CARBON DIOXIDE INDICATING METER

• US 3,720,093 A
• Filed: 12/03/1970
• Issued: 03/13/1973
• Est. Priority Date: 12/03/1970
• Status: Expired due to Term

• Current Assignee: George Herbert Gill
• Original Assignee: George Herbert Gill
• Inventors: Gill, George Herbert
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US05/094,660
• Time in Patent Office: 831 Days
• Field of Search: 73/27
• US Class Current: 73/25.03
• CPC Class Codes: G01N 27/185 using a catharometer

Abstract

A pair of thermistors isolated from one another in a detector housing, are responsive to a gas sample and a reference sample to vary their impedances as a result of the different thermal conductivities of the gases. Varying the impedances unbalances a resistance bridge circuit to provide a signal representative of the percentage concentration of carbon dioxide in the gas sample. Humidifying the gas sample to a predetermined magnitude equaling the relative humidity of the reference gas, providing a spacious heat sink for maintaining the gas sample and reference sample at the same temperature, and providing baffles for preventing the direct impingement of the gas sample onto a thermistor greatly ensures a reliable, accurate determination of CO2 concentration. Including operational amplifier circuits, having linear characteristics, and packaging the detector to minimize the effects of vibration and shock greatly increase reliability over contemporary devices.

Claims

1. An apparatus for rapidly indicating CO2 concentration within a submersible by comparing the known thermal conductivity of a reference gas to the unknown thermal conductivity of a gas sample taken from the enclosure comprising:

a humidifier block connected to receive said gas sample having a wetted longitudinal duct for raising the humidity of said gas sample to a near saturation level;

a gas impeller joined to said humidifier block for ensuring the transfer of said gas sample;

a detector housing connected to said gas impeller shaped with a lateral passageway for receiving and transferring said gas sample, a cavity communicating with said passageway for receiving said gas sample, said passageway and said cavity cooperating to define a T-shaped cross-sectional area for allowing a free access to said gas sample, and a chamber containing said reference gas being disposed opposite said cavity outside of said passageway, said detector housing being constructed of a highly thermally-conductive material to maintain said gas sample and said reference gas at substantially the same temperature;

an orifice member mounted in said lateral passageway downstream from said cavity for restricting the flow of said gas sampled therethrough and for reducing gas flow turbulence in said cavity;

a first and second thermistor responsive To temperature changes to proportionally change their impedances mechanically disposed in said cavity and said chamber, respectively, and a screenlike mesh for blocking the direct impingement of said gas sample on said first thermistor, said first and second thermistors providing a sample impedance and a reference impedance, respectively;

a bridge circuit electrically coupling said first and second thermistor into two of its legs;

a potential source coupled to said first and second thermistor to preset the magnitude of said sample impedance and said reference impedance; and

an amplifier-readout circuit including an operational amplifier suitably connected for minimizing drift providing a visual and audio readout connected across said bridge circuit for receiving a signal representative of the difference of the potential drop across said sample impedance with respect to the potential drop across said reference impedance, the potential drops being attributed to the difference in cooling capacity of said gas sample with respect to said reference gas to indicate said CO2 concentration.