The subject matter of this specification can be embodied in, among other things, a method of sensing that includes activating a first emitter to emit at least one incident wave, transmitting the incident wave along a buffer rod having a first axial end abutted to the first emitter and a second axial end opposite the first axial end, reflecting a first echo of the incident wave by a gap defined along a portion of the buffer rod, detecting the first echo, determining a first amplitude of the first echo, reflecting a second echo of the incident wave by the second axial end, detecting the second echo, determining a second amplitude of the second echo, and determining a reflection coefficient based on the first amplitude and the second amplitude.

The subject matter of this specification can be embodied in, among other things, a method of sensing that includes activating a first emitter to emit at least one incident wave, transmitting the incident wave along a buffer rod having a first axial end abutted to the first emitter and a second axial end opposite the first axial end, reflecting a first echo of the incident wave by a gap defined along a portion of the buffer rod, detecting the first echo, determining a first amplitude of the first echo, reflecting a second echo of the incident wave by the second axial end, detecting the second echo, determining a second amplitude of the second echo, and determining a reflection coefficient based on the first amplitude and the second amplitude.

A method for determining a mass flow of ammonia between two SCR catalytic converters disposed one after the other in an SCR catalytic converter system in an exhaust system, which comprises only one reduction agent dosing unit upstream of the first SCR catalytic converter, characterized in that the determination is carried out from the signal of a NOx sensor disposed between the two SCR catalytic converters and the signal of a NOx sensor disposed downstream of the second SCR catalytic converter.

A method for determining a mass flow of ammonia between two SCR catalytic converters disposed one after the other in an SCR catalytic converter system in an exhaust system, which comprises only one reduction agent dosing unit upstream of the first SCR catalytic converter, characterized in that the determination is carried out from the signal of a NOx sensor disposed between the two SCR catalytic converters and the signal of a NOx sensor disposed downstream of the second SCR catalytic converter.

An example optical measurement system includes: a first light source configured to emit a first light beam; a first optical sensor configured to output first measurements based on detecting the first light beam; a second light source configured to emit a second light beam; a second optical sensor configured to output second measurements based on detecting the second light beam, wherein the first measurements and the second measurements comprise variable components; a third optical sensor configured to output third measurements based on detecting the second light beam or a third light beam, wherein the third measurements comprise a first steady state component; and a compensation circuit configured to control a first light output of the first light beam and a second light output of the second light beam by controlling current to the first light source and the second light source based on the third measurements.

An example optical measurement system includes: a first light source configured to emit a first light beam; a first optical sensor configured to output first measurements based on detecting the first light beam; a second light source configured to emit a second light beam; a second optical sensor configured to output second measurements based on detecting the second light beam, wherein the first measurements and the second measurements comprise variable components; a third optical sensor configured to output third measurements based on detecting the second light beam or a third light beam, wherein the third measurements comprise a first steady state component; and a compensation circuit configured to control a first light output of the first light beam and a second light output of the second light beam by controlling current to the first light source and the second light source based on the third measurements.

Calibrating a plurality of fluid sensors of a remote metering system is disclosed. The system includes a material supply device including a main pump and a main flow sensor for monitoring an output of the main pump. The application system also includes a remote metering system for receiving the material flowing from the material supply device and applying the material to substrates. The remote metering system includes a first applicator assembly including a first applicator and a first flow sensor for monitoring an output of the first applicator, and a second applicator assembly including a second applicator and a second flow sensor for monitoring an output of the second applicator. The remote metering system further includes a controller in signal communication with the remote metering station and the material supply device. The controller performs a first and second calibration operations on the first and second flow sensors, respectively.

Calibrating a plurality of fluid sensors of a remote metering system is disclosed. The system includes a material supply device including a main pump and a main flow sensor for monitoring an output of the main pump. The application system also includes a remote metering system for receiving the material flowing from the material supply device and applying the material to substrates. The remote metering system includes a first applicator assembly including a first applicator and a first flow sensor for monitoring an output of the first applicator, and a second applicator assembly including a second applicator and a second flow sensor for monitoring an output of the second applicator. The remote metering system further includes a controller in signal communication with the remote metering station and the material supply device. The controller performs a first and second calibration operations on the first and second flow sensors, respectively.

A hydrocarbon absorbing air filter box is provided for absorbing evaporative hydrocarbon emissions from an air intake duct of an internal combustion engine. A combined mass airflow sensor and hydrocarbon trap comprising the hydrocarbon absorbing air filter box includes a duct supporting a hydrocarbon absorbing sheet within an interior of a housing. The duct communicates an airstream from an air filter to the air intake duct during operation of the internal combustion engine. An opening in the housing receives a mass airflow sensor into the duct, such that the mass airflow sensor is disposed within the airstream. Guide vanes extending across the duct reduce air turbulence within the airstream passing by the mass airflow sensor. Ports disposed along the duct allow the evaporative hydrocarbon emissions to be drawn into the interior and arrested by the hydrocarbon absorbing sheet when the internal combustion engine is not operating.

A method of converting a directly measured mass flow rate to account for buoyancy is provided. The method includes directly measuring a mass flow rate of a material, measuring a density of the material, and using the measured density of the material to convert the directly measured mass flow rate into a mass value including a buoyancy of a fluid.