Loma IQ3+, Руководство пользователя

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Installation
35
13. Head mechanical insulation: The head must be isolated from the conveyor metal work to
reduce the transmission of vibration into the head. Isolation bushes must be fitted as shown in
the diagram below
Reasoning Behind the Basic Rules
■
Nuisance triggering
Most problems with intermittent or nuisance triggering are due to insufficient appreciation of the
basic rules of construction. For example: A bolted conveyor when brand new may appear to
work perfectly well but over time bolts may work loose leading to nuisance triggering.
■
Conveyor construction
Where the product to be inspected is of a non conductive nature, such as powders or is hard
frozen (<-18ºC / -0.4ºF) these can more than likely be run in the detectors DRY mode. In this
mode it is inherently resistant to vibration/ shock
Where the product to be inspected is wet and salty and of a conductive nature, such as fresh
meats, cheeses, pickles and sauces the detector uses a different mode of operation because it
has to eliminate the product effect. When operating in this mode, the detector’s resistance to
vibration and shock is not as good as when operating in DRY mode.
Loma metal detectors are designed to minimise any vibration or shock effects when operating
with conductive products. To further enhance this resistance the conveyor must be designed
with consideration to the above rules.
The detector is a radio frequency (RF) transmitter and receiver device that sets up an
electromagnetic field in the head aperture. The stainless steel case acts as a screen to prevent
external metal or electrical or magnetic fields, affecting the search coil assembly and to retain
the field within the case.
However because there is an opening (aperture) through which the product to be inspected
must pass, some of this field radiates to the outside and, by induction, causes small electrical
currents (eddy currents) to flow in nearby metallic structures that come within the effect of the
field.
If these structures form closed electrical circuits (loops), then these “closed” loops will form part
of the detector conveyor framework. Provided that the eddy current paths have a constant
electrical resistance, the detector will normally ignore them.
Welding the framework of the conveyor ensures that most of the eddy current paths maintain a
constant electrical resistance. It is impossible to guarantee this if the frame is bolted together –
for example bolts can loosen slightly due to constant vibration or may not be fully tightened after
general maintenance and bonding surfaces can corrode or be painted over, all of which will
affect the resistance of a joint which can result in random false triggering.