If you had one what would you use it for
in [Design]
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From: Joerg on 21 Oct 2009 17:08 John Larkin wrote: > On Wed, 21 Oct 2009 06:21:02 -0700 (PDT), MooseFET > <kensmith(a)rahul.net> wrote: > >> Imagine you had a sensor that could measure very small magnetic >> fields. It measures with a noise floor of about 0.1fT. Unfortunately >> the band width is only a few hundred Hz and it only works inside a >> shield. >> >> What would you use such a sensor for? The best I've thought of is >> detecting the flow of current in a PCB to find a short circuit. > > You need high spatial resolution for a general-purpose board short > finder. Magnetically, you can do it with a pulsed current source and a > really tiny ferrite-core pickup coil. I do it lately with a DC source > and a thermal imager, so you can *see* the current path. > If you crank up the DC current some more you can see the short without the FLIR camera. If you crank it up even more the short may fix itself but you'd have to open the windows for a while. -- SCNR, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 21 Oct 2009 17:36 On Wed, 21 Oct 2009 14:08:25 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Wed, 21 Oct 2009 06:21:02 -0700 (PDT), MooseFET >> <kensmith(a)rahul.net> wrote: >> >>> Imagine you had a sensor that could measure very small magnetic >>> fields. It measures with a noise floor of about 0.1fT. Unfortunately >>> the band width is only a few hundred Hz and it only works inside a >>> shield. >>> >>> What would you use such a sensor for? The best I've thought of is >>> detecting the flow of current in a PCB to find a short circuit. >> >> You need high spatial resolution for a general-purpose board short >> finder. Magnetically, you can do it with a pulsed current source and a >> really tiny ferrite-core pickup coil. I do it lately with a DC source >> and a thermal imager, so you can *see* the current path. >> > >If you crank up the DC current some more you can see the short without >the FLIR camera. If you crank it up even more the short may fix itself >but you'd have to open the windows for a while. I have blown away inner-layer shorts that way. But now we buy tested boards and really never see shorts any more. John
From: Jim Thompson on 21 Oct 2009 17:37 On Wed, 21 Oct 2009 14:08:25 -0700, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Wed, 21 Oct 2009 06:21:02 -0700 (PDT), MooseFET >> <kensmith(a)rahul.net> wrote: >> >>> Imagine you had a sensor that could measure very small magnetic >>> fields. It measures with a noise floor of about 0.1fT. Unfortunately >>> the band width is only a few hundred Hz and it only works inside a >>> shield. >>> >>> What would you use such a sensor for? The best I've thought of is >>> detecting the flow of current in a PCB to find a short circuit. >> >> You need high spatial resolution for a general-purpose board short >> finder. Magnetically, you can do it with a pulsed current source and a >> really tiny ferrite-core pickup coil. I do it lately with a DC source >> and a thermal imager, so you can *see* the current path. >> > >If you crank up the DC current some more you can see the short without >the FLIR camera. If you crank it up even more the short may fix itself >but you'd have to open the windows for a while. In the early '70's I used to have pin hole problems with Alumina substrates, the screened-on metalization would go thru a pin hole and short a trace to ground plane on the back-side. You take a 6V/100A power supply... "click" ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Cranky Old Git With Engineering Mind Faster Than a Speeding Prissy
From: Joerg on 21 Oct 2009 19:01 John Larkin wrote: > On Wed, 21 Oct 2009 14:08:25 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Wed, 21 Oct 2009 06:21:02 -0700 (PDT), MooseFET >>> <kensmith(a)rahul.net> wrote: >>> >>>> Imagine you had a sensor that could measure very small magnetic >>>> fields. It measures with a noise floor of about 0.1fT. Unfortunately >>>> the band width is only a few hundred Hz and it only works inside a >>>> shield. >>>> >>>> What would you use such a sensor for? The best I've thought of is >>>> detecting the flow of current in a PCB to find a short circuit. >>> You need high spatial resolution for a general-purpose board short >>> finder. Magnetically, you can do it with a pulsed current source and a >>> really tiny ferrite-core pickup coil. I do it lately with a DC source >>> and a thermal imager, so you can *see* the current path. >>> >> If you crank up the DC current some more you can see the short without >> the FLIR camera. If you crank it up even more the short may fix itself >> but you'd have to open the windows for a while. > > I have blown away inner-layer shorts that way. But now we buy tested > boards and really never see shorts any more. > I was quite impressed with turn-key lately. Then they pretty much stand by their work. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 21 Oct 2009 19:04
Jim Thompson wrote: > On Wed, 21 Oct 2009 14:08:25 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Wed, 21 Oct 2009 06:21:02 -0700 (PDT), MooseFET >>> <kensmith(a)rahul.net> wrote: >>> >>>> Imagine you had a sensor that could measure very small magnetic >>>> fields. It measures with a noise floor of about 0.1fT. Unfortunately >>>> the band width is only a few hundred Hz and it only works inside a >>>> shield. >>>> >>>> What would you use such a sensor for? The best I've thought of is >>>> detecting the flow of current in a PCB to find a short circuit. >>> You need high spatial resolution for a general-purpose board short >>> finder. Magnetically, you can do it with a pulsed current source and a >>> really tiny ferrite-core pickup coil. I do it lately with a DC source >>> and a thermal imager, so you can *see* the current path. >>> >> If you crank up the DC current some more you can see the short without >> the FLIR camera. If you crank it up even more the short may fix itself >> but you'd have to open the windows for a while. > > In the early '70's I used to have pin hole problems with Alumina > substrates, the screened-on metalization would go thru a pin hole and > short a trace to ground plane on the back-side. > > You take a 6V/100A power supply... "click" ;-) > Sometimes when in a ham radio contest and the plates of the notoriously under-dimensioned output side variable caps fused together I'd occasionally key the transmitter CW at full legal limit ... tunggg ... *PHOOMP* ... problem fixed, some ozone and weld shop smell wafting through the air. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |