In message <4ffca814.5080...@toneh.demon.co.uk>, Tony Holt writes:
>I've never understood why relatively expensive and sophisticated
>instruments don't have significantly lower resistance shunts
Isn't it simply because there are better ways to do it, than to
use an external shunt ?
Flux Gate cu
Tony,
obviously, there is a basic problem with DC current, already beginning
at the definition of the SI Ampère.
This is the worst realized electrical unit, i.e. the 'mise en pratique'
is difficult to an error level of about 1e-7 only. DCV and OHM can be
realized to a much higher degree of s
That which is more fundamental to the problem is the unavoidable (at
room temperature) noise from the resistors. Even a "perfect" resistor
with zero tempco has noise, so if you use resistors to measure
current with a high-precision voltmeter, eventually you reach a
resolution where the noise be
On 07/11/2012 03:49 PM, ed breya wrote:
> That which is more fundamental to the problem is the unavoidable (at room
> temperature) noise from the resistors. Even a "perfect" resistor with zero
> tempco has noise, so if you use resistors to measure current with a
> high-precision voltmeter, eventual
On 7/11/2012 5:15 AM, Frank Stellmach wrote:
This is the worst realized electrical unit, i.e. the 'mise en pratique'
is difficult to an error level of about 1e-7 only.
On 7/11/2012 6:50 PM, Bob Smither wrote:
I may be off here, but I doubt that thermal (Johnson) noise would limit the
precision
On 07/11/2012 09:01 PM, Mike S wrote:
> On 7/11/2012 5:15 AM, Frank Stellmach wrote:
>> This is the worst realized electrical unit, i.e. the 'mise en pratique'
>> is difficult to an error level of about 1e-7 only.
>
> On 7/11/2012 6:50 PM, Bob Smither wrote:
>> I may be off here, but I doubt that
Apropos: http://www.sciencedaily.com/releases/2012/07/120711101042.htm
With regard to the discussion, since in the SI, Amps are the base unit,
Volts are derived from Amps, and Ohms from Volts - remarkable that Amps
are the least realizable in practice? (I guess it's just the difference
between
Yes, the effect can be estimated quite easily. Also, keep in mind
that the 0.13 nV is the RMS noise, so the peak to peak excursions can
be around six times that, or almost 1 nV p-p. If the FS is 1 mA, then
it's about 1 ppm - one count on a six digit DVM, or ten times more
with each additional d
