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9
PART NO: 860029-001
Last Revised 01/06/15
5.2 Thickness
The RF field developed by the sensor is at a maximum on the target surface. There is
penetration below the surface and the extent of penetration is a function of target resistivity and
permeability. The RF field will penetrate aluminum to a depth of 0.022”, a little more than three
“skin depths” (at one skin depth the field density is only 36% of surface density and at two skin
depths it is 13%). To avoid variations caused by temperature changes of the target, the
minimum thickness should be at least three skin depths.
The depth of penetration depends on the actual target material used. In cases where the
sensors are opposing each other, aluminum target thickness must be at least 0.050” to prevent
sensor interaction.
Material Thickness
in
mils
Silver
and
Copper
22
Gold
and
Aluminum
22
Beryllium
25
Magnesium, Brass, Bronze, Lead
58
300
Series
Stainless
110
Inconel
110
Recommended minimum target thickness in mils.
5.3 Size
The minimum target size is at least 2 times sensor diameter.
6.0 SPECIAL HANDLING CAUTIONS
6.1 Sensors
Due to design requirements, the sensor coil is exposed. The sensors are shipped with
protective caps. Keep them in place until installation of the sensors.
CAUTION:
If any sharp object comes in contact with the coil face or edge and damages it in
any way, this could short a number of turns in the coil, alter its impedance, and render the
sensor useless.
