Tentune services
A service provided by InControl in cooperation with Det Norske Veritas (DNV) to determine tension in anchor lines for AMS-5 systems.   

Owners of floating oil-rigs (semi submersibles) and production vessels have been struggling with unreliable measurement systems for anchor line tension. Operators and governments often require calibration to verify indicated load readings, both for newly installed systems, and as a part of a periodic control.
There are methods and equipment available on the market, whereby the chain is unloaded using hydraulic jacks, and the load measured with load cells. This is a time consuming and costly operation that involves heavy equipment.
DNV has developed an alternative method called “TENTUNE”, based on the principle of a vibrating string, where one utilises the relationship between load in a wire and the natural frequency of vibration. This method does not require any vertical movement of the line, enabling measurements to be made without any disturbance to the anchoring system.
Application of the method at several installations in the North Sea showed that calm sea state conditions were sufficient for initiating the anchor line to vibrate at natural frequency. The method has also been used during strong winds and wave heights exceeding 5 meters.
The dominating signals picked up by the accelerometer were the natural frequency of the anchor line and the roll of the platform itself, induced by waves.
A battery-operated notebook computer equipped with a PCMCIA data acquisition card measures the vibration signal. A spreadsheet program, such as Excel or Lotus, can then be used to calculate actual tension in the anchor line and present the frequency or tension response. With skill and knowledge of the approximate actual tension, one can find the response that represents the natural frequency of the anchor line.
InControl, with its expert knowledge in Anchor Monitoring Systems, is responsible for proper calibration of the system. DNV is responsible for getting the right tension values with minimum cost. Together we offer a cost-effective service to increase reliability, security and stability