A power tool comprising a stationary body, a shaft having at least one sensor and being axially and rotationally movable in relation to said body, and a transformer, said transformer comprising: - a stator, being fixed in relation to said body and including one or more stator windings, and - a rotor, being movable with said shaft and including one or more rotor windings, whereby - a magnetic field B is shared by said one or more stator windings and said one or more rotor windings, and is used for creating a contactless signal connection between said body and said at least one sensor of said shaft, characterized in that said stator has a substantially tubular form with a substantially uniform outer peripheral diameter and has a first part of a first length and a second part of a second length, said first part being shorter than said second part, and the first part having a smaller inner diameter than the inner diameter of the second part, - said rotor has a substantially tubular form with a substantially uniform inner peripheral diameter and has a first part of a first length and second part of a second length, the first part being longer than the second part, and the first part having a smaller outer diameter than the outer diameter of the second part of the rotor and smaller than the inner diameter of the second part of the stator, - wherein the rotor is arranged inside the stator such that a portion of the first part of the rotor faces the first part of the stator, forming an air gap between said first part of the stator and said first part of the rotor, another air gap is formed between the second part of the stator and the second part of the rotor, and an air pocket is formed over a portion where the second part of the stator faces the first part of the rotor over a certain length (L air), - wherein the stator windings are arranged along the second part of the stator close to the first part of the stator and the rotor windings are arranged along the first part of the rotor close to the second part of the rotor such that the stator windings and the rotor windings do not overlap, and - wherein at least one of said stator and said rotor is at least partly arranged with shielding means (217, 227) for reducing a flux leakage between said stator and said rotor said shielding means (217, 227) being arranged on one of said stator and said rotor over a portion of the length (L air) of said air pocket, between the stator windings and the rotor windings. - a stator, being fixed in relation to said body and including one or more stator windings, and - a rotor, being movable with said shaft and including one or more rotor windings, whereby - a magnetic field B is shared by said one or more stator windings and said one or more rotor windings, and is used for creating a contactless signal connection between said body and said at least one sensor of said shaft, characterized in that said stator has a substantially tubular form with a substantially uniform outer peripheral diameter and has a first part of a first length and a second part of a second length, said first part being shorter than said second part, and the first part having a smaller inner diameter than the inner diameter of the second part, - said rotor has a substantially tubular form with a substantially uniform inner peripheral diameter and has a first part of a first length and second part of a second length, the first part being longer than the second part, and the first part having a smaller outer diameter than the outer diameter of the second part of the rotor and smaller than the inner diameter of the second part of the stator, - wherein the rotor is arranged inside the stator such that a portion of the first part of the rotor faces the first part of the stator, forming an air gap between said first part of the stator and said first part of the rotor, another air gap is formed between the second part of the stator and the second part of the rotor, and an air pocket is formed over a portion where the second part of the stator faces the first part of the rotor over a certain length (L air), - wherein the stator windings are arranged along the second part of the stator close to the first part of the stator and the rotor windings are arranged along the first part of the rotor close to the second part of the rotor such that the stator windings and the rotor windings do not overlap, and - wherein at least one of said stator and said rotor is at least partly arranged with shielding means (217, 227) for reducing a flux leakage between said stator and said rotor said shielding means (217, 227) being arranged on one of said stator and said rotor over a portion of the length (L air) of said air pocket, between the stator windings and the rotor windings.