Method of controlling an oxygen analyzer of the Hersch galvanic type

• US 6,024,922 A
• Filed: 07/25/1996
• Issued: 02/15/2000
• Est. Priority Date: 01/26/1994
• Status: Expired due to Term

• Current Assignee: Osaka Sanso Kogyo Ltd. (Air Liquide SA)
• Original Assignee: Osaka Sanso Kogyo Ltd. (Air Liquide SA)
• Inventors: Matsumoto, Yoshiro, Tanaka, Yoshiyasu
• Primary Examiner(s): Scheiner, Laurie
• Assistant Examiner(s): PARKIN, JEFFREY S
• Application Number:
  US08/682,607
• Time in Patent Office: 1,300 Days
• Field of Search: 73/865.9, 73/23, 73/198, 73/714, 98/1.5
• US Class Current: 422/82.04
• CPC Class Codes: G01N 33/0011 Sample conditioning in general G01N1/28

Abstract

The claimed invention provides an improved oxygen analyzer of the Hersch galvanic type that is suitable for measuring oxygen concentrations of 1 part per million (ppm) or less in a feed gas, as well as, methods of regulating said analyzer. Modifications have been made to the instrument, or its attendant supporting structures, that reduce or eliminate problems associated with the back flow of gas due to pressure differences between pipes for entrance and egress gases, problems associated with dead zones in the apparatus, or problems associated with dissolved oxygen present in water supplied to the detector. These problems have been addressed by modifying the instrument and its attendant structures, inter alia, to include a bypass pipe coupling between a pipe for gas supply to a detector and a pipe at gas outlet, including a check valve halfway between said bypass coupling, and providing means for detecting the pressure differential between a gas supply pipe and gas outlet pipe. Methods for regulating the flow of atmospheric oxygen into the analyzer, regulating the water level in the analyzer, and performing automatic zero and gain adjustments are also provided.

Claims

1. An oxygen analyzer of the Hersch galvanic type for detecting an oxygen concentration of 1 ppm or less in a feed gas, said analyzer comprising:

a detector comprising electrodes in a solution containing an electrolyte, whereby oxygen in a feed gas to the detector contacts the solution and undergoes a chemical reaction with one of said electrodes to form ions in the solution, the resulting ions migrating through the electrolyte solution to another of said electrodes and reacting therewith to produce an electric current between said electrodes, said current corresponding to the oxygen concentration of said feed gas;

a supply pipe having a valve to supply said feed gas to said detector;

an outlet pipe having a valve for discharging gas from said detector;

a bypass pipe extending between said supply pipe and said outlet pipe;

a check valve in said bypass pipe for regulating gas flow through said bypass pipe and preventing back flow of electrolyte into the gas supply pipe; and

a detector for detecting the pressure difference between said supply pipe and said outlet pipe.

2. A method of controlling the flow of atmospheric oxygen into an oxygen analyzer of the Hersch galvanic type for analyzing an oxygen content of a feed gas having an oxygen content of 1 ppm or less, said analyzer comprising:

a detector having electrodes in a solution containing an electrolyte, whereby oxygen in said feed gas contacts the solution and undergoes a chemical reaction with one of said electrodes to form ions in the solution, the resulting ions rating through the electrolyte solution to another of said electrodes and reacting therewith to produce an electric current between said electrodes, said electric current corresponding to the oxygen content of said feed gas;

a supply pipe having a valve for supplying said feed gas to said detector; and

an outlet pipe in a valve for discharging gas from said detector said method comprising the steps of

closing said valve on the outlet pipe and, immediately thereafter closing said valve on said supply pipe during shutdown of said analyzer to prevent back flow of atmospheric oxygen into said detector, and resuming the supply of a gas, by the steps of first opening the valve on said outlet pipe and then opening the valve on the supply pipe.

3. An oxygen analyzer of the Hersch galvanic type for analyzing a feed gas having an oxygen concentration of 1 ppm or less, said analyzer comprising:

a detector having electrodes in a solution containing an electrolyte whereby oxygen in a feed gas to the detector contacts the solution and undergoes a chemical reaction with one of said electrodes to form ions in the solution, the resulting ions migrating through the electrolyte solution to another of said electrodes and reacting therewith to produce an electric current between said electrodes, said electric current corresponding to the oxygen concentration of said feed gas;

a supply pipe for supplying said feed gas to said detector;

an outlet pipe for discharging gas from said detector; and

a combination valve comprising a directional control valve for supplying an analyte gas to a purifier or to said detector and a check valve in said bypass pipe for supplying said feed gas to said detector and preventing the back flow of electrolyte into said gas supply pipe.

