Description Of Terms - SubSurface Instruments LD-18 Operation Manual

10. Description of terms

The terms used in this operation manual are described in this section.
Notch filter
Selection out of OFF, 50Hz and 60Hz can be made by the operation of the NF switch. The initial status
is OFF.
Types of filters are briefly described below.
Besides those which do not allow passage of waves of a certain frequency and up (or below) such as high-
pass filter and low-pass filter, there are band-pass filters (BPFs) that allow passage of waves of a certain
frequency band only, band rejection filters (BRFs; not called band cut filters, as they do not remove the
target frequency only) that do not allow passage of waves of a certain frequency level, notch filters (NFs)
of particularly narrow frequency bandwidth among band rejection filters and com filters, which are
composite bodies of notch filters.
sound
volume
Low Frequency
High-pass
sound
volume
Low Frequency
Band rejection
A notch filter cuts components of a certain frequency band only as shown above. As the notch filter combines
such filters, it may be more appropriate to call it com filter. But it is indicated as notch filter for this detector.
The notch filter is applied up to five stages in this detector in each of 50Hz and 60Hz.
The exclusive frequency levels in case of 50Hz are 50, 100, 150, 200 and 250Hz; and the exclusive frequency
levels in case of 60Hz are 60, 120, 180, 240 and 300Hz.
If it appears that the pickup is picking higher harmonics of commercial frequency 50Hz or 60Hz, activate
the notch filter function and carry out water leak detection work.
sound
volume
High Low Frequency
Low-pass
sound
volume
Low Frequency
Original frequency characteristics
sound
volume
High Low Frequency
Notch
28
sound
volume
High Low Frequency
Band-pass
High
sound
volume
High Low Frequency
Com
[Hardware]
High
High