Hi Scott, Do you characterize the insertion loss over your frequency range of interest? I suspect most silicon steel transformers go from inductive coupling to inter-winding capacitive coupling at a fairly low frequency. It should be a pretty interesting model.
Brent DeWitt Westborough, MA > -----Original Message----- > From: Scott B. Lacey [mailto:[email protected]] > Sent: Thursday, March 12, 2009 6:40 PM > To: [email protected] > Subject: Re: [PSES] scope probe gnd > > A trick I've used for years to look at low > frequency ac power is to use a small > transformer to couple a single-ended scope > probe. Connect the primary to whatever you > want to look at and clip the probe to the > secondary (usually 12 to 24 V). Avoids letting > the smoke out. > > Scott B. Lacey > > On 10 Mar 2009 at 21:42, Derek Walton > wrote: > > > Hi Doug, > > > > of course you know I'd reply... I'd wager, confidently, that there > is > > more error using single ended scope probes. As you yourself write > about > > adding beads and minimizing loops etc etc etc. > > > > If you can't use a scope and probe properly, you shouldn't be using > one: > > Period. For those people that can, and I include myself in this > group, > > Diff probes are a godsend. > > > > BTW, when I talk probes, I'm not talking about ones made from chewing > > gum, scotch tape and string... I'm talking credible probes. > > > > Cheers, > > > > Derek. > > > > Douglas Smith wrote: > > > Hi Everyone, > > > > > > Differential probes are one of the most misused pieces of equipment > > > and their output should always be verified to be true. It is very > easy > > > for a differential measurement to result in garbage output. From > the > > > discussion, the posters so far seem to be referring to very low > > > frequency probes, below one megahertz. Using two probes and channel > > > subtraction does not work above 20-30 MHz, or at least the common > mode > > > rejection can actually be gain instead of rejection. I present data > on > > > this subject in my classes. If there are two probe cables used, > they > > > should be in close contact for most of their length. Very bad > things > > > can happen if this is not done, including becoming sensitive to > every > > > noise source in the room. > > > > > > The best way to know if your differential probes are working is to > > > short the two tips together and touch them to each node, one at a > > > time, to be measured. Both results, I call it a "null experiment," > > > should be small compared to what you are trying to measure. An > > > alternate method is to reverse the probe tips. The waveform on the > > > scope should be a mirror image. This alternate method only works on > a > > > scope. > > > > > > Except at low frequencies, 20 dB of common mode rejection can be > hard > > > to get. > > > > > > Doug > > > > > > Cortland Richmond wrote: > > >> Hi, Derek. > > >> > > >> I know how it is. I also know there was no way was I going to take > a chance > > >> on a reversed ground to a floating 'scope when I could get rid of > the > > >> problem with one extra probe. FWIW, at 60 Hz it's easy to match > probe and > > >> channel gain, and since we were only looking at decay time there > was no > > >> need to buy a diff. probe. Where I work now we have some. HV > ones, too! > > >> > > >> On a recent assignment, a place I was helping was cited by their > State OSHA > > >> equivalent for not having the power terminals on LISN's covered to > prevent > > >> contact. There's a lot of stuff in a lab that can bite. Hard. > > >> > > >> Cheers, > > >> > > >> > > >> Cortland Richmond > > >> > > >> > > >> > > >>> [Original Message] > > >>> From: Derek Walton <[email protected]> > > >>> Subject: Re: scope probe gnd > > >>> > > >>> Hi Folks, > > >>> > > >>> I was keeping quiet.... but you know sometimes it's just too > much. > > >>> > > >>> Almost all measurements I take in my lab use a differential scope > probe. > > >>> The exception is when High voltages are involved. And I dont mean > the > > >>> rinky dink two probes/scope math function either.... > > >>> > > >>> With diff probes I can connect anywhere to anywhere and measure > it. I > > >>> never cringe hooking up the 0 volt reference side.... never > sparks.... > > >>> > > >>> Give one a try, you will never go back. > > >>> > > >>> Derek Walton > > >>> > > >>> Cortland Richmond wrote: > > >>> > > >>>> In a previous life -- at a company no longer around -- when our > Safety > > >>>> Engineer quit we EMC types had to step in, and one of the very > first > > >>>> > > >> things > > >> > > >>>> I did was get rid of a lethally ungrounded scope setup. It costs > little > > >>>> > > >> to > > >> > > >>>> use probes rated for line voltage or better and dual channel > math > > >>>> > > >> functions > > >> > > >>>> to allow proper safety grounds. > > >>>> > > >>>> Cortland Richmond > > >>>> > > >>>> > > >>>> > > >>>> > > >>>>> [Original Message] > > >>>>> From: Pettit, Ghery <[email protected]> > > >>>>> To: [email protected] <[email protected]> > > >>>>> Date: 3/10/2009 12:43:37 PM > > >>>>> Subject: RE: scope probe gnd > > >>>>> > > >>>>> Or there were the old scopes where you used patch cords and > banana > > >>>>> > > >> jacks. > > >> > > >>>>> > > >>>>> > > >>>> We