Abstract: A decoder for pulse width modulated (PWM) signals comprising an integrator and a sample-and-hold circuit wherein the sample-and-hold output signal is fed back to the input of the integrator. No periodic initialization of the integrator is required. The gains of the integrator and sample-and-hold circuits and the capacitance of the integrator capacitor affect only the settling time of the decoder, not the value to which the decoder output ultimately settles.

Abstract: A method of identifying an operating position of a multiple-position filter changing mechanism situated in an optical path of a spectrophotometer by detecting and measuring a spectral characteristic(s) of light passed along the optical path to the spectrophotometer detector for one or more operating positions of the filter mechanism and comparing the measured spectral characteristic(s) with stored spectral characteristic information for one or more operating positions of the filter mechanism.

Abstract: Moderately narrow band, tunable, birefringent filters are disclosed using zero-twist liquid crystal cells as variable retarders in a Lyot-type birefringent filter. These filters can achieve analytically useful levels of resolution and stray-light ratios for costs that are competitive with prism and grating monochromators. These birefringent filters can be tuned and/or rendered opaque by the application of a suitable voltage to the cells. Thus, a variety of different optical instruments can be constructed with no moving parts. Power requirements are negligible. A useful filter can be designed to occupy a volume less than one cubic inch. These properties render such a filter ideally suited to microprocessor control.

Abstract: A pressure booster system for fluids using one or more injectors for delivering a relatively low pressure output flow of fluid. A fluid accumulator receives the output from one or more injectors. A detector reveals any fluid mass change in the accumulator in relation to a selected value of fluid mass. A relatively high pressure pump increases the pressure of the output flow from the accumulator in accordance with the change of fluid mass within the accumulator which results in high pressure metering.

Abstract: A photometric flow cell for high pressure liquid chromatography having an illuminated passageway therein between open ends of which fluid samples are flowed for analysis. An annular, porous flow impedance element is supported in an annular channel surrounding one end of the passageway. The impedance element reduces turbulence of flow through the open end by evenly distributing the flowing fluid circumferentially about the end opening.

Abstract: A single beam spectrophotometer is conditioned to automatically scan a sample across a wavelength scan range and to measure the sample at selected wavelengths within the range. Methods of setting output signal gain, adjusting signal gain for a selected wavelength range, and automatically scanning and measuring the sample are disclosed.

Abstract: Photometric analysis apparatus having a cylindrical glass sample container which is rotated about its axis during optical measurement of sample in the container. Rotation of the 5 container window areas past an optical detector compensates for optical variations and imperfections in the container wall which would otherwise render the measured photometric signal sensitive to each particular rotational orientation of the container.

Abstract: Output current hysteresis exhibited by a multiple-dynode photomultiplier detector is reduced by inactivating one or more of the dynodes by shorting to the detector anode, and operating the detector with the reduced number of active dynodes while retaining the anode as the output current supply terminal.

Abstract: A light scattering photometer including a rotating segmented mirror intercepting light from a laser source and alternately directing the light into a sample zone along an optical axis in first and second opposite directions. A mask annulus coaxial with the optical axis intercepts light scattered from the sample in an incremental angle .DELTA..theta. at a selected angle .theta. with respect to the axis. As the direction of sample illumination alternates, the annulus alternately intercepts forward scatter and back scatter of light from the sample at angles .theta. and 180.degree.-.theta., respectively, and passes the forward and back scatter in alternate succession to a detector. The detector output signal is demodulated to derive near-simultaneous forward and back scatter measurements from the sample. The photometer permits measurement at small values of .theta. approaching 0.degree. and hence permits near-simultaneous scatter measurements at forward and back scatter angles spaced by an angle approaching 180.

Abstract: In a spectrophotometer including a photomultiplier tube and an operational amplifier responsive to the current from the photomultiplier tube for generating a DC voltage proportional to light intensity, a method and means for simultaneously compensating for the dark current of the photomultiplier tube and the offset of the operational amplifier so that the output voltage of the operational amplifier is zero volts under dark conditions.

Abstract: In a system which measures a parameter of a sample and displays information relating thereto, a circuit including the component elements of the system for testing signal levels at test points within the system and for displaying the test signal levels. Switching means places the system in either a transducing mode for measuring the parameter or in a combined transducing/self-testing mode for simultaneous testing during transducing operation. The testing circuit includes an operator manipulated probe for contacting any of the test points and an analog multiplexer input of the system for multiplexing the probe test signal and the transducing signal. The multiplexed signals are converted to digital form and processed by the system's computer for display. In the combined transducing/self-testing mode, the probe test signal information is outputted to the system display while the transducing output thereto is inhibited.

