Transducer Research, Inc.

Becton Dickinson and Company Limited

The United States of America As Represented by the United States

Illinois Institute of Technology

Gas Research Institute

Arch Development Corporation

Other

The United States of America

Joseph R Stetter

Solomon Zaromb

G Jordan Maclay

William R Penrose

Lawrence Spritzer

Takaaki Otagawa

Donald R Rutt

Peter J Hesketh

Raymond B Cromer

James P Bobis

Zhuang Cao

G Jorgan Maclay

John C Fidler

Li Pan

Chongshan Yue

David S Ballantine, Jr

William J Buttner

Melvin W Findlay, Jr

Melvin W Findlay

Steven M Gendel

In an improved amperometric gas sensor, the structure, composition, and electrode potential are adjusted so as to prevent or minimize any unwanted reactivity at the counter and/or reference electrode of any analyte or interfering component of the matrix that may cross over thereto. The sensor is preferably structured so that the product of the analyte reaction at a first working electrode can be reconverted to the original analyte at a counter electrode or at a second working electrode and then reacted again at the first working electrode, with such back-and-forth reactions repeating many times, so as to yield an amplification of the analyte signal.

Chemical sensing apparatus and methods

A monitoring system for chemical shipments having an apparatus for detection of a leak from a shipment vessel having a shroud. A first chemical sensor is in communication with a chamber of the shroud for detecting the presence of a substance leaking from the vessel. A second sensor is in communication with the ambient environment surrounding the shroud. A monitoring circuit in communication with the first chemical sensor and the second chemical sensor monitors a first chemical sensor output and a second chemical sensor output and signals an information unit dependant on the increase of at least one of the first and second chemical sensors. The information unit emits a signal to an alarm or output device in response to an increase of the magnitude and/or rate of increase of at least one of the first chemical sensor output and the second chemical sensor output. A physical sensor can be in combination with the monitoring circuit. The information unit can be a remote information unit to which the monitoring circuit signals by wireless communication means.

Apparatus and method for leak detection

A biosensor comprising a substrate material, at least one antibody covalently immobilized on the substrate material, and a pair of metal contact electrodes for measuring the impedance of the biosensor. A process for producing a biosensor in accordance with this invention as well as a process for utilizing the biosensor are also disclosed.

Antibody covalently bound film immunobiosensor

Apparatus for the detection of a vapor of a selected chemical substance includes a sensor whose impedance changes upon exposure to such a vapor. The sensor comprises a polymer whose physical structure is altered by the vapor, e.g., through expansion or disintegration, and electrically conductive elements that are interspersed with or separated by the polymer. The interspersed elements may consist of a fine powder of carbon or of a metal in a matrix of silicone or other vapor-sensitive polymer. The electrical contacts between the powder particles are weakened when the polymer swells or disintegrates, which results in increased resistance. Alternatively, the capacitance between two conductive layers separated by a polymer layer decreases, and hence the impedance increases, when the polymer swells upon exposure to the vapor. In yet another embodiment, the polymer exerts a stress on a piezoresistive element and the stress is increased when the polymer swells, which causes a further increase in resistance. The changes are measured by an impedance-measuring circuit, such as a Wheatstone bridge.

A microcalorimeter includes instrumentation for reducing measurement errors due to system fluctuations. One or more sensors is utilized to detect heat content of a sample gas, and create a composition independent system. Instrumentation for automatically compensating for pressure and temperature variations is also employed in the microcalorimeter. A method for continuously measuring the BTU content of a gas utilizing the microcalorimeter includes steps for adjusting system parameters in response to changes in ambient conditions and sample gas composition to further reduce measurement error.

