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In response to: >QUOTE>>>> The calibration data and technical information available from both Campbell Scientific and Automata, in my opinion, fails to meet minimal standards for metrological traceability. Although the instructions for use describe and imply certain performance, actual use varies widely. This variation generally will be associated with soil conditions by both the manufacturer and the customer. Again, in my opinion, much of this variation results from electronic performance deficiencies which are easily identified. Both of these manufacturers claim to integrate the volume of water surrounding the sensors. Neither characterizes this integration in detail. True capacitance does not require direct electrical contact with the dielectric media between the conductors. There must be some other reason for not insulating the probes. <<<<END QUOTE< I am the soil physicist with Campbell Scientific responsible for development of soil moisture sensors. Over the past couple of months I have monitored the discussion of performance of various soil moisture sensors including the CS615. Those participating in this group from the beginning when Bruce took upon himself the huge task of organizing this format will recall that the inaugural article was about the CS615. Bruce has done a admirable job of promoting healthy discussion on a topic which is fundamental to so many different scientific disciplines. I have chosen to simply monitor the discussions but have personally contacted those participants who have expressed concerns about operation and performance of the equipment I am responsible for or have significant experience with. I am sensitive to potential conflicts that may arise from too much input from the commercial realm into a scientific idea exchange. Campbell Scientific has a policy of dedicated customer support via several avenues. Most are aware of such support. I wish to address specific portion of the anonymous message which Bruce has posted. >QUOTE>>>> The calibration data and technical information available from both Campbell Scientific and Automata, in my opinion, fails to meet minimal standards for metrological traceability. Although the instructions for use describe and imply certain performance, actual use varies widely. This variation generally will be associated with soil conditions by both the manufacturer and the customer. <<<<END QUOTE< >Response< It is not clear to me what is meant by "minimal standards for metrological traceability." What other soil moisture sensors are there on the market which meet these standards? I am aware of an effort by some of my colleagues to generate an ASTM standard for TDR measurements. This has proven very difficult because of the very nature of soil moisture measurements. I considered offering some sort of standard such as calibration results from glass beads with deionized water, but this didn't seem all that useful and was received less than enthusiastically from the fellow soil scientists I discussed it with. I chose to offer as much information as I could concerning variables which affect the performance of the sensors. >QUOTE>>>> Although the instructions for use describe and imply certain performance, actual use varies widely. This variation generally will be associated with soil conditions by both the manufacturer and the customer. <<<<END QUOTE< >Response< Some of the applications presently using the CS615 are site specific irrigation, water content in coal, drying of brewing hops, water management on golf courses, preservation of historical sites and soil moisture in research plots for transport studies and barrier design. Modified versions of the probe are being used in forest fuel moisture, water content within approximately 2 cm of the soil surface, water content in human brain tissue and fat content in meat products. Actual use does indeed vary widely. >QUOTE>>>> Again, in my opinion, much of this variation results from electronic performance deficiencies which are easily identified. <<<<END QUOTE< >Response< There in fact are some limitations of the electronics presently available from component manufacturers. There always will be as we continue to push technology for improved accuracy, resolution and versatility. In the meantime, I would be interested in discussing the easily identified deficiencies and possibly a position here at Campbell Scientific for one with such skills. >QUOTE>>>> Both of these manufacturers claim to integrate the volume of water surrounding the sensors. Neither characterizes this integration in detail. True capacitance does not require direct electrical contact with the dielectric media between the conductors. There must be some other reason for not insulating the probes. <<<<END QUOTE< >Response< What detailed characterization is necessary to describe finite integration over the length of the rods? I can't speak for other companies who have products in this market, but our manuals present a description of the instrument operation. I agree that dielectric dependent methods do not require electrical contact. This has never been presented by us. I was disappointed to see this misconception so prevalent in the soil moisture community. There are other reasons for not insulating the probe rods. For one, it is an additional source of variability and potential failure. I have spent a significant amount of time in the lab evaluating several coating methods. I haven't yet found a material that is tough enough to withstand multiple insertions into sandy soils and that does not introduce distortion into the measurement. But I am continuing to study this and think some form of electrical insulation to reduce signal attenuation is needed. >Summary< Specific questions about soil moisture sensors should be posed to the appropriate representatives of the manufacturer. I haven't heard from anyone who has recently expressed concerns in this discussion group. The interactions I have with users are enlightening for both the user and myself, and we nearly always solve the problem and optimize the measurement. Sincerely, Jim Jim Bilskie, Ph.D. Soil Physicist jim@csius.com 801/750-9580