Abstract: A short path liquid junction structure is defined through a porous ceramic layer coated circumferentially on an electrochemical electrode glass body by an elastomeric O-ring sealing member circumferentially engaging the ceramic layer in an annular line contact seal. The length of the liquid junction path is the short distance through the porous ceramic layer around and past the line contact seal.

Abstract: There is disclosed a circuit for generating an error voltage which is proportional to the difference between a desired value of a physical parameter and the actual value of the physical parameter. The circuit operates by alternately switching the current from a source through a fixed reference resistor and a variable resistor, the resistance value of which changes as a function of the physical parameter to be controlled. The current is switched between the two resistors so that the average voltage generated across the variable resistor would be equal to the average voltage generated across the fixed resistor if the physical parameter had the desired value. By determining the difference between the average voltages across the resistors, the error voltage can be generated for controlling the physical parameter.

Abstract: A method of determining the need for post-addition of antigen or antibody to an antigen-antibody reaction to ascertain whether the reaction is in an antigen excess or an antibody excess condition. The time rate of change of a nephelometric signal developed from the reaction is monitored to generate a rate signal having a peak value providing a measure of antigen concentration. The post-addition step is performed only if the peak rate value is ambiguous--, i.e. if it indicates one antigen concentration value for a reaction in antigen excess but another value for a reaction in antibody excess. The need for the post-addition step is determined from measured qualities of the rate signal including one or more of (1) the peak rate value, (2) the elapsed time from the start of the reaction to the peak rate, and (3) the product of the peak rate and the elapsed time. When required, the post-addition step may be performed during progress of the antigen-antibody reaction after measurement of the peak rate value.

Abstract: Apparatus for automatically and selectively supplying a blood sample or a wash/calibration solution to the entrance port of a flow cell which measures characteristics of the sample such as pH, pCO.sub.2 and pO.sub.2. A sample filled syringe and a solution supply conduit are supported by respective first and second fluid delivery mechanisms which rotate to move the syringe outlet and the conduit outlet in generally arcuate paths toward and away from the flow cell entrance port. The delivery mechanisms are rotated simultaneously, one toward and one away from the entrance port, by a common drive gear. Seating of the wash solution outlet in the entrance port is upstream of the seating of the sample outlet to ensure complete flushing of sample from the entrance port by the wash solution.

Abstract: A vacuum operated system for transferring fluid from a container to an open or relatively large sump without applying vacuum to the sump. A small, closed, intermediate chamber is interposed in a flow path between the container and the sump. Vacuum from a small vacuum source is applied to the intermediate chamber and draws fluid from the container through a first conduit into the chamber. A peristaltic pump draws fluid from the chamber through a second conduit to the sump while maintaining a vacuum seal for the chamber preventing loss of vacuum through the second conduit.

Abstract: A method of checking the electrical isolation provided by a gas permeable membrane for a carbon dioxide sensor in an analyzer for simultaneously measuring the carbon dioxide and chloride content of a blood sample as it reacts with a reagent in a sample cell. The method involves actuating the carbon dioxide sensor during its normal "off-time" and measuring any signal generated thereby while a coulometric generator in the analyzer is initially activated to titrate to a repeatable initial value any chloride present in the reagent alone. Any signal generated by the sensor above a predetermined value is indicative of a defective membrane and may be utilized to inhibit further operation of the analyzer.

Abstract: Apparatus for detecting a peak value of an analog signal includes a first counter for counting pulses from a digital clock for successive samplings of the analog signal to convert each sample of the analog signal into digital form and a counting register into which the pulse count in the first counter is transferred to be recounted at a later sampling. With a prior digital count in the register, the digital clock simultaneously (1) increments the counter to count the current signal sampling and (2) decrements the register to zero to recount the prior signal sampling. The counter is constrained to count up until both counting and recounting steps are complete before the count in the counter is transferred to the register. In this manner the counter will always attain the greater of the current and the prior sampling pulse count values and this maximum value will always be transferred into the register.

Abstract: An electrochemical combination electrode assembly having an inner, tubular glass pH electrode body supported within a tubular outer plastic container, a reference electrolyte reservoir defined in an annular space between the container and the glass electrode, and an annular, pressure contact leakage junction defined between an inclined surface and edge on the glass electrode body and plastic container for establishing electrolytic communication between the reference electrolyte and a test solution. Preferably the leakage junction is established at the junction line of an axially tapering exterior surface of the glass electrode body and a circular edge on the plastic container surrounding the tapered surface. The glass electrode is nested in the plastic container until the tapering surface and circular edge engage. The degree of pressure engagement establishes the flow rate through the junction.

