Self-commissioning NDIR gas sensors

Two detectors of the same kind, each having an identical neutral band-pass filter to the target gas, are installed next to Signal channel and Reference channel detectors as pairs in an AB designed NDIR gas sensor layout, which are called Standard Signal channel detector and Standard Reference channel detector. “Standard” GAMMA is the ratio of Standard signal channel detector output over that of Standard Reference channel detector. “Standard” GAMMA is independent of the measurement Physics of NDIR gas sensors, is dependent only upon the performance characteristics of the sensor component and is also independent of the presence of any amount of target gas in the sample chamber. Consequently, “Standard” GAMMA can be used to proportionally correct and update GAMMA of the sensor as its components age over time thereby rendering such an AB designed NDIR gas sensor self-commissioning or staying accurate over time after initial calibration.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patent application Ser. No. 13/149,738, the disclosure of which is specifically incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is in the field of measuring instruments, and specifically relates to a configuration design and method for an NDIR gas sensor.

BACKGROUND OF THE INVENTION

Output instability or drift over time leading to measurement inaccuracies has long been a major deficiency for gas sensors irrespective of what technology or methodology is used for their conception or realization. Output software correction may alleviate the problem somewhat but it is in many instances inaccurate and not even always applicable. It has long been the objective of many researchers in this field to overcome this problem fundamentally and for good.

Recently the present author in U.S. Pat. No. 8,143,581, the disclosure of which is specifically incorporated by reference herein, advanced the teaching of an Absorption Biased NDIR Gas Sensing Methodology which is capable of eliminating substantially all the NDIR gas sensor output drifts over time without the need for re-calibration. As it turns out, the solution to solving this output drift problems for gas sensors actually lies deeper than the availability of superior NDIR gas sensor types even though they can indeed be designed to be capable of maintaining measurement accuracy over time. The fact of the matter is that people have experienced gas sensor output instability for such a long time in the past that when output stable sensors really come along nobody believes it. Until such time that stable gas sensors become widely available and users begin to consider their performance as trustworthy and truly believable, the real need today must be viewed from a completely different perspective, which is to be able to come up with a fast, inexpensive and simple methodology that can easily check the accuracy of gas sensors and inexpensively re-calibrate them when they are found to be inaccurate.

In U.S. application Ser. No. 13/149,738, filed May 31, 2011, of which this application is a continuation-in-part application, the present author advanced the teaching of a novel Re-calibration Methodology for simply and easily re-calibrating Absorption Biased (AB) designed NDIR gas sensors without the need of standard gases. With the recent advent of the Absorption Biased (AB) gas sensing methodology for realizing NDIR gas sensors whose outputs are significantly drift-free over time and also the advent of a complementing methodology that can check and re-calibrate AB designed NDIR gas sensors simply and easily without the need of standard gases, one would think that the gas sensor industry at large, particularly the HVAC industry, would be relatively satisfied and happily go forward in growing its business. But, unfortunately, this is not the case at all. While the HVAC industry is still trying to deal with their old and on-going problem of sensor inaccuracies over time, already the industry is pushing forward in finding new and better solutions for optimizing energy expenditure and achieving superior comfort level for occupants in buildings. One rather obvious approach widely being investigated and considered everywhere today is the grouping of all sensors in a building together into a computer network. These sensors can actually interact and work with one another in an efficient manner with self-commissioning, self-tuning, self-diagnostic and correction, and even self-configuring features. By so doing the energy requirement for buildings can be reduced to an absolute minimum while the comfort level and safety for occupants in the buildings can also be greatly increased.

No doubt from the standpoint of computer networking hardware and smart software availability today, this approach is clearly workable. However, when all the sensors are to be left alone by themselves to interact with one another over time in buildings, the obvious question to ask is whether these sensors are indeed ready to take on this self-policing task of always staying accurate. In other words, who is there to check whether the outputs of some of these sensors are actually staying accurate over time and if not, what are the consequences for the maintenance status of the buildings and the comfort level and safety of their occupants? Thus, while computer hardware and system networking software may be ready for this futuristic approach to building controls, it is very clear that not all the sensors needed to perform perfectly in this approach are here today to meet the challenge. In particular, gas sensors such as CO₂ and dew point might be relatively accurate over time but for how long before they become inaccurate? But would there be anybody or any mechanism scheduled in the networking controls system to perform the checking or re-calibrating tasks for them? To put it bluntly, until such time that all the required sensors in the networking controls system can be self-commissioning or in other words can render themselves capable of automatically staying accurate all the time, the futuristic building controls approach with the use of computer networking and relevant software to connect all the sensors in the system together working interactively simply will not work.

It is the object of the present invention to advance a configuration design and methodology for AB designed NDIR gas sensors such that they can become self-commissioning or in other words capable of automatically maintaining their measurement accuracy indefinitely over time after initial calibration. This invention is achieved via extending the previously disclosed Absorption Biased methodology of U.S. Pat. No. 8,143,581 and Re-calibration methodology without the need of standard gases (U.S. Ser. No. 13/149,738, Wong) for NDIR gas sensors.

SUMMARY OF THE INVENTION

The present invention is generally directed to a self-calibrating NDIR gas sensor and its use in which an infrared source illuminates a signal channel that is longer than a reference channel while electronics are used to calculate a chosen gas concentration in a sample chamber containing the two channels. The difference in length between the two channels creates an absorption bias between outputs of a signal detector and a reference detector, each of the two detectors having an identical narrow band pass filter with the same Center Wavelength (“CWL”), Full Width Half Maximum (FWHM) and transmittance efficiency at the CWL. A second pair of detectors, called standard detectors, are placed in the two channels, and both of these standard detectors have an identical standard narrow band pass filter with the same Center Wavelength (“CWL”), Full Width Half Maximum (FWHM) and transmittance efficiency at the CWL and the CWL of the standard narrow band pass filter is a neutral wavelength. The electronics of the sensor is calibrated by use of a calibration curve generated by using a normalized ratio of the signal channel output to the reference channel output that starts at unity when there is zero concentration of the chosen gas. The calibration curve is self-calibrated by using a stored standard gamma ratio obtained at a first period of time and a measured standard gamma ratio obtained at a second period of time after the first period of time, the standard gamma ratio being the ratio of a standard signal output from a standard signal detector to a standard reference output from a standard reference detector.

