ADS Environmental Services Model 3600 530002 A2 - Manual (Page 31)

3-6 ADS 3600 Flow Monitor O&M Manual
calculates the depth of flow. The pressure depth system also compensates for
temperature, which is measured by a temperature sensor located inside the pressure
sensor.
Doppler Velocity Sensor
The Doppler velocity sensor, called the velocity mouse, is placed at the bottom of the
pipe next to the pressure depth sensor. It emits a wide, omnidirectional sound wave at
a specific frequency upward into the flow. The sound wave bounces off particles in
the flow and returns to the sensor.
The velocity sensor measures the change in the sound wave's frequency from
transmission to reception. This change is used to determine the velocity of the flow
based on the principle of the Doppler effect. The Doppler effect describes the shift in
frequency of a sound wave emitted by a moving object in relation to a stationary point.
In this case of flow measurement, the moving objects are particles in the flow; the
stationary point is the velocity sensor, and the sound wave is the reflection of the
sound wave emitted by the velocity sensor off of the particles.