Abstract: Apparatus for measuring CO.sub.2 in serum with a single pH sensor of the electrolyte flow-through type, the sensor including a gas-permeable membrane selectively passing CO.sub.2 into an electrolyte filled space adjacent a pH sensing electrode for reacting with the electrolyte to produce a pH change therein. The electrolyte space is connected by a conduit to an electrolyte reservoir for flowing fresh electrolyte to and through the electrolyte space prior to a sample measurement. A stainless steel metal electrode directly contacts the electrolyte of constant composition in the conduit upstream of the pH sensor to derive a reference potential thereat. The potential across the pH sensor and the stainless steel electrode is monitored, differentiated, and the maximum value of the differentiated signal measured to determine the CO.sub.2 concentration.

Abstract: A double beam optical null spectrophotometer having sample and reference optical beam paths, a detector common to both paths, and an attenuator feedback loop from the detector for adjusting the position of an optical attenuator in the reference beam path to balance the energy in the two paths. The slider of an attenuator transmitting potentiometer follows the position of the optical attenuator and a signal level sensitive impedance network connected to the slider calibrates the potentiometer such that an output signal therefrom indicates the true transmittance of a sample in the sample beam path over a range of transmittance values from zero to one hundred percent transmittance.

Abstract: A system for chemically analyzing antigens or antibodies by initiating an antigen-antibody reaction in a reaction zone and measuring the light scattered by a precipitate produced by the reaction to determine the antigen or antibody concentration. In order to signal the start of the reaction, a fluorescent tagging substance is included with at least the last antigen or antibody reaction component introduced into the reaction zone. The fluorescent tagging substance does not enter into the antigen-antibody reaction and is selected to emit light in a bandwidth spectrally separated from the light scattered by the precipitate. The reaction zone is monitored for the presence of the tagging substance, and when the substance is detected a trigger signal is generated to signal the start of the reaction.

Abstract: Apparatus for the analysis of samples such as blood or urine includes a reaction cell for reacting the sample with a chemical reagent at a predetermined temperature. A heat exchanger is provided on the reaction cell for establishing the temperature of the cell. Reagent is pumped into the cell through a conduit, and a portion of the conduit is wound around the reaction cell in contact with the heat exchanger to preheat reagent in the conduit before the reagent is pumped into the cell.

Abstract: Method and apparatus for measuring the degree of quench in a liquid scintillation sample by irradiating the sample with a standard source, such as a cesium-137 gamma source, to produce a Compton scattered electron distribution exhibiting a Compton edge configuration as the leading edge thereof. For increasing the quench levels in the sample, the Compton edge shifts to lower pulse height values and the extent of this shift is indicative of the degree of quench. To measure the degree of quench, a unique point on the Compton edge, namely the point at which the second derivative of the edge is zero (i.e. the inflection point), is measured for the quenched sample and the pulse height value corresponding to the inflection point is determined. The pulse height value is compared with the pulse height value determined for a calibration standard in a similar manner, the difference in pulse height values indicating the degree of quench.

Abstract: A variable chart format system for a recorder with a chart print out, the system having a manually selectable switch for simultaneously controlling the abscissa and ordinate formatting independent of scale expansion circuitry normally associated with the abscissa and ordinate. The abscissa formatting is digital and operable in response to a programmable or variable clock, the output of which is selectively passed through a first set of abscissa formatting frequency dividers and then serially through one of a second set of abscissa scale expansion frequency dividers to drive a chart drive stepper motor.

Abstract: A method of measuring the disintegration rate of a beta-emitting radionuclide in a liquid sample by counting at least two differently quenched versions of the sample. In each counting operation the sample is counted in the presence of and in the absence of a standard radioactive source. A pulse height (PH) corresponding to a unique point on the pulse height spectrum generated in the presence of the standard is determined. A zero threshold sample count rate (CPM) is derived by counting the sample once in a counting window having a zero threshold lower limit. Normalized values of the measured pulse heights (PH) are developed and correlated with the corresponding pulse counts (CPM) to determine the pulse count for a normalized pulse height value of zero and hence the sample disintegration rate.