Hach Flo-Dar, Руководство пользователя

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General information
2.2.1 Theory of operation
The Flo-Dar Sensor is mounted above an open channel of water and measures the
surface velocity and depth from above the surface of the water. The two measurements
are used to calculate the flow rate.
During surcharge (submerged) conditions, a pressure transducer measures depth. The
optional surcharge velocity sensor (SVS) can be used to measure velocity during
surcharge conditions.
Surface velocity measurement
The surface velocity of the water is measured using radar technology. A radar beam is
transmitted from the sensor to the water surface at the center of the channel. A portion of
the signal is reflected back at a slightly different frequency. The difference in frequency,
known as the Doppler frequency, is directly proportional to the speed of the flow.
Proprietary algorithms are then used to calculate the average speed of the flow stream.
Note: The radar velocity sensor does not operate under surcharge conditions.
Velocity measurements during surcharge
The optional surcharge velocity sensor (SVS) is activated when the flow level rises to
within 7 inches of the sensor mounting frame and remains active until the flow falls to
7 inches below the sensor mounting frame. The mounting frame is installed 5 to 6 inches
above the crown of the pipe. This places the velocity-sensing electrodes at the correct
location in the flow below the elevation of the crown of the pipe.
The SVS measures velocity using an electromagnetic sensor that generates a magnetic
field. When the water passes through the magnetic field, a voltage is generated that is
directly proportional to the speed of the water passing the sensor.
Figure 1 System overview
1 Flo-Dar sensor with optional surcharge velocity sensor 3 Mounting frame
2 Logger or controller 4 Non-hazardous environment