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Summary: Awtar, Slocum 1 March, 2003
In-plane capacitance probe holding mechanism
Shorya Awtar
Alexander Slocum
Mechanical Engineering, MIT
In precision metrology it is frequently required to hold capacitance probes such that they
are properly aligned and held well. Alignment, i.e., parallelism between the sensor
surface and the target surface, is important for measurement accuracy. Deviation from
parallelism renders the probe's factory calibration incorrect and results in somewhat
inaccurate measurements. The sensor also needs to be held snugly in place by means of a
well distributed nestling force. A loosely held cap probe is prone to mechanical as well as
electrical noise. On the other hand, applying a large localized force, for example by
means of a direct-contact set screw, can damage the cap probe and permanently alter its
calibration. Furthermore, before the sensor is held in place, it must be free to move along
the sense axis to allow an adjustment of the initial gap between the sensor and the target.
Thus, an ideal probe holding mechanism should enable the following:
1. Proper alignment
2. Nestling force distributed over a length of approximately two to three times the
diameter of the probe
3. Easy movement of the probe along the sense axis before it is clamped
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