Measure Structure Current with a
Clamp-On Ammeter
Posted 31 August 1999
How to measure the actual electrical
current flowing in a structure -- say a concrete
column, a ground cable, or a 3 foot diameter pipe.
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36-inch diameter clamp for measuring
structure cathodic protection direct
current with 10 milliampere
resolution |
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A likely answer is a Swain
Meter®, especially if accuracy is important. Swain
Meters in one form or another measure magnitude,
waveform, and direction of electrical current flow
in all manner of large and small conductors -- even
sea water and in a plasma of ions or electrons.
For 20 years the William H. Swain Co. has built
portable DC and AC non-contact ammeters for
measuring 2 milliamperes to 2000 Amperes flowing in
structure from ¼ inch to 5 feet diameter.
Our clamp-on ammeters are reliable tools for
making accurate measurements in a reasonable time,
whether in the factory or in the field. Moreover,
the sensor can even be buried for years in
saltwater. Both Indicator and Sea Clip® or Sea
Clamp™ sensor are ruggedly built. They are usually
portable.
Hommema, one of our customers, has
permanently installed
Sea Clamps six feet below ground to measure
interference current flowing in a gas pipeline.
Reliability of DC Amp Clips™ is enhanced by
strict control of He
-- the zero offset
due to the Earth's magnetic field.
The new MER™ Meter™
(Magnetic Error Reduction) is still better, mainly
because it reduces the zero offset change due to
local magnetism to 1/2 or 1/3. It is also more
stable. One milliampere resolution is solid, even
when the sensor is connected through a 600 ft.
overland or undersea cable.
Accuracy is typically within ± 1% of reading, ± 3
digits, ± zero offset due to local or the Earth's
magnetism.
AC Amp Clip™ Indicators are used to measure
alternating current with the same sensors as for DC.
Resolution is 0.1 milliampere when using a Sea Clip
up to 5 inch diameter aperture, or 1 milliampere
with a 82 inch diameter aperture Sea Clamp.
AC Amp Clips are typically accurate to ± 1%, ± 3
digits, ± stray pickup at 50 to 60 Hz. Output is
useful (3 dB or so) from 10 Hz to 1K Hz. AC Amp
Clips work nicely to measure the current in ground
bus, glass milk pipe in dairies, or on 7500 V phase
lines. Specials work up to 14,400 V.
Transient events can be observed and recorded.
Both the direct current MER™ Meter and the AC Amp
Clip have "Recorder" ("Rcdr") output terminals.
Min/Max and the like can be obtained from a suitable
Fluke meter connected to this "Rcdr" jack. An
oscilloscope or data logger may be used to identify
an interference source by its waveform.
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