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From: Didi on 6 Aug 2010 15:56 On Aug 6, 5:31 pm, "keith...(a)gmail.com" <keith...(a)gmail.com> wrote: > On Aug 6, 8:57 am, Didi <d...(a)tgi-sci.com> wrote: > > > > > On Aug 6, 3:13 pm, John Larkin > > > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > > > ... > > > Most of our VME modules have a calibration connector and a relay per > > > channel, so our customer can switch every channel to a traceable > > > dvm/source and verify calibration before and after every test run, > > > without disconnecting field wiring. That works well with all the gear > > > in one rack, but would be very messy to attempt with distributed i/o. > > > Why do you say it would be messy? Replacing say 32 analog cables with > > a 10/100 Ethernet link should only make it easier from where I look > > at it (clearly not from the same point as you). I ask because I was > > asked recently about a tiny (50x100mm) ADC board with 16 inputs, > > to etherner, the motivation being cabling. > > [Nothing came out of it but then the inquiry was from Pakistan, either > > the floods got them or it was one of the so many "first ask then > > think" > > inquiries coming from these parts of the world :-) ]. > > It's messy because his traceable calibration reference is no longer > where the I/O is. I guess that depends on the cable length then. If the analog cables have to be tens of meters just having the input connector handy for calibration is a poor decision, but if the cables are reasonably short digitizing locally makes no sense since the entire system is local. Dimiter ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/
From: krw on 6 Aug 2010 20:05 On Fri, 6 Aug 2010 12:56:35 -0700 (PDT), Didi <dp(a)tgi-sci.com> wrote: >On Aug 6, 5:31�pm, "keith...(a)gmail.com" <keith...(a)gmail.com> wrote: >> On Aug 6, 8:57�am, Didi <d...(a)tgi-sci.com> wrote: >> >> >> >> > On Aug 6, 3:13�pm, John Larkin >> >> > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> > > ... >> > > Most of our VME modules have a calibration connector and a relay per >> > > channel, so our customer can switch every channel to a traceable >> > > dvm/source and verify calibration before and after every test run, >> > > without disconnecting field wiring. That works well with all the gear >> > > in one rack, but would be very messy to attempt with distributed i/o. >> >> > Why do you say it would be messy? Replacing say 32 analog cables with >> > a 10/100 Ethernet link should only make it easier from where I look >> > at it (clearly not from the same point as you). I ask because I was >> > asked recently about a tiny (50x100mm) ADC board with 16 inputs, >> > to etherner, the motivation being cabling. >> > [Nothing came out of it but then the inquiry was from Pakistan, either >> > the floods got them or it was one of the so many "first ask then >> > think" >> > inquiries coming from these parts of the world :-) ]. >> >> It's messy because his traceable calibration reference is no longer >> where the �I/O is. > >I guess that depends on the cable length then. If the analog cables >have to >be tens of meters just having the input connector handy for >calibration >is a poor decision, but if the cables are reasonably short digitizing >locally makes no sense since the entire system is local. Reread what he's said. His calibration reference is muxed into each input. If you distribute the input functions you have to distribute the calibration signal as well, negating your advantage.
