Analog Ground
- Joined Apr 24, 2019
- 460
Controlling leakage with cleanliness is important but also the use of a "guard ring" on the input to shunt away leakage currents. Just search "op amp guard ring".
Why would you need one? there might be a better way.Hi,
Where and how can easily get 1 GOhm resistor?
Thanks
Adam
Thanks.That will be a very interesting device when it i completed. Years ago I studied the plans published for "the femtofarad Meter" as part of a work project. But we needed to measure dielectric absorbtion and its variation and changes with aging and temperature. So measuring capacitance was not enough, nor was measuring leakage current.
So what capacitor characteristic would the system be evaluating?
Thanks.We commonly use 1GΩ encapsulated in glass in the front end of charge-coupled preamps.
Thanks.I did a lot of measuring in the pA region, In one case, it was better to count Coulombs and divide by time.
Systems were not that difficult to set up, except the first time.
Thanks.Hello,
Define "large".
I think that this 10 Watt version will come closer:
https://www.ebay.com/itm/203232848701?hash=item2f519f2b3d:g:dBsAAOSw2zRcLS47
Bertus
Thanks.Why would you need one? there might be a better way.
Thanks.What's wrong with buying it from your usual supplier for $1 each?
If you are trying to measure capacitance, what range of capacitance values do you want to measure?
What is your method for measuring capacitance?
Only if you keep the voltage across it less than 5000V.Thanks.
Actually for my DIY, a 1/4W be OK?
Thanks.
I am looking for.
Thank you. I'll read it.How high a value do you want to measure?
I built one of these. It doesn't need any unusually high value resistors and it is surprisingly accurate:
https://create.arduino.cc/projecthu...nge-capacitance-meter-10pf-10000microf-e6e797
Thanks.I am going to assume that you are attempting to measure the capacitance value by measuring the time it takes to charge the capacitor to a given threshold voltage.
The reason that your method calls for a very large resistance value is because you want to measure very small capacitances, lower than 10pF?
There is another way to measure small capacitance values.
Instead of measuring period, measure frequency.
Place the unknown capacitor in an oscillator circuit and measure the frequency of oscillation.
I know the glass resistors well. I did an I-V converter design that I used an OP-41. It was the 8 lead TO something package, leads in a circle. I put the one input pin on a PTFE standoff. My ranges for +-10V out were 100, 10, 1 and 0.1mA. I used mercury wetted relays. Since this was designed to be a 4-terminal/2-terminal I-V converter with bias, the measuring leads had 400 M-ohm resistors to ground as bias current bleeders.1GΩ glass encapsulated resistors are mounted on Teflon standoffs to avoid stray leakage currents.