High precision adjustment using capacitive sensors
In the production of thin-film solar cells, multiple functional layers are applied in a defined arrangement and structure onto glass sheets with a size of up to 3m x 5m. This happens in large coating systems. The uniformity of the coating depends on numerous process parameters. The distance between two perforated metal plates, which act as electrodes, is a key factor. These must be adjusted over the entire surface with an accuracy of at least 50µm. This is why continuous calibration and tests should ensure accurate positioning and arching correction. Therefore, a distance measurement is carried out in a vacuum at five different points. Previously, an external provider carried out timeconsuming and costly measurements using mechanical gages. LSA GmbH developed a new all-in-one solution involving non-contact, capacitive sensors from Micro-Epsilon which the system operator can use autonomously.
The capacitive sensor and the preamplifier are encapsulated under vacuum in a measuring box, which is used to measure the distance between the plates. In total, five sensors are connected to the capaNCDT 6500 multi-channel system. The values measured are output via Ethernet.