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TechNet E-Mail Forum <[log in to unmask]>, Hfjord <[log in to unmask]>
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Sat, 1 Dec 2007 16:40:02 +0100
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Thanks Brian,
I'll probably terrorize you offline with questions about your projects. You
really made me curious.
To you all: I've a little document that gives all steps of inventions of
electricity and magnetism all from 900BC until today! I'll post it to
magnetic Steve for those who are interested.

900BC, a shepherd named Magnus walked through a field of black and metallic
stones, whereby the iron nails were pulled out from his sandals...he named
the landscape...Magnesia...and so it started.

Inge



-----Ursprungligt meddelande-----
Från: Brian Ellis [mailto:[log in to unmask]] 
Skickat: den 1 december 2007 12:47
Till: TechNet E-Mail Forum; Hfjord
Ämne: Re: [TN] SV: [TN] SV: [TN] SV: [TN] Low Noise Coaxial Cable Question

Well, with 5 V and 1E14 ohms, the current would be down to 50 fA, which 
ain't too goodly a number of electrons, considering I designed IRMA-1 in 
1986. I discovered all sorts of peculiar ionic effects in FR-4 with it 
and published a few papers on the subject. One polymer science student 
at the Swiss Federal Institute of Technology, Lausanne, used it for his 
dissertation on the electrical characteristics of epoxy resins. I was 
named the external expert adjudicator for his Dipl.Ing. He did some 
really outstanding work and his prof told me that his dissertation would 
have been good enough for a MSc thesis. He won the annual prize for the 
most outstanding graduate. I tried to persuade him to go for his 
doctorate, but he exported himself to a US industry unrelated to his 
undergrad work.

I really was disappointed that the IRMA-2 project was dropped because I 
spent >2 years on its development and it really did work a treat. I 
guestimate it would have cost c. $60k for 96 measurement points, 
complete with custom computer with high data security and UPS for 12 h 
power failure (it would have been really annoying to do a 3-month SIR 
test on 96 samples for the power to fail after 89 days!).

I suppose it's flattering that Keithley copied my idea: I thought about 
applying for a patent in 1985, when I first had the idea, but my 
attorney said that it would be a thorny one proving there was no prior 
art: someone could argue that the controlled discharge of a capacitor 
through a xenon tube in a photographic flash to produce a given number 
of photons was partial prior art, even though the purpose was different. 
The RC discharge formula has been known for over a century!

My trusty AVOmeter is still in the land of the living, covered in dust. 
When I retired and came out to this island, I brought my oscilloscope 
and some other things with me but, believe it or not, I don't think I've 
even switched it on since, and that was 10 years ago!!!! So, no! I'm 
busy with all sorts of non-electronic projects!!!

Brian



Hfjord wrote:
> Brian, it looks like you've been involved in myriades of projects! Anyway,
> your principle is used by Keithley. They make an instrument that can
measure
> attoamperes! 1 attoampere = 6 electrons per second!! They use a
> Voltage/Current source same way as you did, i.e. a kind of capacitor that
is
> discharged through TeraOhm resistors. The discharge current is plotted vs.
> time and a number of such events are integrated and computerized to give a
> readout. Dynamic principal with other words. I have their instrument P/N
> somewhere, if you are interested, or you will find it yourself. I believe
> it's a 100K dollar instrument. Instruments have undergone a remarkable
> evolution. My private and cheap and simple handhold Fluke is capable of
> measuring microamperes with a resolution of 0.1 uA. Price :  350 USD.
> Are you still mixing with electronics at home?
> Can't help admiring you, oldie!
> /Inge
> 
> -----Ursprungligt meddelande-----
> Från: TechNet [mailto:[log in to unmask]] För Brian Ellis
> Skickat: den 1 december 2007 11:03
> Till: [log in to unmask]
> Ämne: Re: [TN] SV: [TN] SV: [TN] Low Noise Coaxial Cable Question
> 
> AAAAAH! Now I understand the question. In the dim and distant past, I 
> designed and built a prototype Insulohmeter IRMA-2, a basic improvement 
> on IRMA-1. Unfortunately, for political reasons imposed by the company I 
> was working with, it was never put into production. Believe it or not, 
> it could measure up to 1E14 ohms ± 30% at 5-100 V or 1E12 ohms ± 2.5% at 
> 5-100 V, without screening/shielding of the PTFE cables. How could this 
> be? Because it did the measurement dynamically, not statically. A PS 
> capacitor was charged to the required volts and allowed to partially 
> discharge through whatever was required to be measured. The voltage 
> across the capacitor was monitored with respect to time and the SIR was 
> calculated from the discharge curve. It worked beautifully. Why was it 
> so noise free? The capacitor effectively short-circuited the measurement 
> circuit and its reactance, even down to <50 Hz, was several orders of 
> magnitude less than the resistance being measured, so any induced 
> voltages were negligible and did not affect the measurement.
> 
> Unfortunately, this is academic, because IRMA-2 never got beyond a damn 
> good working prototype.
> 
> Brian
> 
> Douglas O. Pauls wrote:
>> I will chime in on Joe's behalf.  This actually started with a 
>> conversation between he and I.
>>
>> We do SIR testing.  As such it is not unusual to be measuring resistances

