Sealing the Exposed Site
Prior to sealing the exposed site, it is important to test the integrity of the
vapour seal between the psychrometer and stem. An imperfect vapour seal
can be detected by directing an air stream at the junction of the chamber and
stem with the PSY1 in live mode. If the dT and Thermocouple-C values change
significantly a vapour seal has not been achieved and the site should be
checked again.
An inert silicon grease, stable under high temperatures (eg: Dow Corning
Vacuum Grease) should be applied to any exposed sapwood that remains
after the attachment of the psychrometer. This reduces local evaporation,
which may induce water potential gradients. Grease should also be applied
around the edge of the psychrometer.
After grease is applied, the site should be insulated. The site should be
wrapped with foam or wool, then covered with aluminium foil to reflect
direct radiation.
Note that insulation is not intended to prevent diurnal temperature change,
it is intended to act as a thermal buffer to reduce the rate of temperature
change during the measurement.
