Infrared, multiple gas analyzer and methods for gas analysis

• US 6,313,464 B1
• Filed: 08/16/2000
• Issued: 11/06/2001
• Est. Priority Date: 06/18/1998
• Status: Expired due to Fees

• Current Assignee: Robert J. Schrader
• Original Assignee: Robert J. Schrader
• Inventors: Schrader, Robert J.
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): GAGLIARDI, ALBERT J
• Application Number:
  US09/639,553
• Time in Patent Office: 447 Days
• Field of Search: 250/343, 250/345, 250/344
• US Class Current: 250/349
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A portable, infrared, multiple gas analyzer for measuring the concentration of a plurality of infrared absorbent gases with a simple optical arrangement for transmitting an infrared beam along an optical path along with gas mixtures to be analyzed. Light transmitting tubes arranged in a U-like configuration transmit infrared energy and the gases applied thereto over a small path to an infrared detector from an infrared source and provide electrical analog output signals representative of the detected gases. The detector output signals are processed by D.C. processing circuits including an analog to digital converter and microprocessing circuits for providing digital, binary coded, output signals representative of the detected gas concentration of the infrared absorbent gases. The analyzer can be readily calibrated by applying a non-infrared absorbent gas to the gas analyzer to provide a maximum output signal level with the infrared beam on and the background level or dark level signal with the beam off. The gas mixture having the infrared absorbent gases to be measured are applied to the analyzer for measurement and the resulting analog signals are amplified under control of a microprocessor for determining whether or not a preselected signal level stored in the microprocessor memory is exceeded or not. If not, the gain of the amplifier is increased to compensate for the aging of the analyzer. An offset voltage is applied to the analog to digital converter under control of the microprocessor to the amplified gas signals for increasing the resolution of the converter output signals only during the time intervals the absorbent gases are being measured. The microprocessor is programmed to execute a program for calculating the detected concentration of the gases undergoing analysis based on the previously acquired and stored “zero” gas level, dark level and known gas factors to provide the desired digital, binary coded, gas concentration signal from the analyzer.

Claims

1. A method of detecting the concentration of a plurality of gases in the exhaust gases produced by the operation of a gasoline powered engine including the steps of

arranging infrared light transmitting pipes for transmitting an infrared light beam over a preselected path and to exit said pipes upon transversing said path,

providing an infrared light beam and projecting the beam to be transmitted over a preselected distance defined by said light transmitting pipes,

mounting a first-infrared detector-filter having a narrow band infrared filter for receiving the infrared beam exiting said pipes and transmitting a preselected narrow band of the infrared beam including one of the gases to be detected to the detector and reflecting the remaining portion of the infrared beam,

the step of mounting said detector-filter including mounting the detector-filter at a preselected acute angle to the path of the infrared beam exiting said pipes and receiving said exiting beam,

mounting a second infrared detector-filter having a narrow band infrared filter for receiving the portion of the infrared beam reflected from said first detector-filter and transmitting a preselected narrow beam of said reflected portion of the infrared beam including a second gas to be detected to said second detector-filter and reflecting the remaining portion of said reflected portion of the infrared beam.

2. A method of detecting the concentration of a plurality of gases as defined in claim 1 wherein said second detector-filter is mounted at an angle approximately twice the angle of said first detector-filter to the axis of the path of the infrared beam exiting said pipes for receiving the portion of the infrared beam reflected from said first detector-filter.

3. A method of detecting the concentration of gases sensitive to infrared radiation including the steps of

arranging a plurality of infrared transmitting pipe means in a compact arrangement including a folded optical, space savings short path along with front surface, reflective mirrors so that an infrared light beam is wholly transmitted within said pipe means except when reflected from said plane mirror surfaces for transmitting an infrared beam over a pre-selected short path with a minimum of loss of light energy and to exit said light transmitting pipe means upon traversing said folded path, said light transmitting pipe means being characterized as having smooth, reflective, internal walls for reflecting the infrared beams at said internal walls for continuously transmitting said beam longitudinally thereof,

arranging a non-collimated infrared light beam source to be continuously projected through said light transmitting pipe means,

mounting a first infrared detector-filter having a narrow band infrared filter for receiving the continuous infrared beam emerging from said light transmitting pipe means, said narrow band for the first detector-filter being selected to transmit a narrow band of the infrared beam representative of a first pre-selected gas to be detected and reflecting the remaining portion of said beam and thereby provide a continuous electrical output signal from said first detector-filter representative of the gas concentration of the first pre-selected gas without resorting to interrupting the beam, said reflective beam being useful for the detection of other pre-selected gases,

mounting a second infrared detector-filter having a narrow band infrared filter for receiving the continuous infrared beam reflected from said first infrared detector-filter, said narrow band for the second detector-filter being selected to transmit a narrow band of the infrared beam representative of a second pre-selected gas to be detected and reflecting the remaining portion of said beam and thereby provide a continuous electrical output signal from said second detector-filter representative of the gas concentration of the second pre-selected gas, and

providing means for introducing a gas mixture including the pre-selected gas to traverse said short path defined by said light pipe means and cause the infrared beam to be continuously absorbed or reduced in amplitude by an amount related to the concentration of the pre-selected gas whereby the electrical output signal from said detector-filter is representative of the concentration of said pre-selected gas.

