Thickness measurement and control

UK-based Scalar Technologies has launched the first in its family of in-line measurement systems targeted at process automation and control.

Dubbed the ScalarGauge I-50, the in-line system uses broad-spectrum reflection interferometry in the visible and near infra-red region specially adapted to suit measuring the thickness of transparent films and coatings in production line conditions.

It operates in conjunction with a scanner, designed to mount on coating/converting machinery and comes complete with a software package that provides features such as Profile and Trend measurements.

Being an optical device, ScalarGauge I-50 produces extremely accurate measurements without touching the product to be measured.

In many instances, the system can simultaneously measure multiple layers, a feat beyond the scope of traditional, in-line measurement techniques.

Calibration, often a headache in setting up and maintaining in-line measurement systems, is unnecessary. The system is factory calibrated during manufacture and no further calibration is required during the lifetime of the instrument.

The basic principle of operation is that of thin film interference. When light strikes a transparent film, some is reflected off the top surface and some will reflect off the bottom surface. These reflected light waves interfere with each other and produce an interference pattern, or interferogram. This pattern derives directly from the optical separation of the two surfaces, which is their physical separation multiplied by the refractive index of the material. By analysing the interference pattern using a specially developed software algorithm, the film thickness can be calculated. Measurement accuracy is sub-micron, more than adequate for most in-line process control requirements.

Data are recorded in a standard file format and available for export and analysis through the Ethernet port. Interfacing using standard Ethernet (TCP/IP) connectivity, means that the system can be accessed from anywhere within the corporate enterprise network or even via the internet for remote monitoring.

The process control system also contains an interface to commonly used external signal functions such as Reset, Unwind, Rewind, Tachometer (machine speed) and provides Warning and Alarm level output signals.

There are a number of sensor options available to optimise performance for a specific application. In general, two sensors cover the majority of applications. One version is capable of measuring layer thickness between 0.5um and 100um. A less expensive version has a limited measuring range of 0.5um to 50um.

The system has been developed for the plastic film and converting industry, for in-line measurement of base film thickness, release coatings, adhesives, transparent lacquers and hard coatings. However, if the sensor is mounted on a robot arm, the system can measure coatings on formed shapes or piece parts, such as car headlamps.

Measurements can also be made on coatings applied to semiconductor wafers and optical components.

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