Determining the partial pressure of a gas in a pressure vessel

Abstract

There is disclosed a method and system for determining the partial pressure of at least one gas in a mixture of gasses contained in a pressure vessel, in particular a pressure vessel in the form of a life support pressure chamber/decompression chamber, or a diving gas storage cylinder. The method comprises the steps of: coupling a gas analysis sensor (14) to a pressure vessel (10); directing a portion of the mixture of gasses in the pressure vessel to the sensor for analysis; reducing the pressure of the portion of the mixture which is to be analyzed by the sensor to a level which is below the pressure in the vessel but above local atmospheric pressure; operating the sensor to measure the partial pressure of the at least one gas at the reduced pressure level; and using the partial pressure of the at least one gas, measured at the reduced pressure level, to determine the actual partial pressure of said gas in the mixture contained in the vessel.

1 . A gas analysis system for a pressure vessel, for determining the partial pressure of at least one gas in a mixture of gasses contained in the pressure vessel, the mixture being pressurised to above local atmospheric pressure, in which the system comprises:
 a gas analysis sensor which can be coupled to the pressure vessel so that a portion of the mixture of gasses in the pressure vessel can be directed to the sensor for analysis; and   a pressure control device for reducing the pressure of the portion of the mixture which is to be analysed by the sensor;   in which the system is configured such that, in use:
 the pressure control device is arranged to reduce the pressure of the portion of the mixture to a level which is below the pressure in the vessel but above local atmospheric pressure; and 
 the sensor is arranged to measure the partial pressure of the at least one gas at the reduced pressure level, so that the partial pressure of the at least one gas measured at the reduced pressure level can be employed to determine the actual partial pressure of said gas in the mixture contained in the vessel. 
   
     
     
         2 . A system as claimed in  claim 1 , comprising a processor which is configured:
 to control the pressure control device so that it reduces the pressure of the portion of the mixture to said level; and   to control the sensor is arranged to measure the partial pressure of the at least one gas at the reduced pressure level, so that said partial pressure can be employed to determine said actual partial pressure.   
     
     
         3 . A system as claimed in  claim 1 , in which the sensor is locatable outside the vessel, and in which the system is arranged so that the portion of the mixture to be analysed is directed out of the vessel to the sensor. 
     
     
         4 . A system as claimed in  claim 1 , in which the pressure control device is arranged to reduce the pressure of the portion of the mixture prior to supply of said portion to the sensor. 
     
     
         5 . A system as claimed in  claim 1 , in which the pressure control device is arranged to provide an output at a predetermined pressure level. 
     
     
         6 . A system as claimed in  claim 1 , in which the pressure control device is provided integrally with the sensor. 
     
     
         7 . A system as claimed in  claim 1 , comprising a flow control device for controlling a rate of flow of the portion of the mixture through the sensor. 
     
     
         8 . A system as claimed in  claim 7 , in which the flow control device is arranged to throttle the flow of the mixture upstream of the sensor, and in which the system comprises a back-pressure regulator positioned downstream of the flow control device, for controlling a pressure of the portion of the mixture analysed by the sensor. 
     
     
         9 . A system as claimed in  claim 7 , in which the flow control device is arranged to throttle the flow of the mixture downstream of the sensor. 
     
     
         10 . A system as claimed in  claim 1 , comprising a processor for determining the actual partial pressure of said gas by multiplying the measured pressure at the reduced pressure level by the ratio of the pressure in the vessel relative to the reduced pressure level. 
     
     
         11 . A pressure vessel comprising the gas analysis system of  claim 1 . 
     
     
         12 . A pressure vessel as claimed in  claim 11 , in which the pressure vessel is a life support pressure chamber which is operable to maintain the pressure of the mixture at a substantially constant pressure over a determined period of time. 
     
     
         13 . A pressure vessel as claimed in  claim 12 , in which the pressure chamber is a decompression chamber, in which the pressure of the mixture of gasses in the chamber can be reduced over time in a controlled fashion, employing the determined partial pressure data. 
     
     
         14 . A pressure vessel as claimed in  claim 11 , in which the pressure vessel is a diving gas storage cylinder.