Such an NDIR gas sensor can be made to detect a second gas by including a second signal detector and a second reference detector that function similarly to the signal and reference detector, except that they are designed to detect a different gas. This additional pair of detectors will each have an identical second chosen gas narrow band pass filter with the same Center Wavelength (“CWL”), Full Width Half Maximum (FWHM) and transmittance efficiency at the CWL and will have its own calibration curve generated by using a second chosen gas normalized ratio of the second chosen gas signal output to the second chosen gas reference output that starts at unity when there is zero concentration of the second chosen gas. As was the case with a single gas detection sensor, the second gas calibration curve is self-calibrated by using the stored standard gamma ratio and the measured standard gamma ratio.

The NDIR gas sensor can also be recalibrated by comparing the sample concentration of a gas it is detecting to a second gas measurement of such gas determined by a secondary gas standard and then adjusting the normalized ratio of the signal output to the reference output for the gas based upon a reversed calibration curve algorithm that is a non-linear equation if a difference between the sample concentration of the gas and the second gas measurement exceeds a preselected threshold.

Accordingly, it is a primary object of the present invention to provide an NDIR gas sensor that self-calibrates itself.

This and further objects and advantages of the present invention will be apparent to those skilled in the art in connection with the drawings and the detailed description of the invention set forth below.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrialproducts

Zero drift NDIR gas sensors

Output stability or drift overtime has long been a major performance deficiency for gas sensors irrespective of what technology or methodology is used for their conception. Software correction may alleviate the problem somewhat but it is not always applicable. It has long been the objective of many researchers in this field to overcome this problem fundamentally and for good. The purpose of this paper is to show that this objective has now finally been achieved.

Design/methodology/approach

Conventional non-dispersive infrared (NDIR) dual beam methodology utilizes the ratio of signal channel output over reference channel output for signal processing. The signal filter overlaps the absorption band of the gas of interest while the reference filter does not. However, this ratio changes as the source ages. The current methodology uses an absorption bias between signal and reference channel outputs. This absorption bias is created by using a path length for the signal channel greater than that for the reference channel. Both the signal and reference detectors carry an identical spectral filter overlapping the absorption band of the gas to be measured.

Findings

Implementation of the currently patented NDIR gas-sensing methodology has been carried out in different gas sensor configurations for over a year in the laboratory. Performance results for these sensors showing insignificant output drifts overtime have been repeatedly demonstrated via simulated aging for the source. Originality/value - The paper puts forward the view that the recent breakthrough of the Near Zero Drift methodology for NDIR gas sensors will very quickly change the hierarchy of technology dominance and utility for gas sensors at large.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Re-calibration methodology for NDIR gas sensors

A re-calibration method for a dual-beam NDIR gas sensor uses a calibration curve based upon a combination of physics and sensor measurement components of the sensor to calculate sample gas concentration, then determines a second gas concentration measurement by a secondary gas standard which is used with a reversed calibration curve algorithm to adjust the sensor measurement component. The calibration curve is based upon a gamma ratio (“G”) that has been normalized by G when no sample gas is present in the sample chamber (“G₀”), G being a ratio of a signal channel output (“V_S”) of the sensor divided by a reference channel output (“V_R”) of the sensor. The concentration (“P”) of sample gas in the sensor is calculated through use of the calibration curve by a gas detection equation of P=F(x)=F(y/G₀), where x is a normalized ratio of V_S/V_R and y is G. The reversed calibration curve algorithm is P=F(x)=F(y/G_0N), where G_0N=y₁/x₂, y₁=G for the sensor, x₂=F⁻¹ (P₂) and P₂ is the second gas concentration of the sample gas.

Description

FIELD OF THE INVENTION

The present invention is in the field of measuring instruments, and specifically relates to a method for re-calibrating non-dispersive infrared (NDIR) gas sensors whose outputs have drifted over time and no longer correctly reflect their measurement accuracy.

BACKGROUND OF THE INVENTION

Output stability or drift over time leading to measurement inaccuracies has long been a major deficiency for gas sensors irrespective of what technology or methodology is used for their conception or realization. Output software correction may alleviate the problem somewhat but it is in many instances inaccurate and not even always applicable. It has long been the objective of many researchers in this field to overcome this problem fundamentally and for good. Recently the present inventor in U.S. application Ser. No. 12/859,749 advanced the teaching of an Absorption Biased NDIR Gas Sensing Methodology which is capable of eliminating substantially all NDIR gas sensor output drifts over time without the need for re-calibration (Wong, filed 19-AUG-2010). As it turns out, the solution to solving this output drift problem for gas sensors actually lies deeper than the availability of superior NDIR gas sensor types even though they can indeed be designed to be capable of maintaining measurement accuracy over time. The fact of the matter is that people have experienced gas sensor output instability for such a long time in the past that when output stable sensors really come along nobody would believe it. Until such time that stable gas sensors become widely available and users begin to consider their performance as trustworthy and truly believable, the real need today must be viewed at a completely different perspective and that is to be able to come up with a fast, inexpensive and simple methodology that can easily check the accuracy of gas sensors and more importantly, just as easy and simple, hence inexpensive, to re-calibrate them when they are found to be inaccurate.

It is therefore the primary objective of the present invention for the present author to advance a novel methodology to simply and easily re-calibrate an NDIR gas sensor.

