Campbell TDR100 Manuale delle Istruzioni Scaricare il pdf (Pagina 28)

TDR100

6.2.10 Parameter 10: Probe Offset (meters)

Most TDR probes have a block of epoxy or other material which holds the rods

rigidly spaced and houses an impedance matching transformer (balun) if used.

The algorithm in the TDR100 uses changes in the reflection coefficient to

identify end points of the probe. The transition from the coaxial cable to the

TDR probe occurs inside the probe block and causes an increase in the

reflection coefficient if the probe impedance is greater than the cable

impedance. However, this is not the same physical position as the beginning

of the probe’s exposure to the soil being measured. Therefore, a correction

must be made for the distance which the signal travels inside the probe block.

This offset is determined empirically. For the CS600 probe, the value is 69

mm (enter 0.069 in parameter 10), and for the CS605 and the CS610, the value

is 85 mm (enter 0.085 in parameter 10). The offset for probes not obtained

from Campbell Scientific must determined by the user. Contact Campbell

Scientific for guidance.

6.2.11 Parameter 11: Input Location

Input storage location for measurement result. If waveforms are chosen for

output, this location is occupied by the first data point.

6.2.11.1 Reflection Waveform Values to Input Storage

Saving reflection waveforms or reflection waveform plus first derivative using

Instruction 119 requires manual allocation of datalogger input storage. The

Insert Block function of the Edlog input location editor is used to allocate input

locations for the waveform array header elements (see Table 6-1) and

waveform values. The array header contains nine elements. The minimum

number of locations that must be allocated is the Points value defined in

Instruction 119 parameter 6 plus 9. An array size allocation of 9 more than the

number of waveform points the minimum.

TABLE 6-1. Reflection waveform array header elements.

Description of Array Header Elements

1 averaging

2 propagation velocity

3 number of data points

4 cable length

5 window length

6 probe rod length

7 probe offset

8 multiplier

9 offset

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 55 56

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Campbell TDR100 Manuale delle Istruzioni Pagina 28