Environmental
|
LI-6400XT: Innovative TechnologyCO2/H2O Analyzers in the Sensor HeadThe LI-6400 was the first photosynthesis measurement system to put the gas analyzers in the sensor head - where they ought to be. These analyzers feature a novel, open path design with the optical bench of the sample analyzer open directly to the leaf chamber mixing volume. Leaf dynamics are measured in real time because the return tubing between the leaf chamber and the console has been eliminated. There are no time delays to confound correlations between gas exchange and changes in environmental driving variables such as light, CO2 mole fraction, etc. The absence of time delays allows fast, automatic control of chamber humidity at user-defined set points, even when the transpiration rate is changing. The absence of return tubing to the analyzers also eliminates equilibration times due to water vapor sorption on the tubing walls. The LI-6400XT sensor head has two complete, dual path, non-dispersive infrared analyzers, which both measure absolute concentrations of CO2 and H2O. Analyzer OperationInfrared radiation from the sample analyzer source passes into the leaf chamber mixing volume and is twice reflected 90° by gold mirrors. The mirrors are gold plated to enhance IR reflection and provide long term stability. After being reflected through the leaf chamber mixing volume where IR absorption occurs, infrared radiation passes through a chopping filter wheel and into the sample analyzer detector. The chopping filter wheel has four filters that pass light in absorption and optical reference wavelengths for CO2 and H2O. These filters provide excellent rejection of IR radiation outside the wavelengths of interest, eliminating the effects of other IR absorbing gases. The reference analyzer measures incoming gas concentrations and is located directly below the sample analyzer. The sample and reference analyzers can be matched at any time, either manually or automatically, without altering conditions in the leaf chamber. The sample analyzer detector, reference analyzer detector, and chopping filter wheel are sealed in a housing that is continuously purged of CO2 and water vapor to prevent interference. Through years of experience LI-6400 systems have been proven to be robust and reliable, even in the most rigorous field conditions. |
A fan in the mixing volume of the optical bench pushes air through inlet ports into the upper and lower sections of the leaf chamber. The fan draws air from the leaf chamber through a central flow path. The entire flow path is nickel plated to minimize water sorption and can be disassembled and cleaned in the field without affecting factory calibration.
LI-6400XT ConsoleThe LI-6400XT system console combines a data acquisition system with a high speed computer for dedicated data logging and computations. High speed analog to digital converters support fast response applications. The backlit 8 x 40 character graphical display allows any 12 experimental variables to be displayed at once. All computed variables are calculated and displayed in real time.
The 66 key ASCII keyboard is membrane sealed and designed to be used under harsh field conditions. |
Spare Input and Output ChannelsUser-programmable analog and digital I/O channels are available to support external sensors. Input channels include five differential analog, two digital, and one pulse counting. Digital outputs: 8 open drain. Analog outputs: 7 D/A 8-bit, 1 D/A 12-bit, uncalibrated CO2 and H2O reference and sample analyzer outputs, +5V regulated power supply (100 ma), battery voltage (fused, 200 ma). |
Battery OperationThe LI-6400XT System, including optional accessories like the LED light source, are powered by 12VDC batteries stored in the console. Four batteries and a battery charger are included with the system, providing 4-8 hours of operation. The optional 6400-70 AC Adapter fits in the battery compartment. |
