---

Fig 1.  Foc2 Focus Profile (wide)

 

Fig 2.  Foc2 Focus Profile which was rejected due to "Quadratic values indicate poor/invalid profile"

A Geomagnetic Monitoring Station is being added to the Observatory in Spring 2025 for monitoring changes in the earth's magnetic field and to supplement and build upon the Observatory's existing Aurora monitoring using AllSky Camera and new NorthCam Camera.
Earlier notes regarding selection of SAM III System are covered in: Review - Potential Geomagnetic Monitoring Station (2025-01-24)

SAM III Order arrived today (2025-03-18) and installation plan is being developed.

  

 

Questions:

Q.  How are cable wires fitted to the SAM III Controller Box.
A.  Bared ends of wires are inserted into appropriate slots in the green 10-position pluggable terminal block X2. , and screws tightened. 
    After double checking that correct wires are in their correct slots, insert green adapter bars in port on SAM III controller box
          1 GND X
          2 Signal X
          3 +5Vdc X

          4 GBD Y
          5 Signal Y
          6 +5Vdc Y

          7 GBD Y
          8 Signal Y
          9 +5Vdc Y

         10 Not used.

Q. Identifying Cables to/from Sensor Sensors ?
Three CAT6 cables should be clearly identified at both ends,  marked X, Y, Z according to which axis they will each be connected to.

Q.  A standard 'scheme' should be defined to detail the particular wires in the CAT6 cable that will be used for connecting to the GND, OUT and VCC pins on the FG-3+ sensors and to the relevant slots on the Controller Box.
       GND  -  Blue Wire  = Ground
       OUT   -  Orange Wire     = Sensor output
       VCC  -  Brown Wire  = +5 V Power

Q.  How to ensure that water can't enter to the Piped Sensor Unit at the point of cable entry. (3 Cat6 cables and 1 temperature cable)
A.  Inverted U Tube ?, Expoxy Filler, 

Q.  How to build  'cage' for mounting the three FG-3+ sensors.
A.  Circular Wood Cage ? ,   3D Printed Cages from Torc ?, 

Q.  How to wire up the FG-3+ sensors (including 10 µF, 25 V tantalum capacitor & 100 nF 25 V multi-layer ceramic capacitor ) ?
A.  Refer to wiring plan in manual

Q.  How to connect wires to 3 pin adapter using metal tags. How are the metal tag inserted into plastic adapter ?
A.  From Installation Guide:

 A 3-pin single inline header connector and contacts are supplied for connecting cable to each sensor. Crimp or solder the sensor cable wires to the contacts and insert them in the SIL header connector. The SIL header connector has slots on one side, and the tiny tabs on the contacts must be inserted on this side. Do not solder wires directly to the sensor. The sensor pinout is indicated on the sensor label and in the drawings below.

The socket contacts require a double-crimp, one for the conductor and one for the insulation. If you do not have a crimping tool and must solder the wires, it is suggested you cut the insulation crimp fingers off of the contact (otherwise, it is unlikely you can fold the fingers enough to make them fit the header connector). You will need to fold the conductor crimp with a pair of miniature pliers. Do this very carefully to avoid damaging the contact. Apply a very small amount of solder – if you apply too much solder it will wick up into the socket.

Before inserting the single inline (SIL) header onto the sensor pins, put a small amount of dielectric grease (for example, Permatex 81150 available at most automotive parts stores) on the sensor pins. The amount of grease used should be small enough that it is not visible on the pins. This will help prevent corrosion if the sensor is used in outdoor applications. The header has no built-in polarity indicator so it should be marked with nail polish, paint or tape to indicate proper orientation.

Q.  Does the existing 12mm Male Plug from the A/C Power Adapter Unit need to be replaced with either the longer 14mm plug or with 12mm plug with locking nut. ?
A.  Controller Unit was tested with existing 12mm Male Plug and it initialises ok.  A disconnection/reconnection occurs if the plug is physically rotated, but not under general use. It seems secure enough.
( I'd rather not change the plug as this requires cutting off the existing male plug and soldering/crimping wires to the new plug and then rely on screwed connection on working loose.)

