Multi-point Gas Detector

Abstract

A gas detection apparatus includes a housing which carries a plurality of light emitting diodes which are coupled in parallel and which emit substantially the same wavelength of radiant energy. A closed loop control circuit maintains the radiant energy output of the diodes at substantially a predetermined value. The radiant light radiant light and a sample of a gas of interest are directed to a sensing position at which a gas responsive tape is positioned. Reflected light from the tape is detected at a sensor displaced from the tape. A light collecting element can be positioned between the coupled diodes and the sensing position.

Description

FIELD

The application pertains to gas detectors. More particularly, the application pertains to cassette-type, tape gas detectors which incorporate solid state light sources. Members of a plurality of sources are coupled in parallel to increase radiant energy output for use in the sensing process.

BACKGROUND

Multi-point toxic gas monitoring systems are available which use optically based technologies, including light emitting diodes (LEDs) to provide a beam of radiant energy for the sensing function. One form of gas analyzing cassette system is disclosed in U.S. Pat. No. 8,128,873 entitled, “Gas Analyzer Cassette System” which issued Mar. 6, 2012 and is assigned to the Assignee hereof. The '873 patent is incorporated herein by reference. Unfortunately, low yield and related production problems in connection with the light emitting diodes represent on-going challenges.

LEDs currently available in the market use GaP technology which provides very limited intensity (100 mcd), narrow viewing angle (20 degree) and a specific dominant wavelength 565 nm. The associated die materials exhibit unstable behavior causing LED intensity sudden drop and long term degradation, which can impact product performance and reliability.

One available solution to some of these problems is to change required wavelength so other higher intensity LED technologies (e.g. AlInGaP) can be used. Unfortunately, this approach requires significant efforts to reproduce and correlate gas concentration tables with actual gas tests. The typical test time is between six months to two years.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top plan view of a multi-diode source of radiant energy;

FIG. 1B is an electrical schematic of the device of FIG. 1A;

FIG. 2 is a view, partly in section of a gas sensing station of an optical block;

FIG. 3 is a view of the unit of FIG. 2 with a transparent printed circuit board illustrating multi-sensing station component placement;

FIG. 4 is another view of the unit of FIG. 3 with the printed circuit board illustrated adjacent thereto;

FIG. 5 illustrates a unitary, molded, multiple collimator element; and

FIG. 6 illustrates multiple sample windows obtainable with two of the units of FIG. 3 or 4.

DETAILED DESCRIPTION

While disclosed embodiments can take many different forms, specific embodiments hereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles hereof, as well as the best mode of practicing same, and is not intended to limit the claims hereof to the specific embodiment illustrated.

In one aspect hereof, the current industrial standard LED package, used for tri-color (RGB) LEDs, is packaged with three Green LEDs. The standard package could be a PLCC 6 for example so it is surface mountable, and is compact in size for use in cassette-type gas sensing products. Such configurations can be obtained from suppliers who design/manufacture tri-color LED products, such as Avago, OSRAM, and Kingbright.

By proceeding as above, the currently used, specific wavelength is maintained at the known 565 nm emitted by GaP or similar dies with same optical output parameters. Advantageously, the viewing angle is increased to over 100 degrees by using a surface mount package. Additionally, the output intensity is three times greater, at the desired frequency, than the known, single die LED.

The orientation of the die placement could be further improved by rotating the middle die to have a polarity opposite to the other two dies in the package. This can reduce the trace length on the associated printed circuit board, and, reduce EMC primarily because the LED package is driven by an electrical pulse current with a higher amplitude than prior art DC driven circuits.

It will be understood that packaging of the LED can include both PLCC-6 and PLCC-4 configurations. Other surface mount packages could be used. The polarity orientation is also not limited to left to right or top to bottom or in any other configuration.

In summary, a plug compatible package with three green LED dies could replace current RGB diode versions and provide greater emissions at the preferred wavelength.

A lens or collimator can be provided to remove any hot spots, and, to provide uniform light output.

FIGS. 1A and 1B illustrate aspects of an exemplary multiple diode configuration 10 in accordance with the above. Configuration 10 could correspond in form factor to a standard package, such as a PLCC-6 or PLCC-4 without limitation. Configuration 10 exhibits six contact points, 1-6, and a radiant energy emission port 8.

As illustrated in FIG. 1B, configuration 10 includes three light emitting diodes 10a. Emission wavelengths are substantially identical for each of D1, D2, and D3. When energized simultaneously, the radiant energy emitted from port 8 will have an intensity on the order of three times that of a single LED.

FIGS. 2-4 illustrate different views of a multipoint sensing unit, or optical block, 20. Unit 20 in FIG. 2 is illustrated partly in section. In FIGS. 3, 4 the unit 20 is shown with different orientations.

Unit 20, in addition to carrying the configuration 10, as a source or emitter of radiant energy, can also carry a gas sensing first photodiode 22, and a second feedback photodiode 24 which can sense radiant energy emitted from configuration 10. That sensed radiant energy can provide input to a closed loop control system to maintain composite output from configuration 10 at a predetermined level.

Radiant energy R from configuration 10 can be directed to a collimator, or light pipe 26 whose output is directed to a sensing location 30 adjacent to a region of a paper sensing tape T. Light reflected off of the tape T, indicative of presence of a selected gas (as will be understood by those of skill in the art), is incident on photo diode 22.

