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– 5 –
CORROSION
MITIGATION
INSTRUMENTATION
P.
O.
B
OX
1667
S
AN
B
ERNARDINO
,
C
A
92402
T
EL
:
(909)
890-0700
F
AX
:
(909)
890-0736
P
RODUCT
I
NSTRUCTIONS
external peak reading voltmeters currently available are not as accurate as the
integrated voltmeter of the AP/W, and will not show as accurate results.
5. ACCURACY & CALIBRATION
The Model AP/W voltmeter is accurate to +/- 5% of the output voltage, as shown on
the LCD display on the instrument panel.
It is recommended that the Model AP/W follow an annual calibration cycle to ensure
the instrument is in good working order and that the LCD of the integration voltmeter
is accurate.
6. OPERATING METHODS
A good ground return system for both the pipe and the detector will always provide the
best and most reliable inspection. The pipe to be inspected must be grounded from
the bare pipe to earth at some point along the pipe. If individual joints of the pipe are
to be inspected that are not electrically connected, each joint must be grounded.
The speed of the electrode's travel along the pipe should never be excessive, as faulty
inspection may result.
Occasional checks of the detector operation should be made, particularly if no holidays
are being found. This can be accomplished by testing for the spark and signal at the
edge of the coating where bare pipe exists or by touching the probe end to the bare
pipe and noting the length of the spark and the visual and audible signal effectiveness.
If the visual and audible signal do not both occur when the spark discharges from the
electrode into a known holiday, the ground return (i.e. the path between the metallic
pipe and earth and the earth to the ground trail of the detector) is of high resistance.
In this case, a better ground is required and a direct connection between the metal
pipe and the ground wire may be necessary. This type of grounding is extremely
uncommon unless the soil is very dry (if using a grounding rod) or the detectors output
is low.
The most accurate and recommended inspection voltage should be obtained from the
coating manufacturer spec or by contacting the coating manufacture or rep. Correct
voltage output for a given thickness of coating has long been a matter of controversy.
However, formulas have been suggested which may be used as a guide for correct
peak voltages on various coating thickness. The calculation is as follows:
V
=
K
√𝐓𝐓
WHERE
V
=
Peak voltage in volts
T
=
Thickness of coating in mils
K
=
Constant of 1,250 for coatings over 20 mils thick