Improvements of the surface and constant quality are also part of today's requirements. The following methods are available:

Measuring tubes for fault detection that dynamically react to the smallest capacitance deviations can pinpoint faults manifesting themselves as capacitance variation in the cable segment being measured.

5.1.1. Method
These devices detect faults such as pinholes and cracks in the sheath. Measuring tubes are used where unshielded cables are manufactured. In the case of sheaths, the measurement process is based on the fact that water penetrates into the cable through the faulty spot, which significantly increases the capacitance of the sheathing. The slight vacuum caused by the cooling of the cable makes water penetration easier. The measurement principle also functions if the cable conductors are not grounded since the magnitude of the capacitive coupling with the grounded cooling trough is large enough.

5.1.2. Advantages
Exhaustive range for all cable sizes, rugged and durable execution. High measurement accuracy, even with a non-centered conductor. Very simple operation. Flexible mounting.

5.2.1. Applications and Principle
Sparktesters are used at the end of the extruding line, with sheathing lines or rewinding units, to detect bare patches and faults in the insulating jacket.
Both the internal conductor of the tested product and the sparktester are grounded. The cable passes through a test electrode. A fault in the insulation causes a sparkover between the test electrode and the internal conductor, the armour or the shielding, causing the sparktester to record an insulation fault. The ionised air in the test electrode provides the best possible contact with the surface of the cable and ensures that even the tiniest fault will be detected.

Sparktester

5.2.2. Advantages
It is particularly easy to test the dielectric strength with a sparktester. In addition, production faults are caught at an early stage, namely during the extrusion process rather than following production. Sparktesters have been used for a long time in many countries and some standards even require their use.