Kellyco PULSE STAR II PRO, Инструкция по эксплуатации, Страница: 71 / 89

Li mit ations of the me tal di scri mi na ti on
The PULSE STAR II PRO me tal di scri mi na ti on ana ly zes the de cay func -
tion of the sig nal ge ner ated by the me tal ob ject. In ge ne ral, the form of
this de cay functi on de pends on the fol lo wing ob ject pro per ties: kind of
me tal, sha pe, size, and orientation.
Un for tu na te ly, the in flu en ce of the last three men tio ned pro per ties is
very high for small ob jects (in the ran ge of 10cm and smal ler). For this
rea son, this is the mi ni mum size re qui red for the me tal discrimination.
For lar ger ob jects, the kind of me tal is the main fac tor which de ter -
mines the form of the de cay functi on. The elec tro nics can then clas si fy
the se ob jects to have eit her low or high elec tri cal con duc ti vi ty, in di ca -
ted by a green or red light re spec ti ve ly. It should be no ted that the re is
a thres hold bet ween the se two sta tes, i.e. an ob ject with a con duc ti vi ty
which is very clo se to this thres hold may cau se eit her in con sis tent
measurements or none of the lights to turn on (i.e. the conductivity is
exactly equal to the threshold).
The abo ve ex pla na tion means that the green LED turns on for:
}
Al most all small ob jects
}
Fer rous ob jects
}
Lar ge non-fer rous ob jects with poor con duc ti vi ty (for ex am ple thin
foils, lead)
The red LED turns on for lar ge ob jects with high con duc ti vi ty (for ex am -
ple sil ver, cop per, alu mi ni um, gold).
Plea se note that al loys (for ex am ple bron ze ar ti facts) usu al ly have
much lo wer elec tri cal con duc ti vi ty than pure met als. For this rea son,
the se ob jects may be clas si fied as 'fer rous'. Also, se ve ral small ob jects
(e.g. coins) next to each ot her have com ple te ly dif fe rent pro per ties
than for ex am ple a pla te of the same ma te ri al and the same to tal size
and may therefore be classified as iron as well.
Strong elec tro mag ne tic in ter fer en ce may cau se er ra tic LED in di ca tions.
In this case, a re li ab le di scri mi na ti on is only pos si ble by re du cing the
sen si ti vi ty by ad ding an off set as described in chapter 8.
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