PCWA-L 467.pdf - PCWA Middle Fork American River Project ...

86 MEASUREMENT OF STAGE AND DISCHARGE
m) in diameter and 2 in (0.05 m) high with six cone-shaped cups
mounted on a stainless-steel shaft. A pivot hearing supports the rotor
shaft. The contact chamber houses both the upper part of the shaft
and a slender bronze wire (eat's whisker) attached to a binding post.
With each revolution an eccentric contact on the shaft makes contact
with a head of solder at the end of the eat's whisker. A separate
reduction gear (pentagear), wire, and binding post provide a contact
eacb time the rotor makes five revolutions. A tailpiece keeps the
meter pointing into the current.
In addition to the standard type AA meter for general use there is a
type AA meter for low velocities. No pentagear is provided. This
modification reduces friction. The shaft usually has two eccentrics
making two contacts per revolution. The low-velocity meter normally
is rated from 0.2 to 2.5 ft/s (0.06 to 0.76 mls) and is recommended for
use when the mean velocity at a cross section is less than 1 ft/s (0.3
mls).
In addition to the typeAA meters, the U.S. Geological Survey uses
a Price pygmy meter in shallow depths. (See fig. 44.) The pygmy
meter is scaled two-fifths as large as the standard meter and has
neither a tailpiece nor a pentagear. The contact chamber is an integral
part of the yoke of the meter. The pygmy meter makes one
contact per revolution and is used only with rod suspension.
The U.s. Geological Survey bas recently developed a four-vane
vertical-axis meter. (See fig. 45.) This meter is useful for meas·
urements under ice cover because the vanes are less likely to fill with
slush ice and because it requires a much smaller hole for passage
through the ice. One yoke of the vane meter is made to he suspended
at the end ofa rod and will fit holes made by an ice drill. Another yoke
FlOun 44.-Price type AA meter, top; Price pygmy meter, bottom.