Personnel-carried dosimeter

• US 4,297,689 A
• Filed: 01/08/1980
• Issued: 10/27/1981
• Est. Priority Date: 01/08/1980
• Status: Expired due to Term

• Current Assignee: Interscan Corp.
• Original Assignee: Interscan Corp.
• Inventors: Thatcher, Imbrie, Shaw, Manuel
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US06/110,359
• Time in Patent Office: 658 Days
• Field of Search: 204/195 R, 204/1 T, 204/1 K, 204/195 P, 340/632, 340/633, 340/634
• US Class Current: 340/632
• CPC Class Codes: G01N 27/4045 for gases other than oxygen
• CPC Class Codes: G01N 33/0065 using more than one threshold

Abstract

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.

Claims

1. 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.

2. A dosimeter contained in a package and comprising:

an electrochemical sensing cell according to claim 1, said sensing cell being mounted within said package with the lid of said cell adjacent an exterior wall of said package, there being an opening through said package wall communicating to said channel for the inlet flow of gas from outside said package into said cell,

a pump mounted within said package and connected to said outlet port by a tube, operation of said pump causing a gas sample to be measured by said dosimeter to enter said sensing cell through said inlet port, to flow through said zigzag recess and thence out through said outlet port and pump, and

circuit means, contained within said package and responsive to said current from said cell, for providing respective alarm signals when the short-term or time weighted average long term contaminant concentration exceeds respective threshold limit values.

3. An electrochemical sensing cell for use in a dosimeter, comprising:

a housing including a body having a planar base and upright sides extending therefrom to define an interior region and a lid emplaceable atop said sides to enclose said interior region,

an opening in said base, and a porous plate of sintered polymer covering said opening, said base having only a relatively narrow peripheral portion, said opening comprising the remainder of said base,

a generally planar sensing element disposed in said body interior region atop said base, gas being entrant into said cell by diffusion through substantially the entire area of said plate into contact with said sensing electrode,

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 peripheral portion and said sensing electrode and surrounding said porous plate, said seal preventing the flow of diffused gas from the region between said porous plate and said sensing electrode to the remainder of the cell interior region,

a planar, electrically conductive contact situated between a portion of said seal and said sensing electrode,

a first electrical wire extending through said body and electrically bonded to said planar contact, said sensing electrode pressing against said planar contact in said cell so that electrical current flow from said sensing electrode is via said planar contact and the associated electrical wire, and

a second electrical wire extending through said body into connection with said reference electrode.

4. An electrochemical sensing cell according to claim 3 wherein said sensing electrode comprises particulate platinum bonded together in a plastic matrix, wherein said planar contact is platinum, wherein said reference electrode is lead, and wherein said electrolyte is dilute sulfuric acid.

5. An electrochemical sensing cell according to claim 3 wherein said reference electrode is planar and is disposed atop and separated from said sensing electrode by a fibrous layer, together with additional fibrous layers disposed within said body interior region between said reference electrode and said lid, there being sufficient such layers so as to provide pressure against said reference electrode and said sensing electrode when said lid is emplaced, said pressure maintaining said sensing electrode in electrical contact with said planar contact, said fibrous layers all being impregnated with said electrolyte.

6. 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.

7. A dosimeter according to claim 6 wherein:

said frequency converter provides n pulses per second for a concentration of one part per million of said certain contaminant species, wherein said certain extended time duration is T seconds, wherein said second threshold limit value is L parts per million, and wherein said "time weighted average" alarm circuit produces said second alarm signal when said counter reaches a count C=LnT.

8. A dosimeter according to claim 6 wherein said "high level" alarm comprises:

a comparator, one input of said comparator being a signal proportional to the current from said cell, and

alarm level setting means for providing a settable reference signal to the other input of said comparator, said reference signal being set at a level so that said current proportional signal will exceed said set reference signal level, and thereby cause said comparator to provide a certain output, when the concentration of said contaminant species exceeds said first threshold limit level, said first alarm signal being produced in response to occurrence of said comparator certain output.

9. A dosimeter according to claim 6 and contained in a case, said dosimeter further having an audible alarm that is actuated in response to the occurrence of either of said first and second alarm signals, and having separate visual indicators independently respectively actuated by said first and second alarm signals.

