Campbell PC208 Instruction Manual download pdf (Page 15)

4. Installing the heat-pulse probes.

This section gives advice on how to install the heat-pulse probes into a plant stem. Note:

It is good practice to test the operation of the logger and the probes, and to test all the

wiring connections before inserting the probes into the plant stem. Although the HPV unit

is designed to be operated automatically, the software does allow for a manual test of the

system, as described later in the next section.

4.1. Checking if probes are OK

The pin-out for the connector on the temperature probes (the 9-pin D-plug) is:

1&6 = channel 1 (outer-most sensor, closest to the cambium)

2&7 = channel 2

3&8 = channel 3

4&9 = channel 4 (inner-most sensor, closest to the stem centre)

Each temperature sensors should be electrically isolated. A quick ‘beep-test’ of the

temperature sensors using a multi-meter should confirm each thermocouple is connected,

and isolated from the others. The temperature probes should have a resistance of about 19

ohms. The heater probe normally has a resistance of about 0.4-0.6 ohms. If the heater is

faulty then this resistance will exceed this value.

4.2. Procedure for installing probes.

4.2.1. Locate a fairly straight piece of stem, fairly free of bumps

and knots. Measure the stem circumference, C, to the nearest

mm.

4.2.2. Attach the drilling jig as shown below. Use thick sticky-

tape for the stem, or use a special jig for roots and small

branches.

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Campbell PC208 Instruction Manual Page 15