Microcalorimeter sensor for the measurement of heat content of natural

In solid-state chemical sensors, such as the highly sensitive and selective sensor for the detection of halogenated compounds comprises a bead of sodium lanthanum fluoride silicate, having the molecular formula NaLa.sub.4 (SiO.sub.4).sub.3 F, the performance and lifetime are adversely affected by a build-up of insulating reaction product between two electrodes. To prolong the lifetime, intermittent sensor operation is achieved by applying a voltage between the sensor electrodes during only a small fraction of each measurement cycle and/or by reversing the voltage in successive measurement intervals and/or by switching the connections between additional reserve electrodes and/or by periodically exposing the sensor to chemically filtered air at regular time intervals during a major fraction of each measurement cycle. The response speed and sensitivity of the NaLa.sub.4 (SiO.sub.4).sub.3 F sensor are improved when platinum black is interspersed with or otherwise added to the bead material during the preparation of the sensor. Improved reproducibility and additional sensing capabilities are also achieved by means of a feedback circuit that assures automated temperature constancy of the sensor bead and, at the same time, permits simultaneous estimation of the concentration of both halogen-containing and halogen-free combustible compounds. Provisions for a jump in the sensor temperature and for exposing the sensor to halogen-depleted air at the end of each measurement cycle minimize the effects of baseline drift and thereby yield higher sensitivity and measurement accuracy.

Solid-state chemical sensor apparatus and methods

A relatively inexpensive modular component that can be substituted for, or used in conjunction with, an existing smoke detector in a commercially available residential fire-detection alarm comprises: (A) an amperometric sensor for carbon monoxide, in which the reference and counter electrodes are combined either internally into a single auxiliary electrode or externally by electrical shorting; and (b) a simple current-to-voltage converter circuit that converts the current signals from the sensing electrode into amplified voltage signals. The converter circuit is powered by the same battery (usually a 9-volt dry cell) and is connected to the same alarm-triggering circuit that are used in existing residential fire alarms. The sensor-and-converter module is designed to fit into a commercially available smoke-detector-type fire alarm unit. The electrical output of the module is designed to be compatible with the electrical input requirements of the commercial detection circuitry. An alarm fitted with this module provides early warning of hazardous conditions, such as a smoldering fire, a leaky furnace, or an otherwise heavily polluted atmosphere.

Amperometric carbon monoxide sensor module for residential alarms

An optical waveguide sensor for the detection of acid vapors comprises a chemically sensitive reagent coating of bromothymol blue or thymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562-nm light-emitting diode source and a phototransistor detector. The response to HCl and H.sub.2 S vapors is both rapid and reversible, with an estimated detection limit for H.sub.2 S of less than 15 ppmv (parts per million by volume). The sensor exhibits generalized response to protonic acid vapors, but does not produce an indicator response to CO.sub.2, even at large concentrations (60 volume-%) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a differential approach, either using a reference sensor (Nafion without an indicator) or by monitoring the sensor responses at two wavelengths.

Optical waveguide vapor sensor

A highly sensitive and selective sensor for the detection of halogenated compounds comprises a bead of sodium lanthanum fluoride silicate, having the molecular formula NaLa.sub.4 (SiO.sub.4).sub.3 F, in which are embedded two noble metal electrodes, preferably a straight platinum wire near the center and a helical platinum wire near the periphery of the bead. A current passing through the helical wire maintains the sensor temperature at about 550.degree. C. by resistive heating. The electrical resistance between the two wires is deduced from measurements of the current passing through a fixed external resistor when a substantially constant voltage, preferably about 4 volts, is applied between the wires. A decrease in the measured resistance is an indication of the presence of a halogenated compound in the sample of air to which the bead is exposed. The sensor is preferably controlled by a microprocessor or microcomputer that also performs data processing. This system not only detects a halogenated compound of interest, but also measures its concentration.

Halogenated compounds sensor

A potentiostat for an amperometric sensor uses a voltage-controlled current source (VCCS), which may be either unidirectional or, preferably, bidirectional. An error amplifier compares the potential of the sensor's reference or counter electrode, relative to ground potential, to a set-point potential. The error voltage serves as an input to the VCCS. The output of the VCCS--a current proportional to the error voltage--is supplied to the sensor's auxiliary electrode. In a steady state, the error voltage is just large enough to supply current that is equal to the current through the sensor's working and auxiliary (or counter) electrodes. The error voltage can either serve directly as an output voltage or it can be amplified without introducing a feed-back loop disturbance. The VCCS permits direct grounding of the sensor's working electrode and operation of the error amplifier at a low or moderate gain, so as to increase the circuit's frequency response and reduce the probability of oscillation. Also, in conjunction with an adjustable low-pass filter, the VCCS permits optimization of the system's frequency response so as to yield improved stability.

