EQUIPMENT AND SUPPLIES--Calibration of Electromagnetic Current Meters

In Reply Refer To:                               August 1, 1988
WGS-Mail Stop 415


Subject:  EQUIPMENT AND SUPPLIES--Calibration of Electromagnetic
                                  Current Meters

Several hundred electromagnetic current meters of various manufac-
turers and configurations have been calibrated at the Office of
Surface Water hydraulic laboratory at the John C. Stennis Space
Center (formerly NSTL).  This experience indicates that all elec-
tromagnetic current meters must be individually calibrated at this
facility.  There is no standardization in the calibration method-
ologies used by the various manufacturers of this equipment and
the ratings furnished may not meet Water Resources Division accu-
racy requirements.  Also, a readout check at zero velocity in a
bucket of water does not ensure that the readouts will be correct
over the range of velocities.

Tests by the Hydrologic Instrumentation Facility's Test and
Evaluation Section have shown that the indicated velocity readings
of at least some of these devices are subject to substantial
change dependent on the air temperature at which the electronics
are operated.  They also may be subject to change with varying
water conductivity.

Questions regarding calibration and application of electromagnetic
current meters should be addressed to Jack Hardee at FTS 494-1555
(commercial 601/688-1555).

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

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

This memorandum supersedes Surface Water Branch Technical
Memorandum No. 81.02.