{{short description, Mechanical flowmeter invented by Vagn Walfrid Ekman, a Swedish oceanographer, in 1903
The Ekman
current meter
A current meter is an oceanographic device for flow measurement by mechanical, tilt, acoustical or electrical means.
Different reference frames
In physics, one distinguishes different reference frames depending on where the observer is located ...
is a mechanical
flowmeter
Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways. The common types of flowmeters with industrial applications are listed below:
* a) Obstruction type (differential pressure or variable area) ...
invented by
Vagn Walfrid Ekman
Vagn Walfrid Ekman (3 May 1874 – 9 March 1954) was a Swedish oceanographer.
Born in Stockholm to Fredrik Laurentz Ekman, himself an oceanographer, he became committed to oceanography while studying physics at the University of Uppsala and ...
, a
Swedish
Swedish or ' may refer to:
Anything from or related to Sweden, a country in Northern Europe. Or, specifically:
* Swedish language, a North Germanic language spoken primarily in Sweden and Finland
** Swedish alphabet, the official alphabet used by ...
oceanographer
Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics ...
, in 1903. It comprises a propeller with a mechanism to record the number of revolutions, a compass and a recorder with which to record the direction, and a vane that orients the instrument so the propeller faces the current. It is mounted on a free-swinging vertical axis suspended from a wire and has a weight attached below.
The balanced propeller, with four to eight blades, rotates inside a protective ring. The position of a lever controls the propeller. In down position the propeller is stopped and the instrument is lowered, after reaching the desired depth a weight called a messenger is dropped to move the lever into the middle position which allows the propeller to turn freely. When the measurement has been taken another weight is dropped to push the lever to its highest position at which the propeller is again stopped.
The propeller revolutions are counted via a simple mechanism that gears down the revolutions and counts them on an indicator dial. The direction is indicated by a device connected to the directional vane that drops a small metal ball about every 100 revolutions. The ball falls into one of thirty-six compartments in the bottom of the compass box that indicate direction in increments of 10 degrees. If the direction changes while the measurement is being performed the balls will drop into separate compartments and a weighted mean is taken to determine the average current direction.
This is a simple and reliable instrument whose main disadvantage is that is must be hauled up to be read and reset after each measurement. Ekman solved this problem by designed a repeating current meter which could take up to forty-seven measurements before needing to be hauled up and reset. This device used a more complicated system of dropping small numbered metal balls at regular intervals to record the separate measurements.
Bibliography
H. U. Sverdrup, Martin W. Johnson, and Richard H. Fleming: The Oceans: Their Physics, Chemistry, and General Biology. publisher ''Prentice-Hall'', Inc., 1942.
See also
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Oceanic current
An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, s ...
*
Ekman spiral
The oceanic, wind driven Ekman spiral is the result of a force balance created by a shear stress force, Coriolis force and the water drag. This force balance gives a resulting current of the water different from the winds. In the ocean, there are t ...
*
Ekman water bottle
The Ekman water bottle is a sea water temperature sample device. The cylinder is dropped at the desired depth, the trap door below is opened to let the water enter and then closed tightly. This can be repeated at different depths as each sample go ...