10. A dosimeter comprising:

an electrochemical sensing cell which produces an output signal that is proportional in level to the concentration of a contaminant species in a gas sample, and

an alarm circuit for producing an alarm signal when the time weighted average concentration level of said contaminant species over a certain extended time duration exceeds a threshold limit value, said alarm circuit including;

a frequency converter, cooperatively connected to said cell, for providing output pulses having a frequency proportional to the signal level from said sensing cell, and

a counter connected to count the pulses from said frequency converter, said alarm signal being produced when said counter reaches a preestablished count value within a time interval less than or equal to said certain extended time duration.

11. A circuit according to claim 10 wherein:

said frequency converter provides n pulses per second for a concentration of one part per million of said contaminant species, wherein said certain extended time duration is T seconds, wherein said threshold limit value is L parts per million, and wherein said alarm circuit produces said alarm signal when said counter reaches a preestablished count value C=LnT.

12. A circuit according to claim 10 further comprising:

means for modifying said counter so as to set said preestablished count value.

13. A circuit according to claim 12 wherein said counter comprises a first counter of adjustable modulo in cascade with a second counter of fixed modulo, the modulo of said first counter being set by said means for modifying.

14. A dosimeter comprising:

an electrochemical sensing cell which produces an output signal having a level that is indicative of the concentration of a contaminant species in a gas sample,

a frequency converter, cooperatively connected to said cell, for providing output pulses having a frequency proportional to the signal level from said sensing cell,

counter means, connected when enabled to count output pulses from said frequency converter,

timing means for enabling counting by said counter means in consecutive time intervals, each of fixed length, during an extended time duration,

memory means, cooperating with said counter means and said timing means, for storing in separate storage locations the count reached by said counter means in each of said respective consecutive time intervals, the contents of said memory storage locations thereby representing a history of the time weighted average concentration levels of said contaminant species over said consecutive time intervals,

said electrochemical sensing cell including;

a housing including a body having a planar base and upright sides extending therefrom to define an interior region and a lid emplaceable atop said sides to enclose said interior region,

an opening in said base, and a porous plate of sintered polymer covering said opening,

a generally planar sensing element disposed in said body interior region atop said base, gas being entrant into said cell by diffusion through substantially the entire area of said plate into contact with said sensing electrode, and

a reference electrode and an electrolyte also disposed within said interior region, said output signal being an electrical current developed across said sensing and reference electrodes in the presence of said contaminant species.

15. A personnel-carried 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 sample,

a frequency converter, cooperatively connected to said cell, for providing output pulses having a frequency proportional to the current from said sensing cell,

counter means for counting, when enabled, the output pulses from said frequency converter,

timing means for enabling counting by said counting means during consecutive time intervals each of a fixed duration, and

memory means, cooperating with said counter means and said timing means, for storing in separate storage locations the count reached by said counter means in each of said respective consecutive time intervals, the contents of said memory storage locations thereby representing a history of the time weighted average concentration levels of said contaminant species over said consecutive time intervals.

16. A dosimeter according to claim 15, together with:

readout means, external to said dosimeter but connected thereto, for reading out the contents of said separate storage locations, thereby to recover said history.

17. A dosimeter comprising:

an electrochemical sensing cell which produces an output signal having a level that is indicative of the concentration of a contaminant species in a gas sample,

a frequency converter, cooperatively connected to said cell, for providing output pulses having a frequency proportional to the signal level from said sensing cell,

counter means, connected when enabled to count output pulses from said frequency converter,

timing means for enabling counting by said counter means in consecutive time intervals, each of fixed length, during an extended time duration,

memory means, cooperating with said counter means and said timing means, for storing in separate storage locations the count reached by said counter means in each of said respective consecutive time intervals, the contents of said memory storage locations thereby representing a history of the time weighted average concentration levels of said contaminant species over said consecutive time intervals,

said electrochemical sensing cell including;

a housing including a body having a planar base and upright sides extending therefrom 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 through said circuitous recess in contact with said sensing electrode along substantially the entire length of said recess, said gas then exiting through said outlet port, and

a reference electrode and an electrolyte also disposed within said interior region, said output signal being an electrical current developed across said sensing and reference electrodes in the presence of said certain contaminant species.