had what was left of the power cord for one such scope > hanging in the > > >>>> front of the motors lab in college that showed the importance of > having > > >>>> your setup checked before applying power. Seems the hot and > ground > > >>>> > > >> leads > > >> > > >>>> to the scope from the motor being measured got reversed and the > 120 VAC > > >>>> supply was bypassed to ground through the green wire in the > power cord. > > >>>> For a short period of time. Then the green wire acted as a > fuse. That > > >>>> cord was NOT repairable. And, NO, I was not the culprit. > Didn't > > >>>> > > >> happen on > > >> > > >>>> my watch. > > >>>> > > >>>> > > >>>>> Ghery Pettit > > >>>>> > > >>>>> > > >>>>> -----Original Message----- > > >>>>> From: [email protected] [mailto:[email protected]] On Behalf Of > Ralph > > >>>>> > > >>>>> > > >>>> McDiarmid > > >>>> > > >>>> > > >>>>> Sent: Tuesday, March 10, 2009 9:35 AM > > >>>>> To: [email protected] > > >>>>> Subject: RE: scope probe gnd > > >>>>> > > >>>>> Once for me as well. I never forgot that lesson. > > >>>>> > > >>>>> > > >>>>> Ralph McDiarmid, AScT > > >>>>> Compliance Engineering Group > > >>>>> Xantrex Technology Inc > > >>>>> > > >>>>> > > >>>>> -----Original Message----- > > >>>>> From: [email protected] [mailto:[email protected]] On Behalf Of > John > > >>>>> Woodgate > > >>>>> Sent: Tuesday, March 10, 2009 5:47 AM > > >>>>> To: [email protected] > > >>>>> Subject: Re: Surge testing Questions > > >>>>> > > >>>>> In message > > >>>>> <9D04B979323DCD428297DDA95108893E0120CE6C@bb-corp- > ex2.corp.cubic.cub>, > > >>>>> dated Tue, 10 Mar 2009, "Price, Edward" <[email protected]> > writes: > > >>>>> > > >>>>> > > >>>>> > > >>>>>> What, you never had that happen?! > > >>>>>> > > >>>>>> > > >>>>> Only once - so far! > > >>>>> -- > > >>>>> > > >>>>> > > >>>> - > > >>>> ---------------------------------------------------------------- > > >>>> This message is from the IEEE Product Safety Engineering Society > > >>>> > > >> emc-pstc discussion list. To post a message to the list, send your > e-mail > > >> to <[email protected]> > > >> > > >>>> All emc-pstc postings are archived and searchable on the web at: > > >>>> http://www.ieeecommunities.org/emc-pstc > > >>>> Graphics (in well-used formats), large files, etc. can be posted > to > > >>>> > > >> that URL. > > >> > > >>>> Website: http://www.ieee-pses.org/ > > >>>> Instructions: http://listserv.ieee.org/request/user-guide.html > > >>>> List rules: http://www.ieee-pses.org/listrules.html > > >>>> > > >>>> For help, send mail to the list administrators: > > >>>> Scott Douglas <[email protected]> > > >>>> Mike Cantwell <[email protected]> > > >>>> > > >>>> For policy questions, send mail to: > > >>>> Jim Bacher: <[email protected]> > > >>>> David Heald: <[email protected]> > > >>>> > > >>>> > > >> > > >> - > > >> ---------------------------------------------------------------- > > >> This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. To post a message to the list, send your e- > mail to <[email protected]> > > >> > > >> All emc-pstc postings are archived and searchable on the web at: > > >> http://www.ieeecommunities.org/emc-pstc > > >> Graphics (in well-used formats), large files, etc. can be posted > to that URL. > > >> > > >> Website: http://www.ieee-pses.org/ > > >> Instructions: http://listserv.ieee.org/request/user-guide.html > > >> List rules: http://www.ieee-pses.org/listrules.html > > >> > > >> For help, send mail to the list administrators: > > >> Scott Douglas <[email protected]> > > >> Mike Cantwell <[email protected]> > > >> > > >> For policy questions, send mail to: > > >> Jim Bacher: <[email protected]> > > >> David Heald: <[email protected]> > > >> > > >> > > > > > > -- > > > -------------------------------------------------------------- > > > ___ _ Doug Smith > > > \ / ) P.O. Box 1457 > > > ========= Los Gatos, CA 95031-1457 > > > _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 > > > / /\ \ ] / /\ \ Mobile: 408-858-4528 > > > | q-----( ) | o | Email: [email protected] > > > \ _ / ] \ _ / Web: http://www.dsmith.org > > > -------------------------------------------------------------- > > > > > > > - > > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc- > pstc discussion list. To post a message to the list, send your e-mail > to <[email protected]> > > > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > > Graphics (in well-used formats), large files, etc. can be posted to > that URL. > > > > Website: http://www.ieee-pses.org/ > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > > > For help, send mail to the list administrators: > > Scott Douglas <[email protected]> > > Mike Cantwell <[email protected]> > > > > For policy questions, send mail to: > > Jim Bacher: <[email protected]> > > David Heald: <[email protected]> > > > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc- > pstc discussion list. To post a message to the list, send your e-mail > to <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > Graphics (in well-used formats), large files, etc. can be posted to > that URL. > > Website: http://www.ieee-pses.org/ > Instructions: http://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
