ADS Environmental Services Model 4000 530017 A0 - Manual (Page 41)

3-18 ADS Model 4000 Manual
Installing the ring at least 12 inches upstream from the manhole invert
Keep the following in mind:
Make sure the ultrasonic depth sensor is at the top (crown)
of the pipe, the Doppler velocity sensor is at the bottom of
the pipe above any silt present and below the flow surface
(during minimum flows), and the pressure depth sensor is
near the bottom.
Proper orientation of the ring with the sensors in the pipe with and without silt
present