Abstract: In a system for analyzing the elemental or molecular composition of a sample where the sample components are excited through collision with an active metastable gaseous species, the excited sample components emitting a characteristic wavelength of light which may be detected, the system including a microwave cavity through which the gaseous species flows and a microwave source coupled to the cavity, the microwave discharge exciting the gaseous species, there is disclosed an improved gas and sample introduction system wherein a liquid sample and a water soluble compound are mixed with a diluent and aspirated into the flow, upstream of the microwave cavity, onto a heated filament, the compound being capable of releasing nitrogen or some other suitable gas molecules at high temperature and low pressure whereupon formation of nitrogen and vaporization of the sample occur simultaneously.

Abstract: A liquid junction structure for an electrochemical reference electrode or a reference portion of an electrochemical combination electrode comprising an element of capillary material restrained between first and second plastic shrink tubes.

Abstract: A sample vial guide for scintillation spectrometers or other sample handling systems in which sample vials are moved in a horizontal path to a first operating station, transferred vertically therefrom to a second station such as a radiation measuring chamber, and returned along the vertical path to the first station for continued movement along the horizontal path away from the first station. The sample vial guide includes first and second opposing jaws at the first station on opposite sides of the horizontal path and having opposing interior surfaces which surround and define a constrained area at the first station for a sample vial. The jaws are hinged to pivot laterally away from the horizontal path and include cam surfaces on each jaw for engaging a sample vial as it moves along the horizontal path to or from the first station to move the jaws to an open position to accommodate such horizontal movement of the vial.

Abstract: Titration apparatus for measuring chloride electrolyte in blood samples including a pair of coulometric generating electrodes (anode and cathode) for titrating the chloride with silver ions to precipitate silver chloride and a pair of amperometric detecting electrodes for detecting uncombined silver ions following complete titration of the chloride and hence for signaling the endpoint of the chloride titration. A predetermined potential difference is applied across the amperometric electrodes, and an operating condition of zero current flow is established through one of the amperometric electrodes. Current flow between the amperometric electrode and the coulometric anode is monitored to indicate the presence of uncombined silver ions and thereby the titration endpoint.

Abstract: Photometric analysis apparatus in which a sample to be optically measured is stirred by a rotating magnetic stirring element within a container holding the sample. An optical path through the container and through the sample therein intersects the rotational path of the stirring element and is hence obstructed by the stirring element in one or more rotational positions. Rotation of the stirring element is controlled in a manner which stops rotation thereof in a position out of the optical path thereby allowing optical measurement of the sample material unobstructed by the stirring element.

Abstract: A method of flameless atomic absorption analysis in which an element in a sample is measured by vaporizing the sample in a graphite crucible or cuvette and measuring the absorbance of the atomic vapor at a wavelength characteristic of the element. The method includes the steps of (1) successively introducing a preselected number of aliquots of the same sample into the graphite cuvette, (2) thermally pretreating each sample aliquot upon introduction to remove volatile or decomposable substances therefrom, and (3) vaporizing sample remaining in the cuvette for measurement only after performing the predetermined successive number of sample introduction and thermal pretreatment cycles.

Abstract: Pipetting and diluting apparatus including an interchangeable syringe pump of predetermined volume capacity and a stepper motor for driving the syringe piston at a selected speed for dosing a selected volume of fluid. The piston stroke is calculated from the syringe volume capacity and the volume of fluid to be dosed. Control means controls the acceleration and deceleration characteristic of the piston in accordance with an exponential function dependent upon the selected piston speed and the syringe volume capacity.

Abstract: Apparatus for conveying a blood sample through a flow cell which measures characteristics such as pH, PCO.sub.2, and PO.sub.2 of the sample and for pumping a wash solution through the cell between samples. The flow cell inlet is selectively connected (1) to a sample-filled syringe for driving sample through the flow cell or (2) to a reservoir of the wash solution. The flow cell outlet is connected by a conduit to a waste receptacle. A rotor of a combined peristaltic pump and valve coacts with an elastomeric tubular section of the conduit. The rotor and the elastomeric section are movable in a transverse direction relative to each other between (1) a first or pumping position wherein the rotor compressively engages the section for pumping fluid wash solution through the cell and the conduit and (2) a second or relaxed position wherein the rotor is released from the section to provide an open unrestricted channel for the flow of sample driven by the syringe through the cell.

Abstract: A fluid pump mechanism for delivering a smooth output of fluids to a system utilizing at least one piston in a chamber reciprocative therewithin. The piston has strokes that fill and empty the chamber in conjunction with the action of valve means located at the inlet and outlet of the chamber. Motive means causes reciprocation of the piston within the chamber. Control means is also included for minimizing the time during the piston cycle in which the piston is not emptying the chamber. The invention's scope also encompasses a pressure metering device for a fluid forcing means motivated by an electrical motor.