Campbell PC208 Instruction Manual download pdf (Page 12)

in order to get the expression for the velocity profile as a function of stem radius,

[m].

This curve is then integrated over the sapwood cross-section to calculate the volume sap

flux, Q, as

∫

(

)

(6)

for a stem of cambium radius

[m] and heartwood radius

[m].The stem parameter H

needs to be determined from an analysis of trunk cores taken at the end of the experiment

while

can be derived from the stem circumference and an allowance for the depth of the

bark.

2. Instrumentation

The HPV system described here is based on the ‘compensation’ Heat -Pulse method

(Marshall, 1958; Swanson and Whitfield, 1981) and comprises a set of probes and

associated electronics connected to a data logger (model CR10, CR21X or CR23X,

Campbell Scientific Inc., Utah, USA). Each set of probes comprises a linear heater and

two temperature sensors which are installed radially into the tree stem, as shown in Fig. 1.

The heater probe is made from a length of 19 swg stainless steel tube, containing a central

nichrome resistance wire (5

Ω

-1

) which is insulated inside a fine Teflon tube. The

temperature sensors each comprise four copper-constantan thermo-couple junctions (42

swg) and are made from a length of Teflon tubing (18 swg) which is filled with epoxy

resin. The electronics consists of a heater controller and a set of linear instrumentation

amplifiers which have a gain of about 5000. The simple heat-pulse controllers do not

have any amplifiers.

A data logger (Campbell Scientific Inc., Logan, Utah) is used to activate the heater, for

0.5 to 1 s, in order to introduce a heat-pulse tracer into the moving sap stream. A pair of

temperature sensors are used to monitor subsequent changes in stem temperature which

occur as the heat-pulse is propagated through the sapwood, both by conduction through

the wood and sap matrix and by convection with the moving sap streams. Typically,

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Campbell PC208 Instruction Manual Page 12