3.3. X-Rays Technology

3.3.1. Method
X-rays should constitute the perfect solution since they allow product inspection "from the inside" with absolute sharpness. Using tomographic evaluation, it is possible to display on a screen a profile free of distortion, showing all structures and cavities.

3.3.2. Measurement Set-Up
An example of X-ray measuring technique is provided by the RAYEX system, a Zumbach development. This system is used in CV lines for XLPE, EPR and rubber insulated cables.
A measuring head with 2 X-ray scanners perpendicular to each other is mounted on the telescopic tube, immediately after the extruder.

The X-ray system "sees" through the telescopic tube and through the cable and measures the overall diameter, the ovality and the wall thickness of each internal semi-conductive layer. A complete cross-section of the cable with all significant dimensions is displayed on a high-resolution colour screen.

3.3.3 Measurement Principle

3.3.4. Advantages
This system allows immediate centering of the extruder head and drastically reduces the amount of start-up scrap. Everything is documented and the tolerance limits are never exceeded.

3.3.5. Shortcomings
The only remaining disadvantage is that an application to small product dimensions does not seem to be economically feasible, even at the present time.

The Laser-, Inductive and X-Ray Technology represents today's standard Wall-Eccentricity Measurement. However for the Measurement of sheathing on Datacable this technology has its limits. Ultrasound Technology brings new additional possibilities. In the following chapter we explain the reason why.

4.1. Method

Ultrasound is a sound whose frequency exceeds the human threshold of audibility, i.e. approximately more than 20 kHz. The higher frequency limit is 10 GHz, which is also the beginning of the hypersonic range. One distinguishes in the order of increasing frequency: Audible sound - Ultrasound - Hypersound.

In the past, the generation of ultrasound has been based on the sole use of the Galton whistle and hole sirens (irregular pattern of holes in the rotating disk). Today, the inverse piezoelectric effect and magnetostriction generate ultrasonic waves with higher sound intensity. Ultrasonic waves can be focused and form parallel sound beams. Ultrasonic technology has been used for decades for propagation time measurements in the plastics and rubber industry. It has also been used more and more successfully in the cable industry. Wall thickness and eccentricity measurement, as well as the acquisition of data from hot products, have especially contributed to the increase in popularity of this technology.