Using the FM36 Geoscan Fluxgate Magnetometer
This instrument belongs to Archaeology. Extreme care must be taken of the tube, which must not get distorted (carry in the case wherever possible, do not drop etc.). The logging and download procedure are similar to that for the Geoscan Resistivity Meter.
Zeroing Instrument
1. design grid to be aligned approx. NS (if possible).
2. Switch on
3. Locate suitable base station, where the value obtained varies by less than 1 nT when the instrument is moved in a 0.5m radius sphere around the normal operating position, but maintained aligned with the grid direction.
4. Note reading, invert instrument and note reading. Adjust screw on LHS of instrument using yellow tool until reading is at midpoint of these two observations. Repeat until normal and inverted positions are within 1 nT.
5. Zero instrument.
6. Repeat this procedure to standardise readings facing N and S, using wheel located under NS-labelled cover.
7. Zero instrument.
8. Repeat 6 for instrument acing E and W, adjusting using wheel under EW-labelled housing.
9. Zero instrument
10. Instrument should now give reading within 1 nT of zero whichever way held.
Taking measurements
11. Always walk grids in same order
12. Walk with string to right, instrument to left.
13. Hold instrument other way round as you turn corner, so it always faces the same way (this is not theoretically needed if zeroing was perfect - but in practice helps eliminate striping).
14. Use logger controls to supply individual dummy points/lines as required.
15. typically work with 0.5m between readings along string - and traverses 1m apart.
Downloading
16. Connect logger to PC
17. Switch on PC, run Geoplot
18. select Input, from Logger.
19. Place floppy with template in drive and follow instructions (make certain numlock is off!!)
Last updated by Tim Young (Tim.Young@GeoArch.demon.co.uk) 1st October 1998.