Near Infrared Transmission

OpticsDiagram

Near infrared transmission spectroscopy is the most widely used technology for measuring protein, oil and moisture in grains and oil seeds.  When applying this technology to the combine, the light source is in the sampling head on the side of the clean grain elevator.  Light from a lamp passes through the sample and bounces off the surfaces of the grains or oil seeds and propagates through the sample until it reaches the other side.  The emerging light is focused into a fiber optic bundle that transmits the light back to the spectrometer.

OpticLensDiagram

The light is focused into a flat field spectrograph that separates the light into its individual frequencies, across the wavelength range from 720 – 1100 nm.  The separated light is then directed onto a silicon photo diode array detector.   This array detector measures the intensity of the light at each frequency to product what is called the NIT spectrum of the sample.

NITSpectraGraph

Within this region of the electromagnetic spectrum, N-H (protein), C-H (fats and oils), O-H (water) and C-O-H (carbohydrates) absorb NIR light at specific frequencies of light.  The NIT spectrum contains information about the concentration of these components.