[volt-nuts] Impedance bridge information
brooke at pacific.net
Fri May 25 20:41:10 UTC 2012
In HP speak "meters" have numerical readouts and "analyzers" have graphical readouts.
So the 4-terminal pair LCR meters are good, but the 4-terminal pair LCR analyzers are better.
You can substitute "Impedance" for LCR in the above.
I say better because the you can get an equivalent circuit from an analyzer that has more than two components, which is
the limit of the meters.
Some analyzers can fit complex models automatically, for example Impedance Analyzers and Crystal Impedance meters (which
use swept frequency but only have numerical readouts).
The bible for impedance measurement is HP's "The Impedance Measurement Handbook", see my Related paragraph on the
Impedance web page:
This is a MUST READ if you're into precision LCR type measurements.
There's also the issue of compensation and correction of fixture parasitics. For more on fixtures see the HP
Accessories Selection Guide for Impedance Measurements.
The key idea is that there's a contour plot of accuracy vs impedance and frequency for the different measurement
methods, with the 4-terminal pair method giving the most accurate results. http://www.prc68.com/I/HP4274_4275_LCR.shtml#4TP
A lot of that is because of canceling magnetic coupling between the 4 coax cables (note that not all the coax shields
are are at ground).
The earlier instruments that used 4 each 5-way binding posts are not anywhere as accurate.
Fred Schneider wrote:
> I do not know if it is a topic for here, but it is about precision messurements.
> For my collection and learing through measuring the old , "back to the basics" way, I am looking for a bridge to measure things like small caps, dielectric constants ad other "weard" parameters. I have several VNA's and RLC bridges but they used to make bridges that you can see as a manual VNA. It gave R and jX, sometimes with build in detector and oscillator, sometimes using these external.
> But there are so many bridges, from general purpose to special measuring things ( like the resistance from a detonator) and from general purpose to high precision that I am lost. I think GR or Wayne Kerr made the best ones. I'm to young to have experience with them and never seen one for real.
> Can someone give me a hint what to search for. For instance the right name of such a bridge ( i think Z/Y or admittance cq impedance bridge) and what is important so I can determ if they are for what I want and not just a allround LCR bridge.
> I want to measure the more extreme things like ESR, fF, delectric proporties/losses ect but for most I love old precision measurement instruments which make you think about what you do and have lots of knobs instead of menus.
> Fred PA4TIM
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