Instruction Manual

92
Definitions
This section explains the terms used in this
manual.
● Correlator
A device that obtains the correlation coefficient of
the signals captured by each pre-amplifier.
The pre-amplifiers send the signals from two or
more locations to the main unit, which then
calculates the correlation coefficient of the signals,
calculates the time difference between the signals,
and obtains the leakage location.
● Velocity
The leak detector displays the velocity of the sound
propagating in the pipe (when it is full of water).
Metal pipes allow higher velocities than plastic
pipes, and if the material is the same, the sound
velocity is slower for larger diameters.
● Filter
As already explained in the section on notch filters,
filters are used to extract only the frequency
components required for measurement.
● Td range
This is the delay time setting.
Delay time is the difference between the time it
takes for one pre-amplifier to acquire a signal and
another pre-amplifier to acquire it.
If there is a signal source in the center of the span
between pre-amplifiers, the signal propagation
times are identical and the time difference (Td) will
be 0.
If the source is closer to the reference pre-amplifier,
Td will be a positive value, and conversely if it is
farther away, it will be negative.
● DSP (Digital Signal Processer)
A microprocessor capable of high-speed processing
of digital signals such as audio, image, and video in
real time.
● FFT (Fast Fourier Transform)
In technical terms, the FFT operation calculates the
Fourier coefficients of the Fourier series. The leak
detector digitally samples the input signal
waveform, stores it as data, performs the FFT
operation, and displays the result. The data
acquired by the pre-amplifier is time-dependent,
and it is difficult to analyze the frequencies in this
kind of raw data. Performing the FFT operation
makes it is possible to analyze the frequencies of
signals that change over time.
* The main frequency components of the sound
cannot be identified by listening to the sound
obtained with the pre-amplifier. (What you can
identify are changes in the signal over time.)
After the FFT operation, the frequency analysis
can be performed to identify the main frequency
components of the signal.
● White noise
White noise refers to noise that uniformly contains
all the frequency components within a certain
frequency band.
● Young's modulus (longitudinal elastic modulus)
This property refers to the ability of an object to
return fully to its original state once a load that was
applied within a certain range is removed. This
property is called "elasticity".
Within this elastic region, the displacement is
proportional to the load. The relationship is
expressed as follows.
σ = E · ε (where σ is the stress, E is the Young's
modulus, and ε is the strain)
The proportional coefficient E is called the Young's
modulus.
● LPF (Low Pass Filter)
A filter that allows frequencies below a certain
frequency to pass through.
When the LPF is set to 1250 Hz, frequency
components below 1250 Hz are allowed to pass
through the filter.
● HPF (High Pass Filter)
A filter that allows frequencies above a certain
frequency to pass through.
When the HPF is set to 180 Hz, frequency
components above 180 Hz are allowed to pass
through the filter.