Campbell TDR100 Manuel d'instructions télécharger pdf (Page 31)

TDR100

Mux/ProbeSelect: The Mux/Probe Select parameter is used to define the setup

of any multiplexers and attached probes in the system. The addressing scheme

used is ABCR, where A = level 1 multiplexer channel, B = level 2 multiplexer

channel, C = level 3 multiplexer channel, and R = the number of consecutive

probes to be read, starting with the channel specified by the ABC value

(maximum of 8). 0 is entered for any level not used.

WaveAvg: The WaveAvg parameter is used to define the number of

waveform reflections averaged by the TDR100 to give a single result. A

waveform averaging value of 4 provides good signal-to-noise ratio under

typical applications. Under high noise conditions averaging can be increased.

The maximum averaging possible is 128.

Vp: The Vp parameter allows you to enter the propagation velocity of a cable

when using the instruction to test for cable lengths or faults. Vp adjustment is

not necessary for soil water content or electrical conductivity measurement and

should be set to 1.0 for output Option 1, 2, or 3.

Points: The Points parameter is used to define the number of values in the

displayed or collected waveform (20 to 2048). A entry of 251 is recommended

for soil water measurements. The waveform consists of the number of Points

equally spaced over the WindowLength.

CableLength: The CableLength parameter is used to specify the cable length,

in meters, of the TDR probes. If a 0 is entered for the Option parameter, cable

length is used by the analysis algorithm to begin searching for the TDR probe.

If a 1 or 2 is entered for the Option parameter, cable length is the distance to

the start of the collected waveform.

The value used for CableLength is best determined using PCTDR100 with the

Vp = 1.0. Adjust the CableLength and WindowLength values in PCTDR100

until the probe reflection can be viewed. Subtract about 0.5 meters from the

distance associated with the beginning of the probe reflection.

Note that the specified CableLength applies to all probes read by this

instruction; therefore, all probes must have the same cable lengths.

WindowLength: The WindowLength parameter specifies the length, in

meters, of the waveform to collect or analyze. The waveform begins at the

CableLength and ends at the CableLength + WindowLength. This is an

apparent length because the value set for Vp may not be the actual propagation

velocity. For water content measurements, the WindowLength must be large

enough to contain the entire probe reflection for probes with 20 to 30 cm rods.

A Vp = 1 and Window length = 5 is recommended.

ProbeLength: The ProbeLength parameter specifies the length, in meters, of

the probe rods that are exposed to the medium being measured. The value of

this parameter only has an affect when Option 0, La/L, is used for the

measurement.

ProbeOffset: The ProbeOffset is an apparent length value used to correct for

the portion of the probe rods that may be encapsulated in epoxy and not

surrounded by soil or other medium being measured. This value is supplied by

Campbell Scientific for the probes we manufacture. The value of this

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Campbell TDR100 Manuel d'instructions Page 31

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