Method and apparatus for monitoring gas concentration

A probe for measuring a concentration of a gas in solution in a fluid medium, comprising;

• a measurement chamber defined within the probe;
• a porous wall portion for, in use, contacting the fluid medium such that the gas but not the fluid medium can pass through the porous wall portion into the measurement chamber;
• a sensor in the measurement chamber or extending into the measurement chamber for measuring a concentration of the gas in the measurement chamber;
• and
• a calibration-gas feed connected to the measurement chamber and couplable, in use, to a source of a calibration gas for supplying the calibration gas to the measurement chamber and, optionally, through the porous wall portion, outwardly from the measurement chamber.

A probe for sensing a concentration of a gas in solution in a fluid medium, comprising;

• a measurement chamber defined within the probe;
• a porous wall portion for, in use, contacting the fluid medium such that the gas but not the fluid medium can pass through the porous wall portion into the measurement chamber;
• an electrolytic sensor for measuring a concentration of the gas in the measurement chamber;
• and
• a heater for heating the electrolytic sensor.

A probe for sensing a concentration of a gas in solution in a fluid medium, comprising;

• a measurement chamber defined within the probe;
• a porous wall portion for, in use, contacting the fluid medium such that the gas but not the fluid medium can pass through the porous wall portion into the measurement chamber;
• and
• an electrolytic sensor for measuring a concentration of the gas in the measurement chamber;
• in which the electrolytic sensor comprises a measurement electrode and a reference electrode on opposite surfaces of a solid electrolyte, and the probe comprises an electrical connection for coupling a voltage between the measurement electrode and the reference electrode during storage of the probe.

A method for measuring a concentration of a measurand gas in solution in a fluid medium, comprising the steps of;

• supplying a purge gas to the measurement chamber such that a portion of the purge gas is forced out of the measurement chamber through the porous wall portion and such that the measurement chamber is filled with the purge gas;
• closing a supply of the purge gas and allowing a sampling time to pass, during which time the measurand gas can pass through the porous wall portion into the measurement chamber;
• and
• measuring a concentration, or partial pressure, of the measurand gas in the measurement chamber.