[TangerineSDR] Fwd: another 24hour RM3100 run and comparison with Fredericksburg

Julius Madey hillfox at fairpoint.net
Tue Sep 22 21:44:45 EDT 2020

Dear John,
Yes, temperature information was posted a while back.  PNI initially 
claimed that there was no temperature effect due to the essentially self 
compensating scheme used for field measurement. After I measured as much 
as a 7-10nT per degree C tempco in some controlled oven experiments and 
sharing that data with PNI, PNI eventually replied that engineering had 
measured a maximum of +/- 2nT per degree C for the inductors alone but 
had not characterized the complete sensor.

The data I have taken so far is not complete but indicates that the 
tempco (1) may not be equal on all axes, including differences in sign 
and (2) may not be assumed to be equal for any two units and (3) may not 
be linear with temperature, making algorithmic correction of the 
recorded data difficult.

Hence, my attempts to achieve temperature stabilization to better than 1 
degree C over 24 hours for the recordings I've been doing (sensor in a 
housing that can be easily buried sub surface).

Have also done some experiments with an insulated chamber containing a 
thermal mass, equivalent to a low pass filter, to achieve stabilization.

Another approach is a temperature controlled oven set to a few degrees 
above expected maximum local ambient temp but that requires power, which 
complicates long cable runs.

At just 19-20 inches below grade in my shaded woodlot, 24 hour 
temperature stability has been within 0.7C.  Another 12-16 inches for 
the next install should bring that to a diurnal variation of perhaps 
0.1C in this location.

