Low power gas leak detector

Details Low power gas leak detector Low power gas leak detector

2003-01-23

2004-09-21

Williams, Hezron (Department: 2856)

Measuring and testing

Gas analysis

By thermal property

C073S025050, C073S029050, C073S031050

Reexamination Certificate

active

06792794

ABSTRACT:

BACKGROUND
The invention pertains to detection, identification and analyses of gases. Related art fuel gas leak detectors may be low-cost (and in part reasonably sensitive) but cannot identify the nature of the fuel leak (natural gas, swamp gas, propane or gasoline vapors), while others such as portable GCs (gas chromatographs) are both moderately sensitive and able to identify the fuel, but are very costly, slow (greater than about ten seconds response time) and consume much power.
Aspects of structures and processes related to gas detectors may be disclosed in U.S. Pat. No. 6,393,894, issued May 28, 2002, and entitled “Gas Sensor with Phased Heaters for Increased Sensitivity,” which is incorporated herein by reference, and in U.S. Pat. No. 4,944,035, issued Jul. 24, 1990, and entitled “Measurement of Thermal Conductivity and Specific Heat,” which is incorporated herein by reference.
SUMMARY
A gas leak detector and analyzer may be realized via affordable, in-situ, ultra-sensitive, low-power, low-maintenance and compact micro detectors and analyzers, which can wirelessly or by another medium (e.g., wire or optical fiber) send their detection and/or analysis results to a central or other manned station. A micro gas leak detector incorporating a phased heater array, concentrator and separator as an enhanced detector contribute to the availability of a low-cost multi-gas analyzer and system to provide gas leak detection.
The present gas leak detector is low-power, fast, compact, low cost, intelligent, wireless or not, low maintenance, robust and highly sensitive. It is a phased heater based leak detector that responds in about one second, uses less than one watt of power, can identify the nature of the fuel via its constituents, and is palm-top-sized and thus very portable
The heater elements of a phased heater array may be coated
with an adsorber material on both surfaces, i.e., top and bottom sides, for less power dissipation and more efficient heating of the incoming detected gas. The heater elements may have small widths for reduced power dissipation. There is a heater membrane that has a small number anchor points for little heat conduction from the heater elements.
The surfaces of inside channels of the heater array, except those surfaces intentionally by design coated with an adsorber material, may be coated with a non-adsorbing, thermal insulating layer. The thickness of the adsorber coating or film is reduced thereby decreasing the time needed for adsorption and desorption. A thrifty pump may be implemented for pulling in a sample of the fluid being checked for detection of a possible gas leak from somewhere. Low-power electronics having a sleep mode when not in use may be utilized. Thus, the present leak detector uses very little power.
The gas leak detector may be integrated on a chip with conventional semiconductor processes or micro electromechanical machined system (MEMS) techniques. This kind of fabrication results in low-power consumption, compactness and in situ placement of the detector. The flow rate of the air or gas sample through the detector may be very small. Further, a carrier gas for the samples is not needed and thus this lack reduces the dilution of the samples being tested, besides eliminating the associated maintenance and bulk of pressurized gas-tank handling. This approach permits the detector to provide quick analyses and prompt results, maybe at least an order of magnitude faster than some related art devices. It avoids the delay and costs of labor-intensive laboratory analyses. The detector is intelligent in that it may have an integrated microcontroller for analysis and determination of gases detected, and may maintain accuracy, successfully operate and communicate information in and from unattended remote locations. The detector may communicate detector information, analyses and results via utility lines, or optical or wireless media, with the capability of full duplex communication to a host system over a significant distance with “plug-and-play” adaptation and simplicity. The system is net-workable. It may be inter-connectable with other gas sample conditioning devices (particle filters, valves, flow and pressure sensors), local maintenance control points, and can provide gas leak monitoring via the internet. The detector is robust. It can maintain accuracy in a high electromagnetic interference (EMI) environment such as in the vicinity of electrical power distribution sub-stations where very strong electrical and magnetic fields are present. The detector has high sensitivity. It offers sub-ppm (parts-per-million) level detection which is 100 to 10,000 times better than related art technology, such as conventional gas chromatographs which may offer a sensitivity between the 1 to 10 ppm range. The detector is, among other things, a lower-power, faster, and more compact, more sensitive and affordable version of a gas chromatograph. It may also be lower power-consuming and faster than previous versions of the present kind of phased-heater detectors which require heavy batteries needing many changes or recharges, which may be avoided in the present detector. The latter detector may have structural integrity, and have very low or no risk of leakage in the application of detecting and analyzing pressurized fluid samples, over a very large differential pressure range.
In the leak detector, a small pump, such as a Honeywell MesoPump™ preferably draws a sample into the sensor system, while only a portion of it flows through the phased heater sensor at a rate controlled by the valve (which could be a Honeywell MesoValve™ or Hoerbiger PiezoValve™). This enables fast sample acquisition despite long sampling lines, yet provides a regulated, approximately 1 to 3 cm
3
/min flow for the leak detector. The pump of the leak detector may be arranged to draw sample gas through a filter in such a way as to provide both fast sample acquisition for and regulated flow through the phased heater sensor.
As the sample pump draws sample gas through the leak detector, the gas is expanded and thus increases its volume and linear velocity. The control circuit is designed to compensate for this change in velocity to keep the heater “wave” in sync with the varying gas velocity in the detector. To compensate for the change in sample gas volume as it is forced through the heater channels, its electronics may need to adjust either the flow control and/or the heater “wave” speed to keep the internal gas flow velocity in sync with the heater “wave”.
During leak survey operation, present detector's ability (like any other slower GCs) may sense multiple trace constituents of air such as about 330 to 700 ppm of CO
2
, about 1 to 2 ppm of CH
4
and about 0.5 to 2.5 percent of H
2
O. This enables on-line calibration of the output elution times as well as checking of the presence of additional peaks such as ethane, indicating natural gas, propane or other gas pipeline leak. The ratio of sample gas constituent peak heights thus reveals clues about the source of the trace gases, which could include car exhaust or gasoline vapors.
The leak detector may have sensitivity, speed, portability and low power that make it especially well suited for safety-mandated periodic leak surveys of natural gas or propane gas leaks along transmission or distribution pipeline systems, and gas leaks in chemical process plants.
The detector may in its leak sensing application use some or all sample gas constituents (and their peak ratios) as calibration markers (elution time identifies the nature of the gas constituents) and/or as leak source identifiers. If the presence alone of a certain peak such as methane (which is present in mountain air at about one to two ppm) may not be enough information to indicate that the source of that constituent is from swamp gas, natural/pipeline gas or another fluid.
The proposed leak sensor may be used as a portable device or installed at a fixed location. In contrast to comparable related art sensors, it is more compact than portable flame ionization detectors witho

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