A central axis A1 of the radiant energy path to the sensing region 30 is at a forty five degree angle to an axis A2 of the photodiode 22. Unit 20 defines a gas sample inflow path 32 and a gas sample pressure sensing transducer port 32a. Radiant energy reflected to diode 22 travels through path 34 in unit 20. Unit 20 also defines a radiant energy inflow path 36 which directs the output of collimator or light pipe 26 to the sensing region 30.

Sample gas can flow through tape T at region 30 and exit at port 34.

A printed circuit board 40 carries the configuration 10, sensors 22, 24 and other local electronics, feedback, communications and control circuits 40a. The board 40 overlays the collimator or lens 26, as well as the internal paths 34, 36.

FIGS. 3, 4 illustrate that unit 20 can carry multiple sets of components 10, 22 and 24 to implement multiple sensing regions, such as region 30. The multiple sensing regions, such as region 30, can be used to sense different gasses, or a single gas at different locations simultaneously, best seen in FIG. 6. In the views of FIG. 3 the printed circuit board 40, which overlays the illustrated components for the four sensing locations, can be regarded as transparent for illustration purposes. In FIG. 4, the printed circuit board 40 is illustrated adjacent to the unit 20.

FIG. 5 illustrates a plurality of collimators or light pipes 46 which can be molded as a single unit and inserted into the respective channels, such as the channel 36, of unit 20.

FIG. 6 illustrates multiple samples on tape T. Each of the four sensing stations in unit 20-1 can sensed a sample in window 1. Tape T is then moved and another set of samples can be sensed in windows 2, 3 . . . 7. With two units 20-1, 20-2, eight samples can be obtained at substantially the same time.

In summary, a gas detection apparatus includes a housing which carries a plurality of light emitting diodes which are coupled in parallel and which emit substantially the same wavelength of radiant energy. A closed loop control circuit maintains the radiant energy output of the diodes at substantially a predetermined value.

The radiant light radiant light and a sample of a gas of interest are directed to a sensing position at which a gas responsive tape is positioned. Reflected light from the tape is detected at a sensor displaced from the tape. A light collecting element can be positioned between the coupled diodes and the sensing position.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Further, logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be add to, or removed from the described embodiments.

Claims

1. An apparatus comprising: a housing wherein the housing defines a gas responsive tape port;a multiple diode source wherein the multiple diodes emit radiant energy at substantially the same wavelength wherein the source is carried by the housing with a selected radiant energy emitting orientation;a first sensor of radiant energy reflected from a predetermined location within the housing; anda second sensor carried in the housing and responsive to emitted radiant energy emitted from the source.

2. An apparatus as in claim 1 where the emitting orientation of the source and the first sensor have an orientation substantially forty five degrees relative to one another.

3. An apparatus as in claim 1 which includes a collecting optical element between the source and the predetermined location.

4. An apparatus as in claim 1 wherein the second sensor is coupled to control circuitry which alters an energy output parameter of the source.

5. An apparatus as in claim 4 where the control circuits provide closed loop control signals to the source so that the source emits radiant energy at substantially a predetermined output value.

6. An apparatus as in claim 5 where the emitting orientation of the source and the first sensor have an orientation substantially forty five degrees relative to one another.

7. An apparatus as in claim 6 wherein the tape port defines the predetermined location.

8. An apparatus as in claim 7 where a predetermined tape can feed through the port adjacent to the predetermined location, and wherein radiant energy can be incident thereon.

9. An apparatus as in claim 8 which includes a collecting optical element between the source and the predetermined location.

10. An apparatus as in claim 9 with a radiant energy directing element to direct radiant energy to the second sensor.

11. An apparatus as in claim 1 which defines a plurality of gas responsive tape ports and an associated plurality of second sensors.

12. An apparatus comprising: a housing wherein the housing defines a first plurality of substantial identical gas responsive tape ports;a plurality of radiant energy sources carried by the housing where each member of the plurality is associated with a respective port and wherein the housing defines a first plurality of internal radiant energy paths, where each source is coupled to each port by a respective path; anda second plurality of paths wherein each member of the second plurality is at an angle on the order of forty five degrees to a respective member of the first plurality; anda plurality of radiant energy sensors with each sensor coupled to a member of the second plurality of paths.

13. An apparatus as in claim 12 which includes a radiant energy collecting element coupled between each source and the respective tape port.

14. An apparatus as in claim 12 which includes a strip which carries a plurality of light pipes wherein each member of the plurality of light pipes extends into a respective internal radiant energy path.

15. An apparatus as in claim 14 wherein each light pipe on the strip includes a cylindrical portion with a hemispherical light output region.

16. An apparatus as in claim 15 wherein each light pipe on the strip includes a planar input region.

17. An apparatus as in claim 16 wherein each light pipe on the strip is positioned adjacent to a radiant energy source.

18. An apparatus as in claim 17 where each source comprises a plurality of light emitting diodes wherein each member of the plurality emits light of substantially the same wavelength.

19. An apparatus as in claim 12 which includes control circuits coupled to the sources and sensors.

20. An apparatus as in claim 18 which includes radiant energy feedback control circuits coupled to the diodes and a feedback sensor.