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Peter Toome writes to the sowacs list: ===8<============== Hello Stephanie Good to see that people are still having to start with some decent experimentation. Check the SOWACS archive - you will find there some information in an article from Andrew Skinner, MEA's Engineering Director, on the finer points of building and reading gypsum blocks. Block construction is essentially very simple - two electrodes placed within the gypsum. The sensors must be fed with an A.C Excitation to stop them from being polarised. Also if installing multiple sensors on a site, you must excite each one separately so that readings are not affected by the resistance of the other sensors. The challenge for you is to come up with a calibration relating the resistance figures to kPa. You may also wish to experiment with different materials. If you want any other specifics, check our web site (www.mea.com.au) or that of Irrometer Corp in the US who manufacture the Watermark Granular Matrix Sensor, a sensor based on the gypsum block concept but with longer life and improved performance in the low tension end. Peter Toome Marketing Manager Measurement Engineering Australia (MEA) Data Logging Applications and Measurement Systems Engineers 41 Vine St., Magill, SA 5072 ph 08 8332 9044, fax 08 8332 9577, mob 04 1883 2422 Web www.mea.com.au E-mail peter.toome@mea.com.au -----Original Message----- From: Bruce at Findasensor [mailto:asowacspost@findasensor.com] Sent: Sunday, 15 June 2003 6:59 PM To: list @ sowacs . com Subject: SOWACS: extreme newbie- UK Gypsum block manufacture Stephanie writes to the sowacs list: ===8<============== Hi, my name is Stephanie Henderson and I am sixth form student from the UK. What I am about to ask may sound dense but please hear me out. As part of my A level physics coursework (about first year degree, US) I have to design a half way accurate way of measuring water content in soil using basic equipment, (e.g. digital multimeter, wires etc) and I was wondering if you could perhaps suggest a couple of ideas? I don't want you to go out of your way because I know you are busy, but any help you could offer me would be a great help. I was thinking along the lines of a home make gypsum block? Many Thanks Steph ===8<============== Bruce comments: Stephanie Thank you for your very polite request.. I will post it to the sowacs group and see what the members come up with (Apart from the list of links off the website specifically covering gypsum blocks here): http://www.sowacs.com/sensors/gypsum.html Bruce NOTE: To get off this list, send an email to list@sowacs.com with the subject line: unsubscribe_sowacs For full instructions see this page: <http://www.sowacs.com/subscribe/index.html>