Keterangan :

The Lci is designed to provide truly portable ambient photosynthesis measurement with a high
degree of repeatability and reliability. To accomplish this goal, ADC uses the same high quality
CO IRGA components, and the same high quality laser trimmed relative humidity sensors that 2
are found in their more advanced LCpro+ system.
- All IRGA light sources and sensors made by all manufacturers drift electronically. If
multiple IRGA chambers are used, then all light sources and sensors drift independently and in many
cases they drift in opposite directions. To solve this problem, ADC uses a single CO IRGA that 2
measurements both ambient air, and also air that has flowed through the leaf chamber.
To ensure that the instrument provides highly repeatable and reliable measurements, an auto-zero
routine is preformed every 16 seconds. During this routine the instrument takes ambient air and scrubs
CO and H 0 from the sample. It then enters the IRGA chamber and a measurement is taken. Since this 2 2
reference air does not contain CO or H O, the instrument electronic gain can be automatically adjusted 2 2
to zero out electronic drift.
Auto-Zero
The CO2 IRGA and the H2O sensors are in the hand held leaf measuring head. -
Placing the IRGA next to the leaf chamber, solves a few problems. Measurement response times are
improved dramatically, and other problems associated with longer distances are eliminated.
When the path to the IRGA is long, there can be gas hang-ups and water vapor drop out. Changes in
ambient lighting, sun flecks, and changes in temperature, can be greater sources of error because they
can affect the gases as they flow throw the long tube.
Differential IRGA - There are absolute and differential plant IRGA systems. Absolute systems
measure CO level against an absolute CO calibration. Differential IRGAs compare the measurement of 2 2
CO and H O before the leaf chamber to the measurement of CO and H O after the leaf chamber. 2 2 2 2
Almost all commercial plant IRGA systems are of the differential type. Certainly, the most advanced
systems are of the differential type because they provide more reliable measurements.
- The measurement of H O is a secondary 2
measurement necessary to correct CO measurements. Since CO and H O both absorb infrared in a 2 2 2
similar spectral range, it is important to measure H O content and barometric pressure to provide 2
reliable CO measurements. Other manufactures still use a set of separate IRGA chambers to measure 2
water content. ADC has found that modern solid-state humidity sensors provide a more than reliable
solution for the measurement of relative humidity while offering the advantages of lighter weight, greater
power efficiency, and greater stability. In the 1980' s humidity sensors were highly variable. Today the
opposite is true.
ADC developed the first differential plant IRGA in 1970. Both current plant gas exchange
systems, the LCi and the LCpro+ , are of the differential type.
ADC' s laser trimmed relative humidity sensors offer advantages for 95% of plant applications.
Laser Trimmed Relative Humidity Sensors