Kaman KD-2300 - Manual (Page 25)

22
••••
Part III: The Equipment KD-2300 Instruction Manual
under the face of a sensor. The diagram on the right shows the
corresponding analog voltage assuming the rod remains a fixed vertical
distance from the sensor.
1 2 3
1
2
3
Target Thickness
Nonmagnetic targets with a thickness of 15-20 mils are recommended, and
are typically more than adequate for the majority of applications.
However, depending on the required accuracy, targets as thin as .5 mil
thick have been used. Targets that are very thin may require optimization
of the bridge module and a change in frequency.
Recommended Minimum Target Thickness:
Material
Mils
1 MHz 500 KHz
Silver and Copper 12 24
Gold and Aluminum 12 24
Magnesium, Brass, Bronze, Lead 32 64
300 Series Stainless 60 120
Alloy 60 120
Other Considerations
The density of the electromagnetic field produced by a sensor is greatest at
the surface of the target, even though the field penetrates beyond that
point. The extent of penetration is a function of resistivity and
permeability of the target, and the carrier frequency used in the measuring
system. In turn, temperature effects resistivity and permeability.
Generally, highly resistive targets and lower carrier frequency allow for
deepest penetration.
Field penetration only becomes a concern when the target material is too
thin to capture all of the sensor’s electromagnetic field. This type of
penetration, called “shine-through”, reduces the strength of the interaction
between target and sensor, ultimately reducing linearity, resolution and
long-term stability of the measuring system.