proudly sponsored by
|
archiving of SOWACS proudly sponsored by |
|
Andrew Skinner writes: Here at Measurement Engineering Australia (MEA) we have spent the last 4 years building and field testing loggable gypsum block networks over quite wide areas. We had CSIRO Division of Soils test 16 of our standard production gypsum blocks, and these showed considerable variation in soil moisture tensions below 60kPa. For this reason we do not recommend use of gypsum blocks in sands and sandy loams, which are drained of readily available water before the block gives reliable readings. The Irrometer granular matrix sensor (GMS) would be an ideal sensor for these sandier soils, as its range (claimed by the manufacturer) is something like 10kPa to 200kPa, and it's an AC resistive measurement just like the gypsum block. In theory at least, we should be able to plug them in to our logging systems, with an appropriate change in calibration. Quite some years back we tested some of the older style Irrometer GMS sensors with the PVC bodies in sandy country, and found that the blocks did not drain as the soil dried out, presumably through poor hydraulic conductivity through the small conducting surface area (there weren't many holes in the cylindrical body). Early papers on the original sensors indicated quite some variability and non-repeatability between GMS sensors. I talked to Bill Pogue (CEO at Irrometer) at an Irigation Conference in Sydney some years back, and he showed me a sample of a newer device (a prototype back then?) with more holes per square inch, and a thin stainless-steel mesh replacing the PVC. Does anyone have or know of field data or technical papers on these new GMS sensors with the stainless steel jackets? I am particularly interested in their longevity, as I understand they use a small amount of gypsum as an electrolyte in a coarse granular matrix material. Is this correct? My concern is that once this gypsum has dissolved, the blocks will become inoperable. Andrew Skinner Engineering Director MEA meaust@ozemail.com.au =========== MEASUREMENT ENGINEERING AUSTRALIA =========== Environmental Monitoring and Data Logging Applications Engineers. 27 Rowland Rd., Magill, SA 5072, Australia ph: (08) 8332 9044, fax: (08) 8332 9577 e-mail: meaust@ozemail.com.au