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33
PART NO: 860029-001
Last Revised 01/06/15
Application Variables and Caveats
The following application variables will also affect performance. The effects listed are not
considered in the results of the tables above and must be considered separately
.
Sensor Loading:
Sensor loading by conductive materials that are incidentally in “view” of the
sensors can affect the results significantly and must be considered on a case-by-case basis.
The discussions in this appendix assume that incidental materials do not load the sensor.
Cosine Error:
This is error that occurs when the target movement is from tilting as in a fast
steering mirror assembly and can become significant at larger measuring ranges
.
Cross Axis Sensitivity Errors:
This error occurs in 2 axis measurements of tip and tilt
(common in fast steering mirrors) and can become significant at larger measuring ranges.
Setup Error
:
The system can become very sensitive to the null gap position when setup for
very small ranges. Changes in the null gap will affect both the sensitivity and temperature
coefficient. Usually only significant problem on ranges of <
10 mils (<
0.25 mm).
Target Effects:
Eddy current sensors are significantly affected by the target material
resistivity and permeability. Aluminum targets are considered in this appendix. In general the
KD-5100 is best used with non-magnetic (relative permeability
≥
1), low resistivity targets. The
effect this has on the sensor is dependent on the operating frequency and coil diameter.
Cable Length
:
The KD-5100 sensors are passive. This means that the cable is an integral
part of the sensor and affects measurement performance. The data presented assumes a 2
meter cable length. Actual results may vary with different cable lengths. Long cables are
especially bad for performance because they degrade the effective Q of the sensor and
increase the inherent temperature coefficient of the sensor coil. Long cables will also cause
problems with thermal drift and variations in the output caused by cable movement.
Optimization:
In the data presented, the circuit was optimized for each range. This means
that the component values in the circuit may be different for each specific measuring range.
The system will not get the performance shown simply by changing the range and recalibrating
– it would require factory optimization. The system could also be optimize for a specific
parameter (ex. temperature) and achieve better performance in that category – allowing the
other performance parameters to be worse. The data shown for a specific range is a
compromise of all the performance parameters. At each measurement range listed the linearity,
temperature coefficient, and sensitivity listed are achievable simultaneously.
