Method and apparatus for measuring a parameter of a gas in isolation from gas pressure fluctuations
First Claim
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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Abstract
In measuring a selected parameter of a test gas in isolation from gas pressure fluctuations, a pump draws the test gas through a storage capacitor into a sensor, storing the gas in the storage capacitor. A valve closes a fluid flow path which admits the test gas to the storage capacitor and opens a fluid flow path between the storage capacitor and a constant pressure alternate gas source, isolating the storage capacitor and the sensor from pressure fluctuations in the test gas. The storage capacitor prevents any mixing of the test gas with the alternate gas until measurement of the selected parameter has been accomplished.
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Citations
14 Claims
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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:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. Apparatus for measuring oxygen concentration of a test gas obtained from a source under substantially constant pressure conditions, the apparatus comprising:
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a sensor operative to measure the oxygen concentration, said sensor having anon-linear response; pumping means downstream form the sensor and in fluid communication therewith operative to draw the test gas from said source of the test gas into the sensor for measurement of the oxygen concentration; means for damping fluctuations in pressure in said test gas at said sensor due to said pumping means downstream from said sensor, said means for damping including a first enlarged chamber connected for fluid communication with said pumping means, a second enlarged chamber connected for fluid communication with said sensor, and an elongated constrictor channel for establishing a resistor fluid flow path connected for fluid communication between said first and second enlarged chambers; a storage capacitor upstream from the sensor and 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, said 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, the storage capacitor allowing mixing of the test gas in the storage capacitor while the oxygen concentration is not being measured, and preventing any substantial mixing of the alternate gas with the stored test gas for a sufficient time to enable the sensor to measure the oxygen concentration of the test gas under essentially constant pressure conditions; indicator means in electrical communication with said sensor for providing an output signal representing the measure 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 ti 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. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification