EQUIPMENT AND SUPPLIES--Approval of Standard Rating for PAA Current Meter

In Reply Refer To:                                              June 6, 1988
WGS-Mail Stop 415


Subject:  EQUIPMENT AND SUPPLIES--Approval of Standard Rating for PAA Current

A solid-cup polymer AA current-meter rotor has been developed as an eventual
replacement for the metal bucket wheel in the standard Price AA meter (Surface
Water Branch Technical Memorandum 85.07 dated May 13, 1985).  Standard ratings
for PAA (polymer rotor, catwhisker head) and OAA (polymer rotor, fiber-optic
head, formerly FAA) meters based on a set of prototype rotors were established
in 1985.  Subsequently, a production lot of polymer rotors was procured for
field use.  As part of the acceptance testing for these rotors, a number of
PAA meters were assembled from a random sample of rotors and tested for con-
formity to the established PAA standard rating.  These tests were performed at
the tow-tank facility at the Gulf Coast Hydroscience Center between September
1987 and March 1988 and included tests of 67 rotors.  The tow-tank data were
analyzed between February and May 1988.  This memorandum releases the polymer
rotors for general use in the field.

It was found that the acceptance-test sample of PAA meters is functionally
equivalent to the sample used to develop the PAA standard rating and that no
benefit would be gained by revising the standard rating.  Therefore, the PAA
standard rating, defined by the equation

V = 2.456R + 0.020

with R in revolutions per second and V in feet per second, is approved for use
with the production lot of polymer AA rotors presently in stock at the
Hydrologic Instrumentation Facility.

The acceptance test results show root-mean-square deviations of approximately
1.0 to 1.3 percent between individual measurements and standard rating at
velocities of 0.5 foot per second and greater.  These results are generally
consistent with the PAA rating-development data and with generally accepted
statistical results for standard metal bucket wheels.  However, be aware that
some meters deviate from the standard rating by more than others.  It is not
possible to say whether the larger deviations are due to characteristics of
the rotors, to characteristics of the yoke and bearings, or to details of
assembly and adjustment.  Nonetheless, deviations of 2.5 to 5 percent may be
expected in approximately 2 percent of the meters obtained from the present
stock of polymer AA rotors.  Acceptance of the standard rating does not imply
acceptability of an individual meter that consistently exhibits significant
deviations from the standard rating.  Therefore, any meters put into service
with new rotors should be adjusted to yield a satisfactory spin test (tenta-
tively set at a minimum of 2 minutes with 3 to 4 minutes being ideal, pending
further investigation) and should be scrutinized carefully for consistency of
measurement results with results obtained from other meters.  Operational
procedures for reporting and correcting any identified problems will be
provided in a subsequent Office of Surface Water technical memorandum.

A more detailed discussion of the acceptance results may be obtained from the
Office of Surface Water.

                                       Ernest F. Hubbard, Jr.
                                       Acting Chief, Office of Surface Water

WRD Distribution:  A, B, S, FO, PO

This memorandum does not supersede any previous OSW Memorandum.