1. A sensor for detecting a rotation angle as an electrical signal comprising:
permanent magnets whereof opposite poles are disposed facing each other, and
a flux density detecting unit which performs relative rotation between the permanent magnets, wherein:
the opposite magnetic pole surfaces of the permanent magnets are formed in a curved shape.
2. The rotation angle sensor as defined in claim 1, wherein the opposite magnetic pole surfaces of the permanent magnets are formed in a concave shape.
3. The rotation angle sensor as defined in claim 1, wherein the opposite magnetic pole surfaces of the permanent magnets are formed in a convex shape.
4. The rotation angle sensor as defined in claim 1, wherein a pair of hall elements functioning as the flux density detecting unit are disposed on either side of a rotation centreline.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A process for preparing pyrogenic silica, comprising condensing the offgas from deposition of polycrystalline silicon from chlorosilane and hydrogen to form a condensed offgas fraction; fractionating the condensed offgas fraction in a distillation column, with a bottom fraction from the distillation column comprising a high boiler fraction containing 0.5-20% by weight of high-boiling chlorosilanes and 99.5-80% by weight of silicon tetrachloride, and evaporating at least a portion of the high boiler fraction to form a chlorosilane vapor, and feeding chlorosilane vapor thus obtained to a burner and reacting with air or oxygen and with hydrogen in a flame to give pyrogenic silica, and collecting the pyrogenic silica as a finely divided silica powder.
2. The process of claim 1, wherein the high boiler fraction is distilled again in a downstream distillation step to separate further silicon tetrachloride before the high boilers are vaporized and fed to the burner.
3. The process of claim 2, wherein the high boiler fraction is reacted with chlorine before it is vaporized and fed to the burner.
4. The process of claim 3, wherein the reaction with chlorine is carried out under UV irradiation.
5. The process of claim 1, wherein the high boiler fraction is reacted with chlorine before it is vaporized and fed to the burner.
6. The process of claim 5, wherein the reaction with chlorine is carried out under UV irradiation.
7. The process of claim 1, wherein chlorosilane vapor and air or an oxygen-containing gas mixture are present in the burner in a volume ratio of from 0.06 to 0.18 and chlorosilane vapor and hydrogen are present in a volume ratio of from 0.25 to 0.60.
8. A pyrogenic silica produced by the process of claim 1, which has a specific surface area of 5-600 m2g, a pH of 3.8-4.5 and a boron content of less than 2 ppm.
9. The pyrogenic silica of claim 8, which has a boron content of less than 1.5 ppm and a total content of the trace metals iron, nickel, chromium, copper and zinc of less than 5 ppm.
10. The pyrogenic silica of claim 9, which has a total content of the trace metals iron, nickel, chromium, copper, and zinc of less than 0.5 ppm.
11. The process of claim 1, wherein the finely divided silica powder has a specific surface area of 5-600 m2g.
12. The process of claim 1, wherein the finely divided silica powder has a pH of 3.8-4.5.
13. The process of claim 1, wherein the finely divided silica powder has a boron content of less than 2 ppm.
14. The process of claim 1, wherein the finely divided silica powder has a specific surface area of about 200 m2g.
15. The process of claim 14, wherein the finely divided silica powder has a pH of from 3.8 to 4.5.