Teledyne 4250 Installation And Operation Manual page 105

The flow in this 10" round pipe is uni-
form. The ideal level measurement
point is always within the ultrasonic
cone – point C, but it is not easily
accessible. In this example, level mea-
surement at point A is acceptable due
to the uniform flow.
Note: Not drawn to scale. Depths in all
three examples are to show flow char-
acteristics of each channel.
The flow in this 10" round pipe is not
uniform, due to the low liquid level
and the disturbance caused by the sen-
sor. At point B, the level rises as the
liquid passes over the sensor and
mounting ring. Measure level at C. If
the flow becomes uniform when the
sensor and ring are removed, take a
level measurement close to the sensor
location.
The flow at the a-v sensor is not uni-
form. The level drops sharply into the
lower outfall. Similar effects would be
noted in the case of an elbow or bend
in the channel. In this example, the
sensor should be moved forward to the
uniform flow (between points C and
D). Take the level measurement within
the uniform flow. It might also be nec-
essary to average several level mea-
surements.
Figure 3-7 Methods of Level Measurement
6 Inches
A
2 Inches
A
4 Inches
A
However, if you do install the sensor in a channel that has a
primary measuring device (weir or flume) install it upstream or
downstream from the device, not inside the device.
Primary devices with narrowed passages (most flumes) change
the velocity of the liquid as it passes through the device. To min-
imize this effect, install the AV sensor at a point where the
stream velocity has returned to normal.
Install the AV sensor at the prescribed measuring point of a
primary measuring device if you only want to measure level. In
such instances, program the flow meter using level-to-flow rate
conversion with a secondary indication of velocity, rather than
area-velocity conversion (see Section 2). Information on where to
install the sensor is available for most primary measuring
devices from the Isco Open Channel Flow Measurement
Handbook or from the manufacturer of the device.
Section 3 Installation
Sensor Cable (Note routing)
Sensor
Mounting Ring
6 Inches 6 Inches
B C
2¼ Inches
2½ Inches
B C
5½ Inches 6 Inches
C
B
4250 Flow Meter
6 Inches
D
3-15