Some time ago, in a galaxy far far away at the Rocket Ranch - - - I was involved in a study to determine the dielectric breakdown mechanisms in Solid Rocket Propellant. It was necessary to construct a large number of "stands or Platforms" to hold large blocks of propellant. These blocks were subjected to a variety of charging methods as well as simulated Lightning. As you can surmise these stands were used only ONCE. Because we were consuming these Stands at a high rate we were forced to go to less expensive construction material. Wood was the best 2nd choice. We initiated a detailed study of the dielectric characteristics of various wood types. We found after extensive study that the conductivity of the wood is controlled by both the moisture content (big surprise) and the level of organic salts & minerals contained in the growth ring boundary. We found that the best wood from an insulation standpoint was Balsa. However this wood had no structural strength. The next best was white Poplar or Ash, Triple kiln dried with 2-3 coats of marine varnish. We successfully used these woods in stands that were subjected to charge deposition in excess of 6000 micro Coulombs and direct lightning strikes of 10.7MV without breakdown. Of course the appropriate design constraints were followed for stress equalization and gradient control. As a general rule (if the wood is properly specified and moisture controlled) a value of 0.76 of Teflon can be used for calculation of properties. For what it's worth. Michael Taylor Awaiting winter in Colorado
-----Original Message----- From: Scott Lacey [mailto:[email protected]] Sent: Friday, November 02, 2001 5:04 PM To: POWELL, DOUG Cc: [email protected] Subject: RE: EMC test table construction plans Doug, Wood is ok if you seal it properly to prevent absorbed moisture from causing inconsistancies from one test to the next. Most clear resins do not cause RF problems whereas the metallic pigments in paints often do. If you can, covering the top with laminate (Formica) increases durability and provides a low friction surface. The best design is to make a sturdy table using the following criteria: 4 X 4 or doubled 2 X 4 legs. Top of 2 layers of 3/4" plywood or particle board. Apron to support legs of at least 2 X 4 or 3/4 X 6 cross section. Pivoting top overlay of 3/4" plywood or particle board with a piece of 1 1/2" PVC pipe for a pivot. What you do is either cover the table surfaces (top & bottom) with laminate or sand, seal (multiple coats) and sand again plus wax to allow easy rotation. Drill matching holes through the center of the 3/4" overlay and the tabletop for the stub (4" long or so) of pipe. glue the pipe flush with the top of the overlay (it will protrude from the bottom). You just drop the overlay with pipe onto/into the tabletop with hole. During testing the table is rotated (1/4 turn) manually between tests. If you doubt that laminate can provide a low friction bearing, try this test - turn one table upside down on top of an identical table, rotate the top table, and then try rotating the table with a coworker standing on it. If you find too much friction apply some automotive paste wax. Scott Lacey -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of POWELL, DOUG Sent: Thursday, November 01, 2001 12:38 PM To: EMC-PSTC (E-mail) Subject: EMC test table construction plans Hello all, I plan to construct my own insulated EMC test table for a 5 meter chamber. Seems simple enough to do and I could easily come up with something. I thought I might first ask for input from those of you in the discussion group who have experience or maybe even construction plans. Here are some features I want: 1) I will be testing products that weight up to 200 Lbs (91 kg). 2) I want to minimize metalic fastners. 3) I would like to make it a pivoting table (not motorized). 4) Height is 80 cm. 5) The surface should be replacable if it gets badly worn or scarred. I'm thinking of using hardboard. 6) Suggestions on length & width? -doug ----------- Douglas E. Powell, Compliance Engineer Advanced Energy Industries, Inc. Mail stop: 203024 1626 Sharp Point Drive Ft. Collins, CO 80525 970.407.6410 (phone) 970-407.5410 (fax) mailto:[email protected] ----------- _________________________________________ This message, including any attachments, may contain information that is confidential and proprietary information of Advanced Energy Industries, Inc. The dissemination, distribution, use or copying of this message or any of its attachments is strictly prohibited without the express written consent of Advanced Energy Industries, Inc. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
