In-line thickness measurement of blown film

Both longitudinal and lateral tolerances occur in the material thickness for the extrusion of blown film. Measuring the thickness profile of the film and providing data for the host computer are the tasks of the “Profile measuring system for blown film” developed by Micro-Epsilon.
The system is available in both contact and non-contact versions and is used in production immediately after the film sizing unit. The contact version is used for all non-adhesive film. The non-contact system is used for adhesive (sticky) film. Both systems operate according to the capacitive measurement principle. The electronics inside the sensor are configured to measure non-conducting materials.
In non-contact capacitive film thickness measurement, a constant gap between sensor and film needs to be maintained,  in order to achieve the required measurement accuracy. To achieve this constant gap, an air pocket is produced in front of the sensor  in a control circuit using compressed air. The “pressing force” of the sensor against the blown film is also regulated with this apparatus. The  distance is regulated by a closed loop control system using air gauging principles without using any electronic components.
The contact version of the system is also based on the capacitive measurement principle. Here, the sensor comes into direct contact with the film .