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Photograph 2.--Plumb wire setup.
Photograph 3.--Electric micrometer.
4.1 Plumb Wires
The most common method of obtaining plumb readings is with stainless steel, nonmagnetic
piano wires and an electric micrometer. Four wires are hung 90-degrees apart with a finned
plumb bob (photo 2) attached to each wire and suspended in buckets filled with oil to dampen
movement. The electric micrometer (photo 3) is used to measure the distance from the wires to
the shaft. There are variations in design, but the basic concept is the same. The electric
micrometer is made up of an inside micrometer head, head phones, battery, shaft, and "Y-
shaped" end. A simple circuit is completed when the micrometer head touches the plumb wire,
which causes static in the headphones. Banding material is installed on the shaft to provide a
place to rest the "Y" end of the micrometer and to ensure repeatability in the readings.
piano wires and an electric micrometer. Four wires are hung 90-degrees apart with a finned
plumb bob (photo 2) attached to each wire and suspended in buckets filled with oil to dampen
movement. The electric micrometer (photo 3) is used to measure the distance from the wires to
the shaft. There are variations in design, but the basic concept is the same. The electric
micrometer is made up of an inside micrometer head, head phones, battery, shaft, and "Y-
shaped" end. A simple circuit is completed when the micrometer head touches the plumb wire,
which causes static in the headphones. Banding material is installed on the shaft to provide a
place to rest the "Y" end of the micrometer and to ensure repeatability in the readings.
The readings taken with the
electric micrometer are not
calibrated as would be
done with a normal inside
micrometer. Since the wire
is perfectly plumb, the
plumb of the shaft is
determined by comparing
the difference in readings at
different elevations. If the
turbine and generator shafts
were exactly the same
diameter and neither shaft
had any taper, only two
wires, 90 degrees apart
electric micrometer are not
calibrated as would be
done with a normal inside
micrometer. Since the wire
is perfectly plumb, the
plumb of the shaft is
determined by comparing
the difference in readings at
different elevations. If the
turbine and generator shafts
were exactly the same
diameter and neither shaft
had any taper, only two
wires, 90 degrees apart
would be required to obtain
plumb data. Since the
turbine and generator
shaft are rarely exactly the
same diameter and slight
tapers in the shaft are
common, four plumb
wires are normally used,
90 degrees apart. The
difference in the north-
south and the east-west
readings are used in
determining the shaft
plumb. The four wires
turbine and generator
shaft are rarely exactly the
same diameter and slight
tapers in the shaft are
common, four plumb
wires are normally used,
90 degrees apart. The
difference in the north-
south and the east-west
readings are used in
determining the shaft
plumb. The four wires