16
After the filters have been selected, use the ESC soft key to return to
the main menu.
3.6
Filter selection in the field
Filter selection on the HL 5000
is largely determined by the
type of pipe material the suspected leak is on and whether
the operator is pre-locating or pinpointing the leak. In order to detect
any potential leak sound, an operator may want to use all available
filters when attempting to pre-locate a leak.
When actually
pinpointing the location of the leak, an operator may want to select
only the filter or filters on which the constant minimum leak sound is
most active.
As a general rule, leak sounds on plastic pipes (and very large
diameter pipes of any type pipe material) tend to be low
frequency (106 - 540 Hz); leak sounds on metallic and other
high-density pipe materials (like asbestos cement) tend to be
higher frequency (360 - 1200 Hz). In addition, because the
ground itself muffles sound, leak sounds detected with a
ground microphone tend to be lower in frequency than those
detected with a contact microphone placed in direct contact
with the line. The following are two suggested filter settings:
3.6.1 Filter selection A (Ground microphone GM50, PAM U 40 with
ground plate).
When using a ground microphone, a filter range of 240 Hz -
540 Hz is recommended.
3.6.2
Filter Setting B: Contact Microphone (Pam U 40 w/ Spike or
Extension Rods).
For measurements directly on the pipe with the sensor spike,
a filter range of 540 Hz - 1200 Hz is recommended.
3.6.3
Leak Detection Process and Filter Selection
When conducting leak detection in areas where the specific
pipe material is known, an operator may want to set the filters
