Don's message brings up a key consideration for any type of test that is performed - repeatability.
If you can't repeat the results, you need to re-evaluate your methodology. For instance, in the event you had a failure, it would be difficult to determine if your fix actually worked. John Juhasz Fiber Options Bohemia, NY -----Original Message----- From: umbdenst...@sensormatic.com [mailto:umbdenst...@sensormatic.com] Sent: Wednesday, September 26, 2001 9:05 AM To: emc-p...@majordomo.ieee.org; sco...@world.std.com Subject: RE: Steel ball for impact tests Scott, You had indicated that " A tube is nice but not needed if you can drop the weight accurately. . ." I also used to test "bombs away", somewhat as a sport to see how close I could come to the desired spot. We had an interesting experienced that permanently changed our approach. We had a device with a plastic enclosure with re-enforcing ribs in various locations. When we eyeballed the drop, we would miss critical spots by 1/2". Didn't seem like much at the time, until we discovered that with the tube, we could hit exactly the critical spot and observed that the enclosure failed "unsafely" (and repeatably), i.e., hazardous voltages were exposed. This is something you want to discover prior to having a NRTL witness or perform the test. Searching for a new sport, Don Umbdenstock Sensormatic > ---------- > From: Scott Lacey[SMTP:sco...@world.std.com] > Reply To: Scott Lacey > Sent: Tuesday, September 25, 2001 5:38 PM > To: emc-p...@majordomo.ieee.org > Subject: RE: Steel ball for impact tests > > To the group: > > Having monitored some of the discussion on this thread, I thought that I > would weigh in with some of my experience with this test. The purpose of > the test is to subject the E.U.T. to a specific force of impact from a > hard steel impactor (ball) of known radius. The surface should be smooth > to avoid subjecting the E.U.T. to additional point stress (the "center > punch" effect). Anything else is frosting on the cake. It does not matter > whether the ball is dropped or swung, as long as the force is consistent > and the E.U.T. is firmly mounted. > > A ball bearing is perfect for the job. A typical chrome steel ball is more > than hard enough to meet the specification. If the weight is a little off > just raise or lower the drop height to compensate. An eyebolt is nice but > not really needed. The reason the "official" balls cost so much is the > difficulty of machining the ball for the bolt, and the fact that these are > very low volume items. A trailer hitch ball will also work without > modification. Just weigh it, calculate the drop height, hold it by the > threaded bit and "bombs away". A tube is nice but not needed if you can > drop the weight accurately. The idea of standing on a chair is excellent > as a 1kg ball can make a serious bruise! I would also recommend padding > the floor (except under the E.U.T.) with cardboard or carpeting scraps so > the ball won't get all scratched up. If you really must have an eyebolt > and don't want to spend the money thread a flanged nut onto an eyebolt and > epoxy it onto the ball with a steel-filled epoxy (common at auto parts > stores). It may break off occasionally but you can just re-epoxy it. Just > degrease all the parts before gluing and it works surprisingly well. > > Have Fun > Scott Lacey > ------------------------------------------- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
