Kaman KD-5100 - Manual (Page 31)

31
NONCONTACT POSITION MEASURING SYSTEMS
KD5100
KD5100 Measuring Range and Performance Tradeoffs
The question is often asked what the limitations on the range of the KD5100 are. This question
is typically answered with the question “What performance is required in the application”? This
tech note will present the performance tradeoffs associated with range on the KD5100
differential measurement system. In particular, the performance parameters that matter are non-
linearity, temperature coefficient, and relative sensitivity (which affects resolution and
electronics temperature coefficient).
This tech note gives generalized results based on coil diameter and then applies the results to the
two most popular sensors used with the KD5100 – the 15N and 20N.
Note: This tech note is intended to be used as a guide illustrating typical performance and is not
in itself a specification of performance. The actual specifications vary depending on a number of
application variables and optimizations based on customer input that are not accounted for in
the estimates. Actual performance may vary from these estimates. Please refer to the Kaman
Specification sheet on the KD5100 for specific details on actual performance.
Definitions
There are some definitions that are important when discussing the performance.
Offset: The closest distance from the sensor face to the target that is still within the measuring
range.
Null Gap: The distance from the sensor face to the target when the target is equidistant between
the sensors.
Full Range (FR): The full range (sometimes referred to as Full Scale) of the system is defined
as the total measurement distance. For example, a system with a
± 10 mil ( ± 0.25mm) range
would have a full range of 20 mils (0.5mm). All percentage measurements are percent of the full
range.
Coil Diameter: This is referring to the diameter of the sensing coil itself. Eddy current systems
performance at different ranges can most often be estimated generally (i.e. normalized) when
considered as a percentage of the coil diameter. This allows the results to be applied broadly.
The graphs following are based on this normalization. ‘Full Range as a % of Coil Diameter’ in
the graphs means that for a coil diameter of 0.140” (~3.55mm) the number of ‘50%’ the full
range would be about 0.070” (
± 35 mils) or ~1.77mm ( ± 0.885mm) which is equivalent to ½ of
the coil diameter.