초록 ▼

A dosimeter includes an electrochemical sensing cell and circuitry which provides a first alarm when the contaminant concentration exceeds a short-term exposure limit, and a second alarm when the time weighted average concentration level over a relatively longer term exceeds a different threshold li

A dosimeter includes an electrochemical sensing cell and circuitry which provides a first alarm when the contaminant concentration exceeds a short-term exposure limit, and a second alarm when the time weighted average concentration level over a relatively longer term exceeds a different threshold limit value. In one sensing cell embodiment, the gas sample flows through a circuitous recess on the interior surface of the cell body, which recess is covered by the sensing electrode. A downstream pump urges the gas sample through the cell. In an alternative embodiment, not utilizing a pump, the gas sample enters the cell by diffusing through a sintered porous plate into contact with the sensing electrode. In each cell, the output current is proportional to the contaminant concentration level. To obtain a time weighted concentration level alarm signal, the circuitry employs a frequency converter that produces output pulses at a rate proportional to the cell output current level. These pulses are counted. The alarm signal is produced when the count reaches a value C=LnT, where n is the frequency converter output in pulses per second for a concentration of 1 ppm, T is a certain extended time duration, and L is the threshold limit value.

대표청구항 ▼

An electrochemical sensing cell for use in a dosimeter, comprising: a housing including a body having a planar base and upright sides extending thereform to define an interior region and a lid emplaceable atop said sides to enclose said interior region, a zigzag recess in said base opening into said

An electrochemical sensing cell for use in a dosimeter, comprising: a housing including a body having a planar base and upright sides extending thereform to define an interior region and a lid emplaceable atop said sides to enclose said interior region, a zigzag recess in said base opening into said interior region, together with a pair of openings through said body at the respective ends of said recess, said openings serving respectively as inlet and outlet ports for the flow of gas through said cell, a generally planar sensing element disposed in said body interior region atop said base, gas entrant to the cell through said inlet port flowing throgh said zigzag recess in contact with said sensing electrode along substantially the entire length of said recess, said gas then exiting through said outlet port, a reference electrode and an electrolyte also disposed within said interior region, the electrical current developed across said sensing and reference electrodes in the presence of a certain contaminant in said gas being indicative of the concentration of that contaminant in the gas, an annular seal between said base and said sensing electrode and surrounding said zigzag recess, said seal limiting the flow of gas between said base and said sensing electrode to within a perimeter defined by said seal, and a flow channel extending from said inlet port along the exterior of said base and thence through at least one of said walls and through said lid, gas thereby being supplyable to said recess via said channel from a location atop said lig. A dosimeter comprising: an electrochemical sensing cell and means for enabling the entry of a gas sample into said sensing cell, the current from said cell indicating the concentration of a certain contaminant species in said gas sample, a “high level”alarm circuit means, connected to said cell, for providing a first alarm signal when the current from said cell indicates that the present concentration of said certain contaminant species exceeds a first threshold limit value, and a “time weighted average”alarm circuit means, also connected to said cell and operative over a certain extended time duration, for providing a second alarm signal when the current from said cell, effectively integrated over a time interval less than or equal to said certain duration, indicates that the time weighted average concentration level of said contaminant species has exceeded a second threshold limit value during that interval, said “time weighted average”alarm circuit means including: a frequency converter, cooperatively connected to said cell, for providing an output pulse signal having a frequency proportional to the current from said cell, and a counter connected to count the pulses from said frequency converter, said second alarm signal being produced when the count of said counter reaches a preset value within said certain extended time duration.