4. A method of detecting the concentration of a gas sensitive to infrared radiation including the steps of

arranging a plurality of infrared light transmitting pipe means in a folded, optical, space saving short path along with front surface, reflective mirrors so that an infrared light beam is wholly transmitted within said pipe means except when reflected from said plane mirror surfaces for transmitting an infrared beam over a pre-selected path and to exit said light transmitting pipe means upon traversing said folded path, said light transmitting pipe means being characterized as having smooth, reflective, internal walls for reflecting the infrared beam at said internal walls for transmitting said beam longitudinally thereof,

arranging a non-collimated infrared light beam source to be projected through said light transmitting pipe means,

mounting an infrared detector-filter having a narrow band infrared filter for receiving the infrared beam emerging from said light transmitting pipe means, said narrow band being selected to transmit a narrow band of the infrared beam representative of a pre-selected gas to be detected and reflecting the remaining portion of said beam and thereby provide an electrical output signal from said detector-filter representative of the gas concentration of the detected pre-selected gas,

providing means for introducing a gas mixture including the pre-selected gas to traverse said path defined by said light pipe means and cause the infrared beam to be absorbed or reduced in amplitude by an amount related to the concentration of the pre-selected gas whereby the electrical output signal from said detector-filter is representative of the concentration of said pre-selected gas, and

mounting another infrared detector-filter means for receiving the infrared beam reflected from said first mentioned detector-filter, said filter of said another detector-filter having a narrow band for passing a different narrow band than said first mentioned detector-filter to include a second pre-selected gas to be detected and provide an electrical output signal from said another infrared detector-filter representative of the gas concentration of the detected second pre-selected gas.

5. A method of detecting the concentration of a plurality of gases in a gas mixture including the steps of

arranging infrared light transmitting pipes for transmitting an infrared light beam over a pre-selected path and to exit said pipes upon traversing said path,

providing an infrared light beam and projecting the beam to be transmitted over a pre-selected distance defined by said light transmitting pipes,

mounting a first-infrared detector-filter having a narrow band infrared filter for receiving the infrared beam exiting said pipes and transmitting a pre-selected narrow band of the infrared beam including one of the gases to be detected to the detector and reflecting the remaining portion of the infrared beam,

the step of mounting said detector-filter including mounting the detector-filter at a pre-selected acute angle to the path of the infrared beam exiting said pipes and receiving said exiting beam,

mounting a second infrared detector-filter having a narrow band infrared filter for receiving the portion of the infrared beam reflected from said first detector-filter and transmitting a pre-selected narrow beam of said reflected portion of the infrared beam including a second gas to be detected to said second detector-filter and reflecting the remaining portion of said reflected portion of the infrared beam,

providing a gas input for said light transmitting pipes and a gas output port to allow the input gases or gas mixture including gases that are infrared absorbent to traverse said pre-selected path of the infrared beam between the infrared beam source and the first infrared detector-filter,

providing individual electronic signal processing circuit means for receiving and processing the analog output signals from an individual one of said detector-filters for each of the detected gases,

providing an analog to digital converter having a plurality of individual terminals for individually receiving each of the processed analog output signals at an input terminal from the individual signals from said signal processing signal means and providing corresponding digital output signals for each of the detected gases,

providing a programmable, digital signal microprocessor having a signal storage memory for storing a program to be continuously executed and data signal storage and a plurality of signal input terminals and signal output terminals and coupled to the output signals from said analog to digital converter,

introducing a gas or gas mixture that does not include any infrared absorbent gas or gases therein into said gas input port to provide “

zero”

gas level output signals from said detector-filters when the infrared beam source is fully on,

storing said “

zero”

level signals in the signal memory for the microprocessor,

the stored program for said microprocessor functioning to turn off the infrared beam source and permitting the source to cool for a pre-selected period prior to obtaining dark level output signals from said detector-filters,

after the expiration of the pre-selected cooling period and the infrared beam source is off and cooled, acquiring the “

dark”

level signal and storing the dark level signal in the signal storage memory for the microprocessor,

the stored program for said microprocessor then functions to turn the infrared beam source on.

introducing a gas or gas mixture that includes infrared absorbent gases into said gas input port to traverse said infrared beam path while being exposed to said beam,

continuously maintaining the infrared beam source on during the presence of infrared absorbent gases for deriving analog output signals from said detector-filters that continue to be slowly reduced in amplitude for a pre-selected time period it is exposed to the infrared beam,

acquiring the gas data signals representative of the concentration of the infrared absorbent gases signaled at said detector-filters,

coupling the analog output signals from said detectors to said analog to digital converters for converting said input analog signals to corresponding digital, binary coded signals representative of the individual gas data signals, and

causing the microprocessor to acquire said individual digital gas data signals and individual zero level signals and the individual dark level signals and causing said program to execute a gas analysis process and providing digital output signals representative of the concentration of the detected infrared absorbent gases.

6. A method of detecting the concentration of a plurality of gases as defined in claim 5 wherein said microprocessor is programmed to add an offset voltage to said gas data signals prior to coupling to said analog to digital converter only during the time intervals that infrared absorbent gases are undergoing detection for increasing the resolution of the resulting digital signals.

7. A method as defined in claim 5 or 6 wherein said electronic signal processing circuit means includes amplifying the gas data signals to a pre-selected amplitude level prior to converting the signal to a digital signal,

and including storing a threshold voltage signal representative of the pre-selected amplitude level of the gas data signals in the signal storage memory for the microprocessor,

causing the microprocessor to compare said stored threshold voltage signal with the signal outputs of said detectors during the time intervals a zero gas is introduced into said gas input port to determine if the compared amplified signal levels are above or below said threshold voltage signal, and if the microprocessor determination results in signal output levels below the threshold level, causing th amplifying level be increased above said pre-selected level.

8. A method as defined in claim 7 including the step of filtering out the high frequency noise from the amplified signals prior to conversion to digital signals.

9. A method as defined in claim 5 wherein the gas introduced into said gas input port comprises the exhaust gases from a gasoline powered engine.

10. A method as defined in claim 5 or 6 including repeating the steps of acquiring the zero gas signal and the dark level signals and updating the respective stored signal levels, and then

repeating the step of acquiring the data signal.