SUMMARY OF THE INVENTION

The present invention is generally directed to a method for recalibrating a dual-beam NDIR gas sensor by using a calibration curve that is based upon a combination of a physics measurement component of the NDIR gas sensor and a sensor measurement component of the NDIR gas sensor to calculate a first concentration of sample gas, then using a secondary gas standard to determine a second gas concentration of the sample gas, and then recalibrating the NDIR gas sensor by using the second gas concentration and a reversed calibration curve algorithm which adjusts the sensor measurement component to correct for any difference between the first concentration and the second gas concentration when the difference between the two exceeds a preselected threshold.

In a separate group of aspects of the present invention, the calibration curve (which expresses the concentration of the sample gas as an nth order, e.g., a third order polynomial of G) is based upon a gamma ratio (“G”) that has been normalized by the gamma ratio when no sample gas is present in the sample chamber (“G₀”), G being a ratio of a signal channel output (“V_S”) of the NDIR gas sensor divided by a reference channel output (“V_R”) of the NDIR gas sensor. The concentration (“P”) of sample gas in the NDIR gas sensor is calculated through use of the calibration curve by a gas detection equation of P=F(x)=F(y/G₀), where x is a normalized ratio of V_S/V_R and y is G. The reversed calibration curve algorithm, which is a non-linear equation, is P=F(x)=F(y/G_0N), where G_0N=y₁/x₂, y₁=G for the NDIR gas sensor, x₂=F⁻¹ (P₂) and P₂ is the second gas concentration of the sample gas.

In another separate group of aspects of the present invention, the secondary gas standard (which can be a second NDIR gas sensor) is calibrated within a preselected time period prior to determining the second gas concentration and both the first concentration and the second concentration detect substantially the same concentration within a pre-selected space (e.g., a still space of less than 1,000 cubic feet). The second concentration can be transmitted to the NDIR gas sensor being recalibrated which receives the transmission and calculates gas concentration through electronics which use its calibration curve and recalibrate the NDIR gas sensor and then provide indication of recalibration.

Accordingly, it is a primary object of the present invention to provide an improved methodology for re-calibrating NDIR gassensors whose outputs have drifted over time and no longer correctly reflect their measurement accuracy.

This and further objects and advantages will be apparent to those skilled in the art in connection with the drawings and the detailed description of the invention set forth below.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesaleindustrial products

Super-miniaturized NDIR gas sensor

Two detector elements are optically isolated by having them mounted (die-attached) on the same header so that the thermal tracking of the detectors respectively for the signal and reference channels is close to ideal. Furthermore, such an optical isolation technique or cross-interference suppression between the two detector elements mounted on the same header also allows the use of only one and the same narrow band pass interference filter covering both detectors. Thus the thermal tracking of the filters respectively for the signal and reference channels is also close to perfection as both channels share the same filter.

Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims the priority benefit of U.S. Ser. No. 61/331,327, filed May 4, 2010, the disclosure of which is specifically incorporated herein by reference. This application is also a continuation-in-part of U.S. Ser. No. 12/859,749, filed Aug. 19, 2010, the disclosure of which is specifically incorporated herein by reference, which itself claimed the priority benefit of U.S. Ser. No. 61/274,874, filed Aug. 21, 2009, the disclosure of which is also specifically incorporated herein by reference.

FIELD OF THE INVENTION
The present application is in the field of gas analysis, and specifically relates to apparatus using a Non-Dispersive Infrared (NDIR) gas analysis technique to determine the concentration of a particular type of gas present in a chamber by sensing the absorption of infrared radiation passing through the gas.

BACKGROUND OF THE INVENTION
The Non-Dispersive Infrared (“NDIR”) technique has long been considered as one of the best methods for gas measurement. In addition to being highly specific, NDIR gas analyzers are also very sensitive, stable, reliable and easy to maintain and service. Ever since the NDIR technique of gas measurement was first introduced and practiced in the mid 1950's, a large number of improved measurement techniques based upon the NDIR principle for gas detection have been proposed and successfully demonstrated. The most notable advances over the years in this field are summarized as follows.

Burch et al. (U.S. Pat. No. 3,793,525) and Blau et al. (U.S. Pat. No. 3,811,776) in 1974 were the first to advance a so-called “Double Beam” technique for NDIR gas measurement by taking advantage of the principle of nonlinear absorption for some strongly absorbing gases such as CO2 to create a reference channel. Shortly thereafter, this “Double Beam” NDIR gas sensor technique was greatly simplified with the use of two interposed spectral filters (one absorbing and one neutral) to create a sample and a reference detector channel. Subsequent NDIR gas sensors, designed using this technique, have enjoyed good performance alluded to briefly above.

In U.S. Pat. No. 4,578,762 (1986) Wong advanced the first self-calibrating NDIR CO2 analyzer using a novel two-wheel chopper and mirror arrangement. Another improved type of such gas analyzer is shown and described in U.S. Pat. No. 4,694,173 (1987) by Wong. This gas sensor has no moving parts for effecting the interposition of spectral filters to create both a sample and reference detector channel as in the NDIR gas analyzers described earlier.

In U.S. Pat. No. 5,163,332 (1992), Wong advanced the so-called “wave-guide” sample chamber concept for simplifying NDIR gas sensors into ones that are compact, rugged and low-cost while still maintaining their superior performance characteristics. This concept has subsequently been widely adopted in the design of today's NDIR gas sensors, particularly in low-cost and high volume versions.
All of the NDIR gas analyzers described above for the measurement of the concentrations of one or more gases in a mixture perform well functionally and have contributed successfully to the overall technical advancement in the field of gas analysis during the past two decades. They have been widely accepted in both the medical and industrial communities. Despite their undisputed success over the years, there still remain a number of important sensor performance characteristics that need to be greatly improved in order to further extend the useful applications of these devices in a number of areas.

By far the most deficient performance characteristic of gas sensors of today, inclusive of NDIR gas sensors, is the sensor output stability over time. Unlike the temperature controller or thermostat device which just about everybody is familiar with at home or in their workplaces for sensing temperature that never requires output adjustment or recalibration over time, such is not the case for gas sensors irrespective of their operational principle, functional design, material construct or even costs. Dependent upon the type of gas sensors, just about every one of them requires recalibration once every six months to a year without exception in order that they remain accurate over time. While this performance deficiency has been well tolerated over the years, it remains as a significant drawback for gas sensors and even precludes their use in a number of vital applications and therefore there has been a long-felt need for elimination of this problem.

