Section 3 Getting Started; Installing The Flow Meter-Considerations; Choosing The Proper Site; Dealing With Difficult Sites - Hach 911 User Manual

Section 3

3.1 Installing the Flow Meter-Considerations

3.1.1 Choosing the Proper Site

Site Condition Suggested Remedy
Outfalls Attach the sensor at least ten times the maximum expected level upstream of the outfall.
Attach the sensor at least ten times the maximum expected level upstream of the vertical drop.
Vertical drops in the
channel floor
Attach the sensor at least ten times the maximum expected level downstream of the vertical drop.
Locate the sensor at least ten times the maximum expected level upstream of the obstruction.
Elbows, sharp turns,
and "Y" connections
Locate the sensor at least ten times the maximum expected level downstream of the obstruction.

3.1.2 Dealing with Difficult Sites

3.1.3 Choosing the Appropriate Meter and Sensor Combination

Flow Meter Model Level and Velocity Sensor Configurations
911 Meter plus one Submerged Area/Velocity Sensor or one Velocity-Only Sensor
Meter plus two Submerged Area/Velocity Sensors or
940
Meter plus one Submerged Area/Velocity Sensor and one In-Pipe/Downlook Ultrasonic Sensor.
Getting Started
The accuracy of flow measurement depends on the suitability of individual monitoring
sites. Select sites that have normalized flow and minimal turbulence. Turbulence can
make it difficult to detect an average velocity in the flow stream. Obstructions, vertical
drops, pipe bends, and elbows can create turbulence.
preventing turbulence.
Table 3 Suggestions for Preventing Turbulence
Some sites may be difficult to monitor due to poor site conditions. The direction and speed
of particles in the flow stream contribute to the signal received by the velocity sensor. If the
turbulence near the measurement point is excessive, it may be difficult for the sensor to
determine the average velocity of the stream. The flow meters provide several unique
features to help deal with these problem sites.
Use Table 4 to determine which sensor to use. See
installation instructions.
Table 4 Flow Meter and Sensor Configurations
Table 3 contains suggestions for
Section 6 on page 43 for sensor
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