Q. How should the X, Y & Z Geomagnetometer Sensors be orientated ?   
A. As per construction manual
   X    North-South ,   pins  SOUTH
    Y    East-West,       pins  WEST
    Z    Vertical,            pins  UP

Q. What entries should be made in the SAM_VIEW setup/settings ?
A. Settings
  Owner or Station Name  :  Clair Observatory
  Location :                             Ellon, Scotland 
  Longitude, Latitude            02.00W,   57.32N  
  IARU-Locator :                    IO87xh    

Q. What are expected 3-axis field strengths ?
A. Using the calculator at World Magnetic Model 2025 Calculator (geomag.bgs.ac.uk) the expected field strengths at the Observatory for 2025-04-01.

  X:   16467nT   (4.4 nT/year)
  Y:      -100 nT   (59.1 nT/year)
  Z:   47326 nT   (32.8 nT/year)

  H :   16468 nT  (4.0 nT/year)         (Horizontal Intensity,  from X & Y vector sum)
  F :  50110  nT    (32.3 nT/year)     (Total Intensity)

  D :  -0.348 deg East       (12.4 arc min/year)
   I  :    70.814 deg Incl'n   (0.5 arc min/year)   ' Angle from Horizontal

- See also  What are the geomagnetic components ?  (intermagnet.org)         

Q. What is the geomagnetic latitude of the Station
A.  54.36° N

From IGRF, At Epoch 2025.0 Lat 57.32 N, Long -2.00 E, the Quasi-Dipole Latitude is 53.36°   (vs Dipole Latitude 59.26°)

Update 2025-03-19  (SAM III - PC Connection)

- Created program folder  'C:\More Programs\SAM'   and copy into the folder the files from
     '..\Software-Firmware\SAM3 Applications'
     '..\Software-Firmware\Runtime Libraries'

- Installed SABRENT USB-Serial Driver
.   CD .. /Windows/PL23XX_Prolific_DriverInstaller_v301-WIN11/PL23XX-M_LogoDriver_Setup_v301_20211221.exe

    - Used PL23XX_checkChipVersion_v1020.exe' to check 'COM4' this gave the meessage :
   "This is a PL-2303 GS chip"

- Made a trial connection to SAM III unit
  - Connect USB-Serial Cable to Computer
  - Appears as "Prolific PL2303GS USB Serial Com Port (COM4)             (COM4 on Development/Analysis Computer)
- Connect USB-Serial Cable between Computer and SAM III box via Serial Pass Through Cable)

- Opened SAM_INI_v2-0.exe
- Selected COM Port (COM 4)
- Set default values used to confirm values on Form are defaults.
  (proven by changing a value and then using Set Default Values to see it overwrite the manually changed value)

- Tried 'Send parameters'.
     After running to 100%, 'Error!' dialog shown with message "Error while writing parameter set!"
Tried 'Receive parameters'
    After running to 100%, 'Error!' dialog shown with message "Error while reading parameter set!"

A Port Monitor confirms that data is coming from the SAM Unit with data every second, like
  20.03.25 15:57:01: X,,Y,,Z,

-If SAM_INI_v2.0 is opened and connected to COM4 with the SAM III in command mode (F1) and
'Send Parameters' is used, SAM_INI runs to c. 50% and then displays message "SAM does not respond".

 -  Trying again :
     'Receive Parameters' ,  trackbar runs to 100% and message 'Parameter read successful.." appears

 Trying again
     'Send Parameters' :  trackbar runs to 100% and message 'Parameter write successful.." appears
     After a successful 'Write', the SAM box automatically resets itself.

 To do:  
- Dig a 120 cm deep hole to contain 3-axis geomagnetometer sensor fixture (see Update 2025-03-23 to Updates 2025-03-25 below)
- Prepare 3 CAT6 cables,  one cable for each sensor
- Prepare Temperature Monitor  (see DS18B20 Waterproof Digital Temperature Sensor (2025-03-19)

Update 2025-03-23 (Hole)

Hole that will contain the 3-axis geomagnetometer sensor fixture has been commenced on 2025-03-21 and reached 45 cm depth.  Pictures below show status of hole on 2025-03-23 after reaching 68cm.

Hole that will eventually contain 3-axis geomagnetometer sensor fixture Hole has reached 68cm deep at the time of the photo another 52cm to go in red subsoil / drift deposit		Hole location relative to Observatory where the SAM III Monitor will reside Offset Distance 10m Cables will eventually be run below the lawn.

Update 2025-03-24 (Hole)

Hole that will contain the 3-axis geomagnetometer sensor fixture has now reached 100cm depth.  Another 20cm to go

Update 2025-03-25 (Hole)

Hole that will contain the 3-axis geomagnetometer sensor fixture has been completed after reaching 120cm depth. 

