Abstract: An apparatus and method for making a photometric determination regarding the contents of a sample, such as the absorbance characteristic of a blood serum sample. The improvement allows measurements to be taken after a reduced warm-up period and compensates for variations in the lamp intensity during the period over which measurements are taken. A feedback circuit is provided between a reference photodetector and the light source for causing the light source intensity to asymptotically approach a final stable value in a smooth exponential curve. Signal processing means processes outputs of the reference and sample photodetectors taken at different times so as to compensate for variations in the source intensity over the time period during which the outputs are taken. Still further, the photometer allows resonant frequency mixing of the contents of a cuvette while disposed in the photometer by causing the entire optical assembly, in which the cuvette is mounted, to vibrate at its resonant frequency.

Abstract: An apparatus and method for making a photometric absorbance measurement of hemoglobin in a blood sample utilizing a reusable cuvette and an inexpensive photometer. The cuvette is a unitary plastic body having a flow-through slot of a predetermined height which allows an absorbance measurement to be made with an undiluted blood sample and which permits cleaning by inserting the body in a liquid cleaning solution. Two absorbance measurements are made, the first at a wavelength at which the absorbance of oxyhemoglobin and deoxyhemoglobin are approximately equal, near an isobestic point, and a second measurement at which these components absorb substantially no light. By making the first measurement near an absorbance minimum at about 510 nm, an absorbance measurement can be made with a relatively thick slot required for cleaning and with an undiluted blood sample and an inexpensive photometer.

Abstract: A comparitive colorimeter for use in the field which simultaneously compares the color densities of two liquid samples and designates the degree of difference. The apparatus includes two major subsystems, optical and electronic. The optical subsystem is designed to provide identical light beams through both the sample and standard solutions and to minimize the effect which imperfect sample tubes have on the output. The electronic subsystem includes a log conversion and differential amplifier circuit for generating a difference signal representative of the difference between the optical densities of the sample and standard solutions. The difference signal is evaluated by a comparative circuit consisting of a resistive chain having a plurality of node voltages and hex inverters connected to the node voltages. The hex inverters drive a series of LED indicator lights to designate the relative degree of difference between the optical densities of the sample and standard.

Abstract: A system selectively provides a selected program, such as a movie, to viewers who select the program by pushing a button as an attachment to a television set. The selected program is carried on a standard television channel unused in the area for regular programming having a carrier frequency f.sub.c. This signal is mixed with the second harmonic of the master oscillator at the input of the master antenna TV system to translate the selected program channel to a midband channel between the standard high and low VHF television bands. The master oscillator signal is also injected into the input of the MATV system and used for providing remote control of the room box and as an input to a frequency converter which converts the midband channel back to the standard TV channel when the user presses the selector button on the room box.