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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 Dear Rick If anyone is interested: we have developed and have been using a small circuit designed to switch on our pressure transducers which we use to log tensiometer measurements. The prelog pulse (milliseconds prior to sampling) from the HOBO H8 (4-Channel External) is used to trigger a timing circuit, which learns the sampling interval from the first cycle and subtracts from this, the transducer warm up time (15 seconds). Thereafter, the prelog pulse is used to trigger the transducer switch-on delay, so that, for the next logging cycles, the transducers have been "warmed up" and ready to log a stable signal. Between the log events, the pressure transducers are "put to sleep" and so our 3Ah batteries will last for about 6 months at a 10minute logging interval on 4 pressure transducers. Also, the timing devise does not need adjusting as it "learns" any logging interval that is launched to the HOBO. The HOBO and timing circuit are housed in a new box slightly bigger than the HOBO, with connections convenient for linking to transducers and shuttle. Our circuit and boxing come to about US$ 28.00 for each logger. Until a qualified OEM develops and produces this from the IP version at a comparable combined price, we will continue logging in this way. Regards Simon Lorentz Senior Process Hydrologist School of Bioresources Engineering and Environmental Hydrology University of Natal South Africa >>> <owner-sowacs@aqua.ccwr.ac.za> 03/14 10:12 AM >>> 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 > >> > > > >