Non-dispersive optical gas analyzer

• US 4,772,790 A
• Filed: 10/14/1986
• Issued: 09/20/1988
• Est. Priority Date: 10/14/1986
• Status: Expired due to Term

• Current Assignee: Teledyne Technologies Incorporated
• Original Assignee: Teledyne Industries Incorporated (Teledyne Technologies Incorporated)
• Inventors: Aldridge, Roland H.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Miller, John A.
• Application Number:
  US06/919,893
• Time in Patent Office: 707 Days
• Field of Search: 250/343, 250/344, 250/345, 250/346, 250/349, 374/124, 374/129, 374/179, 136/224, 136/225
• US Class Current: 250/343
• CPC Class Codes: G01J 2005/123 Thermoelectric array
• CPC Class Codes: G01J 5/12 using thermoelectric elements, e.g. thermocouples
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A non dispersive optical gas analyzer is disclosed which uses thermopiles as optical detectors. The thermopiles are formed of an array of interconnected thin films of dissimilar metals deposited on a heat conductive substrate to form a multitude of thermocouples. The array is configured in such a manner that a number of the thermocouples are employed to compensate each thermopile output signal for changes in ambient temperature.

Claims

1. A gas analyzer comprising:

radiation generating means for providing a directed beam of optical energy;

a generally cylindrical cell for containing a gaseous mixture, at least one component of which is to be analyzed to determine its concentration in the mixture and having first and second ends transparent to the optical energy;

a first thermopile comprising a multitude of thermocouple junctions, each of which generates a thermal EMF proportional to the temperature of the junction and including;

a first plurality of thermocouple junctions, arranged in rows in a first column;

a second plurality of thermocouple junctions arranged in rows in a second column which is located beside the first column;

a third plurality of thermocouple junctions arranged in rows in a third column which is located beside the second column;

a fourth plurality of thermocouple junctions arranged in rows in a fourth column which is located beside the third column;

first connecting means for connecting a first group of A rows of thermocouple junctions in the first column in series with a first group of B rows of thermocouple junctions in the second column to form a first series circuit such that the thermal EMF generated by each of the first A rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the first B rows of junctions;

second connecting means for connecting a second group of C rows which follow the A rows of thermocouple junctions in the first column in series with a second group of D rows which follow the B rows of thermocouple junctions in the second column to form a second series circuit such that the thermal EMF generated by each of the C rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the A and D rows of junctions;

third connecting means for connecting a third group of E rows which follow the C rows of thermocouple junctions in the first column in series with a third group of F rows which follow the D rows of junctions in the second column to form a third series circuit such that the EMF generated by each of the E rows of junctions is of a common polarity which is opposite to the polarity of the EMF generated by each of the C and F rows of junctions;

fourth connecting means for connecting a first group of G rows of thermocouple junctions in the third column in series with a first group of H rows of thermocouple junctions in the fourth column to form a fourth series circuit such that the thermal EMF generated by each of the G rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the first A and H rows of junctions;

fifth connecting means for connecting a second group of I rows which follow the G rows of thermocouple junctions in the third column in series with a second group of J rows which follow the H rows of thermocouple junctions in the fourth column to form a fifth series circuit such that the thermal EMF generated by each of the I rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the C and J rows of junctions;

sixth connecting means for connecting a third group of K rows which follow the I rows of thermocouple junctions in the third column in series with a third group of L rows which follow the J rows of junctions in the fourth column to form a sixth series circuit such that the EMF generated by each of the K rows of junctions is of a common polarity which is opposite to the polarity of the EMF generated by each of the E and L rows of junctions;

seventh connecting means for connecting the first through sixth series circuits together in series to form a first thermopile series circuit such that the A, D, E, H, I and L rows of junctions are connected in a series-adding configuration;

a second thermopile comprising a multitude of thermocouple junctions, each of which generates a thermal EMF proportional to the temperature of the junction and including;

a fifth plurality of thermocouple junctions, arranged in rows in a fifth column;

a sixth plurality of thermocouple junctions arranged in rows in a sixth column which is located beside the sixth column;

a seventh plurality of thermocouple junctions arranged in rows in a seventh column which is located beside the sixth column;

an eighth plurality of thermocouple junctions arranged in rows in an eighth column which is located beside the seventh column;

eighth connecting means for connecting a first group of M rows of thermocouple junctions in the fifth column in series with a first group of N rows of thermocouple junctions in the sixth column to form a seventh series circuit such that the thermal EMF generated by each of the first M rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the first N rows of junctions;

ninth connecting means for connecting a second group of O rows which follow the M rows of thermocouple junctions in the fifth column in series with a second group of P rows which follow the N rows of thermocouple junctions in the sixth column to form an eighth series circuit such that the thermal EMF generated by each of the O rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the M and P rows of junctions;

