Alvestad Marin AS

- Pendulum Current Meter

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Feed spill is costly Feeding in strong currents means that many particle of feed will drift out of the facility without being eaten. When there is no current, the appetite normally gets weaker and this results in low exploitation of the feed. Feeding adapted to the prevailing local ocean current conditions will exploit the feed to a maximum. FeedFlow® is a simple, robust and dependable pendulum current meter which gives continuous information about the current in the facility and stops waste of feed caused by feeding at too high or low velocity. The pendulum has low sensitivity for fouling, has no moving components or sensors, and it can easily be connected to all types of feeding apparatus.

Manner of operation FeedFlow® is suspended from a flexible cable from a fixing point in the fish farm facility. The instrument measures the force of the current by exploiting the current’s pulling force. When there is no current, the instrument will only be influenced by the power of gravity andthus it will hang perpendicularly. When the current increases, the flow will create a horizontally directed pulling force which will pull the instrument at an angle ø away from the perpendicular (figure 1). A built-in control system will measure the angle and calculate the velocity of the current v on the basis of a pre-entered calibration curve. Finally, a real time current velocity is presented in the form of a 4-20 mA electric current circuit signal.

Mechanical construction. The main features of the mechanical construction of the instrument. The instrument consists of a cylinder with 4 pull amplifying, longitudinal fins that is suspended in a flexible cord. The instrument’s total current pull compared to its weight in water determines its sensitivity and measuring range.

Electronic construction The instrument’s electronics has been mounted on a circular sensory card which contains a two axes angle meter and a computer processor. The angle signals are transmitted to the processor which continuously calculates the angel ø independently of the direction of the slope. Afterwards, the processor transmits a 4-20 mA current circuit generator and a 9600 baud RS-232 generator. The RS-232 generator presents the angle of inclination ø in ASCII format with an update frequency of about 1 second.

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