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Hi All,<br><div> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="Apple-interchange-newline">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.</span></font></div><div><br></div><div>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).</div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br></span></font></div><div>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.</div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Cheers,</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">John</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="webkit-block-placeholder"></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">John R. Evans</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">U.S. Geological Survey</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">345 Middlefield Rd, MS-977</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Menlo Park CA 94025</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">650-329-4753</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><a href="mailto:jrevans@usgs.gov">jrevans@usgs.gov</a></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="webkit-block-placeholder"></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><b>Intermittently at:</b></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">USGS/ASL</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">P.O. Box 82010</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Albuquerque NM 87198-2010</span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">505-846-1793</span></font></div><div><div style="page-break-after: avoid; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="khtml-block-placeholder"></span></font></div></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="webkit-block-placeholder"></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="webkit-block-placeholder"></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><br class="webkit-block-placeholder"></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "></span></font></div></span></div></body></html>