Potentiostatic apparatus and methods

A method capable of detecting low concentrations of a pollutant or other component in air or other gas, utilizing a combination of a heating filament having a catalytic surface of a noble metal for exposure to the gas and producing a derivative chemical product from the component, and an electrochemical sensor responsive to the derivative chemical product for providing a signal indicative of the product. At concentrations in the order of about 1-100 ppm of tetrachloroethylene, neither the heating filament nor the electrochemical sensor is individually capable of sensing the pollutant. In the combination, the heating filament converts the benzyl chloride to one or more derivative chemical products which may be detected by the electrochemical sensor.

Method for detecting toxic gases

A portable instrument for use in the field in detecting, identifying, and quantifying a component of a sampled fluid includes a sensor which chemically reacts with the component of interest or a derivative thereof, an electrical heating filament for heating the sample before it is applied to the sensor, and modulator for continuously varying the temperature of the filament (and hence the reaction rate) between two values sufficient to produce the chemical reaction. In response to this thermal modulation, the sensor produces a modulated output signal, the modulation of which is a function of the activation energy of the chemical reaction, which activation energy is specific to the particular component of interest and its concentration. Microprocessor which compares the modulated output signal with standard responses for a plurality of components to identify and quantify the particular component of interest. In particular, the concentration of the component of interest is proportional to the amplitude of the modulated output signal, while the identifying activation output energy of the chemical interaction indicative of that component is proportional to a normalized parameter equal to the peak-to-peak amplitude divided by the height of the upper peaks above a base line signal level.

Selective chemical detection by energy modulation of sensors

Selective detection of an analyte in a gaseous mixture is achieved by a chemical, especially amperometric, sensor, that is responsive to the analyte, and a pump-and-valve system, controlled by programmed electronic circuitry, which causes: a) ambient air to pass first through a chemical filter, that removes those air constituents to which the sensor may be responsive, and next through a sorbent-containing tube and the sensor; b) a portion of the gaseous mixture to be first drawn into a sample port and next flushed from the port into the sorbent tube; c) analyte-containing eluent from the sorbent tube to reach the sensor; and d) another mixture component to which the sensor may be responsive to be prevented from reaching the sensor. The sorbent-containing tube has a different retentivity for the analyte than for the other mixture component. The air flow rates and paths can be programmed and the volume of the mixture portion may be auto-ranged to maximize the accuracy of the sensor signals. Speedy analyses of CO in the presence of H.sub.2, of H.sub.2 S in the presence of organosulfur interferences or of other volatiles, such as methanol, methylene chloride or formaldehyde in the presence of interfering compounds of heavier molecular weight are thereby achieved with a portable instrument having improved reliability and relatively low cost.

Sorption separation apparatus and methods

The BTU content of a sample of natural gas is measured using a computer controlled microcalorimeter micro-sensor instrument employing a catalytic sensor. The instrument is portable for in field use and is able to obtain measurement accuracy of better than .+-.1%. A carrier gas, a standard reference gas and the sample gas to be measured are injected in a controlled manner through use of computer controlled solenoid valves and flow control valves, and a measurement loop injects precise gas volumes to enable a highly accurate BTU measurement by the catalytic sensor.

A portable system for analyzing a fluid sample includes a small, portable, low-pressure and low-power chromatographic analyzer and a chemical parameter spectrometry monitor including an array of sensors for detecting, identifying and measuring the concentrations of a variety of components in the eluent from the chromatographic analyzer. The monitor includes one or more operating condition controllers which may be used to change one or more of the operating conditions during exposure of the sensors to the eluent from the chromatography analyzer to form a response pattern which is then compared with a library of previously established patterns. Gas and liquid chromatographic embodiments are disclosed. In the gas embodiment, the operating condition controllers include heated filaments which may convert electrochemically inactive components to electrochemically active products. In the liquid chromatography embodiment, low-power, liquid-phase equivalents of heated filaments are used with appropriate sensors. The library response patterns may be divided into subsets and the formed pattern may be assigned for comparison only with the patterns of a particular subset.

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Naperville, IL, United States of America

Joseph R Stetter