Fiber-optic quartz voltage sensor
AssigneeABB Research Ltd.
InventorMathias Ingold
Life of this patent
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Abstract
The sensor comprises at least one quartz body (1) sectioned from a quartz crystal, an optical fiber connected to the quartz body in at least one given length, and means for detecting changes in length of the optical fiber which are caused by piezoelectrically caused changes in shape of the quartz body in an electric field. It is shown how the mostly undesired temperature dependence of the sensor measurement signal can be influenced and, as the case may be, even eliminated in a purely passive manner by a mixture of the two independent piezoelectric coefficients d.sub.11 and d.sub.14 which contribute to the piezoelectrically caused change in dimension of the quartz body.
Claims10
A fiber-optic sensor for measuring electric field strengths or voltages,
- a) comprising at least one quartz body made from a quartz crystal with piezoelectric coefficients d.sub.11 and d.sub.14 and with mutually orthogonal crystallographic main axes x, y, z which form a right-handed coordinate system,
- b) the z-axis being a threefold optical axis, in whose direction the polarization plane of a linearly polarized light is rotated, in the case of a direction of view opposing the direction of propagation of said light, counterclockwise in the case of left quartz and clockwise in the case of right quartz,
- c) the x-axis denoting one of 3 twofold electric axes and the positive x-direction being oriented such that in the case of a tensile strain of a left quartz in the direction of this x-axis a positive charge occurs, and in the case of a right quartz a negative charge occurs on a surface perpendicular to the x-axis due to the piezoelectric effect,
- d) the y-axis being the so-called mechanical axis,
- e) at room temperature the piezoelectric coefficients of 0th order, represented as d.sub.11.sup.(0) and d.sub.14.sup.(0), are d.sub.11.sup.(0) >0 and d.sub.14.sup.(0) >0 for the left quartz, and d.sub.11.sup.(0) <0 and d.sub.14.sup.(0) <0 for the right quartz,
- f) the temperature coefficients of 1st order of the piezoelectric coefficients, represented as d.sub.11.sup.(1) and d.sub.14.sup.(1), being d.sub.11.sup.(1) <0 and d.sub.14.sup.(1) >0 for left quartz and d.sub.11.sup.(1) >0 and d.sub.14.sup.(1) <0 for right quartz,
- g) having at least one optical fiber which is attached to the quartz body over a prescribable section or a length of the quartz body in such a way that in the dimensioning of the quartz-body changes in length are transmitted to the optical fibers, wherein
- h) the temperature coefficients of 1st order of the piezoelectric coefficients d.sub.11.sup.(1) and d.sub.14.sup.(1) of the quartz body are combined proportionally in accordance with d.sub.eff.sup.(1) =A.multidot.d.sub.11.sup.(1) +B.multidot.d.sub.14.sup.(1), in such a way that a change in length of the optical fiber which is effected by the piezoelectric coefficients of 0th order d.sub.11.sup.(0) and d.sub.14.sup.(0) and is proportional to d.sub.eff.sup.(0) =A.multidot.d.sub.11.sup.(0) +B.multidot.d.sub.14.sup.(0), and/or an optical measurement signal due to this sensor, are at least approximately independent of temperature, d.sub.eff.sup.(0) is effective piezoelectric coefficient, d.sub.eff.sup.(1) is associated temperature coefficient for the strain of the quartz body along the support surface of the optical fiber, and A, B are parameters which depend on the shape of the at least one quartz body relative to the crystallographic axes and/or on the length and position of the at least one length of the optical fiber which is codected to the at least one quartz body.
Dependencies are inferred from the claim text.