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NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs John, Thanks for the update on what Onset Corp. proposes to offer concerning switched excitation. I am disappointed that Onset has chosen not to offer this option for the Hobo H8 4E Outdoor/Industrial Logger, or even for the Hobo H8 indoor logger. I believe that this may be a missed opportunity to provide a ready unit directly from the manufacturer that could be used with any number of resistance based soil water sensors. I disagree that the soil sensor technology is the hard part. But even so, I do not see where this obviates the potential or need to produce inexpensive, field-ready logger units that can be interfaced by the user with his/her soil water sensors. Thanks for the update. Rick Allen > > Hello Rick, > > You are correct that Onset can provide a 4-channel data logger for use > with most analog output sensors. However, we have not been directly > marketing our standard 4-channel logger for soil moisture logging > because we recognise that the data logger is the low-tech system > element in that application. The "hard part" of soil water sensing is > understanding and properly applying the sensor technology. There > are companies, and individuals such as yourself, that are better > qualified for that role than Onset, and we have chosen to support > them with what we do best by offering OEM versions > of our data logger(s). > > The sensor polarization problem you descibe has been solved in the > -IP version of our 4-channel OEM logger. The -IP logger is one of two > OEM loggers available from Onset. Those loggers are not in end > user configurations, and do require some added value by the purchaser. > They are provided to qualified OEM's as unprogrammed, or board level > parts, for integration into their proprietary systems. For example, > the -IP version is uniquely programmed by the OEM with channel > switching and delay timing specific to their sensor. The -IP is also a > board level product that requires additional packaging for use outdoors. > > We do not recommend that an end user purchase our standard data > loggers directly for use with most common low cost soil moisture > sensors because each sensor type has specific interface considerations. > We do recommend that end users contact their preferred supplier of > low cost soil moisture monitoring systems for additional information > on the data loggers they have available. > > Regards, John Johnston > Onset Computer Corporation > P.O. Box 3450 > Pocasset, MA 02559-3450 > Web: www.onsetcomp.com > (800) 564-4377 > (508) 759-9500 Ext 158 > (508) 759-9100 FAX > > > > > >John Johnston, > > > >Your recent Email indicated that the tipping bucket is the only soil- > >water related application thus far from Onset Corp. What about the > >company's retrofit of the Hobo datalogger to facilitate the > >measurement of four WaterMark sensors? My understanding was > >that all engineering had been worked out on this and that it was > >merely a matter of production. The product would be a datalogger for > >around $150 that is weather proof and that can measure four WM or > >other resistance-based soil sensors. Can you bring us up to speed > >on the status? > > > >As I've indicated to Onset in the past, if one can produce a low-cost > >data logger (in say the $100 range) that can record a near- > >continuous record of soil water content or potential, one may see > >these planted by the tens of thousands as farmers utilize them to > >monitor how well they have been managing irrigation or other land > >applications. The system must be cheap enough that it can be > >cultivated out by a 15 year high school kid on a tractor, but then > >replaced by the kid's father, because the cost is relatively low as > >compared to the benefit. > > > >In this type of situation, the absolute accuracy of the reading is of > >much less importance than is the relative change in recorded signal > >over time. This is what a farmer will evaluate at the close of an > >irrigation season. He can look back over the record of soil water > >content or potential (relative readings) and evaluate trends and > >changes over time as they are impacted by how he has managed the > >system. He'll use this information to improve his management the > >following season. > > > >It would be even better to have a display on the logger that can > >provide a graph of the last four weeks or so of measurements at a > >glance, for example like that used on the AM400 system being > >produced by M.K. Hansen Company of East Wenatchee, WA. ( > >mikeh@nwi.net ,2216 Fancher Blvd. East, Wenatchee, Wa 98802 > >1-509-884-1396, fax 2218). Hansen's system can read up to six > >Watermark probes at a time (using AC excitation) along with soil > >temperature and sells for approximately $250 in bulk (I believe), > >which isn't a bad price. The graphical display is invaluable for > >allowing a farmer to quickly review the recent trends in soil water > >change and the need for any on the spot actions. The logger can > >retain a year's worth of data in memory and downloads to a notebook > >computer. > > > >Regarding the less expensive Hobo datalogger, I can send a three > >page writeup on how to connect the Onset Hobo datalogger to > >WaterMark or other resistance based sensors to anyone interested. > >Send a request to RALLEN@Kimberly.uidaho.edu . The Hobo > >logger uses DC excitation in its reads which can cause some > >electrolysis effect (i.e., micro gas bubbles) at the electrodes. This > >can bias the electrical conductance and therefore the resistance > >reading. However, my understanding is that the retrofit that has been > >reengineered by Onset for soil-water applications will shorten the > >time of excitation on each of the four channels so that the magnitude > >of the electrolysis effect may become insignificant. > > > >Thanks. > > > >Rick Allen > >Water Resources Engineer > >Univ. Idaho > > > >> John Johnston writes > >> > >> Hello Again SOWACS > >> > >> I was formerly with ESI in San Diego, CA, and occasionally gave inputs > >on > >> the use of TDR in soil moisture applications. About 20 months ago I > >joined > >> Onset in Pocasset, MA, but until recently haven't had anything useful to > >> present to SOWACS. Early this year Onset offered its first product > >related > >> to soil water in the form of a fully integrated tipping bucket rainfall > >> logger. http://www.onsetcomp.com Please take a look at it, and if you > >have > >> comments let us know on > >> our site registration page under "Request a Catalog". I had our internet > >> site administrator add a source code selection called SOWACS under the > >> links and newsgroups pulldown, so that you could leave your "tracks".. > >> > >> Although I haven't been in a position to make a useful contribution, I > >> have continued to monitor SOWACS as a learning experience. Thanks again > >to > >> Bruce and everyone for continuing my education on this continually > >> challenging instrument application. > >> > >> John Johnston > >> Onset > >> Web: www.onsetcomp.com > >> (800) 564-4377 > >> (508) 759-9500 Ext 158 > >> (508) 759-9100 FAX > >> > > > >