Portable measuring apparatus for determining the oxygen content of a gas, in particular of an air mixture in a mine working

Claim 1

PORTABLE MEASURING APPARATUS FOR DETERMINING OR COMPARING THE OXYGEN CONTENT OF GASES, COMPRISING: A GAS CHAMBER; MEANS TO ESTABLISH A NON-HOMOGENEOUS MAGNETIC FIELD IN SAID CHAMBER; MEANS FOR FEEDING TO SAID CHAMBER A GAS WHOSE OXYGEN CONTENT IS TO BE DETERMINED; MEANS FOR FEEDING A COMPARISON GAS TO SAID CHAMBER; A MAIN GAS FLOW SYSTEM COMMUNICATING WITH SAID CHAMBER ADAPTED FOR THE FLOW OF GAS THEREIN IN RESPONSE TO PRESSURE DIFFERENCE OCCURRING BETWEEN SAID FIRST-MENTIONED GAS AND SAID REFERENCE GAS UNDER THE INFLUENCE OF SAID MAGNETIC FIELD; A SECONDARY GAS FLOW SYSTEM ARRANGED IN PARALLEL WITH THE SAID MAIN SYSTEM A SYMMETRICAL BRIDGE CIRCUIT INCLUDING FIRST THERMAL FLOWMEASURING MEANS IN SAID MAIN GAS FLOW SYSTEM AND SECOND THERMAL FLOW-MEASURING MEANS IN SAID SECONDARY SYSTEM; AND ADJUSTING MEANS FOR ADJUSTING THE FLOW RESISTANCE OF SAID SECONDARY GAS FLOW SYSTEM, SAID BRIDGE CIRCUIT BEING EFFECTIVE TO INDICATE DIFFERENCE IN OXYGEN CONTENT BETWEEN SAID FIRST-MENTIONED GAS AND SAID COMPARISON GAS GIVING RISE TO GAS FLOW IN SAID MAIN GAS FLOW SYSTEM.