Data logger science experiment


Appendix - Mechanical Construction

Suitable for
Ages 16 +
KS 5


Educational data loggers

Sensor Head
As has been discussed previously, the sensor is sensitive to temperature, but the sensitivity can be reduced with a combination of thermal inertia and insulation.

A temperature-sensing device is placed in contact with the FGM-3. The sensor assembly should then be suspended in a vacuum flask so that the two sensors are positioned centrally. Dry sand is then poured into the flask, which should be tapped very gently to settle the sand around the devices.

Use a piece of shaped polystyrene in place of the stopper to retain the sand. The connections can either be brought out along the side of the stopper, or through a prepared hole in the middle.

A box should be constructed from thick polystyrene insulation sheets and tape, with inside dimensions that will comfortably accommodate the thermos flask. When constructing the polystyrene box all the edges should be taped inside and out to make them sand-proof, and for strength.

The additional components, e.g. voltage regulator and de-coupling capacitors that are required at the sensor head can be housed in a small plastic box which might include an LED indicating that the supply is reaching the unit.

The case can be secured to the sensor head with double sided servo tape to prevent the cables connecting to the FGM3 and internal LM35 from being accidentally tugged free.


Appendix - an outline diagram of the instrument

magnetometer circuit diagram

Figure 2: Circuit diagram of magnetometer

Download large circuit diagram

The manufacturers data sheets should be consulted in conjunction with this diagram for additional components, eg. de-coupling capacitors, etc.


Appendix - using Excel to derive the calibration factor

The calibration formula in the form 'y=mx+c' may be derived as follows:

  1. Allow the system for run for a significant number of samples, eg. 500
  2. Use the 'View spreadsheet' facility in PicoLog to display the output from the f/v, and the output from the temperature sensor
  3. Copy the figures to the clipboard and paste them into a blank spreadsheet in Excel
  4. Using the graphing facility, create an 'xy (scatter)' graph with the temperature on the horizontal axis, and the output from the sensor on the vertical axis
  5. Add a trend line (Chart > Add Trendline)
  6. By right-clicking on the displayed line, the options to format the trendline are available, including showing the formula, under 'Options, Display equation on chart'
  7. The equation will be in the form: y = 2.6022x - 101.80
  8. Go into PLW Recorder, and then 'Calculated Parameters'
  9. Add a parameter and name it, 'temperature corrected'
  10. Select the output from the sensor as one parameter, eg. 'A', and the output
    from the temperature sensor as the other, eg. 'B'
  11. Add the correction formula, eg A-(( 2.6022*B) - 101.80)
  12. Select the additional data for display - this can be multiplied by the previously derived nT / mV figure for display in nT if desired, for example : (A-(( 2.6022*B) - 101.80)*1.6)
  13. The displayed output shows deviation from the nominal 'norm' during the course of the sampling run.


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