# Presentation: 821023

*Different Approach compared to *
*Auto-DIF and GAUSS *

*Volker Auster, *_*Ronald Kroth,*_
*Olaf Hillenmaier, Markus Wiedemann*
*Magson GmbH, Berlin, Germany*

*Automated Absolute Measurement based on Rotation of a **Proton Vector Magnetometer*

## Fundamentals

***Requirement on ABSOLUTE measurement***
*Field vector **has to be **embedded in geographical reference system*
*Elimination of systematic errors*
* *
***Fundamentals of the proposed methods***
*A PVM measurement is an absolute measurement of the field component directed to the magnetic axis of the coil.*
*Two components and the total force F are theoretically sufficient for a unique determination of the field vector.*
* *
***The problem***
*How do we know whereto the magnetic coil axis is oriented?** *

## Our Approach: to rotate a PVM

*PVM equipped with telescope, CCD and level tube will be rotated by motor and worm gear about vertical axis. Measurements are done each 30° measured precisely by angle decoders. Close to the nominal azimuth mark direction pictures are taken.*

## Orientation vs. vertical direction

*Inclination of rotation plane versus horizontal plane is determined by tilt sensor measurements (resolution 0.5arcsec, offset of tilt meter can be neglected due to rotation)*
*Inclination **γ** of coil axis versus rotation plane can be calculated from constant term A**0** of sine fit*

## Orientation vs. azimuth mark

*Telescope, digital camera and image processing shall be used to determine the orientation with respect to the azimuth mark*
*Advantage of this method compared to laser beam options are the flexibility regarding targets and distances*
*Misalignment of optical axis versus mechanical and magnetic coil axes have to be considered.*

*Both alignment errors can be determined by rotation of the bias coil*
*Optical axis error will be adjusted (only horizontal one is relevant)*
*Misalignment of magnetic axis will be rotated into vertical direction, which can be eliminated by the rotation of the table*
*Due to the long cylinder geometry of bias coil and telescope, the axes differences are constant (proven over more than one year operation) *

## The rotation table

*The rotation table*

*High mechanical precision required*

*Worm Gear *
*globoid structure to keep the contact as large as possible*
*Slide bearing*
*Both parts are made from AlZnMdCu1.5*
*Both parts manufactured on the same 4 axes CNC  machine*
*Surface of bearing anodized with Teflon contribution*
*Bearing clearance 0.01mm!*

*Excentricity error in arcsec:*

## Drive unit and angle measurement

***Rotation angle is measured by two decoders***
*(1) on the worm axis *
*	**Res: 1/1120000 (1.16 arcsec)*
*(2) directly at the table*
*	**Res: 1/2400000 (0.54 arcsec)*
***Error sources***
*Worm gear*
*Excentricity*
*Decoder accuracy*
***Error determination***
*PVM replaced by standard Theodolite (magnetic)*

## The optical system

## The control unit / software

## Results of the measurement

**Amplitude    ****	****	****= 0.16nT**
**Phase          ****	****	****= 378,90°**
**Mean Value  ****	****= 48957,17nT**

## Results of the measurement

*Results of the measurement*

**Amplitude    ****	****	****= 18468,92nT**
**Phase          ****	****	****= -1,98°**
**Mean Value  ****	****= 1083,23nT**

## Results of the measurement

*Results of the measurement*

**Mean Value ****	****	****= 0.00nT**
**St. Deviation****	****= 1,02nT**

## Results of the measurement

*Results of the measurement*

## Summary

***Basis for the presented automated system are:***
*Well proved PVM design (homogenous coil for bias fields),*
*Experiences with** manually performed absolute measurements in various configurations (e.g. on top of a Zeiss Theodolite) since 1980.*
*High precision mechanics (Steingross** Feinmechanik**, GER) *
* *
***High reliability and comparable low costs******:**** can be achieved by usage of well tested commercial parts: Industrial PC, Industrial Camera, Tilt sensor (Fredericks, USA), DC Motor (Faulhaber, GER), Incremental decoder (Kuebler, Numerikjena**, GER**)*
* *
***Comparison with Auto DIF and GAUSS:***
*The PVM measurement has the advantage that components are measured directly and the total force F is already included.*
*The optical system is more flexible compared to laser approaches.*
* *
***Acknowledgment:****  Our Mechanical Engineers** *