Jules K2KGJ

On 9/22/2020 7:52 PM, John Gibbons wrote:
> All,
> I have not kept up on this thread due to other commitments, but I 
> don't see any mention of the temperature data and plotting 
> correlated to the data acquisition of the 3 axis magnetometer (or more 
> likely I missed it).
> I believe that the RM3100 uses ferrite core inductors for the 3 axis 
> magnetic pickups and ferrites definitely have a tempco (voice of 
> experience...). Even a 1 Deg C may have an impact on the mu of the 
> ferrite at the 1nT measurement levels.
> You've probably already done this (if so please point me to it) but 
> has this been looked at / tested for / quantified?
> John N8OBJ
> John C. Gibbons
> Director - Sears Undergraduate Design Laboratory
> Dept. of Electrical Engineering and Computer Science
> Case Western Reserve University
> 10900 Euclid Ave, Glennan 314
> Cleveland, Ohio  44106-7071
> Phone (216) 368-2816 <tel:216-368-2816> FAX (216) 368-6888 
> <tel:216-368-6888>
> E-mail: jcg66 at case.edu <mailto:jcg66 at case.edu>
> On Mon, Sep 21, 2020 at 4:18 PM Julius Madey via TangerineSDR 
> <tangerinesdr at lists.tapr.org <mailto:tangerinesdr at lists.tapr.org>> wrote:
>     Forgot to mention that one thing to keep in mind is the difference
>     in raw data processing between the absolute value sliding 1minute
>     average plots I do with a spreadsheet with the more complex
>     algorithm delta B plots from Intermagnet.  I'm not sure how the
>     10nT anomaly would appear if the same Intermagnet processing
>     algorithm was used.
>     Hyomin ?????
>     On 9/15/2020 10:38 AM, Phil Erickson wrote:
>>     Hi Dave,
>>       The X and Y traces return after 24 hours to nearly the same
>>     relative value in both the reference and RM3100 traces.  The Z
>>     trace does not.  Ionospheric currents flowing in the E region
>>     should not affect Z exclusive of X and Y under most any geometry
>>     I can think of, so I wondered whether the uncalibrated RM3100 was
>>     likely causing this.  (I have never professionally calibrated a
>>     magnetometer, so Hyomin might need to comment here.). In other
>>     words, I always assume there is some measurement systematic until
>>     it has been completely ruled out before assigning it to
>>     geophysical variation.
>>     73
>>     Phil W1PJE
>>     On Tue, Sep 15, 2020 at 10:34 AM David Witten <wittend at wwrinc.com
>>     <mailto:wittend at wwrinc.com>> wrote:
>>         @Phil,
>>         Correlation is great, and surely some further calibration
>>         issues may remain.  But these sensors are NOT colocated -
>>         (200-300+ mi apart?) . Wouldn't it be suspicious if they did
>>         correlate perfectly?  If they did, shouldn't  we ask if we do
>>         really need an extensive array of these sensors? 
>>         Presumably there will always be some local variation at this
>>         scale?  (don't know, just asking)
>>         Dave Witten, KD0EAG
>>         On Tue, Sep 15, 2020 at 7:21 AM Phil Erickson
>>         <phil.erickson at gmail.com <mailto:phil.erickson at gmail.com>> wrote:
>>             Hi all,
>>               There appears to be a 10 nT drift in the Z component
>>             for the RM3100 that is not in the Fredericksburg traces. 
>>             Is that slow systematic bias expected?  Maybe things are
>>             not calbrated over that time frame quite yet?
>>             73
>>             Phil W1PJE
>>             On Mon, Sep 14, 2020 at 10:49 PM David Witten via
>>             TangerineSDR <tangerinesdr at lists.tapr.org
>>             <mailto:tangerinesdr at lists.tapr.org>> wrote:
>>                 I don't believe that my previous post carried the
>>                 file K2KGJ provided.
>>                 ---------- Forwarded message ---------
>>                 From: *Julius Madey* <hillfox at fairpoint.net
>>                 <mailto:hillfox at fairpoint.net>>
>>                 Date: Mon, Sep 14, 2020 at 4:26 PM
>>                 Subject: another 24hour RM3100 run and comparison
>>                 with Fredericksburg
>>                 To: Kim, Hyomin <hmkim at njit.edu
>>                 <mailto:hmkim at njit.edu>>, David Witten
>>                 <wittend at wwrinc.com <mailto:wittend at wwrinc.com>>, Dr.
>>                 Nathaniel A. Frissell Ph.D.
>>                 <nathaniel.frissell at scranton.edu
>>                 <mailto:nathaniel.frissell at scranton.edu>>, Dave
>>                 Larsen <kv0s.dave at gmail.com <mailto:kv0s.dave at gmail.com>>
>>                 All,
>>                 I was hoping to record a relatively short term event
>>                 but missed one about 10 days ago.  However, there was
>>                 a good run on the 12th with an ~30nT excursion on the
>>                 Y axis lasting about an hour.  In the attached pdf,
>>                 the three axes of the RM3100 again track the
>>                 Fredericksburg magnetometer station data quite
>>                 closely.  The RM3100 plotted data points are simple
>>                 running 60second averages and not the more complex
>>                 filtering algorithm used by Intermagnet stations for
>>                 their 1 minute data points.
>>                 The vertical axes scales on all plots are as close as
>>                 I could match them by eye in cutting and pasting.
>>                 I believe the value to the right on the Intermagnet
>>                 plot is the mean for the 24 hour period.  I did not
>>                 try to compute a 24 hour mean.
>>                 One of the products for the future for general
>>                 interest would be a running plot like those available
>>                 on Intermagnet.org.  I guess we can dream a bit.
>>                 Jules - K2KGJ
>>                 -- 
>>                 TangerineSDR mailing list
>>                 TangerineSDR at lists.tapr.org
>>                 <mailto:TangerineSDR at lists.tapr.org>
>>                 http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
>>             -- 
>>             ----
>>             Phil Erickson
>>             phil.erickson at gmail.com <mailto:phil.erickson at gmail.com>
>>     -- 
>>     ----
>>     Phil Erickson
>>     phil.erickson at gmail.com <mailto:phil.erickson at gmail.com>
>     -- 
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