Completed Hole for the 3-axis geomagnetometer sensor fixture Hole depth is 120cm		Detailed image showing lower part of hole
Side view of hole 120cm depth		Side view of hole 120cm depth.

c

Pipe work for the building the fixture that will house the 3-axis geomagnetometer sensors (X, Y & Z) & the temperature sensor was purchased today (2025-03-26) form local hardware shop.   Items comprised FloPlast 40/43 mm diameter straight pipe, angled junctions, and end stops. Junctions will eventually be joined/sealed using special FloPlast solvent cement.

A mock-up of the fixture showing the rough positions of sensors is shown in the picture below.  Note that the straight pipe has not been cut to size yet, and the top horizontal sensors will be placed at 90 deg to each other in the final build (not the 180 deg positioning used in the rough mock-up).  Cables to the magnetometer sensors is'nt shown here.




Update 2025-03-27 (Sensor Fixture Progress)

Pipe work for the building the buried sensor fixture has been cut to length and the entire assembly loosely fitted together (see pictures below) :


  

3 x 15m lengths of CAT6 Cable have been cut from 100m reel previously purchased.  Required cable length is around 12.5m, so these 15m lengths have an excess which will be trimmed off during final tieback to the Observatory.

Update 2025-03-27 (Sensor Fixture Progress)

End caps and axis endings were joined together with solvent glue.  (x4)
Wooden  Circles glued in place internally (these will hold the magnetometre sensors in place)  (x3)

Small circuit board built for each magnetometer,  and connected to a Cat6 cable and to the magnetometer. (x3)

Each circut / magnetometer was connected to the SAM III controller in turn and tested to ensure it was worked (x3)
(one circuit initially didn't work due to a bad solder connection and had to be fixed).

Made a matrix of tests after noticing that one of the magnetometers showed readings that were offet from the others when all 3 sensors were pointing the same direction, as if it had a different bias.

Each magnetometer was connected in turn to Circuit 1 (x), Circuit 2 (y) & Circuit 3 (z) and the reading recorded when the magnetometer was pointing North (X),  East (Y), and Down (Z). This produces a 9 x 3 matrix of values (see below)

Sensor	Circuit		Sensor Orientation
			North (X)	East (Y)	Down (Z)
Magnetometer 1	Circuit A (x)
	Circuit B (y)
	Circuit C (z)
Magnetometer 2	Circuit A (x)
	Circuit B (y)
	Circuit C (z)
Magnetometer 3	Circuit A (x)
	Circuit B (y)
	Circuit C (z)
Expected Values			16467	-100	47326
(BGS 2025 Model)

Update 2025-03-30
Calculated required Magnetometer Offsets to sensors
 X -833    Y +13584    Z+11815
 
Using -82000 + required offset we get
X -82833,  Y -68416   Z -70185
  
These were applied to SAM unit via SAM Init
 


Update 2025-04-02 (System Burn-In)

A 72 hour 'burn-in' has been commenced on the workbench (aka dining room table) with sensors hooked up to SAM III Unit and PC. This is too check that everything is working reliably and there are no failures of any of the components (better to find out something now than after the fixture is buried !).   The Burn-In period will allow Bx, By, Bz readings to be followed in an attempt to understand the cause and effect of any deviations seen in the readings

Update 2025-04-02 (Sensor sensitivity)

A 72 hour 'burn-in' has been successfully completed.  System working throughout period, though not connected to the PC for the entire period.

The magnetograms show that the sensors are very sensitive to temperature, which is of no surprise given the relativey large temperature coefficient of the sensors (between -100 & -150nT/°C), the fact that sensors are not insulated and are subject to various daily changes to temperatures and to central heating cycles.  

The sensors are also demonstrated to be very sensitive to any small or larger movement of the sensor.

Other effects such as changes to ferro-magnetic environment caused by a car on the driveway (10m) or a new skip / moving wheelbarrows on the estate road (20m) are detectable but cause much lower deviations to magnetometer readings than temperature/precise position & orientation do.

During the 72 hour burn in there was geomagnetic changes (noted by the presence of viewable aurora and Scandinavian magnetometers deviations), but these effects (the signal) is much smaller than the other changes (especially temperature)









Noise due to i) thermal effects,  ii) movements of the magnetometer sensors,  iii) changes in large ferro-magnetic objects in front of the house will be largely eliminated by enclosure in magnetometer fixture assembly and by burial in the rear garden to a depth of at least 80cm below ground surface.

