Teledyne 4250, Installation And Operation Manual, Page: 104 / 204

4250 Flow Meter
Section 3 Installation
3-14
In such cases, make sure you measure depth at a point inside
the cone. In large channels, you may have to measure several feet
upstream from the sensor.
Measure the diameter of the pipe. Then measure from the top
center of the pipe to the liquid surface and subtract this distance
from the pipe diameter to get the level. If the stream is not calm,
average the measurements from the crest and the trough of the
waves. Measure some distance
upstream from the installed AV
sensor. We suggest using a distance equal to the depth of the flow
stream. For example, if the flow stream is one foot deep, you
would measure level at a point one foot upstream from the
sensor. Do not measure right at the sensor, as the profile of the
sensor and the mounting strap may cause a “jump” or localized
rise in the level. If you cannot measure upstream after instal-
lation of the sensor and strap, measure the level before installing
the sensor. Do
not measure downstream from the sensor.
If the level is low enough that you can see a visible jump or dis-
turbance in the liquid surface where it flows over the sensor and
mounting ring, you should measure the level with the sensor and
ring out of the stream.
Changes in channel shape that affect the stability of the flow
such as elbows, outfalls, inverts, etc. should be considered when
locating the sensor. Avoid installation in areas where such
changes in channel shape nearby make the flow turbulent.
Instead, install where the flow has stabilized.
• You do not have to install the sensor with a primary
measuring device.
(Top view of channel)
A-V Sensor
Ultrasonic Cone
Channel center line
Effect of offset mounting of sensor
Jump in stream over sensor
Side view of channel
A-V Sensor