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 CH<sub>4</sub> and CO<sub>2</sub> are
The present 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/cm<sup>2</sup>). 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.
Fixed gas detection equipment for the petroleum industries is no ordinary equipment. It is designed for continued
unattended surveillance in harsh environments. The equipment must be reliable and require limited field maintenance.
An additional requirement is a high resistance to false alarms and interferences, which can potentially reduce the
detector's efficacy and the level of protection provided. In recent years, several manufactures of IR imaging devices have
launched commercial models that are applicable to a wide range of chemical species and suitable for industrial use.
These cameras are rugged and sufficiently sensitive to detect low concentrations of combustible and toxic gases.
Nonetheless, as users become acquainted with these imaging systems, questions of resilience to solar and flame radiation
and other IR sources, interferences by fog or steam, have begun to emerge. These questions, in fact, reflect similar
concerns as those raised with open path IR gas detectors when they first appeared in the market over 20 years ago. This
paper examines an IR gas imager's performance when exposed to several false alarm sources. Gas detection sensitivity
in the presence of false stimuli and response and recovery times under an uncontrolled outdoor environment were
measured. The results show the specific model tested is reasonably immune to false alarms, while response times were
unaffected by the presence of these sources.
Uncooled thermal cameras using microbolometer focal plane arrays may be used in the long wave infrared (LWIR) for
the optical detection of hydrocarbon gas leaks. The strong absorption of hydrocarbon gases in the LWIR may be used to
advantage along with the LWIR optical transmission window of the atmosphere. Improvements in the detection
algorithm and more robust electronic hardware have produced a gas imager that is well adapted to the detection of large
hydrocarbon leaks. The new imaging system relies on a single set of filters to identify a growing list of gases, up to four
of them simultaneously. The new detection algorithm reduces the incidence of false alarms by masking portions of the
field of view. Because of the camera's long detection range (2 km) and wide field of view, the system is particularly
suitable for the supervision of large industrial zones. Results from a field test of leaking gas at a refinery and natural gas
processing facility are presented.
We propose an ultrasonic gas leak localization system based on a distributed network of sensors. The system
deploys highly sensitive miniature Micro-Electro-Mechanical Systems (MEMS) microphones and uses a suite of
energy-decay (ED) and time-delay of arrival (TDOA) algorithms for localizing a source of a gas leak. Statistical
tools such as the maximum likelihood (ML) and the least squares (LS) estimators are used for approximating
the source location when closed-form solutions fail in the presence of ambient background nuisance and inherent
electronic noise. The proposed localization algorithms were implemented and tested using a Java-based simulation
platform connected to four or more distributed MEMS microphones observing a broadband nitrogen leak from an
orifice. The performance of centralized and decentralized algorithms under ED and TDOA schemes is analyzed
and compared in terms of communication overhead and accuracy in presence of additive white Gaussian noise
A model for an infrared (IR) flame detection system using artificial neural networks (ANN) is presented. The joint time-frequency
analysis (JTFA) in the form of a Short-Time Fourier Transform (STFT) is used for extracting relevant input
features for a set of ANNs. Each ANN is trained using the backpropagation conjugate-gradient (CG) method to
distinguish all hydrocarbon flames from a particular type of environmental nuisance and background noise. Signal
saturation caused by the increased intensity of IR sources at closer distances is resolved by an adjustable gain control. A
classification scheme with trained ANN connection weights was implemented on a digital signal processor for use in an
industrial hydrocarbon flame detector.
Mn<SUB>1.56</SUB>Co<SUB>0.96</SUB>Ni<SUB>0.48</SUB> is RF magnetron sputtered in a series of oxygen partial pressures, and non-stoichiometric films are produced. Conduction is small polaron hopping for all stoichiometries as evidenced by near temperature independent thermopower, and decreasing conduction activation energy with decreasing temperature. The carrier type transitions from p to n type with a decrease in the ratio of Mn<SUP>3+</SUP> to Mn<SUP>4+</SUP> concentration. The resistivity, and conduction activation energy are decreasing functions of the oxygen partial pressure. The Debye frequency increases with oxygen partial pressure as measured from the resistivity, and this is consistent with the observed shift of both the Raman and IR active lattice vibrations. The material has the spinel crystal structure, and as such is an optical window with the 3 phonon cutoff occurring at 17 micrometer. The material is transparent between 6 micrometer to 17 micrometer.
The identification of gases and the measurement of their concentration in a mixture is important in a variety of applications such as gas leak detection, process monitoring and control, and pollution control. Many gases can be uniquely identified by their optical absorption spectra. In a mix of gases, the individual species can be identified by measurements at several wavelengths and the knowledge of the absorption strengths. The advantages of these optical absorption techniques can often be utilized to the fullest only if the technology used is capable of measurements over a wide wavelength range. Instruments based on pyroelectric array detectors can utilize both dispersive and nondispersive techniques, and operate over the entire infrared region since the detectors themselves are not intrinsically wavelength sensitive. In this paper, the construction and use of infrared pyroelectric arrays suitable for gas detection and monitoring are described.
The thermistor infrared detector or bolometer is the detector of choice in many classical remote sensing applications such as horizon sensing, noncontact thermometry, and industrial applications. In recent years, the authors have developed a thin film process where the thermistor material is deposited from a target directly onto the substrate. This is an advance over the labor intensive ceramic technology, where sintered flakes of the thermistor are bonded to the substrate. The thin film technique permits a variety of device constructions and configurations. Detectors fabricated on heat-sunk ceramic substrates can withstand high operating temperatures and large incident optical power, in both pulsed and CW laser measurements. For dc or low frequency measurements, the films can be deposited onto a thermally isolated membrane with applications in motion sensing, gas detection, and temperature measurement. Utilizing advances in micromachining a 2D array of thermally isolated microbolometer sensors, integrated onto a silicon wafer containing readout circuitry may be achieved. This paper describes the construction of the sputtered film thermistor detectors, their operation, and applications.
Earth horizon sensors utilizing pyroelectric detectors are finding increasing use in infrared horizon sensing systems. These detectors, like the earlier thermistor bolometer sensors, observe the Earth's carbon-dioxide emission in the 15 micron wavelength band. This paper describes the design, construction and performance of a pyroelectric detector suitable for use in horizon scanner systems. The procedures being developed to ensure the space qualification of this detector will be described. The design of more advanced staring arrays which have been developed will also be discussed.