Whitham Reeve has looked at the Magnetometers (2025-04-06) and beside the recommendation to continue the tests for longer to fully appreciate the cause and effect from different factors, he considers that the magnetogram traces look normal for the test conditions described and that there is nothing fundamentally holding me from final assembly of sensor fixture and its burial.

Update 2025-04-07  (Extended Monitoring)
Monitoring was continued the following day


Update 2025-04-08 (Temperature Relationships)

A 14 hour test was run during during which magnetometer sensor positioning was stable (no knocks or changes etc) and temperature monitoring running. The test occured through a time interval in which the central heating (thermostat in an adjacent room) is automatically turned down to 16°C at 21:30 UT, turned up to 20°C at 07:00 UT, and turned slightly down to 19°C at 08:30 UT,  producing a nearly 4°C change in ambient room temperature. 

Data was compiled using AstroMag (a custom application that read the SAM III data file and the DS18B20 temperature sensor) and then plotted in Excel.

The following chart shows the changes in Bx, By, Bz and Bh (blue, red, green & magenta lines) from the point that the run commenced, Temperature (black line), and the modelled magnetometer change based on temperature coefficients of 100 nT/°C and 150 nT/°C (dashed line).  



The Central Heating Controller (thermostat located in an adjacent room) is set to reduce thermostat threshold turns down to 16°C at 21:30 UT, turns up to 20°C at 07:00 UT, and turns slightly down to 19°C at 08:30 UT.  This effectively means that radiator heating is off during the chart period 22:00 to 07:00 and then on again at 07:00 to around 09:00 or so.  During this time there is around a nearly 4°C change in ambient room temperature.  Minimum outdoor temperature during the night was 1°C ( It is possible that there is some central heating between 06:30 and 07:00 dependant on the temperature in the adjacent room (c. +/- 16°C). It is also possible that the workbench room begins to stabilise in temperature at this time due to daytime solar radiation from outdoors)

The setup used during the test is shown in the following photo. The 3 magnetometer sensors are all located together (within 30cm of each other) at a distance of around 2.2m from the room's radiator and around 1.4m from the room's window. 



The graph above shows a firm (inverse) relationship between Magnetometer Change and Temperature.

However it is unclear why

i) the Y sensor shows a significantly stronger relationship to temperature than that expected (based on the published -100 to -150 nT/°C coefficient range), and
ii) the X sensor shows a significantly weaker relationship to temperature than that expected.  

- Do the 3 sensors have a significantly greater range in temperature coefficient than the 'published' range
- Does the self-built circuitry associated with each sensor cause the wider variation ?

I'm a poor amateur at soldering (I'm too embarrassed to show the photos here!). Whilst the circuits all work, I've almost certainly used more solder than an expert would.  I purposely applied solder to both upper and low sides of the mini-boards (to minimise chance that any one solder join fails through the life-time of the Station).  The precise distances between the circuit and the sensor is slightly different between the 3 builds (e.g. 4.5 cm for X , 5.5cm for Y) and there are potentially other small points of difference on the 3 boards. Whilst the capacitors are all in the correct place in a circuit sense and the (longer) pin of the tantalum capacitor is in the correct "+" position on all the 3 boards, the height at which I have the tantalum capacitor mounted above the board varies (due to my poor skill level).  For the X Sensor Circuit it is mounted close to the board but in the Y sensor Circuit it is mounted around 6mm higher than for X.  Ideally I would have constructed all the circuits to be precisely identical but I was learning as I was going using a new (digital controlled) solder iron.    With tiny boards one really needs 4 hands (one to hold the soldering iron, one to hold the solder wire , one to hold board and  one to hold the electrical wire or component !) Q. Can any of this explain the difference in Temperature Coefficients ?

Earlier tests using each sensor with each circuit in turn and in each of the 3 orientations was inconclusive regarding the impact of the each circuit. This was due to the precise effect of sensor positioning and the large thermal effects). Those tests did show that each sensor needed a significantly different offset to bring its readings in line with those expected for my location.
 
In the final installation where thermal variations will be much smaller, differences in the temperature coefficient between the 3 sensors (including self-built circuit) will be much less important. However if there are strong differences in the sensitvity/responses of the 3 sensors to non-thermal magnetic changes that is of more concern.


