Accelerometers are transducers designed to be placed in physical
contact with the pipe. The vibration that results from the sound waves
is sensed by a piezoelectric crystal in the accelerometer that generates
a small electrical signal proportional to the vibration. The amount of
signal in volts is determined by the intensity of the vibration as
measured in units of gravity, or "g's". Therefore, the sensitivity of an
accelerometer can be measured in Volts/g.
Because they use sensitive crystals to produce the electrical signal,
these accelerometers are susceptible to damage by mechanical shock.
They are rated for a shock of approximately 5000 g's; dropping the
accelerometer onto a hard surface from 3.5 feet results in a shock of
approximately 50,000 g's. HANDLE THE ACCELEROMETERS WITH
CARE, AS THEY ARE SENSITIVE PIECES OF EQUIPMENT.
6.0 LEAK DETECTION WITH THE S30
To utilize the S30 for detecting unknown leaks, a leak survey must be
conducted. A leak survey is the process of monitoring the distribution
system for the sound of leaks.
6.1 ACCESS POINTS AND SURVEY FREQUENCY
The typical access points that are used when conducting a leak
survey are: Main Line Valves, Fire Hydrant Valves, Fire
Hydrants and Service Connections. The number of access
points to be monitored will vary depending on how thorough a
survey you wish to conduct.
There are some rules of thumb that are helpful in determining
"how much is enough" with respect to leak surveys. These rules
are based on extensive field experience, but should still be used
only as guidelines. The predominant factor in determining the
distance between listening points is the type of pipe. For the
distances listed below, the most significant leaks in a system will
be monitored.
METALLIC (Iron, Steel, Copper) - sound on access points at
least every 500 ft.
ASBESTOS-CEMENT (Transite, etc.) - sound on access points
at least every 250 ft.
PLASTIC (PVC, Polyethylene) - sound all available access
points (i.e. services, gate valves, hydrants, etc.).
