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From: John Larkin on 6 Aug 2010 21:18 On Fri, 06 Aug 2010 16:35:43 -0700, Rich Grise <richgrise(a)example.net> wrote: >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. Some people have no sense of adventure. > >Maybe you could have Jim Thompson design a clamp chip for you. ;-P I don't deal with people who deliberately insult my wife. Or with people who are obviously senile rednecks. John
From: Jim Thompson on 6 Aug 2010 22:09 On Fri, 06 Aug 2010 18:18:02 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 06 Aug 2010 16:35:43 -0700, Rich Grise <richgrise(a)example.net> >wrote: > >>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. > >Some people have no sense of adventure. > >> >>Maybe you could have Jim Thompson design a clamp chip for you. ;-P > >I don't deal with people who deliberately insult my wife. Or with >people who are obviously senile rednecks. > >John Why! BU Pimp, What is it you mean ?:-) Are you really that stupid, or are you pretending? ...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 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: Didi on 7 Aug 2010 05:19 On Aug 7, 3:41 am, "k...(a)att.bizzzzzzzzzzzz" <k...(a)att.bizzzzzzzzzzzz> wrote: > On Fri, 6 Aug 2010 17:19:41 -0700 (PDT), Didi <d...(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. It is a trade-off indeed, it is just that I would have made it in favour of the acquired signal integrity rather than the calibrating signal source. One can do things about the latter (average multiple measurements etc.) which cannot be done with the input signal. Dimiter ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/
From: Tim Shoppa on 7 Aug 2010 07:46 On Aug 7, 12:41 am, "k...(a)att.bizzzzzzzzzzzz" <k...(a)att.bizzzzzzzzzzzz> wrote: > On Fri, 6 Aug 2010 17:19:41 -0700 (PDT), Didi <d...(a)tgi-sci.com> wrote: > >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. The secret is, to pipe around only the standards that can be measured digitally. e.g. times and frequencies and counts. e.g. instead of measuring current, simply count electrons flowing past. I'm only half-joking. Any measurement that can be done digitally without reference to analog standards ought to be done digitally. In one case the traditional instrumentation for wheel speed consisted of a tachometer, followed by a frequency to voltage converter to make a voltage representing RPM, that we piped back to the DAQ system as an analog voltage, then converted back to a digital number. We would then integrate this analog voltage times wheel diameter to arrive at distance traveled. We would also used the reading from a fancy-pants 20-turn precision potentiometer which had been carefully set using precision test equipment to get the wheel diameter, a multiplication factor in the above calculations. Zero offsets were super-duper-extra- critical and a PITA. Now we just count turns of the wheel and use landmarks to measure wheel wear dynamically. Tim.
From: krw on 7 Aug 2010 17:48
On Sat, 7 Aug 2010 02:19:29 -0700 (PDT), Didi <dp(a)tgi-sci.com> wrote: >On Aug 7, 3:41�am, "k...(a)att.bizzzzzzzzzzzz" <k...(a)att.bizzzzzzzzzzzz> >wrote: >> On Fri, 6 Aug 2010 17:19:41 -0700 (PDT), Didi <d...(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. > >It is a trade-off indeed, it is just that I would have made it in >favour >of the acquired signal integrity rather than the calibrating signal >source. That may be the right decision, maybe not. It certainly is not an obvious one to make on a newsgroup, no less. >One can do things about the latter (average multiple measurements >etc.) >which cannot be done with the input signal. Maybe. But it's not always possible to make a choice that simple. I'm quite sure John has considered the issue. |