SENSOR MOUNTING LOCATION
The position of the sensor is one of the most important considerations for accurate Doppler flow
measurement. The same location guidelines apply to Doppler as most other types of flow meters.
Before permanently mounting a Doppler sensor onsite testing is recommended to determine optimum
mounting position. Use the sensor coupling compound (supplied with each Greyline flow meter, or
petroleum gel, acoustic compound or electrocardiograph gel). Take several readings around the axis of
the pipe and then at several points upstream and downstream from the selected position, checking for
consistent readings. Avoid high or low reading areas. Mount the sensor where consistent (average)
readings were obtained or continue testing on another pipe section.
VERTICAL OR HORIZONTAL PIPE - Vertical pipe
runs generally provide evenly distributed flow. On
Horizontal pipes and liquids with high concentrations
of gas or solids, the sensor should be mounted on the
side (3 or 9 o’clock position) to avoid concentrations
of gas at the top of the pipe, or solids at the bottom.
For liquids with minimal gas bubbles (e.g. potable
water) the sensor should be mounted on the top of a
horizontal pipe (12 o’clock position) to obtain the best
signal strength.
VELOCITY INCREASING DEVICES: Generally the sensor must be mounted away from flow
disturbances such as valves, pumps, orifice plates, venturis or pipe inlets and discharges which tend to
increase flow velocity. Velocity increasing devices often cause cavitation, or rapid release of gas
bubbles, and readings both up and downstream may show much higher velocity. As a guideline, mount
the sensor at least 20 diameters upstream or 30 diameters downstream from velocity increasing devices.
Required distance from a velocity increasing device will vary in applications depending on the flow
velocity and the characteristics of the liquid itself.
TURBULENCE INCREASING DEVICES: Elbows,
flanged connections and tees tend to introduce
desirable conditions of an evenly distributed flow
profile with some air or gases entrained in the flow.
Sensor mounting 6 pipe diameters upstream and 10
diameters downstream from these disturbances is
generally optimum.
The sensor is designed to mount longitudinally on a straight section of pipe. Do not attempt to mount it
on bends, elbows or fittings.
Page 14
PDFM 5.0 Portable Doppler Flow Meter
VERTICAL PIPE USUALLY
HAS EVENLY DISTRIBUTED FLOW
12 O'CLOCK POSITION WITH
LOW GAS CONTENT
3 O'CLOCK POSITION WITH HIGH
GAS OR SOLIDS CONTENT
FLOW
SENSOR MOUNTS 6 DIAMETERS
UPSTREAM OR 10 DOWNSTREAM
FROM AN ELBOW
