Fred: You can measure the capacitance of a series connected capacitor with high resolution. Have a look a manual for the Keithley 590 CV Analyzer. The concept is explained in the manual. See the diagram(s) and text. I regularly measure Schottky diode junction capacitance with sub fFarad resolution. The analogy is to use a VNA to measure a capacitor in the series mode (S21) rather than in shunt mode (S11). By measuring a DUT in a series measurement mode the full dynamic range of the receiver can be used. For measuring impedances that are less than 50 ohms, measure the DUT in shunt mode. For measuring impedances that are greater than 50 ohms, measure the DUT in series mode. This concept is also explained, (by looking at the equations and diagram(s)) in the HP4275A LCR Meter. Some concepts can be used in many measurement instruments, i.e. a CV Analyzer, LCR Meters, and VNAs. Some of the early NBS documents showed how to build a ring guarded, circular, parallel plate capacitor. I do not have a reference handy at the moment. A Google Scholar search with the right set of key words should turn up something. PS The Keithley 590 CV Analyzer is set to measure at 100KHz or 1MHz. I have used the Keithley 590 , HP4275A and VNAs for the last decade (or more). Some concepts work in all three instruments. Ivan Cousins

Thanks you all for the usefull info. Very interesting I can not find the app note/book about the "shunt" methode I use. I thought it was Agilent but I have a lot of books about network analysis so I can be wrong. Agilent app note: 5989-5935EN describes the way to use a shunt measurement for very low impedances. Port 1 sends the incident to the DUT and and the voltage drop over it is very low, the current high and the combined resistance of the ports convert that to a voltage. A sort of Kelvin measurement. You use S21 and a custom trace or calculate the result. 25(Rho/(1-Rho)) To measure high impedances you use a series measurement like Ivan writes. But then I have to calculate. What I did in my high impedance measurement was placing the High Z capacitor in shunt with 50 ohm. The parallel impedance of the XL and the 50 ohm are parallel allmost 50 ohms and a VNA is very accurate around 50 ohm. But I do a 2 port sweep and use the RX as 50 ohm shunt and measure S11 because my VNA needs a two port SP2 measurement to do the 12 term error correction and calculate the right Cp from the resulting corrected S11. On my old HP8407 I use just a 50 ohm terminator paralleled with the capacitor and a directional bridge so maybe shunt methode is the wrong word in this case and a better word is maybe parallel measurement. But with the HP VNA the problem is my homemade bridge, that has only a 30dB directivity but the results are usefull. I will test the S21 series methode too. Did that in the pre-tests while I was searing the4 different ways. Today I made a coaxial capacitor but I made a mistake. I made two plastic inner rings to hold the center conductor in the tube. After calculation the ringparts together have a bigger capacitance as the airpart and because I do not know if it is PE or nylon I have no clue about the value. between 16-18pF total. So I am gonna change the internal rings into endcaps so there is no dielectrium other then air in the tube.Mount it on a board and make the inner conductor slidable so I can change capacitance. Fred Ivan Cousins schreef op za 14-01-2012 om 10:38 [-0800]: > Fred: > You can measure the capacitance of a series connected capacitor with > high resolution. > Have a look a manual for the Keithley 590 CV Analyzer. > The concept is explained in the manual. See the diagram(s) and text. > I regularly measure Schottky diode junction capacitance with sub fFarad > resolution. > The analogy is to use a VNA to measure a capacitor in the series mode > (S21) rather than in shunt mode (S11). By measuring a DUT in a series > measurement mode the full dynamic range of the receiver can be used. For > measuring impedances that are less than 50 ohms, measure the DUT in > shunt mode. For measuring impedances that are greater than 50 ohms, > measure the DUT in series mode. > This concept is also explained, (by looking at the equations and > diagram(s)) in the HP4275A LCR Meter. > Some concepts can be used in many measurement instruments, i.e. a CV > Analyzer, LCR Meters, and VNAs. > > Some of the early NBS documents showed how to build a ring guarded, > circular, parallel plate capacitor. > I do not have a reference handy at the moment. > A Google Scholar search with the right set of key words should turn up > something. > > PS The Keithley 590 CV Analyzer is set to measure at 100KHz or 1MHz. > I have used the Keithley 590 , HP4275A and VNAs for the last decade (or > more). > Some concepts work in all three instruments. > > Ivan Cousins > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.