From: Didi on 6 Aug 2010 20:19 On Aug 7, 3:05 am, "k...(a)att.bizzzzzzzzzzzz" <k...(a)att.bizzzzzzzzzzzz> wrote: > On Fri, 6 Aug 2010 12:56:35 -0700 (PDT), Didi <d...(a)tgi-sci.com> wrote: > >On Aug 6, 5:31 pm, "keith...(a)gmail.com" <keith...(a)gmail.com> wrote: > >> On Aug 6, 8:57 am, Didi <d...(a)tgi-sci.com> wrote: > > >> > On Aug 6, 3:13 pm, John Larkin > > >> > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> > > ... > >> > > Most of our VME modules have a calibration connector and a relay per > >> > > channel, so our customer can switch every channel to a traceable > >> > > dvm/source and verify calibration before and after every test run, > >> > > without disconnecting field wiring. That works well with all the gear > >> > > in one rack, but would be very messy to attempt with distributed i/o. > > >> > Why do you say it would be messy? Replacing say 32 analog cables with > >> > a 10/100 Ethernet link should only make it easier from where I look > >> > at it (clearly not from the same point as you). I ask because I was > >> > asked recently about a tiny (50x100mm) ADC board with 16 inputs, > >> > to etherner, the motivation being cabling. > >> > [Nothing came out of it but then the inquiry was from Pakistan, either > >> > the floods got them or it was one of the so many "first ask then > >> > think" > >> > inquiries coming from these parts of the world :-) ]. > > >> It's messy because his traceable calibration reference is no longer > >> where the I/O is. > > >I guess that depends on the cable length then. If the analog cables > >have to > >be tens of meters just having the input connector handy for > >calibration > >is a poor decision, but if the cables are reasonably short digitizing > >locally makes no sense since the entire system is local. > > Reread what he's said. His calibration reference is muxed into each input. If > you distribute the input functions you have to distribute the calibration > signal as well, negating your advantage. It certainly does not negate the advantage of having the _analog_ input cables an order of magnitude shorter. Having them that long will degrade the quality of the sampled signal, there is no reasonable way around that unless the signals are DC, perhaps. Dimiter ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/
From: Rich Grise on 6 Aug 2010 19:35 On Tue, 03 Aug 2010 13:35:01 -0700, John Larkin wrote: > > I was just wondering if anybody did this and knew of gotchas. No, other people know better than to even try such a dumb stunt. Maybe you could have Jim Thompson design a clamp chip for you. ;-P Good Luck! Rich
From: krw on 6 Aug 2010 20:41
On Fri, 6 Aug 2010 17:19:41 -0700 (PDT), Didi <dp(a)tgi-sci.com> wrote: >On Aug 7, 3:05�am, "k...(a)att.bizzzzzzzzzzzz" <k...(a)att.bizzzzzzzzzzzz> >wrote: >> On Fri, 6 Aug 2010 12:56:35 -0700 (PDT), Didi <d...(a)tgi-sci.com> wrote: >> >On Aug 6, 5:31�pm, "keith...(a)gmail.com" <keith...(a)gmail.com> wrote: >> >> On Aug 6, 8:57�am, Didi <d...(a)tgi-sci.com> wrote: >> >> >> > On Aug 6, 3:13�pm, John Larkin >> >> >> > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> > > ... >> >> > > Most of our VME modules have a calibration connector and a relay per >> >> > > channel, so our customer can switch every channel to a traceable >> >> > > dvm/source and verify calibration before and after every test run, >> >> > > without disconnecting field wiring. That works well with all the gear >> >> > > in one rack, but would be very messy to attempt with distributed i/o. >> >> >> > Why do you say it would be messy? Replacing say 32 analog cables with >> >> > a 10/100 Ethernet link should only make it easier from where I look >> >> > at it (clearly not from the same point as you). I ask because I was >> >> > asked recently about a tiny (50x100mm) ADC board with 16 inputs, >> >> > to etherner, the motivation being cabling. >> >> > [Nothing came out of it but then the inquiry was from Pakistan, either >> >> > the floods got them or it was one of the so many "first ask then >> >> > think" >> >> > inquiries coming from these parts of the world :-) ]. >> >> >> It's messy because his traceable calibration reference is no longer >> >> where the �I/O is. >> >> >I guess that depends on the cable length then. If the analog cables >> >have to >> >be tens of meters just having the input connector handy for >> >calibration >> >is a poor decision, but if the cables are reasonably short digitizing >> >locally makes no sense since the entire system is local. >> >> Reread what he's said. �His calibration reference is muxed into each input. If >> you distribute the input functions you have to distribute the calibration >> signal as well, negating your advantage. � > >It certainly does not negate the advantage of having the _analog_ >input >cables an order of magnitude shorter. Having them that long will >degrade the quality of the sampled signal, there is no reasonable >way around that unless the signals are DC, perhaps. Ok, let me try this another way... How do you propose to do the muxing of this traceable standard? Cable *it* around to each point. Place one at every node? Of course it's a trade-off. |