Nace CP 1, Course Manual

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Field Measurements 5:31
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
02/01/05
Resistivity Probe
This single-probe method is used to determine soil resistivity in the
immediate vicinity of the tip of a probe driven into the ground to a depth of
the desired measurement. This method is useful for:
•
Rapid determination of local resistivity at intervals along a pipeline
trench during construction (for later use during cathodic protection
system design).
•
Spot checks of soil or water resistivity.
The single-probe method is illustrated in Figure 5.15.
Metal tip of controlled
dimensions insulated
from the rest of the
metal probe rod,
contacting soil at a
depth of desired soil
resistivity measurement
Insulated wire,
inside of rod,
from tip to
terminal
Hollow bare
metal probe
rod
Terminals:
One to rod
One to tip
Soil
Resistivity
Instrument
Figure 5.15 Single Probe Soil Resistivity Measurement
Measuring pH
Electrolyte pH can be measured in several ways. For liquids, pH (litmus)
paper or a pH meter may be used. For soils, a pH meter may be used, or a
filtrate may be made from distilled water and a soil sample and the pH
measured with litmus paper, pH meter, or a pH test kits. Note that a pH
meter uses a glass electrode with a rather fragile glass bulb on the bottom.
Care must be taken when using these instruments not to break the electrode
bulb.
Soil pH may also be measured using an antimony electrode and a copper-
copper sulfate electrode. The antimony electrode consists of a slug of