Angling The Beam; Calibrating The In-Pipe Ultrasonic Sensor - Hach 911 User Manual

Sensor Installation
1 Sensor
2 Bracket Thumbscrew
3 Bubble Level
4 Sound Waves

6.2.2 Angling the Beam

6.2.3 Calibrating the In-Pipe Ultrasonic Sensor

6.2.3.1 Calibrating the Temperature
50
Figure 27 End View of In-Pipe
The narrow beam of sound that emanates from the bottom of the in-pipe ultrasonic sensor
spreads out at an angle of ±12° (-10 dB) as it travels away from the sensor. This means
that if the sensor is mounted too high above a narrow channel, the beam may be too wide
when it reaches the bottom of the channel. This may cause false echoes from the sides on
the channel walls.
Calibrate the in-pipe sensor each time the sensor is installed at a new site. Calibrate the
in-pipe via one of two methods; Liquid Depth or Sensor Height. Each method has its own
advantages and disadvantages. Liquid Depth calibration is the recommended calibration
method; use the sensor height method only when Liquid Depth calibration is not an
option. An Invisible Range can also be set which allows the transducer to ignore
reflections from obstructions between the sensor and the water surface, such as ladder
rungs, channel side walls, etc.
The speed of sound in air varies with the temperature of air. The in-pipe sensor is
equipped with temperature compensation to help eliminate the effect of temperature
variation under normal site conditions. Enter the ambient air temperature at the transducer
location. For optimum results, allow enough time (100 minutes) to ensure that the sensor
is at equilibrium with the surrounding air temperature.
5 Wastewater
6 Vibration Isolation Gasket
7 Mounting Clip
8 Pipe (size may vary)