The second most prominent performance deficiency for gas sensors of today irrespective of their operational principle is their output dependence as a function of the temperature of the environment wherein the sensors are located. This performance deficiency for just about all gas sensors is universally, albeit reluctantly, dealt with by specifying the output correction per degree of temperature change with respect to the output stipulated at a standard temperature. In some gas sensors these output temperature corrections are quite large and in many cases severely limit the use of these sensors outdoors. It would be a significant step forward in the development of future gas sensors, particularly for the NDIR type, because of its prevalent use in most industries, that this performance deficiency be also overcome and, again, there has been a long-felt need for overcoming this problem.
The afore-mentioned serious NDIR gas sensor performance deficiencies, namely sensor output drift over time and output dependency as a function of exposed sensor temperature, have earlier been addressed by the present inventor in a provisional patent application 61/274,874 to the US Patent Office filed on Aug. 21, 2009 and entitled “Absorption Biased NDIR Gas Sensing Methodology.” In this recent patent disclosure, the present inventor takes advantage of the fact that if the spectral content of radiation from the source and/or convoluted with those from the surroundings be always kept the same for both the reference and the signal channels of an NDIR gas sensor, assuming that this sensor uses the most widely deployed dual-channel methodology, the output of the sensor taken as the ratio of the signal output over the reference output can always be kept constant or unchanged over time except when the gas of interest is present in the sample chamber.

In order that this recently disclosed Absorption Biased methodology be implemented, both the signal and the reference channel must be provided with exactly the same spectral narrow band pass filter designed for detecting the gas of interest in front of the respective infrared detectors. In order to differentiate between the signal and the reference channel outputs from the respective detectors in the presence of the gas of interest, an absorption bias is designed between the two channels via the use of different sample chamber path lengths for the two channels. Thus, if the sample chamber path length for the signal channel is longer than that for the reference channel, the signal channel detector output will change greater (or be reduced more) than that for the reference channel when the same concentration level of the gas of interest is present in the sample chamber. In other words, the sensor output will change as the concentration level of the gas of interest changes in the sample chamber as reflected by the calibration curve which can be prepared for the sensor.

The fact that both detection channels have the same narrow band pass spectral filter and they receive radiation from one and the same single infrared source as taught by the widely deployed dual-channel NDIR gas detection methodology, they are all affected in the same way to first order when there are spectral changes caused by temperature variations in the sample chamber and/or by the short or long-term operational changes (e.g. aging) of the infrared source. Thus the outputs of the dual-channel NDIR gas sensor for the detection of any gas of interest implemented using the inventor's recently disclosed Absorption Biased methodology will stay virtually drift-free over time without the need for any periodic re-calibration or software correction.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products 

A High-Precision NDIR Gas Sensor for Automotive Applications

A new high-precision spectroscopic NDIR gas sensor measuring carbon dioxide (CO2) for harsh environmental conditions of automotive applications is presented. The carbon dioxide concentration is the primary parameter for sensing in cabin air quality, as well as an important safety parameter when R744 (carbon dioxide) is used as the refrigerant in the air conditioning system.

The automotive environment challenges the potential sensor principles because of the wide temperature range from -40degC to +85degC, the atmospheric pressure from 700 to 1050 mbar, and relative humidity from 0% to 95%. The presented sensor system is based on the nondispersive infrared principle with new features for reaching high precision criteria and for enhancing long-term stability.

A second IR source is used for internal recalibration of the primary IR source, redundancy purposes, and software plausibility checks. The CO2 sensor system achieves an accuracy of better than plusmn5.5% over the whole temperature, pressure, and humidity ranges, with a resolution below 15 ppm and a response time shorter than 5 s. The operating time of the sensor system is more than 6000 h over a corresponding lifetime of more than 15 years. Experimental results show outstanding results for the intended automotive applications

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products 

Ultra low power NDIR gas sensor fire detector

A fire detector and method for generating an alarm signal in response to a fire uses an NDIR sensor to generate a detector signal based upon one or more absorption bands selected from the 15.1μ absorption band of CO2, the 6.27μ absorption band of H2O and the 4.67μ absorption band for CO and generates an alarm signal when a signal processor receives the detector signal and a preselected criterion is met that is indicative of the onset of a fire based upon an analysis of the detector signal using a detection algorithm that relies upon a trending pattern of the detector signal such as recognizing a substantial drop in the detector signal strength.

The fire detector has a waveguide sample chamber (which can be of a re-entrant design) with at least one opening covered by a thin filtering membrane and a heat exchanger thermally connected to the sample chamber with at least one opening covered by another thin filtering membrane. If the NDIR sensor is to detect H2O molecules, the filtering membrane on the heat exchanger (which can be integrally formed out of aluminum with the sample chamber) allows H2O molecules to pass through it and inside surfaces of both the sample chamber and the heat exchanger are coated with a hydrophobic coating to prevent condensation of H2O molecules.

Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. Ser. No. 11/284,460 filed Nov. 21, 2005, entitled “Ultra Low Power NDIR CO2 Gas Sensor Fire Detector,” the disclosure of which is specifically incorporated herein by reference.

FIELD OF THE INVENTION
The present invention is in the field of gas analysis and more particularly relates to an ultra low power gas sensor designed to be used as a compact, reliable, low cost, fast responding and false alarm resistant fire detector.

BACKGROUND OF THE INVENTION
The Non-Dispersive Infrared (“NDIR”) technique has long been considered as one of the best methods for gas measurement. In addition to being highly specific, NDIR gas analyzers are also very sensitive, stable, reliable and easy to maintain. The major drawback of the NDIR gas measurement technique has been its relatively expensive implementation and high power consumption.
Ever since the NDIR technique of gas measurement was first introduced and practiced in the mid 1950's, a large number of improved measurement techniques based upon the NDIR principle for gas detection have been proposed and successfully demonstrated. The most notable advances over the years in this field are summarized as follows.

