Gas exchange system flow configuration
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.
1. A gas exchange analysis sensor head apparatus comprising:
an active flow splitting device having a first output port and a second output port, the active flow splitting device configured to variably split an incoming gas flow between the first and second output ports;
a sample chamber having an inlet and an outlet, the inlet coupled with the first output port of the active flow splitting device;
a first gas analyzer coupled with the outlet of the sample chamber and configured to measure a concentration of a gas exiting the outlet of the sample chamber;
a second gas analyzer coupled with the second output port of the active flow splitting device and configured to measure a concentration of said gas exiting the second output port of the active flow splitting device;
a flow meter coupled between the first output port of the active flow splitting device and the inlet of the sample chamber the flow meter configured to measure a flow rate of gas entering the inlet of the sample chamber; and
a feedback control circuit adapted to control the active flow splitting device to adjust the gas flow provided to the first output port responsive to a flow rate signal from the flow meter.
2. The apparatus of claim 1 , wherein flow meter is coupled between the first output port of the active flow splitting device and the inlet of the sample chamber, the feedback control circuit controlling gas flow based on flow to the sample chamber.
3. The apparatus of claim 2 , wherein measurements from the first and second gas analyzers are configured to be compared, thereby comparing gas analyzed from the sample chamber with excess gas diverted by the flow splitting device.
4. The apparatus of claim 2 , wherein the feedback control circuit controls the active flow splitting device to adjust the gas flow provided to the first input port according to a user-selected flow rate.
5. The apparatus of claim 1 , wherein the active flow splitting device includes a piezoelectric material.
6. The apparatus of claim 5 , wherein the active flow splitting device comprises:
a piezoresistive actuator having a first end secured within the active flow splitting device and a second end located proximal to both the first and second output ports of the active flow splitting device; and
electrical contacts operatively coupled with the piezoresistive actuator, configured to apply a voltage to control a position of the second end relative to the first and second output ports and thereby control the flow ratio to the first and second output ports.
7. The apparatus of claim 6 , wherein the actuator includes a metal strip coated on at least one side with a piezo-bender material.
8. The apparatus of claim 7 , wherein the piezo-bender material comprises lithium tantalite.
9. The sensor head of claim 6 , wherein an applied control potential controls the second end of the piezoresistive actuator to adjust the position of the second end relative to the first and second output ports such as to controllably adjust the gas flow provided to the first and second ports.
10. The apparatus of claim 1 , wherein the active flow splitting device is located less than 12 inches from the sample chamber.
11. A gas exchange analysis sensor head apparatus comprising: A gas exchange analysis sensor head apparatus comprising:
an active flow splitting device having an input port, a first output port and a second output port, the active flow splitting device configured to controllably and variably split an incoming gas flow received at the input port to the first and second output ports;
a sample chamber having an inlet and an outlet, the inlet directly coupled with the first output port of the active flow splitting device;
a first gas analyzer coupled with the outlet of the sample chamber and configured to measure a concentration of a gas exiting the outlet of the sample chamber;
a second gas analyzer coupled with the second output port of the active flow splitting device and configured to measure a concentration of said gas exiting the second output port of the flow splitting device;
a flow meter directly coupled with and between the second output port of the active flow splitting device and the second gas analyzer, the flow meter configured to measure a flow rate of gas entering the second gas analyzer; and
a feedback control circuit adapted to control the active flow splitting device to adjust the gas flow provided to the second output port responsive to a flow rate signal from the flow meter.
12. The apparatus of claim 11 , wherein the feedback signal controls the active flow splitting device to adjust the gas flow provided to the second output port or to the second output port according to a user-selected rate.
13. The apparatus of claim 11 , wherein the active flow splitting device is located less than about 12 inches from the sample chamber.