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2150EX Area Velocity Flow Module
Section 3 Programming
3-4
In round pipes it is possible to measure the level without disturb-
ing the stream surface. This method is preferred. Refer to the di-
agram in the margin. First measure the inside diameter of the
pipe (D). Then measure the airspace (a) from the liquid surface to
the peak of the inside diameter. Average this measurement if the
surface is not calm. The level measurement that you enter (h) is
calculated by subtracting the distance above the liquid (d) from
the diameter (D). If difficult channel conditions keep you from
making the measurements as described above, another site
should be considered.
3.3.2 Zero Level Offset AV Sensors are sometimes offset in the channel to avoid heavy
concentrations of silt, or to maximize the level resolution over a
specific range. When the AV Sensor is offset, an offset distance
must be entered on the Velocity measurement tab in Flowlink.
Refer to Figure 3-3. Enter a value for the vertical distance the
sensor is installed above the true zero level of the stream. For
example, if the sensor is mounted on the side of the pipe two
inches higher than the true zero level (the bottom center of the
pipe), the Zero Level Offset is two inches. If the sensor is
mounted at the bottom of the channel, enter zero.
Note
Do not confuse the circumferential distance between true zero
and the location of the AV Sensor with the vertical distance
(height). If you install the AV Sensor at the true zero level of the
pipe or channel, you would enter “0” for the offset (ignoring the
thickness of the mounting ring).
Figure 3-3 Zero Level Offset Measurement
a
h
D
Level (h) = D − a
Circumferential
Distance
Offset
Distance
AV Sensor
True Zero Point
of channel