Burch et al. (U.S. Pat. No. 3,793,525) and Blau et al. (U.S. Pat. No. 3,811,776) in 1974 were the first to advance a so-called “Double Beam” technique for NDIR gas measurement by taking advantage of the principle of nonlinear absorption for some strongly absorbing gases such as CO2 to create a reference channel. Shortly thereafter, this “Double Beam” NDIR gas sensor technique was greatly simplified with the use of two interposed spectral filters (one absorbing and one neutral) to create a sample and a reference detector channel. Subsequent NDIR gas sensors, designed using this technique, have enjoyed good output stability as a function of time.

In U.S. Pat. No. 4,578,762 (1986) Wong advanced the first self-calibrating NDIR CO2 analyzer using a novel two-wheel chopper and mirror arrangement. Another improved type of such gas analyzer is shown and described in U.S. Pat. No. 4,694,173 (1987) by Wong. This gas analyzer has no moving parts for effecting the interposition of spectral filters or absorbing and non-absorbing cells to create both a sample and reference detector channel as in the NDIR gas analyzers described earlier.

In U.S. Pat. No. 5,163,332 (1992), Wong advanced the so-called “wave-guide” sample chamber for simplifying NDIR gas sensors into ones that are compact, rugged and low-cost while still maintaining their superior performance characteristics.

All of the NDIR gas analyzers described above for the measurement of the concentrations of one or more gases in a mixture perform well functionally and have contributed overwhelmingly to the overall technical advancement in the field of gas analysis during the past two decades. They have been widely accepted in both the medical and industrial communities. Despite their undisputed success over the years, there still remains an important application, namely the commonplace household fire detector, not successfully realized to date due to the fact that NDIR gas sensors are sill too costly and consume too much power when used as sentinel fire detectors.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Want to PURCHASE Light Sources for NDIR Gas Sensors? Click for PRODUCTS & PRICES

NDIR (Non-Dispersive Infrared) sensors are simple spectroscopic devices often used for gas analysis. The key components of an NDIR sensor are an infrared source (lamp), a sample chamber or light tube, a wavelength filter, and an infrared detector. The gas is pumped or diffuses into the sample chamber and gas concentration is measured electro-optically by its absorption of a specific wavelength in the infrared (IR).
The IR light is directed through the NDIR sample chamber towards the detector. The detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb. Other gas molecules do not absorb light at this wavelength, and do not affect the amount of light reaching the detector. The IR signal from the source lamp is usually chopped or modulated so that thermal background signals can be offset from the desired signal.
For greater optical efficiency, a reflector assembly can surround the lamp used for the NDIR sensor. The reflector is usually parabolic in shape to collimate the IR light through the sample chamber towards the detector. The use of a reflector can increase available light intensity by two to five times. The reflector surface can also be gold-coated to further enhance its efficiency in the infrared.
The intensity of IR light that reaches the NDIR detector is inversely related to the concentration of target gas in the NDIR sample chamber . When the concentration in the chamber is zero, the detector will receive the full light intensity. As the concentration increases, the intensity of IR light striking the detector decreases. Beer's Law describes the exact relationship between IR light intensity and gas concentration:
Beer's Law:
I = I 0 e kP
where:
I = the intensity of light striking the NDIR detector
Io = the measured intensity of an empty NDIR sample chamber
k = a system dependent constant
P = the concentration of the gas to be measured
NDIR sensors can be used to measure practically all inorganic and organic gases, but are most often used for measuring carbon dioxide because no other sensing method works as simply and reliably for this gas. Calibration gases of specific concentration are available for determining the NDIR system constant k for any particular sensor design.
Applications for NDIR Gas Sensors
• indoor air quality
• cycle regulation in self-cleaning ovens
• automotive and flue gas emissions
• greenhouse farming
• hazardous area warning signals
• gas leak detection
• landfill gas monitoring
• alcohol breathalyzers
• patient monitoring for anesthesiology
The NDIR gas sensor needs an infrared source for the excitation of the gas molecules. Thermal radiators such as ILT's Visible/IR lamps are often employed for this task. Their operating temperature should be as high as possible to obtain a large output intensity and detector signal. Glass envelope lamps operate at higher filament temperatures when compared to other filament or ceramic heating elements. The envelope can be a gas-filled or a vacuum. However, the transmission of the glass envelope limits the useful spectral range and constrains the types of gas molecules that can be measured by NDIR.
The transmission characteristics of a typical lamp glass are illustrated below together with the center wavelength of some common gas absorption bands. The intensity of the IR light decreases significantly above 4 mm with a cutoff wavelength located at 5 mm.
A Visible/IR lamp is a very cost-effective component for an NDIR sensor, but it has a limited IR range. For carbon dioxide (CO2) and hydrocarbon (HC) detection, it is an ideal technique.
The most desirable NDIR lamp characteristics are:
• high IR output
• accurate filament position
• small size
• long lifetime
• low thermal time constant
The last characteristic is important if the NDIR lamp power supply is to be modulated during operation to offset thermal background signals.
ILT Visible/IR lamps feature thin glass envelopes that reduce infrared absorption and provide more output in the infrared. Double-coiled filaments operate at high temperatures, and are rugged and geometrically precise for applications requiring broad spectral emission and superior optical performance.
ILT NDIR Gas Sensor Lamps are offered in T-1 and T-3/4 sizes with wire leads or bi-pin bases and operate at 5 volts. Several versions are available that operate from 45 mA to 150 mA with rated lifetimes from 5,000 to 100,000 hours.
ILT also offers a large line of reflector lamp assemblies with both fixed and adjustable focus options. Please contact the sales department at International Light Technologies to request more information.
View/Download the NDIR Gas Sensor Lamp Application Note


iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

A Review of Industrial Microwave Sensors

This paper reviews the field of microwave sensors. The field is broad and the applications numerous. This review will therefore only be able to present the broad outlines.

