ADS Environmental Services FlowShark Pulse QR 775004 A1 - Manual (Page 32)

4-2 ADS FlowShark Pulse O&M Manual
Combination Sensor
The FlowShark Pulse uses a combination (combi) sensor that can simultaneously
determine both flow velocity and flow depth. A combi sensor may contain up to two
2 depth measurement devices: a water-ultrasonic device and/or a hydrostatic
(pressure) device.
1 Ground Plate
2 Acoustic Coupling Layer
3 Temperature Sensor
4 Flow Velocity Sensor
5 Ultrasonic Depth Sensor
6 Electronics
7 Pressure Measurement Cell
8 Pressure Measurement Duct
9 Cable Gland
Fig 4-1: Combination sensor with additional pressure measurement cell for installation at pipe bottom
Water-Ultrasonic Depth Measurement
Water-ultrasonic depth measurement involves using a horizontal sensor crystal to
determine flow depth based on the time difference between transmitting and receiving
a pulse reflected off the flow surface (the transit-time method).
2
•
l
t c
h
l
=
Where,
h = Depth Level
c = Transit Time of Sound
t
1
= Time Elapsed Between the Transmitted and Received Signals
Sound travels in water at a speed of 4856 feet per second (1480 m/s) at 68 °F (20 °C),
varying at a rate of 0.13 % for each difference in degree Fahrenheit (0.23% for each
degree Centigrade). To ensure accurate depth measurements, all calculations must
compensate for the flow temperature and the travel time of sound in the flow.