Gas exchange system flow configuration
Inventors
Johnson, Mark • Eckles, Robert D. • McDermitt, Dayle K.
Assignees
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Publication Number
US-8910506-B2
Publication Date
2014-12-16
Expiration Date
Abstract
Active compensation designs to offset the impact of gas diffusion sources and sinks in a photosynthesis and transpiration measurement system are disclosed. A sensor head for use in a gas exchange analysis system includes an active, piezoelectric flow splitting device for splitting a flow between a sample chamber and bypass pathway. The active flow splitting device is controlled by feedback from a downstream flow meter. A continuous measurement system for rapidly and accurately surveying large numbers of samples is described.
Core Innovation
The invention is a gas exchange analysis sensor head apparatus and related methods and system for measuring gas exchange using gas analyzers coupled to an enclosed sample chamber and to an active flow splitting device. The active flow splitting device variably splits an incoming gas flow in continuously varying proportions between a first output port and a second output port. A first portion of the split flow is directed to a sample chamber inlet and then to a first gas analyzer at the sample chamber outlet, while a second portion is routed directly from the second output port to a second gas analyzer.
To address diffusion-susceptible tubing, gaskets, connectors, fittings, and parasitic gas sources and sinks, the flow splitting is performed near the remote sensor head sample chamber. The active flow splitting device is coupled with downstream flow metering and a feedback control circuit to control the active flow splitting device responsive to a flow rate signal from the flow meter. The feedback control circuit adjusts the incoming gas flow to the first and second output ports to maintain or establish a flow split ratio.
The disclosed system also includes determining concentrations and concentration differentials at inlet and outlet ports over a plurality of times and integrating the concentration differential over time. In an open-path gas exchange analysis system with an enclosed sample chamber, a processing module determines a concentration differential at each of the plurality of times and integrates it over time, optionally to determine an evapotranspiration rate, with the gas including CO2 and/or H2O. Reported results include a reduction in CO2 concentration difference (Cs−Cr) when splitting at the head compared to other placements.
Claims Coverage
The document contains five independent claims. Across these claims, the main inventive focus includes an active flow splitting device with continuously varying proportions, concentration measurement at both split paths and at inlet/outlet ports in time-resolved workflows, flow-rate measurement, and feedback control to adjust the flow split ratio, together with determining and integrating concentration differentials over time in open-path systems.
Active flow splitting with continuously varying proportions for sensor head gas exchange
An active flow splitting device having a first output port and a second output port configured to variably split an incoming gas flow in continuously varying proportions between the first and second output ports.
Split-path coupling of sample chamber and direct analyzer measurement
A sample chamber having an inlet coupled with the first output port of the active flow splitting device and a first gas analyzer coupled with the outlet of the sample chamber, with a second gas analyzer directly coupled with the second output port of the active flow splitting device and configured to measure the concentration of said gas.
Flow metering and feedback control responsive to flow rate signal
A flow meter configured to measure a flow rate between the active flow splitting device and the inlet of the sample chamber, or between the active flow splitting device and the second gas analyzer, and a feedback control circuit adapted to control the active flow splitting device responsive to a flow rate signal from the flow meter.
Time-resolved inlet/outlet concentration differential integration
A method measuring a first concentration of a gas at an inlet port at each of a plurality of times, measuring a second concentration at an outlet port at each of the plurality of times, determining a concentration differential at each of the plurality of times, and thereafter integrating the concentration differential over time.
Open-path system processing module integrating concentration differential over time
An open-path gas exchange analysis system including an enclosed sample chamber with a gas inlet port and a gas outlet port, a first gas analyzer measuring a first concentration entering the gas inlet port at the plurality of times, a second gas analyzer measuring a second concentration exiting the gas outlet port at the plurality of times, and a processing module configured to determine a concentration differential at each of the plurality of times and integrate the concentration differential over time.
Together, the independent claims cover an active flow splitting sensor head that continuously variably splits flow between a sample chamber path and a direct reference/analyzer path, use of flow metering with feedback control to adjust the split based on measured flow rate, and time-resolved determination and integration of inlet/outlet or analogous incoming/outgoing concentration differentials in open-path gas exchange systems.
Stated Advantages
A reduction in CO2 concentration difference (Cs−Cr) when splitting at the head, reported as near an order-of-magnitude reduction.
Documented Applications
Open-path gas exchange measurement systems using an enclosed sample chamber and gas analyzers, where integrated concentration differential can be used to determine an evapotranspiration rate.
Gas exchange analysis sensor head use for measuring photosynthesis and transpiration-related gas exchange via CO2 and/or H2O concentration measurement in a sample chamber and a split reference/analyzer path.
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