Applied Physics Fluxgate Magnetometer Model 520
- Former user (Deleted)
- jr_roth
Exp 393
Since the cable nut for the Fluxgate probe (Bendix style PT02A-12-10P female) typically is the strongest component in the probe and cable's magnetic profile, a nut was designed and 3D printed out of PLA (with help from Mintz), which is both non-magnetic and not paramagnetic (Figure 1). The cable's magnetization was measured in the SRM and are show in Figure 2. The PLA nut is several orders of magnitude weaker magnetically than the metal alloy nut.
Figure 1: 3D-Printed Fluxgate cable nut
Figure 2: The Fluxgate cable measured on the SRM showing the metal allow nut on the left orders of magnitude stronger magnetically than the PLA nut on the right.
Exp 396
received fluxgate magnetometer Probe A S/N1096 and control unit N2300 from applied Physics after calibration
Exp 395E
received word from applied physics that the magnetometer which was sent back (probe A) was bad. After calibration, the X axis was drifted. A repair was authorized. See vendor note here.
Exp 390R
SRM
Fluxgate probe A was demagnetized in the SRM to 80 mT as a training exercise to become familiar with the process. Both probes were measured in the SRM and had intensities of ~3x10-2 A/m which was deemed acceptable.
On 12/26/2020 the ship lost power and the chill water supply was interrupted while the technical staff was off shift. The SRM null field was lost during this time so a new field was trapped.
The SRM cryomech compressor hours are approaching 18,000 hrs. The adsorber must be replaced every 20,000 hrs. When it comes time to replace the adsorber, the spare cryomech compressor should be connected to the SRM and the new adsorber (when it arrives) installed into the compressor which was just taken offline. This way, both compressors get exercised. We still have some time but keep this on the radar.
When attempting to zero the fluxgate probe, it was observed that there was a +.2 to +.4 mOe shift on the X and Y axis of control unit N2300 when changing from the 10 mOe range setting to the 100 mOe range setting. The shift was specific to the control unit because it was present with either probe connected. Control unit 90348 also had a shift when switching ranges but it was much smaller (~.1 mOe) and could more easily be attributed to rounding or noise. The shifting values are documented in the excel workbook here: fluxgate_range_shifts.xlsx. At first, I suspected the cables might be the cause. The cables were swapped with no improvement. The probes were zeroed inside the smaller mu metal shield which was nested inside the larger mu metal shield (Figure 1.). It was also observed that probe B was much more stable than Probe A, regardless of which control unit it was connected to.
Figure 1.
SRM field profile data was collected to document the fluxgate probe behavior. All of this data was collected with probe A connected to control unit N2300 (acquired in 2018 from Brad Clement's lab) and probe B connected to control unit 90348. Over 60 profiles were collected so to save time, they were only measured from 250 cm to 350 cm to focus on the SQUID measurement region.
January 16th: Both control unit/probe setups were zeroed inside the nested mu-metal shields. Probe B was zeroed using the 1 mOe setting since it was stable enough. Probe A was not stable enough to zero on 1 mOe so the 10 mOe setting was used. This setting shouldn't make a large difference if the field is within range but since there seems to be an offset when switching between certain ranges I have been careful to note which range was used for what. The probe was zeroed according to the vendor manual although on the ranges used, the amplitude was near zero (probe still read zero on the selected axis when rotated 180 degrees). The probe was rotated inside the shield for each axis so that each axis was aligned in the same direction (up) when it was zeroed. After both probes were zeroed, a new null field was trapped in the SRM using probe B. This field is referred to as the B-Field. This null field was trapped with the control unit set to the 1 mOe range since it was very stable on this range.
January 17th: Field profiles were measured using each probe setup on the 1, 10, and 100 mOe ranges. These profiles are in the excel workbook 20210117 B-Field combined range tests.xlsx located in T:\IODP_Share\PMag\PMag_Documents\SRM\Field Profiles . A new null field was then trapped using the A probe setup. This null field is referred to as the A-field. The A-Field was also trapped using the 1 mOe setting for consistency. It was difficult to use this setting due to the noise although I monitored the 10 mOe setting periodically and I dont think I could have done any better with that setting (still had fluctuations on the order of .02 mOe but it was easier on the eyes when watching).
January 18th: Field profiles were measured using each probe set up on the 1, 10, and 100 mOe ranges. I also repeated all the field profiles with the fluxgate probe rotated 90 degrees to starboard such that the Z axis corresponds to the -Y axis. After applying the rotation corrections, I wanted to see if the X and Y axis would read the same (or similar) values as they should. Although the field was trapped using the A probe, the profiles measured by the A probe had intensities close to 40 nT in some cases (in the measuring region). The profiles measured by the B probe on the other hand were pretty good. I checked the zero reading of both probes inside the mu metal shielding. Probe B was still zero on all axis, Probe A was reading ~.3 mOe on both the Y and Z axis. The X axis was still at zero. I re zeroed the A probe and collected all the profiles again, including the YZ rotated profiles. Profiles collected from the A-Field are saved in the excel workbook 20210117 B-Field combined range tests.xlsx. This workbook only includes the A-probe readings after it was re-zeroed.
Some PDFs of some key plots are located here: 20210118_Field Charts.pdf. The data is probably be more clear in the workbooks though where you can sort and filter the data. I found it most helpful to click in the upper right of the chart sheet. There are three buttons, the bottom of which will allow you to filter which series to display. The series naming follows the convention of Axis range_setting Probe (i.e. X 1mOe A is the X axis, measured with the 1 mOe setting on Probe A). If the probe was rotated, this is noted by the text YZrotate.
A couple things that stand out:
Probe A is much noisier than Probe B. This is very apparent at this scale. On a typical profile measured along the length of the SRM, this noise is not apparent until you zoom in. I did a quick scan through a few previous field profiles. Around mid 2019 the profiles have similar noise to probe A. Prior to that, it is much quieter.
Probe B has good agreement between the YZ axis when rotated (within 2 nT). The Z axis on probe A has a difference of ~9 nT when rotated (Z becomes Y axis). The Y axis records a similar value when rotated (Y becomes Z). See charts A-Field: Probe B 10 mOe Range with YZ rotation vs A-Field: Probe A 10 mOe Range with YZ rotation. THis is a very interesting point because the idea for this came from the fact that in the ambient ship environment, on the 100 mOe setting, probe A reads ~138.2 mOe on all axis while Probe B reads ~138.2 on the X and Z axis and 127.8 mOe on the Y axis.
The two null fields have a different shape on the x axis (corresponds to SRM Z axis). Perhaps adjusting the gradient could fix this?
Probe B has good agreement on intensities measured by each range setting whereas probe A is all over the place. See chart A-Field: Probe A all Ranges vs A-Field: Probe B all Ranges.
Not sure how probe A became so offset from zero so quickly. Ill keep an eye on it to see if there is any consistent drift. It was handled in the same manner/locations as probe B.
Both Probes look pretty good on the 10 mOe range which is the most useful for the SRM.
It was decided to send control unit N2300 and probe A back to Applied Physics for calibration. Prior to sending the unit back, a new label for probe A was made (Figure 2).
Figure 2
Exp 390C
X390C SRM Field Trap and Magnetized Fluxgate Probes (fluxgate-gate)