In Reply Refer To:
Mail Stop 415
January 15, 2016
OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM 2016.01
SUBJECT: Quality Assurance Checks of Mechanical Current Meters and Meter Configuration
The purpose of this memorandum is to establish new U.S. Geological Survey (USGS) policies regarding (1) routine quality assurance (QA) checks of mechanical current meters used for making velocity and discharge measurements and (2) upgrades to convert wiper-switch current meters to mag-head meters. This memorandum and the attached appendix state the policies and provide a description of how to register and schedule appointments for the QA program.
This memorandum is specific to mechanical current meters currently in use by the USGS including all variations of the Price Type AA, Pygmy, and Winter (Ice) meters. With this memorandum, OSW and the HIF are retiring the "Current Meter Exchange Program" associated with triennial surface-water reviews. Mechanical current meters will no longer be exchanged as part of the WMA Water Science Center (WSC) surface water reviews.
Mechanical Meter Use
Data from the National Water Information System (NWIS) demonstrates that mechanical current meter use has declined. While mechanical meters were used for greater than 90 percent of USGS discharge measurements in the 1990s, in the last 5 years only about 20 percent of discharge measurements were collected using mechanical meters. In addition, for exchanged meters during fiscal years 2000 through 2015, one third of meters had one or more velocity points outside the accuracy tolerance limits of Standard Rating No. 2 (Hubbard et al, 2001). In 2013 HIF began collecting data on the type and use of meters being exchanged. The majority of meters tested under the "Current Meter Exchange Program" from 2013-2015 were backup meters. Results show that only 35 percent of AA and 24 percent of Pygmy meters exchanged are used regularly. However a higher percentage of "backup meters" had all velocity points fit within the accuracy tolerance limits of Standard Rating No. 2 than meters described as "in use". This data suggests that "in-use" meters are receiving infrequent/inadequate maintenance possibly due to lack of routine use and inspection and reduced emphasis and training on the use and care of mechanical meters.
Mechanical Meter Quality Assurance Program
In order to ensure that only well maintained mechanical meters remain in use, beginning in fiscal year 2016, the HIF (under the authority of OSW) is implementing a Mechanical Current Meter Quality Assurance Program for checking and documenting the performance of all mechanical current meters used in the USGS WMA programs. Every mechanical current meter used for measuring velocity in the USGS WMA will be required to be registered with the HIF and checked by the HIF Hydraulic Laboratory (HIF-HL) at least once every three years. Mechanical meters used for discharge measurements entered into Site Visit will be compared to the list of registered meters during triennial surface-water reviews. Existing registered meters may continue in use until they are scheduled for a QA check sometime during the first 3 years. WSCs will be responsible for scheduling QA appointments around field work to ensure the 3-year cycle is maintained. In addition to QA checks on existing meters, all new Price type mechanical meters and/or meters sent to the HIF to be rebuilt, must be QA checked in the HIF Hydraulic Laboratory (HIF-HL) before being placed into service for the first time or back in service. All instruments returned to the HIF for QA check will need Return Materials Authorization paperwork and an Appointy appointment to be processed. HIF-HL will perform a visual inspection, timed spin test, and test the meter's ability to fit within a standard rating equation at speeds ranging from 0.25 ft/s to 3 ft/s for Pygmy meters and 0.25 ft/s to 8 ft/s for AA meters. Please see the attached Appendix for details on registration, cost, scheduling, individual ratings and WSC responsibilities. OSW is requesting that all mechanical current meters be registered by March 1st, 2016.
Conversion of Wiper-Switch Current Meters to Mag-head Meters
OSW Technical Memorandum 2014.07 mandates that electronic methods be used to upload measurement data into NWIS. Electronic discharge calculators provide a means to comply with the OSW memo and offer proven field efficiencies. In addition, long-term experience and HIF inspection and repair of exchange meters indicates that current meter wiper switches (cat whiskers) are a significant source of problem performance and failure of meters to rate within established rating tolerances. As an alternative to cat whiskers, magnetic switch heads provide superior and more consistent performance, do not require extensive maintenance, and provide cleaner output signals needed by electronic digitizers and interfaces. In order to reduce the failure rate of the mechanical current meters and facilitate use of electronic methods for documenting flow measurements, mechanical current meters that use wiper switches (cat whiskers) must to be upgraded to magnetic switches.
Upgrade kits to the Type AA mechanical current meters are available at HIF (Item No. 1101060) and can be ordered and installed by a WSC technician. Type AA meters can be upgraded and continue to be used with the Standard Rating No.2. Pygmy meters however, must be upgraded at HIF and have their calibration checked. For the rare situation requiring use of a headset, AA meters equipped with the older, original AA maghead or the most resent SK2 maghead can be used with a headset; the SK maghead is damaged by using a headset and will stop functioning.
Securing sufficient numbers of new pygmy meters that meet HIF specifications has proven to be difficult and expensive. Yet there is a large supply of old, infrequently used and noncompliant pygmy meters and spare parts in many WSCs. In order to replenish Pygmy warehouse stock and reduce the number of meters in the field that are not routinely used, and that may not be configured properly, the HIF will offer partial credit towards a magnetic switch upgrade for each of the first 50 complete trade-in Pygmy meters received in good condition. A trade-in of two complete Pygmy meters in good condition will result in one free magnetic switch upgrade for either a Price Type AA or Pygmy meter. Any additional excess bucket wheels, complete meters, and meter parts that are no longer in use but are still in good condition can be returned to the HIF to be recycled. The full details on how to participate in these programs will be released at a later date.
Robert R. Mason, Jr.
Chief, Office of Surface Water
Hubbard, E.F., Thibodeaux, K.G., Turcios, L.M., 2001, Price Current Meter Standard Rating Development by the U.S. Geological Survey, Journal of Hydraulic Engineering, Vol. 127, No. 4, p. 250-257, accessed January, 11, 2016 http://ascelibrary.org/doi/pdf/10.1061/(ASCE)0733-9429(2001)127:4(250)
Distribution: GS-W All