US 5,966,018 AGranted

Apparatus for measuring variations in thickness of elongated samples of thin plastic film

OwnerKevin D. Edmunds, Neil A. Stichainventors

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Abstract

A capacitance gauge for measuring changes in the thickness of dielectric film, such as plastic film, is automatically temperature and humidity compensated by utilizing a primary measurement sensor and a reference sensor which monitors changes in perceived capacitance caused by ambient temperature and humidity changes or other environmentally induced interferences. The reference sensor counterbalances in an equal an opposite fashion, and thereby automatically cancels, any imbalance in the primary sensor caused by temperature, humidity, or other, fluctuations. An improved film transport assembly for serially examining plastic film material which eliminates errors in thickness measurement location and eliminates variation in distance between individual sensor readings, while at the same time allowing the user of the invention to select from a full variable range of distances between individual sensor readings and also allows accurate positioning of the film in the sensor.

Claims26

Dependent claims

A capacitance electrode assembly adapted for attachment to a mounting plate for measuring changes in thickness of a dielectric film comprising:

a) a back plate;
b) means for connecting the back plate to the mounting plate;
c) a primary sensor assembly and a reference sensor assembly;
d) means for connecting the primary and reference sensor assembly to the back plate;
e) each sensor assembly having;
1) a lower housing connected to the back plate having an elongated upper portion projected away from the back plate;
2) an elongated first electrode extended along said upper portion of the lower housing;
3) an upper housing connected to the back plate having an elongated lower portion located in substantial vertical alignment with said elongated first electrode;
4) electrical insulator means mounted on the elongated lower portion of the upper housing;
and
5) said primary sensor assembly having a second electrode mounted on the electrical insulator means, said reference sensor assembly having a third electrode mounted on the electrical insulator means, said second and third electrodes being axially spaced from each other and spaced from the first electrode;
f) guide means for preventing the film from passing between the first electrode and third electrode and allowing the film to pass between the first electrode and second electrode;
g) a bridge circuit electrically coupled to the second and third electrodes whereby the reference sensor assembly counterbalances the bridge circuit and cancels any imbalance in the primary sensor assembly caused by temperature, humidity or other fluctuations;
and
h) means for moving the film between the first and second electrodes.

12 more elements

Dependencies are inferred from the claim text.