Xylem MJK 713 Open Channel Flowmeter - Manual (Page 10)

10
Manual
US 3.10 713 Flow Converter 1210 - Sw 833062
MJK North America, Inc.
37 Sherwood Terrace, #126
Lake Bluff, Il 60044
Tel.: 847-482-8655
Fax: 847-482-8654
[email protected]
www.mjk.com
The spread of the ultrasonic signal
the table and illustration below show the spread of the
ultrasonic signal in conjunction to the measuring distance:
Measuring Beam Minimum distance to
SMOOTH
distance: spread: wall (from center line):
1’ 5” 2.3”
2’ 5” 2.6”
3’ 6” 2.9”
Table 1: The ultrasonic signal spread along a smooth wall and minimum
distance to center line in conjunction to the measuring distance.
Accordingly, as the measuring distance increases, the
distance from the center line to a smooth wall should also
be increased.
to avoid false echoes from e.g. edges, a minimum dis-
tance as shown on the drawing must be kept. the sensor
can be mounted in a smooth pipe if the distance cannot
be obtained. (See figure 1.)
Figure 1: The signal spread in conjunction with the measurement distance. The
signal spread should be increased by 50 - 100 % if the surface is not
smooth!
Flow measurement with smaller flumes / weirs
Smaller flumes may cause problems if the ultrasonic sig-
nal reflects on the edges of the flume as shown below
(fig. 2a).
the edges should be cut off (fig. 2c) or the ultrasonic
sensor should be mounted in a pipe (fig. 2b) with smooth
inner surface.
Measuring along a wall or other plane
the values in table 1 assume the ultrasonic signal is sent
along a smooth surface like a wall or plane without any
projections, joints, butts etc.
If the surface is not smooth or has projections (i.e. joints
on prefab elements), the ultrasonic signal will be im-
pedeaded too much, and for that reason
the values for minimum distance to wall in table 1 should
be increased with 50 - 100 % !
(min. dia. 5 in)
Figure 2: Use a pipe (B) or cut off the edges (C) on small weirs to prevent
disturbing reflections from the flume edges.
Blocking
distance!
A B C