7
Metal Detector Principle Of Operation
The DSP 2 model metal detector operates on the balance coil full loop detection system.
Three equally spaced coils surround the aperture or opening through which the product to be inspected passes. The center coil
is connected to an oscillator circuit to produce an electromagnetic field. This signal is received by two coils one on either side of
the oscillator coil. These are the receiving or input coils. (See Figure 6)
Since the receiving coils are equally spaced from the oscillator, they receive equal amounts of signal. The coils are wound in
such a way that their signals oppose each other; therefore, the net signal across the coil is zero.
When a piece of metal enters within the electromagnetic field, it alters the field strength around it. As this metal passes through
the aperture, it changes the balance of the receiving coils so that the net signal is no longer zero.
This error signal is amplified, demodulated and converted to a digital signal to be processed by the Digital Signal Processor or
DSP. The DSP performs all the product compensation, phasing, residual compensation filtering, and produces a reject signal.
A metal detector is a high performance measuring instrument. The quality of the installation will have a direct effect upon
performance and reliability. Please read the installation instructions completely prior to installing the unit and contact Goring
Kerr if you have any questions.
Figure 6
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