A gas detection system includes a gas sensor, and a filter unit. The gas sensor is configured to detect detection target molecules. The filter unit is disposed at a reference gas supply passage. The reference gas supply passage connects a reference gas inlet port from which a reference gas is introduced, and a sensor chamber in which the gas sensor is housed. The filter unit includes at least a first filter configured to reduce the detection target molecules in the reference gas, and a second filter configured to reduce moisture in the reference gas. Each of the first filter and the second filter has a separation membrane including hollow fibers.

A method of using mass and force indicators in electrochemical gas sensor management is provided. The method includes measuring a change in mass of an electrochemical gas sensor and determining a status of the electrochemical gas sensor based on results of the measuring of the change in mass.

A method of determining a presence, concentration or change in concentration of a first or second material in an environment is disclosed. The method comprises measuring a response of a first sensor to the first and second material, wherein the first sensor is one of a metal oxide sensor, an electrochemical sensor, a photoionisation sensor, an infrared sensor, a pellistor sensor, an optical particle monitor, a quartz crystal microbalance sensor, a surface acoustic wave sensor, a cavity ring-down spectroscopy sensor, or a biosensor. The method further comprises measuring a response of a second sensor to the first and second material, wherein the second sensor is another one of a metal oxide sensor, an electrochemical sensor, a photoionisation sensor, an infrared sensor, a pellistor sensor, an optical particle monitor, a quartz crystal microbalance sensor, a surface acoustic wave sensor, a cavity ring-down spectroscopy sensor, a biosensor or a field effect transistor sensor. The method further comprises determining from first and second sensor measurements, a presence, concentration or change in concentration of the first or second material.

A system and method for testing a gas sensor with a test gas and that recovers the test gas after testing. The test gas is stored in a test gas source, and delivered to the gas sensor through a supply circuit. After the test is completed, gas is withdrawn from the supply circuit into a recycle circuit. A compressor in the recycle circuit pulls the test gas into the recycle circuit, pressurizes the test gas and discharges the pressurized test gas back into the test gas source. Valves are in the supply and recycle circuits, which when selectively opened and closed changes between testing and recycle configurations. The recycle flow is filtered to prevent air and other non-test gas substances from being introduced into the test gas source.

A method of analyzing a functional layer of an electrochemical cell or an electrochemical sensor application includes conveying a predefined amount of test gas to a first surface of the functional layer, and quantitatively determining an amount of test gas that has passed through the functional layer using a detection unit located on a second surface of the functional layer, which second surface is opposite the first surface of the functional layer, wherein the test gas conveyed to the first surface of the functional layer is provided in a test gas chamber arranged on the first surface of the functional layer, characterized in that the test gas chamber is open towards the first surface of the functional layer and has an opening which has a defined length in the longitudinal direction (X) of the functional layer and a variably adjustable width in the transverse direction (Z).

An internal combustion engine has a humidity sensor that is disposed in an intake passage of the internal combustion engine, a temperature sensor configured to detect an intake air temperature in a position of the humidity sensor, and a controller configured to correct an offset error of the sensor value by adding a correction value to the sensor value. The controller is configured to acquire the intake air temperatures respectively at a plurality of timings in a process of the intake air temperature changing, acquire the sensor values at the respective plurality of timings, calculate values excluding influences of temperature differences of the intake air temperatures from the respective sensor values as humidity index values respectively, and determine a correction value so that a variation degree of the humidity index values becomes small.

Provided is a gas sensor and methods of monitoring the same. The gas sensor may detect gas restrictions within the gas sensor. The gas sensor may include a test gas diffusion path allowing for monitoring of restrictions within the gas sensor. A pulse of test gas may be electrochemically generated into a void disposed between the membrane and capillary of the gas sensor. The resulting transient signal on the sensing electrode may be analyzed to determine the degree of restriction present in the gas sensor.

An O.sub.2 sensor has a sensor element, which includes a solid electrolyte layer and a pair of electrodes, while the solid electrolyte layer is interposed between the electrodes. The O.sub.2 sensor outputs an electromotive force signal in response to an air-to-fuel ratio of exhaust gas of an engine, which serves as a sensing subject. A constant current circuit, which induces a flow of a predetermined constant electric current between the pair of electrodes of a sensor element, and a current sensing arrangement, which senses a current value of an actual electric current that is conducted through the sensor element, are provided. A microcomputer determines whether an abnormality of the constant current circuit is present based on the current value of the electric current, which is sensed with the current sensing arrangement, in a case where the constant current is induced by the constant current circuit.

A method and apparatus for compensates for oxygen sensor aging determines a correction of by measuring oxygen content above a specified threshold value and measuring current flowing through the sensor over time.

An abnormality diagnosis system of an air-fuel ratio sensor acquires a blowby gas flow ratio showing a ratio of the flow of blowby gas to the flow of gas to a combustion chamber and an output current of an air-fuel ratio sensor during fuel cut control in which an internal combustion engine stops the feed of fuel to the combustion chamber and at a plurality of points of time of different flows of blowby gas passing through a blowby gas passage and flowing to the downstream side of a throttle valve in the intake passage, calculate an output current of the air-fuel ratio sensor corresponding to a blowby gas flow ratio smaller than the blowby gas flow ratios acquired at the plurality of points of time, based on the acquired blowby gas flow ratio and output current, and judge the air-fuel ratio sensor for abnormality based on the calculated output current.