[ANSS-netops] ANSS-netops Digest, Vol 15, Issue 9
John R. Evans
jrevans at usgs.gov
Fri Feb 26 19:02:05 UTC 2010
Hi All,
RefTek uses the negative-side power line at the recorder power input
as ground, which leads to large currents in the ground lines and
therefore to significantly unstable ground voltage. They have been
very stubborn about fixing this design issue -- they really should
provide an independent primary grounding point not carrying
significant currents, and this may be one source of the steps you are
seeing. Disk startup used to make 4-bit swings in an otherwise
stable RefTek -- an issue mitigated by flash memory but perhaps
brought back by cycling radios drawing similar power at startup.
Another source could be "popcorn" noise but I doubt that from the
descriptions (the graphics were not attached so I have not seen
waveforms). Popcorn generally looks like a ragged boxcar of quasi-
random duration and quasi-quantized amplitude (steps on steps
possible but rare) -- trashes any double integration. These pops may
happen fairly rarely so a long record (hour plus 200 sps) is useful
in looking for them -- MatLab script attached (likely forgot to
include something so let me know; it is also not PC ready, only Mac).
I concur that some sort of regulation on the sensor power may help
but you may also need to modify the ground path (careful about ground
loops, of course). A super cap is an alternative to a big capacitor
but maybe not worth the additional cost and long charge times.
Simple regulator and proper ground probably the simplest robust
solution.
Cheers,
John
John R. Evans
U.S. Geological Survey
345 Middlefield Rd, MS-977
Menlo Park CA 94025
650-329-4753
jrevans at usgs.gov
Intermittently at:
USGS/ASL
P.O. Box 82010
Albuquerque NM 87198-2010
505-846-1793

On 26 Feb 2010, at 10:21, anss-netops-request at geohazards.usgs.gov wrote:
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> Today's Topics:
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> 1. stepping noise in sensor (Greg Steiner)
> 2. Re: stepping noise in sensor (Doug Given)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 26 Feb 2010 10:22:29 -0600
> From: Greg Steiner <vlf at cablerocket.com>
> To: anss-netops at geohazards.usgs.gov
> Subject: [ANSS-netops] stepping noise in sensor
> Message-ID: <4B87F545.60000 at cablerocket.com>
> Content-Type: text/plain; charset="us-ascii"; Format="flowed"
>
> Don,
> After looking at your plots, I'm thinking that it is not RF getting
> into
> the sensor and being rectified, but that it is changes in power supply
> voltage to the sensor caused by the freewave transmitter being
> activated. put a scope on your dc power line to the sensor, or try
> some
> realy big (10,000Uf caps across the line. If it is realy stubborn you
> might want to use a 3 terminal regulator to supply power to the
> episensor. Let me know if this helps, Ive seen that the episensor is
> very succeptible to passing through power line disturbances. It seems
> like there are no internal regulators.
> Greg
> --
>
> Greg Steiner
>
>
>
> VLF Designs
>
> 1621 Bella Vista Dr.
>
> Jackson, Mo. 63755
>
>
>
> Ph: 573-204-1286
>
> Fax:573-204-1286
>
> Ph: 573-388-2117
>
>
>
> Email: vlf at cablerocket.com
>
>
>
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> ------------------------------
>
> Message: 2
> Date: Fri, 26 Feb 2010 10:21:14 -0800
> From: "Doug Given" <given at caltech.edu>
> To: "'Greg Steiner'" <vlf at cablerocket.com>,
> <anss-netops at geohazards.usgs.gov>
> Cc: 'Bob Dollar' <dollar at gps.caltech.edu>
> Subject: Re: [ANSS-netops] stepping noise in sensor
> Message-ID: <CB9FDCFA07084E10862EDB87280F617B at Joshua>
> Content-Type: text/plain; charset="us-ascii"
>
> We see the steps also. Note that the plot attached is
> from an
> Episensor hooked up to a Basalt with not telemetry connected - so,
> at least
> for this case, it's not the radio.
>
>
>
> This plot was produced by Bob Dollar working with Arnie
> Acosta.
>
> +-----------------------------------------------------------------+
> | Douglas Given | Project Chief |
> | U.S. Geological Survey | S. California Earthquake Monitoring |
> | Caltech Seismological Lab | (626)583-7812 FAX: (626)583-7827 |
> | 525 So. Wilson Ave. | given at caltech.edu or doug at usgs.gov |
> | Pasadena, CA 91106 | http://pasadena.wr.usgs.gov/given |
> +-----------------------------------------------------------------+
>
>
>
>
>
> _____
>
> From: anss-netops-bounces at geohazards.usgs.gov
> [mailto:anss-netops-bounces at geohazards.usgs.gov] On Behalf Of Greg
> Steiner
> Sent: Friday, February 26, 2010 8:22 AM
> To: anss-netops at geohazards.usgs.gov
> Subject: [ANSS-netops] stepping noise in sensor
>
>
>
> Don,
> After looking at your plots, I'm thinking that it is not RF getting
> into the
> sensor and being rectified, but that it is changes in power supply
> voltage
> to the sensor caused by the freewave transmitter being activated.
> put a
> scope on your dc power line to the sensor, or try some realy big
> (10,000Uf
> caps across the line. If it is realy stubborn you might want to use
> a 3
> terminal regulator to supply power to the episensor. Let me know if
> this
> helps, Ive seen that the episensor is very succeptible to passing
> through
> power line disturbances. It seems like there are no internal
> regulators.
> Greg
>
> --
>
>
>
> Greg Steiner
>
>
>
> VLF Designs
>
> 1621 Bella Vista Dr.
>
> Jackson, Mo. 63755
>
>
>
> Ph: 573-204-1286
>
> Fax:573-204-1286
>
> Ph: 573-388-2117
>
>
>
> Email: vlf at cablerocket.com
>
>
>
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