Kaman KDM-8200 - Manual (Page 24)

24
Kaman Precision Products
Targets smaller than
the recommended size
are position sensitive
in the horizontal plane Target position
The Equipment
Target
Measurements taken using targets smaller than the recommended size are dependent on both
Size the vertical and horizontal position of the target. A vertical view shows a rod passing left to right
(three different positions) 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
Nonmagnetic targets with a thickness of 15-20 mils are recommended, and are typically
Thickness 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
Silver and Copper 12
Gold and Aluminum 12
Magnesium, Brass, Bronze, Lead 32
300 Series Stainless 60
Alloy 60
Other
The density of the electromagnetic field produced by a sensor is greatest at the surface of the
Considera- target, even though the field penetrates beyond that point. The extent of penetration is a function
tions of resistively and permeability of the target, and the carrier frequency used in the measuring
system. In turn, temperature effects resistively 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.
ROD
POSITION ANALOG
VOLTAGE