Or, you could "make" a resistor by rubbing a pencil on a piece of paper as was done in an episode of the old Macgyver TV series :)
Scott B. Lacey On 8 Oct 2008 at 12:35, Robert Richards wrote: > > This reminds me of years ago when I did board level repair. Occasionally we > needed a resistor of > some very specific value (bridge circuit) so we would take a carbon film > resistor of a slightly lower > value and shave some of the material off to get the exactvalue. A coat of > epoxy finished the job. > > Bob Richards, NCT > > > [email protected] wrote: > Well, there is laser trimming, and there is laser trimming. > > For commodity resistors with leads and cylindrical bodies, a spiral cut is > fairly common. By varying the pitch of the spiral and number of turns, a > large number of values can be had from a single base part. This also > retains most of the resistive material so that usable area for heat > dissipation is not reduced a lot. The disadvantage is that the voltage > from > turn to turn can be high enough (especially for impulsive waveforms) that > there can be arc over between the turns. > > The other way of trimming is to take straight cuts along the axis of the > resistor. The voltage gradient along the resistor is not affected. > However, > the base part needs to be close to the final value so that large amounts > of > resistive material are not removed, causing the heat dissipation to > concentrate over a small area. This is more expensive to do, but yields a > more robust component, appropriate for high voltage use. > > Donald Borowski > Schweitzer Engineering Labs > Pullman, WA, USA > > > > > "John McAuley" > .ie> To > Sent by: "'Joe Randolph'" > [email protected] , "'Ralph > McDiarmid'" > , > 10/08/2008 03:55 > AM cc > > Subject > Please respond to RE: IEC60225-5 surge test > .ie> > > > > > > > > > > High voltage resistors are becoming more readily available with thick film > technology. > > See > > http://radionics.rs- > > online.com/web/search/searchBrowseAction.html?method=getProduct&R=2509032292 > > A combination of these could meet the surge current requirement. > > You need to be careful with some of these though, they use laser trimming > which results in affine line across the resistor that causes arcing. I > understand that the one listed above does not use laser trimming. > > BR > > John McAuley > www.cei.ie > [email protected] > ***************************************************************** > DISCLAIMER: The information contained in this e-mail may be confidential > and is intended solely for the use of the named addressee. Access, copying > or re-use of the e-mail or any information contained therein by any other > person is not authorised. If you are not the intended recipient please > notify us immediately by returning the e-mail to the originator > > > From: [email protected] [mailto:[email protected]] On Behalf Of Joe > Randolph > Sent: 08 October 2008 02:02 > To: Ralph McDiarmid; [email protected] > Subject: RE: IEC60225-5 surge test impedance? > > On 10/7/2008, Ralph McDiarmid wrote: > > > Is it possible to insert a resistor between surge generator and CDN to > provide the correct impedance? Here is one source of high-voltage, > power resistors. > > http://www.caddock.com/Online_catalog/high_voltage/high_voltage.html > > > Hi Ralph: > > It is common practice to insert an external resistor in series with the > output of a surge generator to reduce the short-circuit current. In fact, > some standards call out different values of external resistance in their > tests. The resistor will influence the short-circuit current waveform, so > you may need to pay attention to that. > > You must be very careful about the power rating and construction of any > resistors you add. The resistors must be able to handle the surge power, > and they must be non-inductive (not wire wound). Interestingly, one of the > best types of construction for this application is the old > carbon-composition type, but these are getting hard to find. > > As long as the resistor construction you use is non-inductive, you can > achieve whatever surge tolerance you need by connecting several resistors > in parallel. > > > > > > Joe Randolph > Telecom Design Consultant > Randolph Telecom, Inc. > 781-721-2848 (USA) > [email protected] > http://www.randolph-telecom.com > - ---------------------------------------------------------------- This > message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. Website: http://www.ieee-pses.org/ > > > To post a message to the list, send your e-mail to [email protected] > > > 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] > > > All emc-pstc postings are archived and searchable on the web at: > > > http://www.ieeecommunities.org/emc-pstc > > > - ---------------------------------------------------------------- This > message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. Website: http://www.ieee-pses.org/ > > > To post a message to the list, send your e-mail to [email protected] > > > 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] > > > All emc-pstc postings are archived and searchable on the web at: > > > http://www.ieeecommunities.org/emc-pstc > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > 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] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > > - ---------------------------------------------------------------- This > message is from the IEEE Product Safety > Engineering Society emc-pstc discussion list. Website: > http://www.ieee-pses.org/ > To post a message to the list, send your e-mail to [email protected] > 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] > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