>> on the order of 1E11 or 1E12 ohms.  In general, a voltage is applied to
an
> 
>> unknown resistance and a resulting current is induced.  We are both doing

>> testing at DC, not AC domains.  A very good text on low level
measurements
> 
>> comes from Keithley Instruments, originally authored by John Yeager.  In 
>> John's experience, the measurement world changes a great deal between
1E11
> 
>> and higher decades of resistance measurement.  Above 1E12 ohms, you have 
>> to start watching other sources of current generation that can
erroneously
> 
>> add to your desired signal.  This includes things like EMI coupling and 
>> triboelectric currents from moving cables.  EMI coupling and guarding is 
>> why co-ax and other shielded cables are used. 
>>
>> Keithley, in their very low current measuring instruments and switching 
>> cards, makes use of "low noise cables", which essentially have graphite 
>> coating the outer surface of the inner dielectric, to reduce
triboelectric
> 
>> charges from the braided shield whenever the coax is flexed.  Of course, 
>> such specialty coax is pricey and led to Joe's more generic questions 
>> regarding specifications or measurements of "low noise" and how low a 
>> noise is "low noise". 
>>
>> That Joe is a demon when it comes to trying to exactly understand 
>> measurement signals.  That's a good thing.
>>
>> Doug Pauls
>>
>>
>>
>>
>> Hfjord <[log in to unmask]> 
>> Sent by: TechNet <[log in to unmask]>
>> 11/30/2007 12:27 PM
>> Please respond to
>> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
>> Hfjord <[log in to unmask]>
>>
>>
>> To
>> [log in to unmask]
>> cc
>>
>> Subject
>> [TN] SV: [TN] SV: [TN] Low Noise Coaxial Cable Question
>>
>>
>>
>>
>>
>>
>> Exellent! However, Joe has still not told us WHAT he wants to do with the
>> cable. I doubt he is on a level, that dielectric intrinsic noise will
play
> 
>> a
>> role. Few test engineers work with such problems. If he isn't a Nobel 
>> Prize
>> aspirant of some kind. I suggest someone finds remedy against Tinnitus.
>> He/she will get the prize, I'm sure. And the inventor will create a lot
of
>> noise...he-he
>> /Inge
>>
>> -----Ursprungligt meddelande-----
>> Från: TechNet [mailto:[log in to unmask]] För Seth Goodman
>> Skickat: den 30 november 2007 18:55
>> Till: [log in to unmask]
>> Ämne: Re: [TN] SV: [TN] Low Noise Coaxial Cable Question
>>
>> Joe,
>>
>> Some of what has been mentioned is really part of other cable
>> specifications and has nothing to do with noise created in the cable
>> itself.  For instance, penetration of electromagnetic fields inside a
>> cable shield is often described by the manufacturer's specification for
>> shielding effectiveness.  To the extent that the cable has in imperfect
>> coaxial shield, it can convert ambient electric or magnetic fields into
>> a loop voltage or flowing current.  If external fields are the source of
>> your problem, you want cable with high shielding effectiveness as
>> opposed to low-noise cable.  For electric fields, improving the shield
>> means thicker braid, finer wire in the braid, better conductivity of
>> braid wire and plating, more than one braid and/or a foil shield.  For
>> magnetic fields, a shielded twisted pair may do better.
>>
>> The traditional electronic noise sources, which are Johnson (thermal)
>> noise, shot noise and a group of unrelated mechanisms that produce 1/f
>> noise, do not produce appreciable noise in cables.  When cable
>> manufacturers list a cable as low-noise, they usually mean triboelectric
>> noise.  If the connected circuit puts a dc potential on the cable, then
>> mechanical flexing can change the capacitance between conductors, which
>> will cause current to flow in the external circuit.  The triboelectric
>> and capacitance change with motion can together be called microphonics,
>> as they are both motion-related.  Another source or noise in
>> high-voltage cables is leakage.
>>
>> Regards,
>>
>> Seth Goodman
>>
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