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Luke, You should be aware that the Campbell Sci CS615's are not true TDR and they measure the dielectric constant at a lower frequency range than TDR. Apparently, this means the calibration is more temperature and soil dependent. We are using about 50 of these sensors in the field and are planning to do lab calibrations for our soils for both the moisture conent vs frequency calibration and the temperature correction. CS should be able to advise on long cable lengths but because you are just counting a square wave signal (as opposed to sending a receiving a microwave pulse) the cable length requirements are quite different to TDR and longer cables are possible as far as I know. But beware, the longer cables might cost more than extra loggers???? Also in some ways I like using multiple loggers because it gives you a bit of redundancy - if a logger fails you only lose the data from a subset of the sensors. I guess whether this is an advantage depends on your experiment. We have found the sensors to be reasonably robust out in the field - they've been installed for about a year now. cheers Andrew. At 17:58 2/02/99 GMT, you wrote: >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 > >Hi All > >Currently I am using a TDR system supplied by Campbell Scientific and >comprises CS615 sensors and a CR10X logger. I need to measure the soil >water contents on different silvicultural treatments. Now these plots are >really large and I will need to have cables up to 200m in length between the >logger and sensor. Does the cable length affect the accuracy of the reading >and what is the maximum cable length that can be used with these sensors? >Second, I suppose like the neutron probe the best way to calibrate the >sensors is gravimetrically? Anyone else using the same equipment? > >Any comments or suggestions? > >Regards > >Luke > > >Luke Esprey >BSc (Hons), MSc (Hydrology) >>Soilwater Research Officer >>Institute for Commercial Forestry Research >>P.O. Box 100281, Scottsville, 3209, Republic of South Africa >> >e-mail lukes@icfr.unp.ac.za >Tel: Int+27 331 62314 >Fax: Int+27 331 68905 >URL: http://www.icfrnet.unp.ac.za/~lukes/index.ssi > ==> GPS : S29,37,575' E30,24.379' <== > > > ------------------------------------------------------------------------------ Dr Andrew Western Centre for Environmental Applied Hydrology Department of Civil and Environmental Engineering The University of Melbourne 3052 Australia Ph +61 3 9344 7305 Fax +61 3 9344 6215 email: a.western@civag.unimelb.edu.au www: http://www.civag.unimelb.edu.au/~western -------------------------------------------------------------------------------