4. A method of controlling the water level in an oxygen analyzer of the Hersch galvanic type for analyzing an oxygen content of a feed gas having an oxygen concentration of 1 ppm or less, said analyzer comprising:

a detector having electrodes in a solution containing an electrolyte whereby oxygen in said feed gas contacts the solution and undergoes a chemical reaction with one of said electrodes to form ions in the solution, the resulting ions migrating through the electrolyte solution to another of said electrodes and reacting therewith to produce an electric current between said electrodes, said electric current corresponding to the oxygen concentration of said feed gas;

a supply pipe having a valve for supplying said feed gas to said detector;

an outlet pipe having a valve for discharging gas from said detector;

a sensor for detecting the liquid level of said electrolyte solution in said detector;

a water tank connected to said detector;

a supply pipe for supplying water from a water tank to said detector;

an outlet valve on said water tank operatively coupled to said sensor, said method comprising sensing a liquid level in said detector below a predetermined level in said detector, and

activating said outlet valve to supply water from said water tank to said detector to replenish said water to said predetermined level in said detector, and

closing said outlet valve upon replenishment of water to said predetermined level.

5. An oxygen analyzer of the Hersch galvanic type for analyzing the oxygen content of a feed gas having an oxygen concentration of 1 ppm or less, said analyzer comprising:

a detector comprising electrodes in a solution containing an electrolyte whereby oxygen in a feed gas to the detector contacts the solution and undergoes a chemical reaction with one of said electrodes to form ions in the solution, the resulting ions migrating through the electrolyte solution to another of said electrodes and reacting therewith to produce an electric current between said electrodes, said electric current corresponding to the oxygen concentration of said feed gas;

a supply pipe having a valve for supplying a feed gas to said detector;

an outlet pipe having a valve for discharging said gas from said detector;

a sensor for detecting the liquid level of said solution in the detector;

a water tank coupled to said detector;

a supply pipe for supplying water from said water tank to said detector;

an outlet valve on said water tank operatively associated with said sensor and being actuated by said sensor when said sensor senses a liquid level in said detector below a specified level for replenishing said detector with water to said specified level.

6. An oxygen analyzer of the Hersch galvanic type for analyzing the oxygen content of a feed gas having an oxygen concentration of 1 ppm or less, said analyzer comprising

a detector comprising electrodes in a solution containing an electrolyte whereby oxygen in a feed gas to the detector contacts the solution and undergoes a chemical reaction with one of said electrodes to form ions in the solution, the resulting ions migrating through the electrolyte solution to another of said electrodes and reacting therewith to produce an electric current between said electrodes, said electric current corresponding to the oxygen concentration of said feed gas;

a supply pipe having a valve for supplying a feed gas to said detector;

an outlet pipe having a valve for discharging said gas from said detector;

a sensor for detecting electrolyte level in said detector;

a water tank connected to said detector;

an oxygen impermeable pipe for supplying water from said water tank to said detector;

an outlet valve on said water tank coupled to said sensor and being actuated when said electrolyte level in said detector is below a predetermined level.

7. A method for performing automatic zero and gain adjustments in a Hersch type oxygen analyzer comprising a detector comprising electrodes in a solution containing an electrolyte, whereby oxygen in a feed gas to the detector contacts the solution and undergoes a chemical reaction with one of said electrodes to form ions in the solution, the resulting ions migrating through the electrolyte solution to another of said electrodes and reacting therewith to produce an electric current between said electrodes, said current corresponding to the oxygen concentration of said feed gas;

a supply pipe having a valve to supply said feed gas to said detector;

an outlet pipe having a valve for discharging gas from said detector;

said method comprising the steps of

freeing the gas to be measured of oxygen with a purifier to thereby prepare a zero gas and supplying the zero gas to the detector for measurement, wherein freeing of oxygen is carried out until the difference between maximal and minimal values of detection of oxygen concentration within a specified time becomes smaller than a specified value relative to a full scale, thereby performing zero adjustment; and

mixing said zero gas with a gas produced by electrolysis of water thereby preparing a gas for gain adjustment, and supplying said gain gas to the detector for measurement, which is carried out until the difference between maximal and minimal valves of detection of oxygen concentration within a specified time becomes smaller than a specified value relative to full scale, thereby performing gain adjustment.