Method and apparatus for measuring light reflectance absorption and or transmission

• US 3,910,701 A
• Filed: 07/30/1973
• Issued: 10/07/1975
• Est. Priority Date: 07/30/1973
• Status: Expired due to Term

• Current Assignee: David A. Grafton, George R. Henderson
• Original Assignee: David A. Grafton, George R. Henderson
• Inventors: Henderson, George R., Grafton, David A.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Koren, Matthew W.
• Application Number:
  US05/384,026
• Time in Patent Office: 799 Days
• Field of Search: 356/39,40,41,51,173,180,201,209,211,226,73 250/226
• US Class Current: 356/39
• CPC Class Codes: G01N 2021/8466 Investigation of vegetal material, e.g. leaves, plants, fruits
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres
• CPC Class Codes: G01N 2201/024 Modular construction
• CPC Class Codes: G01N 2201/0627 Use of several LED's for spectral resolution

Abstract

A method and apparatus for measuring light reflectance, absorption and/or transmission having a plurality of light emitting diodes (LEDs) arranged to direct light emissions toward a test piece, with the various diodes being selected to emit light of different wavelengths and at least one light-responsive sensor disposed to receive light reflected and/or transmitted by the test piece and originating with each of the light-emitting diodes. Electrical drive circuit means are provided for alternately or sequentially energizing the plurality of LEDs of different wavelengths, such that the reflected or transmitted light received by the sensor is a function of the various wavelengths of the respective LEDs. In one embodiment, the sensor is operative to generate an output signal indicative of the characteristics of the test piece as a function of the different wavelengths of the LEDs which signal is processed to provide a display of the '"'"''"'"''"'"''"'"'differential'"'"''"'"''"'"''"'"' light reflectance, transmission and/or absorption characteristics of the workpiece and the wavelengths of the LEDs. In another embodiment, a plurality of LEDs each having a different frequency is operative to generate a range of signals which provide a measurement of reflectance, transmission and/or absorption as a function of the wavelengths of the various LEDs employed. The plurality of LED sources and the sensor may be mounted within a self-contained module which may be detachably connected to an instrument housing containing the drive and output circuitry and display means, such that a number of different source modules may be provided each having LEDs of unique wavelength with the various modules being interchangeable to permit a wide variety of measurement frequencies.

Claims

1. Apparatus for measuring light reflectance, transmission and/or absorption of a test object at different light wavelengths, comprising:

a plurality of light emitting diodes disposed to direct light emissions toward the test object, said plurality of light emitting diodes including two sets of diodes with one set emitting light of one wavelength and the second set emitting light of a different wavelength;

at least one light sensor disposed to receive light emanating from said test object, said light being a function of the characteristics of the test objects;

drive circuit means connected to and for alternatedly energizing said two sets of said plurality of light emitting diodes such that said light emissions of different wavelengths are produced at alternately different times;

means coupled between said drive circuit means and one set of said diodes of one wavelength for adjusting the drive level of the signal from said drive circuit means to said certain of said diodes of one wavelength to facilitate calibration;

output means conneced to said sensor means for registering a measurement of the light emissions received by said sensor means; and

means coupled to said output means for adjusting the signal gain in said output means to facilitate calibration.

2. The apparatus of claim 1, said drive circuit means being connected to and for energizing said two sets of diode such that said two different light wavelengths are alternately produced, and said output means including alternating current amplification means for receiving and amplifying an alternating electrical signal from said sensor means representing the variation in the electrical output therefrom caused by said different light wavelengths.

3. The apparatus of claim 2, said drive circuit means being connected to and for alternately energizing each set of light emitting diodes such that the plurality of diodes within each set are jointly and simultaneously energized, whereby each set of light emitting diodes produces a relatively high intensity light emission at the associated wavelength.

4. The apparatus of claim 2 further comprising:

switch means for selectively enabling one set of diodes associated with one of the wavelengths and disabling the second set of diodes associated with the other wavelength whereby light emissions at each of the sets of diodes may be independently adjusted and calibrated.

5. The apparatus of claim 1, further comprising:

an additional light sensor means, one of said light sensors being disposed to receive light reflected by said test object and the other said light sensor means being disposed to receive light transmitted by said test object; and

said output means being connected to both said sensor means for registering measurements of the amount of light received by each of said sensor means, whereby measurements of the light reflectance and light transmission can be utilized to provide a measurement of absorption.

6. The apparatus of claim 1, said plurality of light emitting diodes being selected to provide light emissions of a corresponding plurality of different wavelengths;

said drive circuit means being connected to and for alternately and sequentially energizing said diodes such that said light emissions of different wavelengths are sequentially produced;

said output means comprising a plurality of sample and hold circuit means for each diode wavelength for receiving and storing the output signal from said sensor means during the light emission from the diode of the associated wavelength, whereby a plurality of output measurement signals are registered by said sample and hold circuit means as a function of the various wavelengths produced by said light emitting diodes.

7. An instrument for performing measurements of light reflectivity, transmission and/or absorption, comprising:

an instrument housing;

a plurality of modules each having at least one light source and one light sensor And each having electro-mechanical connection means for detachable connection to said housing;

said at least one light source including two sets of light emitting diodes each associated with and mounted in each of said modules for directing light emissions therefrom toward a test object;

impedance adjustment means mounted in each of said modules and coupled to the associated plurality of light emitting diodes whereby the light intensity of each of said sets of light emitting diodes may be adjusted to permit the attainment of uniform illumination by each of said modules;

said at least one light sensor mounted in each of said modules along with said light emitting diodes for receiving light emanating from said test object, said light being a function of characteristics of said test object; and

circuit means mounted in said housing and connectable to said two associated sets of diodes and said sensor of each of said plurality of modules for providing electrical drive signals for alternately exciting said two associated sets of diodes to cause light emission therefrom and for receiving and developing a measurement signal in response to an electrical output from said sensor representing the amount of light received thereby.

8. The instrument of claim 7 and wherein at least one diode of one set of each of said two sets of light emitting diodes is operative to provide light of a different wavelength than the diodes in the other set of light emitting diodes.

9. The apparatus of claim 7, at least one of said modules comprising means for receiving a test object in a position such that light emissions from said plurality of diodes is at least partially transmitted through the test object before impinging on said sensor, whereby light transmission measurements can be performed on said test object.

10. A method of measuring light reflectance, transmission and/or absorption at different wavelengths, the steps comprising:

selectivity and alternately energizing a plurality of light emitting diodes having light emissions of different wavelength;

reflecting said light emissions from said diodes with respect to a test object and receiving said reflected light emissions at a light sensor to produce an alternating current electrical output signal having an amplitude representing the difference in reflectivity of the test object as a function of the different wavelengths to produce a differential light reflectance signal;

receiving the electrical signal produced by said sensor means in response to the diode light emissions reflected by the test object; and

rectifying the alternating current signal to produce a direct current signal to be displayed as a measure of said differential light reflectance signal.

11. The method of claim 10, and further comprising the step of amplifying said alternating current signal to produce a signal of amplitude proportional to the differential light reflectance of the test object at the differential wavelengths of light.