR Gas detectors
utilise an IR source and a detector which measures the intensity of the IR of
the received IR radiation at the appropriate wavelength. A separate
Transmitter/Receiver configuration provides the most reliable basis for open
path gas detection of up to 200meters.
There are also point type IR gas detectors.
There are also point type IR gas detectors.
A beam of IR energy is emitted between a source and detector and any attenuation caused by hydrocarbons in the beam being electronically processed to give a reading in LEL metres.
In order to ensure that dirty lenses, mirrors or other
related issues do not cause errors two detectors are generally utilised and
their measurements compared. In order to reduce or eliminate the effects of
other interfering light sources, particularly direct and reflected sun light,
but also flames and welding arcs, higher-specification instruments employ strong
pulsed light sources, and the times at which measurements are taken are
synchronised with the timing of the light pulses. Transmitter
and Receiver units may incorporate heated optics designed to minimise the
build-up of humidity, condensation, snow or ice on the glass windows, which
could obscure the optics in extreme conditions. The sophisticated open-path
technology provides immunity to sunlight and minimises the effects of
environmental factors such as rain, fog, ice, snow and condensation.
The sample detector input is filtered at wavelengths where
strong infrared absorption is exhibited by
the target gas. The reference detector input is filtered at nearby
wavelengths, where strong infrared
absorption is not exhibited by the target gas. By calculating the ratio of the
sample to reference signal it is possible to measure the quantity of gas in the
beam, whilst compensating for the effects of rain, fog, dirt etc.
Gases measured include Methane, Ethane, Propane, Butane,
Pentane, Hexane, Ethylene, Propylene, Butadiene, Methanol and Ethanol.
Calibration for a gas concentration is expressed in LEL -
metres. For various gases low and
high test filters are used for calibration eg.,methane employs polypropylene
sheets of specific thicknesses. For
more complex situations, gas tubes that can be inserted in the beam path and
filled with specific gas mixtures may be employed to calibrate Open Path Gas
OPGD beam paths need very careful design to ensure an
uninterrupted Line of sight, this should occur at the detailed design stage. It
is recommended that if a 3D model is available this tool is used to verify this.
References: Honeywell Analytics Searchline Excel Infrared Gas Detector Technical Handbook.
Principle of operation
Infra-red (IR) gas detection is based on the absorption of
energy by hydrocarbons. The bond between hydrogen and carbon absorbs proton
energy at a wavelength of 3.3 µm
A beam of IR energy is emitted between a source and
detector and any attenuation caused by hydrocarbons in the short beam being
electronically processed to give a reading in LEL (Lower Explosive Limit).
Commonly a reference beam is utilised to overcome any reduction in beam
intensity due to fouling of the optics, fog, temperature effects etc.
Gas Detection -Technical Engineering References for Instrument and Fire &
Gas Design Engineers
The following Infra-Red Gas Detector references are from sources which provide what ICEweb considers to be the best technical and educational information on the subject. We always acknowledge the author and source. Should there be any issue with ICEweb providing this information, please contact us and we will remove it immediately. We also welcome non-commercial technical documents (subject to editorial review) and post them free. - ICEweb is a Free Technical Information Website for Instrument, Control, Fire & Gas and SIS Engineers and the sponsorships provide the funding to cover running costs.
Infra-Red Gas Sensors - Today, many IR instruments
are available for a wide variety of applications. Many of them offer simple,
and reliable designs. In general, for toxic and combustible gas monitoring
applications, IR instruments are among the most user friendly and require the
least amount of maintenance. There is virtually an unlimited number of
applications for which IR technology can be used. This really excellent and
comprehensive book chapter from International Sensor Technology covers;
- Key Components for Analysis
- Infra-Red Source
- Self-Sampling Gas Cell
- Characteristics of an IR Detector
- Applications of IR Detectors
Infra-Red Open Path Detector - Infrared open-path gas detectors send out a beam of infrared light, detecting gas anywhere along the path of the beam. This linear 'sensor' is typically a few metres up to a few hundred metres in length. Open-path detectors can be contrasted with Infrared point sensors.They are widely used in the petroleum and petrochemical industries, mostly to achieve very rapid gas leak detection for flammable gases at concentrations comparable to the lower flammable limit (typically a few percent by volume). They are also used, but so far to a lesser extent, in other industries where flammable concentrations can occur, such as in coal mining and water treatment. In principle the technique can also be used to detect toxic gases, for instance hydrogen sulfide, at the necessary parts-per-million concentrations, but the technical difficulties involved have so far prevented widespread adoption for toxic gases - From Wikipedia, the free encyclopedia.
Honeywell Analytics Gas Book - This handbook is intended to offer a simple guide to anyone considering the use of gas detection equipment. It provides an explanation of both the principles involved and the instrumentation needed for satisfactory protection of personnel, plant and environment. The aim has been to answer as many as possible of the most commonly asked questions about the selection and use of industrial gas detection equipment. Be patient, this document may take a while to download.
