Pre tension monitoring solution

A tension monitoring system, comprising:

• an object part of fastening means securing a first object in relation to a second object, provided with at least one pattern located on the surface of said object and where the pattern comprises pattern portions arranged relative each other with a distance between pattern portions on a distance scale suitable for detecting tension within a pre determined range and resolution, wherein the pattern portions comprises a plurality of points and where each point is arranged fixedly on the object;
• at least one camera (4, 33, 33′, 701) for acquiring at least one image of the at least one pattern (3, 23, 32, 32′, 704) located on the object (2, 22, 31, 707);
• a computational device (500) arranged to receive image information from the at least one camera;
• wherein the computational device is arranged to analyze the acquired image for detecting the position of each pattern point using an image analysis algorithm arranged to determine the geometrical centre of a point using a contrast detection method, determining the distance between at least two pattern portions, and calculating the tension induced in the object using a reference value of distance between the two pattern portions when the object is mechanically relaxed.