CIRAS-3 Operation Manual V. 1.09 94 support@ppsystems.com
Z-Diff Bal (F7)
To manually access either Zero or Diff Bal functions at any time during measurements, press Z-Diff Bal
(F7). Press the arrow keys to select Zero or Diff Bal. Press ESC to cancel.
Use Diff Bal when you have selected Manual Zero/Diff Bal Mode and you are prompted to run Diff Bal
with a message in the status bar, “Diff Bal required, ensure CO2r is stable”. Otherwise, run Diff Bal as
often as is practical, for instance when sampling very small leaf areas or generally when your data
suggests very low gas exchange rates. Zero and Diff Bal will otherwise be performed automatically at
regular 31 minute intervals by CIRAS-3. Diff Bal will help ensure that detectable Analysis gas differentials
are real, and not simply artifacts of unbalanced IRGA cells.
Be sure that CO2r is not changing at the time that you run Diff Bal. Remember that Diff Bal diverts the
Reference gas stream through both Reference and Analysis cells and corrects for any small differences
between the Reference and Analysis cells measuring the same gas sample. If CO2r was changing
substantially during the Diff Bal process, the resulting difference and applied offset would be artificial, a bit
like trying to hit a moving target versus a stationary target. In this sense, it is possible to perform a “bad”
Diff Bal. Run Diff Bal more frequently if you are operating at very fine tolerances in your gas exchange
data, for example, if it is important to detect differences in assimilation rate that are <1.0 µmol m
-2
s
-1
.
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