Gas Detection Infrared Sensors Broaden Scope of Platform Gas Analysis - Jeff Markley - Catalytic detectors reveal the presence of combustible gases through a change in the resistance of the embedded coil - but their sensitivity can be affected by airborne contaminants. Infrared sensors allow open path detectors to detect gas up to 200 metres away - from Honeywell Analytics.
IR Open Path IR Gas Detector
Simrad, section 1 describes the principal of operation thanks to Simrad
Optronics and ICEweb sponsor Redetect
Open-Path Detector - Infrared open-path gas detectors send out a beam of
infrared light, detecting gas anywhere along the path of the beam. This linear
'sensor' is typically a few metres up to a few hundred metres in length.
Open-path detectors can be contrasted with Infrared point sensors. They are
widely used in the petroleum and petrochemical industries, mostly to achieve
very rapid gas leak detection for flammable gases at concentrations comparable
to the lower flammable limit (typically a few percent by volume) - From
Wikipedia, the free encyclopedia
Reducing Costs and Enhancing Safety with Open Path Infrared (IR) Gas Detection - It is fair to say that Infrared (IR) technology has revolutionised the gas detection market, providing a principle of detection that offers many tangible benefits in terms of performance, functionality and reduced ongoing costs. Since IR’s introduction into gas detection during the late 1970s, a variety of principles have subsequently emerged, the most impacting of which has been Open Path. This is a detection technique that allows gas to be monitored across a large range. Unlike a single Point IR device, an Open Path detector usually has two components with a beam of IR light between them, allowing this type of device to detect a gas cloud that drifts into the beam. This configuration provides the instant benefit of an increased chance of detecting a gas leak. Designed to monitor a diverse variety of Hydrocarbon gases, Open Path IR has a number of key benefits that add real value, when compared to solutions like catalytic bead detection. It is essential to consider the build, configuration and value of the Open Path devices currently available, when selecting a system, as they can vary considerably in terms of performance capability and ability to reduce ongoing costs - from Honeywell Analytics.
Detection of Combustible Gas Leaks Using Open Path Infrared (IR) Gas Detectors
- Edward Naranjo and Shankar Baliga - Open path IR gas detectors are a mainstay
in the oil and gas industry. They are used in a variety of instances to identify
gas accumulations or monitor gas cloud migrations. In offshore installations,
open path optical gas detectors are used to monitor drilling and production
operations, crude oil separation, compression, and exhaust and ventilation
systems. Because they can monitor a perimeter or fence line, they are ideally
suited for detecting gas in open facilities, where point gas detectors would be
difficult or expensive to deploy. Despite their widespread use, open path
optical gas detectors are rarely employed to detect low level concentrations of
combustible gases. Standard models are typically set to alarm at 50% LEL-m (50%
LEL extended over one meter), providing sufficiently early warning when gas
accumulations occur. Nevertheless, in cases in which a combustible gas is
diluted quickly, such as ventilation exhaust ducting, it may be necessary to set
the detector to alarm at the lowest predictable level. Further, interest in low
level infrared gas detection has been growing as gases such as CH4 and CO2
aregreenhouse gases. This paper describes a mid-wave infrared (MWIR) open path
system designed to detect combustible and carbon dioxide gas leaks in the
parts-per-million-meter (ppm-m or mg/cm2 ). The detector has been installed in
offshore platforms and large onshore facilities to detect a variety of flammable
gases and vapors. Advantages and limitations of the system are presented. False
alarm immunity and resilience to atmospheric interferences are also discussed -
from Research Gate.
Upgrading to Infrared Technology Made Easy - Pellistors or catalytic bead sensors already installed into various industries can easily be replaced by IR – without any technical hurdles. Neither the control system nor the electrical wiring need to be adapted - from Draeger Australia.
Infrared Technology for 'Fail to Safe' Hydrocarbon Gas Detection - Dr Shankar Baliga and Shafiq Khan - Continuing advances in infrared technology have resulted in fail-to-safe hydrocarbon gas point detectors that continuously monitor combustible gases and vapors within the lower explosive limit (LEL) and provide alarm indication. Other features of these detectors include operation in oxygen deficient or enriched areas, lack of routine calibration, immunity to poisons, and RS-485 communications link along with 4-20 mA output. Another application of infrared technology is open path detection, which complements point detection. With an open path system there is no definite fixed path length for measuring gas leaks so the measurement is expressed in terms of concentration times path length. The open path system incorporates many of the same advantages of the optical point detector and includes a dual range, ppm.m for small hydrocarbon leaks and LEL.m for more catastrophic leaks.
Comparison of Optical Detection Systems for Infra Red Hydrocarbon Gas Detection - This document gives a good comparison of IR techniques.
Gas Safety Monitoring - Infrared vs. Catalytic Gas Detectors - When
designing a combustible gas safety monitoring system for oil/gas, petrochemical
or other applications, how do you decide whether to use infrared or catalytic
gas detector technology? Both sensing technologies have their advantages
dependent upon your application’s specific requirements. A thorough analysis
of your application’s unique field environment is needed to ensure optimal
performance, safety, reliability and cost-effectiveness. A quick decision, of
course, can lead to poor detector choices as well as safety, performance,
maintenance, and life-cycle cost consequences.