measuring very high resistances about 10**15 ohms - Page 1
Forum section: electronics / general

author: Physikfan
author_rank: Regular Contributor
timestamp: November 17, 2020, 08:05:07 pm
content: To all friends of challenging measurementsPlease does someone have experience by measuring very high resistances, for example about10**15 ohms?regardsPhysikfan

author: bsw_m
author_rank: Frequent Contributor
timestamp: November 17, 2020, 08:26:10 pm
content: Several weeks ago I measured the leakage current of a small sapphire insulator. At a test voltage of 15V, it was approximately 1.5E-17AFor measurements I used B7-45. The DUT was located in a small measuring chamber located directly at the electrometer input. The DUT was connected directly to the electrometer input.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: November 17, 2020, 08:47:13 pm
content: I've used LMC6001 CMOS op-amp and a T-network feedback to get a large gain.

author: bsw_m
author_rank: Frequent Contributor
timestamp: November 17, 2020, 08:50:50 pm
content: Quote from: maxwell3e10 on November 17, 2020, 08:47:13 pmIt is possible, but using T-network leads to increased noise

author: bdunham7
author_rank: Super Contributor
timestamp: November 17, 2020, 09:01:15 pm
content: The first step would be to think about whether what you are measuring is ohmic--does it obey Ohm's Law? And at what test voltages?Then it is a matter of supplying the test voltage and measuring the current with a picoammeter or electrometer. You'll likely need an enclosed chamber to eliminate air currents and so forth. I can't say I have experience with 10^15 ohms, the biggest resistor I have is 10T, or 10^13 ohms, and for that using 100 volts and a picoammeter, well it's not easy, especially if you don't turn the ceiling fan off. It sort of worked for me. What are you measuring?

author: guenthert
author_rank: Frequent Contributor
timestamp: November 18, 2020, 05:55:21 pm
content: Measuring resistances in the order of 10^15Ohms sounds like quite a challenge.I was wondering whether such resistances can actually be measured in an environment where air is present. I couldn't readily find the answer to that, the best I found ishttps://apps.dtic.mil/dtic/tr/fulltext/u2/a056235.pdfThere the resistance for "dry air" is stated (p.16) to be as high as 10^26Ohm/cm (is this limited by charge carrying ions due to natural background radiation?). For not so dry air, the answer is considerably more complicated and very much depends on rel. humidity and temperature (and pressure and air-velocity).What I took away from that article is, that you might want to keep the area of your test electrodes small, if you can't ensure the air to be dry (flood with N2?).

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 18, 2020, 06:21:13 pm
content: HP4329A is typical. It gets to 2E16 ohms but probably needs 1000 volts to do it. Surface leakage of the sample could be all over the place.

author: HighVoltage
author_rank: Super Contributor
timestamp: November 18, 2020, 07:04:35 pm
content: I would use the Keithley 6517B Electrometer, in theory it can measure up to 10^17 Ohm.This Keithley Engineer is measuring 100 Tera Ohm to 1 Peta Ohm with an interesting setup:

author: MegaVolt
author_rank: Frequent Contributor
timestamp: November 23, 2020, 06:24:11 am
content: Quote from: HighVoltage on November 18, 2020, 07:04:35 pmThank you for this very interesting video.Can you see the details of this setup? Does the red wire have a large coil at the bottom which is in the water? And we measure the resistance between water and the center conductor?