Loma IQ2 Service Manual page 14

Other EMC Considerations
Any external sensor connected to the Metal Detector should be in screened
cable, grounded at the point of entry into the metal detector control box and kept
free from sources of electrical noise (e.g. mains supplies for large electrical
machines).
The metal detector is a highly sensitive RF measuring device, which is well
screened from outside interference and has excellent electronic discrimination
against unwanted electromagnetic fields. However, due to it's sensitivity it is
possible that other devices that emit high levels of RF noise at the operating
frequency of the detector may cause interference, thereby degrading the
performance of the detector.
NOTE
These guidelines are based on the PPMA EMC Code of Practice, which
should be referred to if in doubt about any aspect of making external
electrical connections to the detector.
Radio Frequency Interference
A metal detector is, essentially, a Radio Frequency (RF) receiver. As such it is
sensitive to RF noise in the general vicinity of the detector location. While those
frequencies not close to the operating frequency of the detector will usually be filtered
out (this includes most 'walkie talkie' frequencies, unless the transmitter is held very
close to the detector aperture). It is not uncommon for the control frequency (or a
multiple of it), used in modern speed controllers, to cause interference.
To reduce the risks of such interference causing false rejects or other symptoms of
undesirable operation at the metal detector, the following recommendations should be
followed:
Always route speed controller input and output wiring away from the metal detector
area. NEVER put speed controller wiring in the same conduit or on the same supply
as the metal detector wiring.
Run speed controller wiring in the general vicinity of the metal detector in a rigid steel
conduit or use other techniques to ensure 100% screening of the cable. Always follow
the speed controller manufacturer's instructions for installation, wiring, screening and
grounding.
In addition to following these guidelines, most speed controller manufacturers can
supply input and output filters which can be fitted to the field wiring to dramatically
reduce RF emissions if necessary.
Module 5092
Product Description and Environment
3-5