A method of determining the OD of a printed colorant, comprising: determining a visible wavelength region in which the color is at or near saturation; and if a portion of a determination of saturation is found, determining the OD in a wavelength region at which the color is not at or near saturation.

A blood glucose monitor which is particularly applicable for use as an implant for controlling an insulin pump, or as a portable device for use by a diabetic for home blood glucose monitoring. The glucose monitor measures the glucose level of blood by utilizing a refractometer which measures the index of refraction of blood adjacent to an interface with a transparent surface of the refractometer, by directing light at the interface to measure the index of refraction of the blood by the amount of radiation reflected by the interface, particularly light incident near the critical angle. In a preferred embodiment, polarized light is directed against an interface in an implant between a transparent material and the blood. As the glucose concentration in the blood changes, its index of refraction changes, as does the intensity of light reflected from the interface. The angle of incidence of the light is selected to be slightly less than the critical angle for total internal reflection, with the result that the reflected intensity varies dramatically with index of refraction and with glucose concentration. A differential amplifier compares the intensity of the light reflected from the blood and the intensity of the beam before reflection. The output signal from the differential amplifier indicates only a change in the intensity of the reflected light caused by a change in the glucose concentration from a standard setting.

A generated signal is passed through an elongated signal conveying element positioned preferably perpendicular to the surface of a fluid the level of which is to be measured. The signal is directed from the signal conveying element to a detector element which senses the signal output from the signal conveying element. The signal output detected in an optical embodiment varies logarithmically with the depth of immersion of the signal conveying element into the fluid. A preferred embodiment employs an electromagnetic wave, e.g., light, signal which passes through a light pipe signal conveying element. By nearly matching the light pipe index of refraction with that of the fluid, a predetermined percentage of the wave is lost into the fluid each time the light is reflected further along the pipe. The portion of light sensed at the detector, which is located where the unrefracted light exits, is readily converted to an output which varies linearly with the depth the light pipe signal conveying element is immersed into the fluid length.

A flow chamber includes a flow passage having a knee with a window through which cells in liquid suspension pass. An optical system establishes an observation plane through the passage at the corner enclosed in the knee and illuminates the two portions separated by the corner with light at different wavelengths. Fluorescence of the cells is detected and measured.

A portable infrared spectrophotometer for nondestructive testing of coatings, plastics, rubber and other organic construction materials. A single source of infrared light is formed into two beams. One beam is directed to the surface of a sample where it is reflected off the surface of the sample at least four times. The other beam follows a similar path but bounces off a neutral surface. The two beams are combined and focused onto a detector. The output of the detector is proportional to the energy absorbed by the surface of the test sample. A pen recorder is used to provide a graphic display of the spectrum generated.