Firstly the historical perspective and the physical background are briefly described, and the general advantages and disadvantages are listed.

An overview of the various working principles of microwave sensors is given with a few examples of the applications mentioned. Important fields of applications and interesting examples are treated separately, starting with the measurement of moisture, which is the single most important field of applications in microwave sensors.

Applications in the petroleum industry are also mentioned, because they are relatively new, they play an exceptionally important economical role, and represent the field in which the author is currently working. Followed by some trends for the future.

 ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

NDIR Gas Sensor for Spatial Monitoring of Carbon Dioxide Concentrations

The tracer gas ratio method, using CO2 as natural tracer, has been suggested as a pragmatic option to measure emissions from naturally ventilated (NV) barns without the need to directly estimate the ventilation rate.

The aim of this research was to assess the performance of a low-cost Non-Dispersive Infra-Red (NDIR) sensor for intensive spatial field monitoring of CO2 concentrations in a NV dairy cow house. This was achieved by comparing NDIR gas sensors with two commonly applied methods, a Photo-Acoustic Spectroscope (PAS) Gas Monitor and an Open-Path laser (OP-laser).

First, calibrations for the NDIR gas sensors were obtained in the laboratory. Then, the NDIR sensors were placed in a dairy cow barn for comparison with the PAS and OP-laser methods.

The main conclusions were: (a) in order to represent the overall barn CO2 concentration of the dairy cow barn, the number of NDIR gas sensors to be accounted for average concentration calculation was dependent on barn length and on barn area occupation; and (b) the NDIR CO2 sensors are suitable for multi-point monitoring of CO2 concentrations in NV livestock barns, being a feasible alternative for the PAS and the OP-laser methods to monitor single-point or averaged spatial CO2 concentrations in livestock barns.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Reducing Warm Up Time of NDIR Gas Sensors

MEMS-based electrically-efficient infrared sources from Axetris — In a number of gas detection applications, a short warm-up time of the NDIR gas sensor is critical. Especially for applications where discrete measurements need to be made, and where the gas sensor is not continuously switched on, a short warm-up time is absolutely essential. This is the case for portable gas detection devices, e.g. for combustible and toxic gas detection, refrigerant leak detection or breath alcohol measurement.

Gas sensors based on non-dispersive infrared (NDIR) spectroscopy can guarantee accurate gas concentration values only after a thermally stable state is achieved. The MEMS-based infrared sources from Axetris are produced using a unique thin-film process, and exhibit very high electrical efficiency. This leads to lower optical losses in the form of dissipated heat. 

Additionally, the emitting blackbody structure has a very low thermal mass, leading to a quick heating time constant of 11 milliseconds.

Besides the inherent advantages offered by the design of the infrared sources, Axetris supports its customers with comprehensive characterization information, as well as by suggesting efficient integration practices in order to achieve a quick warm-up phase. 

Thermal management thus becomes an easy task, and a quick warm-up time of the NDIR gas sensor can be achieved.

iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrialproducts

Microwave Sensor Applications in Industry

Microwave measuring methods can be applied to determine the properties of materials and hence it is possible to develop microwave sensorsfor processing industry. The first applications were in moisture measurement but lately many new sensor applications have appeared.

Microwave sensors especially suitable in forest industry (wood, paper), in chemical industry (plastics, chemicals), in food industry (tobacco, butter) etc. In developing sensors several problems must be solved. The dielectric properties of the material in question must be known. They can be measured or in some cases determined theoretically by applying mixing theories.

The sensor is often some kind of a resonator. Its structure must be such that the electric field penetrates the material as required, and allows free flow of material. Displacements occurring normally in the material flow or dirt in the sensor must not cause measuring errors. Several examples of lately developed sensors are given.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrialproducts

NDIR Gas sensor and modules MH-410D

MH-410D is a miniature universal intelligent sensor, which adopts NDIR theory to detect concentration of CO2 in air and has good selectivity, stable performance, long life, also is independent of Oxygen. The inside temperature sensor could be used for temperature compensation.

It could be used to replace catalytic component, widely used in occasions with flammable and explosion.

Are you still wondering where to find the best-quality sensors around the world. ISweek.com provides a lot of sensors, such as, NDIR gas sensor, gas sensors, humidity sensors, Oxygen sensors, Air flow sensors and so on. Isweek is an industry sourcing wholesale supplier that sells industrial products and electronic products to global buyers.


ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Use of NDIR Sensors for rea-time monitoring of CO2 levels in coal mine drainage discharge

The chemical weathering of limestone in abandoned coal mines by both carbonic and sulfuric acids can lead to aqueous concentrations of dissolved CO2 much higher than those predicted to be in equilibrium with the atmosphere. After water is discharged from a mine portal, dissolved CO2 degasses rapidly as a function of distance and topography and becomes more aerated in the process.

The accurate monitoring of CO2 in such environments by conventional methods, such as alkalinity titration, is difficult due to the geochemical instability of the water during sample processing. Earlier work in our laboratories showed that a volume expansion method used in the beverage industry worked well in determining CO2 in mine waters under field conditions, but it still suffered from the need to collect grab samples and transfer them to a carbonation meter, a step that results in the loss of some CO2.

Additionally, the ability to collect CO2 data remotely to determine natural fluctuations over time is desirable. Here we report on the preliminary use of a non-dispersive infrared (NDIR) CO2 sensor enclosed in a gas-permeable membrane to make measurements directly in the discharge of an abandoned bituminous coal mine in southwestern PA. Results showed that this method was superior to both alkalinity titration and volume expansion as a method of CO2 detection in this environment.

Long-term measurements in the fluctuation of dissolved CO2 were possible, especially in waters nearest the portal, where the active precipitation of iron did not interfere with gas transfer across the synthetic membrane covering the NDIR sensor. Additional examples of the benefits of this analytical approach will be presented.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

NDIR Gas Sensors – Smaller, Leaner and more Cost-Effective

Gas sensors based on Non-Dispersive Infrared (NDIR) techniques have continuously gained in popularity over the past decades.