The recorded magnetometer values during the same time period are shown in the chart below:



These compare with expected readings at the Observatory location of
X:   16467nT ,  Y:      -100 nT ,   Z:   47326 nT ,   H :   16468 nT

These include following offsets from raw (-82000 based values) :
X -833    Y +13584    Z+11815

Note : These offsets will be updated again once sensor fixture is installed & buried at final site.

Update 2025-04-09 (Sensors)

Based on the Sensor2's higher sensitivity to temperature changes (Y in above burn-in & monitoring tests) it has been decided to use it as the Z Axis Sensor.  This means it will lie deepest of the 3 sensors and can be expected to experience the least temperature fluctuations.

As a consequence Sensor3 (Z in above burn-in & monitoring test) will be used as the Y Axis Sensor

Sensor1 will continue as the Z Axis Sensor

The sensor cables have been re-coded with coloured electrical tape at both ends for identification

X Axis (Sensor1 / CableA)   - Blue
Y Axis (Sensor3 / CableC)  - Red
Z Axis (Sensor2 / CableB)  - Green

Began assembly but ran into problems with
i) a couple of wire to 3-pin terminal breaking (at circut board end and/or terminal end)  requiring resoldering,
ii) the 3 socket plastic terminal coming loose from SG-3+1 pins when trying to work the circuit board into place in the Side-Elbow Junction.
One of them was eventually reinserted  but in the other case
iii) the blue wire to the Y Axis Sensor broke again and the after reattaching to the terminal socket it was found that
iv) the socket could not be inserted far enough into the terminal so that
v) a reliable connection to the SG-3+ GND Pin couldn't be archieved

 May need to buy some new pipework for housing the Y axis Sensor (End Piece, Straight Junction and Side-Elbow Junction.)

Update 2025-04-10 (Sensors, Assembly)

New End Piece, Straight Junction and Side-Elbow Junction bought from Hardware Shop in order to replace the housing that had to be sacrificed to get the FG-3+ sensor out in order to reconnect it again.  

New housing successfuly built.

Assembly commenced with building/assembly of  Y and Z housing.

Update 2025-04-11 (Assembly)

Assembly of magnetometer sensor fixture completed including Temperature Sensor Probe. 
Cable inlet sealed with two plugs of Epoxy Fller

Assembly of X and Y Axis Solvent Glue used to connect part of pipe together Hot Glue used to hold cable internally in place		Assembly of Z and Y Axis together After this the Temperature Sensor Probe was installed internally at position indicated
Assembly of X, Y Axis & Cable Inlet X Axis and Y Axis units assembled with an angular offset of 90 deg, taking care that in final position the FG-3+ pins will be in South direction (X Axis) & West direction (Y Axis) respecively		X, Y Axis & Cable Inlet (Detail) X & Y axis are positioned 90 deg apart
Use of Epoxy Filler to seal the Cable Inlet (stage 1)		Cable Inlet (detail) Showing first plug of epoxy filler
Use of Epoxy Filler to seal the cable inlet (stage 2)		Cable Inlet (final) Showing second plug of epoxy filler with 3 magnetometer sensor cables (Cat6) and 1 temperature sensor cable emerging
Completed Assembly
Final Fixture Tests Confirming that connections to the 3 magnetometer sensors are still working		Final Fixture Tests - Relief !! SAM III Unit is still seeing all 3 sensors

Update 2025-04-12 (Installation Prep)

- External surface of pipe joints and the cable inlet/filler have now been double coated with PVC solvent glue.

- Cables have been bound into a cable bundle, and threaded through the flexible pipe.  There was too much friction/ bend to allow the cable to be passed through the entire 10.5m flexible cable in one go and it decided to cut the flexible pipe into 4 pieces to allow the cable bundle to be successfully passed through.

- The middle shelf in the Observatory Computing Bay has been cleared in preparation for placing the SAM III unit on. Lower shelf is confirmed to be loosely position which will allow it to be temporarily removed for drilling hole in floor of the Observatory Computing Bay for pulling through the cable bundle from the Magnetometer Sensor fixture.

