Technical information

GENERAL OPERATING INSTRUCTIONS
3/31/2008 Rev. 4.3 3-3
GENERAL OPERATING INSTRUCTIONS
This section will familiarize you with start-up procedures and guide you on how to move from one
function to another. Specific instructions for each separate function will be found under their
individual heading in the main body of the manual.
For greatest accuracy, the instrument should be turned on 30 minutes prior to any calibrations to
allow it to be fully warmed up. Measurements can be made about 3 minutes after the displayed CO
2
value starts to drop from its maximum.
1. The instrument needs to warm up awhile before it is used to measure. The warm up is measured
from the time the instrument is powered on (it does not matter if it is measuring or not). A warm up of
about 4 minutes would be the minimum time to get measurements and about 20 minutes for more
precise measurements.
It is best to put the leaf into the chamber before you start the measurement so the leaf has time to
acclimate to the leaf chamber conditions and the instrument has time to react to the changes the leaf
causes. The "Working" display is a period that the instrument uses to stabilize itself. The actual
measurement starts when the display changes from "Working".
2. Variations in the CO
2
readings or Pn readings can often be caused by changes in the air stream
going into the instrument. The CO
2
content of the stream must be very stable. Some researchers use
a long tube to get the intake away from human activity. Some use compressed air (with a pressure
regulator and a T in the hose). Some use a volume buffer (a 2 liter bottle or larger with the hose from
the instrument drawing air from inside that is vented to allow outside air in) that will average out CO
2
changes over time. If the experiments are done near a road with vehicles, it is difficult to get stable
CO
2
readings. If you do not have a source of compressed air, you may try putting several volume
buffers in series (the instrument draws from the first bottle that draws from the second which then
draws from the third which is vented) The instrument is sensitive enough to detect fires that are
hundreds of meters away if they are upwind.
3. The flow rate can be reduced when the photosynthesis is minimal. Try 0.3 lpm for most situations
and 0.25 lpm if the readings are low.