A number of clear trends in gas sensor design are visible today – gas sensors are getting smaller, consuming lesser power, and unit sensor cost is decreasing. NDIR gas sensing technology continues to build on the potential to complement and replace conventional gas measurement technologies, such as Electrochemical, PID, TCD, etc.

Axetris Infrared Sources based on thin film technology help gas sensor designers capitalize on these trends.

Smaller
The trend to miniaturize gas sensors is driven by increasing demand for portable implementation. Though NDIR gas sensors have continuously shrunk in size over the years, this trend is expected to further accelerate with increased adoption of gas sensors in mobile, wearable and IoT (internet of Things) applications.

Axetris offers the EMIRS50 product line of Infrared Sources, where the emitting area is a tiny 0.8x0.8 mm². The EMIRS50 products have been designed especially for use in miniature gas sensors.

Leaner
Parallel to the trend towards miniaturization of gas sensors, the demand to decrease power consumption for battery-based use has intensified. Today, gas sensors are being developed which use a few milliwatts of power during normal operation.

Axetris Infrared Sources have a very short time constant which enables the possibility to use a very short duty cycle. This means, that a meaningful signal for gas concentration can be generated, even at very low nominal power. At the same time, the black platinum emissivity layer used in Axetris Infrared Sources delivers high electrical/optical efficiency.

Cost-Effective
For high-volume gas sensor applications in the automotive industry or for wearable devices, a very low unit sensor cost is a prerequisite.

Axetris Infrared Sources are manufactured using a wafer-based fabrication process. This allows for ease of production scalability, enabling very low unit costs at high volumes.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrialproducts

Application of CO2 NDIR gas sensors in air quality monitoring

This paper explains the use of Non-Dispersive InfraRed (NDIR) sensor that is built into the complex system for the air quality monitoring. It is known that CO2 is an important

indicator of the current state of the environment, especially in urban areas and indoor air quality.

Latest CO2 NDIR gas sensors are low cost, low power consumption, miniature and have a long lifetime so that the increasingly built into new systems for measuring environmental parameters. By using commercially available detectors and advanced knowledge of the design of electronic circuits, measuring the concentration of CO2 is explained in detail in this paper.

In this paper NDIR sensors are discussed, targeting only commercially available solutions for measuring CO2 concentration. As a representative of NDIR sensors, Alphasense IRC-A1 sensor is selected. This sensor will be used as an example to explain the principles of operation of NDIR sensors. It will also be explained electronic circuit for processing signals from the sensor and the methods to calculate the final concentration of CO2 from collected data. Finally, an example of measurement in field conditions with a detailed analysis is given.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrialproducts

Zero drift NDIR gas sensors

Output stability or drift overtime has long been a major performance deficiency for gas sensors irrespective of what technology or methodology is used for their conception. Software correction may alleviate the problem somewhat but it is not always applicable. It has long been the objective of many researchers in this field to overcome this problem fundamentally and for good. The purpose of this paper is to show that this objective has now finally been achieved.

Design/methodology/approach

– Conventional non‐dispersive infrared (NDIR) dual beam methodology utilizes the ratio of signal channel output over reference channel output for signal processing. The signal filter overlaps the absorption band of the gas of interest while the reference filter does not. However, this ratio changes as the source ages. The current methodology uses an absorption bias between signal and reference channel outputs. This absorption bias is created by using a path length for the signal channel greater than that for the reference channel. Both the signal and reference detectors carry an identical spectral filter overlapping the absorption band of the gas to be measured.

Findings

– Implementation of the currently patented NDIR gas sensors methodology has been carried out in different gas sensor configurations for over a year in the laboratory. Performance results for these sensors showing insignificant output drifts overtime have been repeatedly demonstrated via simulated aging for the source.

Originality/value

– The paper puts forward the view that the recent breakthrough of the Near Zero Drift methodology for NDIR gas sensors will very quickly change the hierarchy of technology dominance and utility for gassensors at large.

ISweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrialproducts

Sensing Carbon Dioxide for Total Organic Carbon Monitoring (NDR Gas Sensor)

Organic carbon compounds are often specified in terms of carbon mass. Recent developments in TOC (total organic carbon) analysis have resulted in considerable improvements, which allow for complete and direct measurement of the quantity of carbon with a biological source. Where there are fluctuations and differences, the cause and effect on biological processes in waste water study can be identified.

The TIC (total inorganic carbon) is usually removed from a sample by means of purging prior to oxidizing the residual organic carbon in the water sample to carbon dioxide (CO2) and then quantifying the amount of CO2 generated (Figure 1).

Figure 1. Typical TOC process
A number of techniques are available which can be used to oxidize the organic carbon, such as oxygen, UV radiation, wet chemistry, or heat to generate CO2. Regardless of the method, the resulting CO2 is dissolved in a carrier gas, such as oxygen. This carrier gas is passed via the TOC level will also be higher and the water sample will be more contaminated.

Based on the cleanliness of the water being analyzed and the methods utilized, different concentrations of CO2 can be anticipated in the carrier gas, from wastewater to drinking water. Edinburgh Sensors’ Gascard® NG is a high performance OEM gas detector that provides real-time measurement of CO2 0-500ppm to 0- 3%.

OEM Gascard® NG
A suitable OEM solution for TOC monitoring, Gascard NG can be easily integrated into a range of gas detection solutions where lasting stability, high quality, superior repeatability and reliable measurement of carbon , CO2 and methane gas concentrations are needed. These features are due to Edinburgh Sensors’ proprietary dual wavelength fail to safe InfraRed NDIR gas sensor technology. The Gascard NG range offers ideal solutions for measuring and testing industrial as well as environmental gases. Table 1 shows the Gascard NG models for gas measurement range of CO2.
The Gascard NG from Edinburgh Sensors comes with different interface options, such as true RS232 communication, analogue 4-20 mA/0-20 mA/0-5 v, serial interface for interfacing relay alarms and optional on board LANsupport. The on-board firmware is capable of supporting a modern graphical display or a conventional 4 segment LCD.