Sensor Fixture completed and moved outside Cables emerging from the pipework fixture are Blue:  X Axis Cable (cat6), Red: Y Axis Cable (cat6) Green:  Z Axis Cable (cat6), Yellow:  Temperature		Sensor Fixture - Alternate View
Measuring & laying out flexible corrugated pipe in preparation for taking cables back to Observatory		Cables formed into a bundle
Cables formed into a bundle (foreground)  in preparation for passing through flexible corrugated pipe (background)		Cable Bundle passed through Corrugated Pipe There was too much friction / cable bend to pass through  the 10.5m corrugated pipe in one go, and it was cut into 4 pieces

Update 2025-04-13 (Installation)

- Hole has been marginally deepened (in the area of the Z Axis Sensor) to allow the entire Sensor Fixture to be placed as deeply as possible.
 
- A trench between the Sensor Hole and the Observatory has been dug for taking the flexible corregated pipe which contains the cable bundle from Magnetometer Sensor fixture.

- Flexible Pipe / Cable Bundle have been laid back to the Observatory, and cable bundle passed through hole into the Observatory.

- Flexible Pipe backed away from Observatory, and breaks between Pipe Sections joined with tape.

- Trench back filled and lawn repaired.

Trench dug back to Observatory 7cm wide & 20-25cm deep, 10m long		Trench dug to below Observatory Computing By
Cable Bundle / Corrugated Pipe ready be installed into trench		Cable Bundle / Corrugated Pipe in trench
Cable Bundle / Corrugated Pipe entering Sensor Hole		Lawn after filling trench and replacing turf

- Ardunio connected to Lindy USB Hub (in Observatory Computing Bay) - Appears as COM8 in DeviceManager

- AstroMag modified to use COM8 as default port for Temperature Data and issued as AstroMag 1.2.1

- Sabrent USB-Serial Convertor Driver installed on Observatory Computer

C:/Data/Computer/Home Computers/SABRENT USB-Serial Converter Driver/Windows/PL23XX_Prolific_DriverInstaller_v208/PL23XX-M_LogoDriver_Setup_v208_20211221.exe

- SAM III connected - Appears as COM9 in DeviceManager

Update 2025-04-14 (Installation)

- Sensor Cables tied into SAM III Unit and Ardunio Project Box, using existing wire ends
(cables still need to be trimmed back to an optimal and equal length)

- Confirmed that signals are being received, and that SAM_VIEW and AstroMag are working

- Sensor Fixture has been installed in the Hole, oriented N-S , E-W & Vertical, half buried
- Last 1m of cable bundle has been buried at depth in the hole
- Hole back filled and lawn repaired
- Sensor Hole geolocated to allow the Sensor Fixture to be recovered in future, should it be required

- Sensor signals monitored for stabilisation

Sensor Fixture sitting at bottom of hole Picture taken prior to alignment		Sensor Fixture at bottom of hole (detail) shows 1m length of cable bundle that will be buried  at same depth as the sensor also shows North-South axis (blue), East-West Axis (red) and Vertical Axis (green, at bottom of hole)
Setting up North-South Survey Line This was done by creating a line parallel to Observatory's North-South Alignment Picture is looking Due North along string line (see Observatory N-S Alignment, 2018)		Sensor Unit Positioned according to Survey Line Unit positioned vertically, centred on the North-South Survey String, and with X Axis aligned with the North-South Survey String 4 canes pushed into the bottom of hole hold the Sensor Unit in position pending burial
Sensor Unit Alignment Due to location of sensor at bottom of hole its alignment had to be done by eye.		Sensor Unit in Finalised Position ready for burial
Sensor Unit being buried Z & Y Sensor Axes have been buried at this point		Sensor Unit being buried All 3 sensor axes and cable inlet have been buried at this point. Just the top of the sensor unit is visible Hole was subsequently back filled up to the level of the lawn

Update 2025-04-15 (Analysis / Potential Calibration)

Magnetograms from 1st day (2025-04-14) plotted and analysed.

First plot shows readings from the morning and early afternoon from time that Sam III unit was powered up with the Sensor Fixture positioned in the 1.2m deep hole, but not yet fully aligned and not yet buried.  Data trends are consistent with a negative relationship to temperature. Data is quite noisey.  Would there be a benefit in using moving averages ? (or average the 10s samples to create a 1 min binned average).

After this the Sensor Unit was fully aligned and the hole backfilled with soil, during which readings were highly unstable and are not shown.

Once buried the reading were renormalised to 0 nT, and charting continued.

			X	Y	Z
Expected Values			16467	-100	47326
Prior Fixes			-833	+13584	+11815
Currently used offsets			-82833	-68416	-70185
Current Av Values			21540	13280	45030
Additional Fixes			-5083	-13380	+2296
Proposed New offsets			-87916	-81796	-67889

Update 2025-04-16 (Analysis & Diagnostics) 

- Some issues occuring with AstroMag encountering with exceptions which causes SamMonitor loop to exit, which stops data recording.
Fixed in AstroMag 1.2.5.

