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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 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 > > > >