I received 4 replies to my question about custom probes and TDR = equipment. I was also told that a very similar question was posed on = ecolog a few years ago. The digest of that discussion can be found at: = https://listserv.umd.edu/cgi-bin/wa?A2=3Dind0306D&L=3DECOLOG-L&P=3DR2263&= I=3D-3.
In summary, although some of the older probes had all the electronics = incorporated in the probe (e.g. Campbell Scientific's CS 616), it = appears that custom probes can be easily manufactured for Campbell's = TDR100, and Trase's TDR analyzer; i.e. there are no electronics in the = probes. Several respondents replicate Campbell's epoxy handle for the = 3-probe guides, but it seems there would be no problem to keep using the = 2-probe alligator-clip method with these instruments on the probes (some = of which I've had buried for 16 years). (I know the waveguide field is = more uniform for the 3-rod probes, but simplicity and speed allows for = great sample sizes.) Thanks to everyone for sharing their insights. Andrew Gray *********************************** From: Asko Noormets [mailto:[EMAIL PROTECTED] Sent: Fri 9/8/2006 7:27 AM To: Gray, Andrew -Forestry Subject: Re: Soil moisture measurement with TDR and custom probes? =20 Dear Andrew, >From the four systems that I have used (CSI TDR 100, Juniper-based=20 system, which is similar to yours, CS620 and CS616), I like the=20 CS616. We bundle together a battery pack (CR21 base with custom lid),=20 CSI datalogger (CR510), CR10KD key pad and of course the sensor. I=20 like it for two reasons - it allows direct comparison with=20 permanently installed CS616-s, and it gives a consistent reading=20 unlike the traditional TDR systems). Asko Asko Noormets, Research Assistant Professor Dept. EEES, Mail Stop 604 2801 W. Bancroft St. The University of Toledo Toledo, OH, 43606 United States phone: 419-530-5498 fax: 419-530-4421 e-mail: [EMAIL PROTECTED] *********************************** From: Stan Harpole [mailto:[EMAIL PROTECTED] Sent: Thu 9/7/2006 9:33 PM To: Gray, Andrew -Forestry Subject: tdr =20 Hi Andrew, we've been using the "minitrase" from Soil Moisture Inc. http://www.soilmoisture.com/prod_details.asp?prod_id=3D895&cat_id=3D19 We make our own probes from 1/4" stainless steel rod (I think it =20 works out to ~$3 for a set of 20cm probes with machine shop labor to =20 cut and grind the ends) and permanently hammer them them into the =20 soil; sounds similar to your application. What's nice about this =20 system is that they also sell waveguides that can be buried =20 permanently as well as a slammer waveguide connector that lets you =20 pound the probes into compacted soil for one-time measurements. =20 Another feature I like about this system is that it stores the data =20 redundantly on both the palm pilot readout as well as on the main tdr =20 unit. It uses rechargeable Makita power tool batteries and is =20 provided with a backpack - it's quite portable. It's worked quite =20 well for us and the tech support is good. Stan W. Stanley Harpole, PhD 321 Steinhaus Hall Dept. of Ecology and Evolutionary Biology University of California, Irvine Irvine, CA 92697 949-824-1772 [EMAIL PROTECTED] http://www.cedarcreek.umn.edu/harpole *********************************** From: Rosie Wallander [mailto:[EMAIL PROTECTED] Sent: Thu 9/7/2006 3:25 PM To: Gray, Andrew -Forestry Subject: RE: Soil moisture measurement with TDR and custom probes? =20 Hi Andrew, This question has come up on the ecolog list a couple of years ago. = Perhaps that person found an answer - maybe you can search search the list and = find an answer. We will be making our own probes for use with a Campbell TDR100 next = year. We know how to make them, but we'll need to practice a bit before we'll = be happy with our product. Basically we fill a PVC mold with resin. The mold is the head of the = probe. Before filling with resin, 3 stainless steel rods (1/8th " from the = welding store - cut to our desired length) are held in parallel position with a = form and soldered (silver solder) to the wires from a coaxial cable. I = forget which wires connect to which part of the coaxial cable. The tough part = is containing the resin in the mold while it hardens. Our first trial, the resin went through our seals and all over everything. We were able to purchase coaxial cable with the correct connection for the TDR100, so we = did not need to solder the cable to the connector. Our experience is very limited. Our soil physicist Dr. Jon Wraith and his postdoc Dr. Paolo Castiglione ([EMAIL PROTECTED]) make their own probes and perhaps they may be = willing to help you. Good luck, Rosie Rosie Wallander Research Associate mail: PO Box 173120 UPS: Room 334 Leon Johnson Hall =20 Montana State University - Bozeman Bozeman, MT 59717-3120 418 Leon Johnson Hall 406-994-7661 [EMAIL PROTECTED] ******************************************** From: Kristin H [mailto:[EMAIL PROTECTED] Sent: Thu 9/7/2006 3:36 PM To: Gray, Andrew -Forestry Subject: RE: Soil moisture measurement with TDR and custom probes? =20 I do know enough about the probes to answer that without talking to the = soil physics lab. There are no electronics. The probes I used were three = rods which went into a block of epoxy. The epoxy also contained a piece = of wire mesh to conduct the electricity and the cable was attached to = that mesh. I will try and get some pictures tomorrow if you'd like a = more visual description of the probe and send those on with any other = tips from the soil lab. "Gray, Andrew -Forestry" <[EMAIL PROTECTED]> wrote: RE: Soil moisture measurement with TDR and custom probes? That would be great! The key item I'm wondering about is whether there's = any electronics in the probe itself, or whether the cable simply splices = to each of the metal rods (I have been using a two-rod setup where the = cable ends in alligator clips and simply clips onto the ends of the bare = rods). =20 Thanks! Andy -----Original Message----- From: Kristin H [mailto:[EMAIL PROTECTED] Sent: Thu 9/7/2006 3:06 PM To: Gray, Andrew -Forestry Subject: Re: Soil moisture measurement with TDR and custom probes? =20 I have some second hand experience with "homemade" probes for the TDR = 100. The soil physics lab in my department makes them and has had luck = with them, although they don't give quite as strong a signal. If you're = interested, I will talk to the lab and get detailed instructions for = making them. =20 Kristin Harbuck Master's student Department of Land resources and environmental science Montana State UniversityFrom: Kristin H [mailto:[EMAIL PROTECTED] Sent: Thu 9/7/2006 3:06 PM To: Gray, Andrew -Forestry Subject: Re: Soil moisture measurement with TDR and custom probes? ******************************* -----Original Message----- From: Ecological Society of America: grants, jobs, news on behalf of = Gray, Andrew -Forestry Sent: Thu 9/7/2006 1:10 PM To: [email protected] Subject: Soil moisture measurement with TDR and custom probes? =20 I've been using a Tektronix 1502c TDR to measure soil moisture for =3D years, primarily because it was possible to install hundreds of probes = =3D (consisting of two steel rods) across a site and measure the same probes = =3D over time. Tektronix no longer sells the thing (or anything that will do = =3D the same thing), and the beast is kind of big and bulky anyway. Most =3D outfits that sell TDR-soil moisture packages seem to require the use of = =3D their own probes, but the cost makes permanent installation of many =3D probes prohibitive. If anyone has any suggestions, or has found a way to rig custom probes = =3D with these newer products (e.g., Campbell Scientific's TDR100), I would = =3D like to hear from you! Please reply to me and I will compile responses = =3D (if any) and send them to the list. thanks, Andrew Gray