- Spiky temperature values that started the day before was in partly due to temperature values being sampled every 60s for graphing. A more valid and smoother temperature is producing by averaging  temperature values (that are read every1s) over a 60s window.

- Anomalous jumps in Y reading are still occuring (eg. an anomalous -283 nT shift in Y reading at  2025-04-16 11:50 UT that was proceeded by an anomalouus +1400nT spike).  This is ranked a Major Issue.

- Began some diagnostics tests that aim to understand high noise levels, but might cast some light on the Sensor Shift issue.  The first test which was to turn-off the power to the Temperature Sensor at 13:23 UT which showed an immediate and significant downward shift in all 3 sensor reading , with X,Y, Z readings shifting by  -716nT,  -548nT & -454 nT respectively.

- It was hoped that running the station with the Temperature Sensor turned off would fix the issue with anomalous shifts in Y reading with associated smaller shifts in X and/or Z reading, however after around 5 hours the problems with shifts in Y reading resumed again.



Update 2025-04-17 (Further Diagnostic Testing) 

- As part of continued testing SAM III Unit was turned off in order to disconnect the Y Magnetometer and to see if this would eliminate anomalous shifts in readings. Obviously the Y readings (which have shown the biggest shifts) won't be now available, but it is hoped to tell if smaller shifts in X & Z readings continue or not.  After a delay of 15 minutes of so the SAM III unit was restarted and data log resumed. Piecing together data it would seem that after turning on the X and Z Magnetometers (without the Y Magnetometer running) saw an upward shift in X and Z readings of +400 and +100 respectively.   The net shift gradually reduced to +350 and +50 after 1 hour.

Update 2025-04-18 (Further Observation) 

- Some 25 hours of observations have been completed with the Y Axis Magnetometer turned-off and there have been no anomalous shifts during this time

- Data Readings are still rather noisy and with, as yet, no definate explanation or cure.

- The noise can be cleaned up using a 7 min moving average (averaging data +/- 3 mins of the plotted time point), and this highlights the key trends in the data which are of geomagnetic origin.

- The geomagnetic origin is highlighted by the following comparison of the X Axis magnetometer readings and a stackplot of Scandinavian magnetograms.  The X Axis Magnetometer appears to show deviations that are twice as large as those shown by dob-sol-kar stations.  This isn't understood. Is the scale bar on the mkstackplot being misunderstood ?

- Downhole Temperature Monitoring has been turned back on at 13:20 (12:20 UT) in order to understand its effect on X & Z magnetometers, beyond the expected initial shift in readings. Provide the shift is remains static it is manageable.

The magnetogram (below) shows there was a +370 nT shift in X Axis Readings and a +498 nT shift in Z Axis Readings when the Temperature Sensor was turned on.  These compare with the earlier shifts of  -716nT and -454 nT respectively when the Temperature Sensor was turned off two days earlier (2025-04-16 14:23 (13:23 UT).)

During the first 6 hours with Temperature Sensor running there have been no anomalous shifts in X & Z readings
This would seem to point to the Y Axis Magnetometer as being the cause of the random large shifts in magnetometer readings.

2025-04-18 (Remedial Plan)

It seems that the Y Axis Magnetometer is compromised in some way.

Rather than dig up the existing 3-axis Sensor Fixture and pull out the working X & Z sensors and build into a new 3-axis fixture using a new Y axis magnetometer, it is proposed to build a dedicated Y axis fixture for setting beside the existing fixture.

Requires
 - new FG-3+ magnetometer (£67.70 from https://robosavvy.co.uk/fgsensors-fg-3-sensor.html)
 - new fluxgate capacitors
      10 uF, 25v Tatalum Capacitor  (£ 1 + delivery_
     100 nF, 25v Ceramic Capacitor (£ 1 +delivery)
- new piping  (3 ends caps, 1 x 90 deg bend, 1 x 135 deg bend, 2 connectors - £10)
- new 15m length of Cat6 cable required (already available)

Work
  Assembly / test new magnetometer & fixture
  Part dig existing hole, install new Y Axis fixture
  Dig up trench,  thread new cablethrough corrugated pipe (if possible) or run cable beside corrugated piper