Instruction manual
Single frequency detectors, like X-TERRA, perform discrimination based on the time delay (phase) of
the received (Rx) signal with respect to the transmitted (Tx) signal.
Given the way the signals are processed in electronics and in software, non-ferrous objects can only
have positive phase angles. This can be shown on a phase diagram.
Ferrous objects generally have negative phase angles, because the magnetic response is stronger
than the eect of the inductance and conductance.
81Understanding your X-TERRA - Technology
Ferrous/non-ferrous discrimination works better at low frequencies. Even though the magnetic
response of a target is frequency independent, inductance eect increases as the frequency
increases. Therefore, at high frequency, the eect of the inductance can be stronger than the
magnetic response resulting in a ferrous object being misclassied as a non-ferrous one.
This is more likely to happen with larger ferrous targets of particular shapes and/or in particular
orientations. Although higher frequency detectors have somewhat poorer ferrous discrimination,
they have excellent sensitivity for low conductivity objects, so there are advantages and
disadvantages for single frequency detectors having one xed frequency. This is why the X-TERRA
detectors were designed with 3 kHz, 7.5 kHz and 18.75 kHz options by changing coils.
Please note: these
phase angles actually
overlap but have been
simplied for ease of
understanding.
Non-Ferrous
Targets eg. coins,
gold rings, etc
Ferrous Targets
Mineralized
Ground
Conductance
InductanceMagnetic Response
Q
P
Time delay (phase) diagram