Gas detector unit

• US 3,909,386 A
• Filed: 09/11/1972
• Issued: 09/30/1975
• Est. Priority Date: 11/10/1970
• Status: Expired due to Term

• Current Assignee: National Draeger, Inc. (FPS Vermögensverwaltung GmbH)
• Original Assignee: Harry G. Oswin, Howard W. Bay
• Inventors: Oswin, Harry G., Bay, Howard W.
• Primary Examiner(s): Tung, T.
• Application Number:
  US05/287,806
• Time in Patent Office: 1,114 Days
• Field of Search: 204/1T,195R,195P 323/68
• US Class Current: 204/408
• CPC Class Codes: G01N 27/4045 for gases other than oxygen

Abstract

An electrochemical device for detecting and quantitatively measuring a select gas in a gaseous medium which includes an electrochemical cell comprising a working electrode, a counterelectrode, and an electrolyte which is independent of, or unaffected by temperature and humidity changes is described. The device incorporates temperature-compensating circuitry comprising thermistors which automatically and simultaneously adjusts for both the zero (signal output when the gas being detected is not present) and span (signal output when the gas being detected is present) changes as a result of variation in temperature. The described device compensates for humidity change through use of a relatively large, predetermined electrolyte volume in contact with the working electrode of the cell. The device provides accurate readings under all temperature and humidity conditions.

Claims

1. A GAS DETECTING AND MEASURING UNIT FOR DETECTING AND QUANTITATIVELY MEASURING A GAS IN A GASEOUS MEDIUM COMPRISING IN COMBINATION INTAKE MEANS, AN ELECTROCHEMICAL CELL MEANS FOR DRAWING A GAS THROUGH SAID INTAKE MEANS AND INTO SAID ELECTROCHEMICAL CELL AT A CONTROLLED FLOW RATE, READOUT MEANS FOR READING THE QUANITITY OF SAID DETECTED GAS, AND AN ELECTRONIC CIRCUIT COMPRISING TWO THERMISTORS, BOTH SAID THERMISTORS BEING ARRANGED WITH SAID CELL TO SENSE THE TEMPERATURE OF SAID CELL, ONE THERMISTOR COMPENSATING CHANGE IN BACK GROUND CURRENT WITH TEMPERATURE AND THE OTHER COMPENSATING CHANGE IN SPAN WITH TEMPERATURE, SAID CIRCUIT AUTOMATICALLY ADJUSTING FOR BACKGROUND AND SPAN FOR ANY CHANGE IN TEMPERATURE SENSED BY SAID THERMISTORS, WHEREBY SAID CELL PROVIDES A SUBSTANTIALLY CONSTANT SIGNAL FOR A GIVEN VOLUME OF SAMPLE AT VARYING TEMPERATURES.

2. The gas detecting and measuring unit of claim 1 wherein said cell comprises a working electrode, a counterelectrode, and an electrolyte in contact with said working electrode and said counterelectrode;

the electrolyte volume being sufficiently large in relation to the surface area of said working electrode to substantially nullify, the effect of any change in electrolyte volume due to a change in humidity, whereby said cell provides a substantially constant signal for a given volume of sample at varying temperatures and humidities.

3. The gas detecting and measuring unit of claim 2 wherein the electrolyte of said cell is contained in an electrolyte chamber, said chamber having a larger cross-section than the cross-section of said working electrode.

4. The gas detecting and measuring unit of claim 1 wherein said electrochemical cell comprises a housing, an anode, a cathode, and an electrolyte between said anode and said cathode, said housing comprising a first end plate, a second end plate, and a central section, said central section forming an electrolyte chamber for said electrolyte, said electrolyte chamber having a greater cross-sectional area than the cross-sectional area of at least one of said anode and cathode, said anode and cathode being sealed to one of said central sections or end plates;

said cell being tied together by suitable means, and having first and second O-rings providing redundant seals, said first O-ring being inward of said first-mentioned seal and said second O-ring being external of said first-mentioned seal.

5. The gas detecting and measuring unit of claim 4 wherein the electrodes comprise a hydrophobic polymer substrate and a catalytic layer on a section of said substrate to form the active electrode working surfaces, said substrate being sealed to said central section or end plates, and said O-rings being outward of said catalytic area.