Patent Application
20120181432
The present invention relates generally to gas exchange measurement systems, and more particularly to open photosynthesis measurement systems having dual analyzers with an optimized flow swapping configuration to compensate for analyzer offset.
Plant photosynthesis, transpiration, and respiration measurements are commonly made by measuring gas exchange. Broadly, gas exchange measurements can be performed in open or closed systems. Open gas exchange systems place a portion, or sometimes the entirety, of the plant in a sample chamber. A flowing gas with known concentrations (CO2 for photosynthesis and H2O for respiration) is injected into the sample chamber at a known mass flow rate. This gas stream will be referred to later as the chamber influent. The gas concentrations are measured at the chamber exit, and this exit gas stream will be referred to later as the chamber effluent. Under steady state assumptions, the concentration differences between influent and effluent streams, along with the mass flow rate, are then used to calculate the rate of gas exchange (e.g. photosynthesis using the CO2 difference and transpiration using the H2O difference).
Gas exchange measurements of low photosynthesis and transpiration rates, especially on small leaf areas, requires accurate measurement of minute differences between influent and effluent concentrations. The calculated difference of these absolute concentrations is then used to calculate photosynthesis and transpiration rates.
Open gas exchange systems generally use either one or two gas analyzers. Single analyzer systems use valves to swap the flow through the single analyzer from the chamber influent to the chamber effluent, and back again. Dual analyzer systems use one analyzer to measure the chamber influent, and the other analyzer to measure chamber effluent.
A fundamental complication in dual analyzer systems is that one analyzer can be offset from the other. This offset is usually slowly varying, due to aging of the analyzer components or operating environment changes. Moreover, the offset can be a function of the absolute concentrations being measured. Any analyzer offset artificially appears as gas exchange. Thus, dual analyzer systems must have a mechanism for compensating these analyzer offsets. Single analyzer systems do not suffer from this, as both influent and effluent streams are measured by the same analyzer.
Therefore it is desirable to provide systems and methods that overcome the above and other problems.
The present invention provides gas exchange measurement systems and methods using an optimized flow swapping configuration to compensate for dual analyzer offset error.
Various embodiments provide systems and methods of compensating analyzer offsets in a dual analyzer gas analysis systems. The various embodiments are approximately two-times faster than known methods for dual analyzer systems; the reduced time translates to an overall faster gas exchange measurement.
According to one aspect of the present invention, a sensor for use in a gas exchange analysis system is provided. The sensor typically includes a sample chamber defining a measurement volume for analysis of a sample, the sample chamber having a gas inlet port coupled with a gas source, and a gas outlet port. The sensor also typically includes a first gas analyzer configured to measure a concentration of a gas, a second gas analyzer configured to measure a concentration of said gas, and a flow swapping device having a first input port coupled with the gas outlet port of the sample chamber, a second input port coupled with the gas source, a first output port coupled with the first gas analyzer, and a second output port coupled with the second gas analyzer. In typical operation, responsive to a control signal the flow swapping device automatically switches between a first configuration and a second configuration, wherein in the first configuration the flow swapping device couples the first input port with the first output port, and the second output port with the second input port, and wherein in the second configuration the flow swapping device couples the first input port with the second output port, and the second input port with the first output port.
According to another aspect of the present invention, a sensor head for use in a gas exchange analysis system is provided. The sensor head typically includes a sample chamber defining a measurement volume for analysis of a sample, the sample chamber having a gas inlet port coupled with a gas source, and a gas outlet port. The sensor head also typically includes a first gas analyzer configured to measure a concentration of a gas, a second gas analyzer configured to measure a concentration of said gas, and a flow swapping device having a first input port coupled with the gas outlet port of the sample chamber, a second input port coupled with the gas source, a first output port coupled with the first gas analyzer, and a second output port coupled with the second gas analyzer. In typical operation, responsive to a control signal, the flow swapping device automatically switches between a first configuration and a second configuration, wherein in the first configuration the flow swapping device couples the first input port with the first output port, and the second output port with the second input port, and wherein in the second configuration the flow swapping device couples the first input port with the second output port, and the second input port with the first output port.
According to yet another aspect of the present invention, a method is provided for measuring a concentration differential of a gas in a gas exchange analysis system having a sensor head having a sample chamber defining a measurement volume for analysis of a sample, the sample chamber having an inlet port coupled with a gas source and an outlet port. The method typically includes providing a first flow path configuration, using a flow swapping device, the first configuration having a first flow path between the output port of the sample chamber and a first gas analyzer, and a second flow path between the gas source and a second gas analyzer. The method also typically includes measuring a first concentration of a gas exiting the sample chamber at the output port using the first gas analyzer, measuring a second concentration of said gas from the gas source using the second gas analyzer, determining a first concentration differential of said gas based on the first concentration and the second concentration, and thereafter responsive to a control signal, automatically switching to a second flow path configuration using the flow swapping device, the second configuration having a third flow path between the output port of the sample chamber and the second gas analyzer, and a fourth flow path between the gas source and the first gas analyzer. In certain aspects, the method further includes measuring a third concentration of a gas exiting the sample chamber at the output port using the second gas analyzer, and measuring a fourth concentration of said gas from the gas source using the first gas analyzer. In certain aspects, the method further includes determining a second concentration differential of said gas based on the third concentration and the fourth concentration. In certain aspects, the method additionally includes determining an error based on the absolute value of the difference between the first concentration differential and the second concentration differential, said difference being divided by two.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.