tenth connecting means for connecting a third group of Q rows which follow the O rows of thermocouple junctions in the fifth column in series with a third group of R rows which follow the P rows of junctions in the sixth column to form a ninth series circuit such that the EMF generated by each of the Q rows of junctions is of a common polarity which is opposite to the polarity of the EMF generated by each of the O and R rows of junctions;

eleventh connecting means for connecting a first group of S rows of thermocouple junctions in the seventh column in series with a first group of T rows of thermocouple junctions in the eighth column to form a tenth series circuit such that the thermal EMF generated by each of the S rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the M and T rows of junctions;

twelfth connecting means for connecting a second group of U rows which follow the S rows of thermocouple junctions in the seventh column in series with a second group of V rows which follow the T rows of thermocouple junctions in the eighth column to form an eleventh series circuit such that the thermal EMF generated by each of the U rows of junctions is of a common polarity which is opposite to the polarity of the thermal EMF generated by each of the O and V rows of junctions;

thirteenth connecting means for connecting a third group of W rows which follow the U rows of thermocouple junctions in the seventh column in series with a third group of X rows which follow the V rows of junctions in the eighth column to form a twelfth series circuit such that the EMF generated by each of the W rows of junctions is of a common polarity which is opposite to the polarity of the EMF generated by each of the Q and X rows of junctions;

fourteenth connecting means for connecting the seventh through twelfth series circuits together in series to form a second thermopile series circuit such that the M, P, Q, T, U and X rows of junctions are connected in a series-adding configuration;

thermopile mounting means for locating the first and second thermopiles on a common heat conducting substrate;

positioning means for positioning the radiation generating means, the cell and the thermopile substrate so that the beam of optical energy is directed axially through the cell to the firt and second thermopiles;

masking means for shielding the A, B, C, E, F, G, H, J, K and L rows of thermocouple junctions in the first thermopile and the M, N, O, Q, R, S, T, V, W, and X rows of thermocouple junctions in the second thermopile from the beam of optical energy exiting the cell;

first filter means positioned between the cell and the D and I rows of thermocouple junctions in the first thermopile for limiting the wavelength of the optical energy which impinges upon the D and I rows of junctions to a range at which the optical energy is absorbed by the one component of gas in the gas mixture;

second filter means positioned between the cell and the P and U rows of thermocouple junctions in the second thermopile for limiting the wavelength of the optical energy which impinges upon the P and U rows of junctions to a reference wavelength range;

control means to measure the EMF generated by the first thermopile series circuit representing a first signal related to the amount of optical energy impinging on the D and I rows of junctions, to measure the EMF generated by the second thermopile series circuit representing a second signal related to the amount of optical energy impinging on the P and U rows of junctions, to subtract the first signal from the second signal, to produce a third signal, and to divide the third signal by the second signal.

2. The analyzer of claim 1 in which the numbers of thermocouple junctions in each of rows A, H, E and L are equal to each other, the numbers of thermocouple junctions in each of rows C and J are equal to each other, the numbers of thermocouple junctions in each of rows D and I are equal to each other, and the numbers of thermocouple junctions in each of rows B, G, F and K are equal to each other.

3. The analyzer of claim 1 in which the numbers of thermocouple junctions in each of rows M, T, Q and X are equal to each other, the numbers of thermocouple junctions in each of rows O and V are equal to each other, the numbers of thermocouple junctions in each of rows P and U are equal to each other, and the numbers of thermocouple junctions in each of rows N, S, R and W are equal to each other.

4. The analyzer of claim 1 in which the thermocouple junctions are formed of connected thin films of dissimilar

5. A gas analyzer comprising:

a cell for containing a gaseous mixture;

means for transmitting a directed beam of optical energy through the cell;

a plurality of thermopiles each positioned to receive a portion of the directed beam of optical energy,

each of the thermopiles comprising a substrate and a plurality of series-connected thermocouples comprising dissimilar thin-film metals deposited on the substrate in two columns,

the thermocouples in each column lying parallel to each other,

each column being divided into a center and two end sections of thermocouples,

the thermocouples in the center section being arranged to have a first polarity and the thermocouples in the end sections being arranged to have a polarity opposite the first polarity,

all of the sections of a column being connected in series,

the total of thermocouples in the two end sections of each column being approximately equal to the number of thermocouples in the center section,

each column of thermocouples being connected in series to the other column, and

the thermocouples of each section of each column being positioned with polarities which are the mirror-image of the polarities of the adjacent section in the adjacent column of the same thermopile;

means for selectively transferring optical energy of selected wavelengths to only the adjacent ends of the thermocouples of the central sections of each column in each thermopile; and

means for comparing signals generated by at least two of the thermopiles to determine the components of a gaseous mixture in the cell.