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Method and apparatus for measuring a parameter of a gas in isolation from gas pressure fluctuations

  • US 5,325,861 A
  • Filed: 11/23/1992
  • Issued: 07/05/1994
  • Est. Priority Date: 04/12/1989
  • Status: Expired due to Term
First Claim
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1. In a system for measuring oxygen concentration of a test gas, the system including a source of the test gas, a sensor having a substantially linear response to said oxygen concentration in a first desired pressure range and a non-linear response to said oxygen concentration in a second pressure range, said sensor being connected in selective fluid communication with and downstream from the source of the test gas for measuring the oxygen concentration of the test gas, and pump means in fluid communication with the sensor to draw the test gas from the source of the test gas into the sensor, an improvement for isolating the sensor from fluctuations in the pressure of the test gas and maintaining the pressure of the test gas substantially in said first desired pressure range for measuring the oxygen concentration, the improvement comprising:

  • a storage capacitor upstream from the sensor in fluid communication therewith and operative to store a quantity of gas;

    a source of an alternate gas having an essentially constant pressure;

    fluid flow control means for isolating the storage capacitor and the sensor from any fluctuations in the pressure of the test gas while said oxygen concentration is being measured, said fluid flow control means having a first fluid flow path connectable between said storage capacitor and said source of the test gas, and a second fluid flow path connectable between said storage capacitor and said source of alternate gas, the fluid flow control means being switchable between a first setting opening the first fluid flow path for the test gas into the storage capacitor and a second setting closing said first flow path and opening the second fluid flow path between the storage capacitor and the alternate gas source;

    indicator means in electrical communication with said sensor for providing an output signal representing the measurement of the oxygen concentration; and

    timing control means in electrical communication with said fluid flow control means and said indicator means for controlling said indicator means to provide said output signal only when the pressure of the test gas in the sensor is held constant, said timing means including means for controlling said fluid flow control means to open the first fluid path to fill said storage capacitor and said sensor with said test gas, and to close said first fluid path and open said second fluid flow path when said storage capacitor and said sensor are filled with said test gas to hold the pressure of the test gas constant during measurement of said oxygen concentration.

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