The present invention provides systems and methods for compensating for dual analyzer offset error in a gas exchange measurement system.
Broadly, there are two techniques for measuring chamber influent and effluent gas stream concentrations: 1) dynamically switching a single gas analyzer from chamber influent to effluent, and vice-versa, and 2) simultaneously measuring chamber influent and effluent streams using two independent gas analyzers.
The first technique is generally simple and compact, as only a single gas analyzer is required. Gas exchange measurements often assume steady-state conditions. For single analyzer systems, the sample conditions must be suitably stable during the time required to switch from chamber influent to effluent, or effluent to influent. In addition to the time required to affect the flow swap, transient phenomena in the analyzer must dissipate as the flow is switched from influent to effluent, and back again.
The second technique generally increases system size and complexity, as an additional analyzer is required. Two analyzer systems have faster response times during a measurement, as there are no transients associated with the flow swapping in single-analyzer systems. Unlike single analyzer systems, dual analyzer systems suffer from offsets between the two analyzers at the same gas concentration. Any offset between analyzers will appear as a non-zero difference, and this non-zero difference will be interpreted as gas exchange (e.g., photosynthesis/transpiration). Correcting for offsets between analyzers is particularly important for the accurate measurement of small exchange rates, as the offset is a more significant fraction of the concentration difference.
It is important to note that the slope of the analyzer responses of Analyzers 1 and 2 in
Various conduits and connectors provide fluid flow paths coupling the various system components as shown. For example, in one embodiment, the conditioned air supply from air supply 20 is split into two streams by variable flow divider 30. A controlled and known mass flow is delivered to the gas inlet port of chamber 40, via flow meter 35 and the flow remainder bypasses the leaf chamber 40 and is provided to flow swapping device 50. The gas outlet port of chamber 40 is also fluidly coupled with flow swapping device 50 so as to enable chamber effluent to be delivered to flow swapping device 50. Flow swapping device 50 in certain aspects includes a match valve as shown, having 2 possible configurations. In
By changing the configuration of the match valve, the gas analyzer initially connected to the chamber effluent is connected to the chamber influent. Conversely, the gas analyzer initially connected to the chamber influent is connected to the chamber effluent. By changing the valve configuration, the gas streams measured by each gas analyzer are effectively “swapped.”
In
Existing instruments such as the LI-COR LI-6400 and Walz GFS-3000 instruments use a series matching method. That is, the analyzers are arranged in series during the matching process, and both see the identical gas stream at an identical flow rate. This operational state does not allow chamber influent and effluent concentrations to be simultaneously measured. These systems have a specific match mode state during which no gas exchange measurements can be made. Series matching requires approximately two times the analyzer flush time (td above) to complete a matching cycle. There is an initial delay (td) while the analyzers come to equilibrium in the match-mode, and a second delay time (td) during which transients dissipate after the analyzers are restored to their normal operating configuration.
Embodiments disclosed herein advantageously reduce the time for analyzer matching compared to the series matching used by existing instruments such as the LI-COR LI-6400 and Walz GFS-3000 instruments, by a factor of about 2 or more. An initial delay td is required when the match valve configuration is changed, but after this delay time, the present embodiments are capable of immediately resuming measurements. Single analyzer systems do not require an offset correction or match mode, but do require a similar delay time of td to account for transients introduced by switching the analyzer from effluent to influent, or vice-versa.
In the embodiments disclosed herein, the gas analyzers do not receive an identical gas stream. Thus, it is important that the gas concentration of the conditioned air supply be stable during the matching process. Any change in concentration of the conditioned air supply would be interpreted as additional analyzer offset. This erroneous analyzer offset would then be applied inappropriately to future offset calculations.
In step 450, the gas concentrations of the flows in each of the gas analyzers in the second flow path configuration are measured. For example, a third concentration of the gas exiting the sample chamber (chamber effluent) is measured using gas analyzer 2 and a fourth concentration of the gas from the gas source is measured using the gas analyzer 1. In step 460, a second concentration differential of the gas based on the third measured concentration and the fourth measured concentration is determined. In step 470, an offset error is determined based on the first concentration differential and the second concentration differential determined in steps 430 and 460. In one embodiment, for example, an offset error based on the absolute value of the difference between the first concentration differential and the second concentration differential is determined, with the difference being divided by two. In step 480, data representative of the offset error is displayed on a monitor or other display device or otherwise further processed or used to generate (and display) corrected gas concentration measurements.
Steps 430, 460 and 470 can be performed using an intelligence module such as a processor or computer system that is integrated in the sensor head and/or in the console of a gas analysis system and/or in a remote computer system that is communicably coupled with the gas analysis system. Code for implementing the various calculation and control steps can be stored on a memory coupled with, or otherwise accessible by, the intelligence module or provided on any tangible computer readable medium such as a CD, DVD, hard disk, etc.
While the invention has been described by way of example and in terms of the specific embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