In addition, the Gascard NG series needs only minimum maintenance and thus eliminates significant amount of costs. Automatic pressure and temperature correction features allow real-time environmental condition measurements and thus provide consistent measurement and exact concentration readings of target gases.

The sensor head and electronics of the Gascard NG series are positioned on a Eurocard PCB with several bit-switches, which allow users to control different aspects of the sensors behaviour such as filter type and analogue output selection.

The Gascard NG is backward compatible with outputs from current generations of Gascard series and includes onboard true RS232 communications with the option of TCP/iP communications protocol and on-board data logging. With built-in features for multi-sensor and multigas operation, the Gascard NG can integrate additional gas detection technologies.

 iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Absorption biased single beam NDIR gas sensor

An Absorption Biased (AB) methodology for NDIR gas sensors is used with a single infrared source and a detector to detect a single gas of interest by using a motion device to change the path length between that of the signal and reference channels.

As in the case of the AB designed NDIR gas sensor, the ratio of the output of the Signal channel, measured during location arrangement X, over that of the Reference channel, measured during location arrangement Y, will be used to process the gas measurement.

Multiple gases of interest can be detected by using one detector to detect multiple gases and/or by locating a second detector to detect multiple gases more distant from the source than the first detector, thereby creating longer path lengths for the second detector.

BACKGROUND OF THE INVENTION
All molecules vibrate and rotate at characteristic frequencies in the electromagnetic spectrum. These vibration/rotational frequencies cause asymmetric molecules such as CO2 and H2O, but not symmetric molecules like N2 or O2, to absorb light at very specific wavelengths, particularly in the infrared. The NDIR gas measurement technique targets these characteristic absorption bands of asymmetric molecules of gases in the infrared for their detection. The term “non-dispersive” which actually implies “non-spatially-dispersive” as used herein refers to the apparatus used, typically a narrow-band infrared transmission filter instead of a spatially-dispersive element such as a prism or diffraction grating, for isolating for the purpose of measurement the radiation in a particular wavelength band that coincides with a strong absorption band of a gas to be measured.

The NDIR technique has long been considered as one of the best methods for gas measurement. In addition to being highly specific, NDIR gas sensors are also very sensitive, relatively stable and easy to operate and maintain. In contrast to NDIR gas sensors, the majority of other types of gas sensors today are in principle interactive. Interactive gas sensors are less reliable, short-lived and generally non-specific, and in some cases can be poisoned or saturated into a nonfunctional or irrecoverable state.

Despite the fact that interactive gas sensors are mostly unreliable and that the NDIR gas measurement technique is one of the best there is, NDIR gas sensors still have not enjoyed widespread high volume usage to date. The main reasons for this can generally be attributed to their high unit production cost, relatively large size and output drifts over time.

Just about all gas sensors ever designed and manufactured to date, irrespective of what technology is being employed, invariably have significant output drifts over time. While NDIR gas sensors can be recalibrated as part of a periodic maintenance program or service, the cost of such recalibration has prevented NDIR gas sensors from being widely adopted for many applications.

 iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Infrared CO2 sensor working principle

In nature, plants use CO2 for photosynthesis. CO2 combinate with moisture under the action of the sun to produce sugar (and oxygen). We know about how much  Infrared CO2 sensor? How does it work?

CO2 can absorb infrared wavelengths of light. The absorption can be used to measure the concentration of carbon dioxide per unit volume. The infrared absorption function of CO2 is causing part of the greenhouse effect. The greenhouse effect is one of the characteristics of all the planet's atmosphere, it makes the planet's surface temperature is higher than without the atmosphere. Any gas absorbs the sun's rays will lead to the greenhouse effect, the most important greenhouse gas for surface of the earth include: water vapor, CO2 and methane, they can absorb infrared wavelengths of light.

Most of gas sensors could give the corresponding signal according to the molecular density, even down to one over one million as units. According to the ideal gas law, when the pressure and/or temperature change, density of molecules will change, and PPM value is displayed on the sensor. Accuratly say this is wrong, as density of the gas (in PPM) will not change with the change of temperature and pressure. The change of gas sensor readings can also be used to correct for the temperature and the pressure change of gas sensor readings errors.

Considering the water vapor to the effect of CO2 sensor, the information is very important. For example: in the same pressure, temperature and volume, add water vapour in the process of gas drying, then water had taken over of general mixture of other gas molecules.

Our CO2 gas sensors could be used for accurate CO2 detection.

iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products

Reducing Warm Up Time of NDIR Gas Sensors

MEMS-based electrically-efficient infrared sources from Axetris — In a number of gas detection applications, a short warm-up time of the NDIR gas sensor is critical. Especially for applications where discrete measurements need to be made, and where the gas sensor is not continuously switched on, a short warm-up time is absolutely essential. This is the case for portable gas detection devices, e.g. for combustible and toxic gas detection, refrigerant leak detection or breath alcohol measurement.

Gas sensors based on non-dispersive infrared (NDIR) spectroscopy can guarantee accurate gas concentration values only after a thermally stable state is achieved. The MEMS-based infrared sources from Axetris are produced using a unique thin-film process, and exhibit very high electrical efficiency. This leads to lower optical losses in the form of dissipated heat. Additionally, the emitting blackbody structure has a very low thermal mass, leading to a quick heating time constant of 11 milliseconds.

Besides the inherent advantages offered by the design of the infrared sources, Axetris supports its customers with comprehensive characterization information, as well as by suggesting efficient integration practices in order to achieve a quick warm-up phase. Thermal management thus becomes an easy task, and a quick warm-up time of the NDIR gas sensor can be achieved.

 iSweek（http://www.isweek.com/）- Industry sourcing & Wholesale industrial products