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Infra Red Gas Detection Technical Overview Notes

Honeywell Analytics – Experts in Gas Detection

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 | Gas Detection | Planning and Designing Gas Detection Systems | Infra-Red Gas Detection | Open Path Infra-Red Gas Detectors | Point Type Infra-Red Gas Detectors | Comparison of Infra-Red and Catalytic Gas Detection Systems

 

Open Path (Line of Sight) Infra Red Gas Detectors

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 mm. 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.

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 by Open Path Infra Red Gas Detectors

Gases measured include Methane, Ethane, Propane, Butane, Pentane, Hexane, Ethylene, Propylene, Butadiene, Methanol and Ethanol.  

Calibration of Open Path Infra Red Gas Detectors

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 Detectors.

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.  

Advantages and Disadvantages of Open Path Infra Red Gas Detectors

Advantages

  1. Unit is ideal for open areas without obstructions as the beam must have a clear path.
  2. Covers large areas, thus minimising the number of units required.
  3. Very fast response.
  4. Limited maintenance required.

Disadvantages

  1. Unsuitable for hydrocarbons which have various compositions ie., if one day the leak could be Methane and the next Propane the readings will change and will not be representative.
  2. Cannot measure non hydrocarbons eg., hydrogen.

References: Honeywell Analytics Searchline Excel Infrared Gas Detector Technical Handbook.


Infra Red Point Gas Detection

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.

Advantages

  1. Unit is ideal for areas where gas is likely to collect, it is more commonly being used in conjunction with line of sight gas detectors..
  2. Very fast response, however the use of sinters can effect this.
  3. Limited maintenance required.
  4. Minimal drift.
  5. Limited covert (hidden) failure potential, hence being used in 1oo1 (one out of one) configurations. This however has some drawbacks- see disadvantages below.

Disadvantages

  1. Only measures at a particular point.
  2. Greater sensitivity to heavier hydrocarbons, for instance if you are measuring methane and there is a condensate release it is likely that high LEL readings will result. Therefore it is essential that the possible gas compositions are carefully considered before opting for a 1001 configuration. ( In this combination under these circumstances false trips may result).
  3. Cannot measure non hydrocarbons eg., hydrogen.
  4. Gassing the detector with test gas can be a problem with some detectors, however most manufacturers have test cells. it must be noted that test cells require a higher concentration of test gas as it is only introduced across a small part of the optical path. The use of test wands with a clear plastic sheet being introduced is likely to become a feature because of consistent results.

Infra-Red 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 Detection 

Infra-Red Gas Sensors - Today, many IR instruments are available for a wide variety of applications. Many of them offer simple, rugged, 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;
- Principle of Operation
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Key Components for Analysis
-
Detectors
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Infra-Red Source
Self-Sampling Gas Cell
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Configuration
-
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. 

The Benefits of IR Gas Detection for Oil and Gas Applications - Gem Bayless - Gas detection has been through a number of evolutions since the birth of the industry over 50 years ago. A major milestone in its history has been the introduction of Infrared (IR) gas detection, which uses a Hydrocarbon gases ability to absorb IR light at a pre-determined wavelength. Thanks to its notable value, which includes a fast speed of response (typically T90 in less than 5 seconds), fail-to-safety operation, immunity to poisons and ability to work in inert atmospheres, IR detection is fast becoming a popular method of detection - particularly within the oil, gas and petrochemical industries -from Honeywell and PetroOnline  

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.

Open Path Infra-Red Gas Detectors

IR Open Path IR Gas Detector Manual from Simrad, section 1 describes the principal of operation thanks to Simrad Optronics and ICEweb sponsor Redetect 

Infrared 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.

Early 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.  

Point Type Infra-Red Gas Detectors

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.

IR Point Gas Detector Manual from Simrad, section 5 describes the principal of operation thanks to Simrad Optronics and ICEweb sponsor PROdetec 

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 Infra-Red and Catalytic Gas Detection Systems

Comparison of Optical Detection Systems for Infra Red Hydrocarbon Gas Detection - This document gives a good comparison of IR techniques.

Combustible 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.