EQUIPMENT AND SUPPLIES--Approval of Standard Rating for PAA Current Meter In Reply Refer To: June 6, 1988 WGS-Mail Stop 415 OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 88.09 Subject: EQUIPMENT AND SUPPLIES--Approval of Standard Rating for PAA Current Meter 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.