[volt-nuts] Impedance bridge information
pa4tim at gmail.com
Sat May 26 19:32:57 UTC 2012
Thanks for the info, the HP impedance measurement handbook is a bit my bible so I know it.
About analysers, i know a modern impedance analyser, be it a vna, IV, or just a LCR meter can be more accurate and has more possibilities.
I have two digital vna's ( DG8SAQ VNWA) one that has the RF-IV test head designed by Paul and an analog one from HP. The latter I yesterday used to make RF-IV measurements as an experiment. A tek CT currentprobe from splitter to reference and the other output via a shunt fixture to the test port. The result was above wat I expected, a nice impedance curve that has a resolution of 40 dB under 1 ohm.
I am most time busy doing network analysing, component research, most of them involve capacitors and parasitic behaviour of components. And playing with calibrators.
But I teached my self everything and i have no math education so I always avoided that ( i have discalculus too) but I like it a lot and the lat time I try to get back to the basics for deeper understanding about what I am meaduring and for most practice and learn some math. The result is new ( that is for me) ways to measure things. I ( re ?)invented a CF converter, build snd designed a IV-meter like fF meter, did coulomb and C ( under 10pF) measurements with a O plugin in an old Tek 547 ( after that i found out it was, in a different form, described in the manual). Did tek-130 style C measements like described by Terman. Measured capacitanceusing DC, tryed about 10 ways to measure ESR, recently tried to measure the parasitics of 10 m bare wire. Things like inductance, resistance, skineffect, Q, capacitance ect. Very intresting, the meaurements worked, grapical it made sense and gave an idea, but the math was to complex for me to extract it to numbers, gave the data ( thoughstone files) and graphs to a friend who is a math , RF engineer and RF guru but he had to admit it was even to complex for him. He could probably do it but it would take to much time. I could not anlyse the data my self. This is pure hobby, I do not even have an electronic education.
I have a marconi TF1313A, 0,1% bridge and a HP ( the same, like the damaged one you have)
I builded a simpke complex measurement bridge based on the arrl antenna handbook. Also made a poor mans wobbulator based on a noise source, external signal generator and audio SA software ( involved mixing so it could be used for the whole HF band)
But it would be great to have an old bridge like the GR ones. With lots of knobs and after that calculate from there, to the corrections ect. Mostly to measure capacitove stuff.
I'm offered a GR1620 from a list member that I will buy, i read the manual and I allready love it.
With the info gathered I also would like to have a passive RF type bridge. I know I can easy use a vna but I like to measure the basics and try to extract the other parametrs from there as a learning experience. I am now doing some 3 voltmeter experiments. It is nice to compare results from this experiments to my vna. Some times I'm way of but it feels good if it worked out well. Like meauring capacitance and esr on a curvtracer, that was fun. Or the RI-IV meaurement of a cap. After that I had calculated esr capacitance and esl from that I did a simulation and that gave the same SRF. That gives me a kick.
So to be short ( very difficult for me ;-) ) , i do not have a need for a frequency or so, i adjust/ make up my experiments around an instrument.
Thanks to the answers from you and the others and your link i now know were to look for and use the right search terms. First wait for answer from the seller of the GR about transport and hopr we find a way abd then play with that nice instrument and then look for a RF admitance/impedance bridge.
Short question, keithley makes source meters, They are in the micromeasurements handbook but I can not really place this. It sounds like a sort of IV meter, or coulomb meter but for DC. Not planning to buy one, just curious.
Op 25 mei 2012 om 22:41 heeft Brooke Clarke <brooke at pacific.net> het volgende geschreven:
> Hi Fred:
> 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.
> Have Fun,
> Brooke Clarke
> 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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