Teledyne 4250, Installation And Operation Manual, Page: 103 / 204

4250 Flow Meter
Section 3 Installation
3-13
Although the sensor is easiest to calibrate when located
at the bottom of the stream, you can locate it off-center in
a larger pipe, if there are good reasons to do so. Streams
that have large amounts of silt would be suitable for this.
You can still calibrate the level accurately by using the
offset distance to set the zero level in the program (see
Page 2-14).
Note
For installations where the sensor is mounted off-center, you
must always have enough flow above the sensor to meet the
minimum measurement depth. The AV sensor
cannot mea-
sure either level or velocity if the flow stream falls below the
sensor.
3.6.1 Level Measurement in
Open Channels (No
Primary Device)
When measuring level to calibrate an area-velocity installation,
keep in mind the following:
• Make the measurement as accurately as possible.
• Measure the level at a point inside the ultrasonic “cone”
extending upstream from the AV sensor.
• Measure level in an area of stable flow. (This may affect
sensor location.)
The sensor may be installed at a point offset from the bottom
center line of the channel in cases where silting is a problem.
However, typical installations are at the bottom center. Note how
offset mounting of the sensor will change the dispersal of the
ultrasonic “cone.”
Top view of channel
A-V Sensor
Ultrasonic Cone
Ultrasonic Cone
Side view of channel
A-V Sensor