Making Measurements
Stability Considerations
Using the LI-6400
4-41
Stability Considerations
In New Measurements mode, the LI-6400 measures and computes continual-
ly, regardless of the state of equilibrium of the leaf in the chamber. It can also
log data with the same disregard for stability. The question is, how do you
know when the system is stable enough to record meaningful data? Also,
when you log an observation, how can you tell later, when you are looking at
the data, how stable the reading was?
Stability Variables
There are some system variables that can help, and they are found in display
group
e
of the default display.
These variables (formally defined in
coefficients of variation over the past 30 seconds of the three important vari-
ables in the system. When the sum of these (totalCV%) is sufficiently small
(say, less than 1% or 0.5%), then you can be assured that the system is stable.
Also, if you include this information in your logged data
6
you can tell after
the fact how stable the system was for any given observation.
Real Time Graphics
A useful visual indicator of stability can be had with judicious use of New
MeasurementÕs strip chart mode (
plot photosynthesis and conductance as a function of time, and watch for any
trends over the past minute or two, or more.
If you are using a buffer volume, it is useful to keep an ongoing plot of ref-
erence CO
2
, so that if photosynthesis doesnÕt seem to be stabilizing, you can
Table 4-1.
The stability variables.
Display Label
Description
totalCV%
Sum of the three other variables.
ÆCO2CV_%
CV of
D
CO
2
ÆH2OCV_%
CV of
D
H
2
O
Flow_CV%
CV of flow rate
6.
They arenÕt there by default - you must add them to the log list if you want them.
See
Summary of Contents for LI-6400
Page 1: ...Using the LI 6400 Portable Photosynthesis System ...
Page 15: ...Part I The Basics ...
Page 16: ......
Page 174: ...Making Measurements Answers to Questions 4 56 Using the LI 6400 4 ...
Page 175: ...Part II Useful Details ...
Page 176: ......
Page 200: ...Standard Tools Power ON Hooks 5 24 Using the LI 6400 5 ...
Page 214: ...Real Time Data Real Time Graphics 6 14 Using the LI 6400 6 ...
Page 234: ...Environmental Control Light Control 7 20 Using the LI 6400 7 ...
Page 244: ...Light Sensor Considerations Gallium Arsenide Phosphide GaAsP Sensor 8 10 Using the LI 6400 8 ...
Page 288: ...Data Logging Making Your Own AutoPrograms 9 44 Using the LI 6400 9 ...
Page 289: ...Part III Working With Files ...
Page 290: ......
Page 312: ...The LPL File System Troubleshooting 10 22 Using the LI 6400 10 ...
Page 340: ...Downloading Files Using a Data Capture Program 11 28 Using the LI 6400 11 ...
Page 375: ...Part IV Configuration Issues ...
Page 376: ......
Page 420: ...Defining User Variables Old Style vs New Style 15 18 Using the LI 6400 15 ...
Page 454: ...Using an Energy Balance Further Reading 17 12 Using the LI 6400 17 ...
Page 455: ...Part V Maintenance Troubleshooting ...
Page 456: ......
Page 572: ...Troubleshooting Useful Information 20 46 Using the LI 6400 20 ...
Page 593: ...Part VI Programming ...
Page 594: ......
Page 622: ...Programming with LPL Compiler Directives 22 28 Using the LI 6400 22 ...
Page 846: ...Index I 16 Using the LI 6400 ...