I just gotta put it out there. It's been that sort of week online.

 

Then what was this about in post one?

SLK001 said: ↑
Where does one get a 100GΩ resistor?

This thread was a SPIN-OFF by the mods. I asked the question in the thread listed above. I DID NOT CREATE THIS TREAD AND I WAS SIMPLY ASKING A RHETORICAL QUESTION!!

 

I replaced a 1 Megohm 200 W resistor once. HV power supply (~15 kV) bleeder. The voltage divider was a bunch of 625K WW resistors in series.

 

This thread was a SPIN-OFF by the mods. I asked the question in the thread listed above. I DID NOT CREATE THIS TREAD AND I WAS SIMPLY ASKING A RHETORICAL QUESTION!!

I was not aware of that since no mention was made and took it to be a legitimate thread.

 

1.1 Megohm high power and very high voltage series resistor.

 

Yes, it would but if you read the title of the thread.

Well, at least my math was right.

Yes, I got 0.00001 amps - now that I have the right numbers. 10 µA.

 

Where does one get a 100GΩ resistor?

You may get it from here.

 

Hello,

@Techno Tronix , the resistors you show are 100 Ω and not the requested 100 GΩ
The highest value I have seen is 10 GΩ here on ebay
In this site there are resistors available upto 1TΩ:
http://www.high-voltage-resistors.c...ylindrical-high-voltage-power-surge-resistors

Bertus

 

Rethorical it was; here is the logical follow up: how to measure it? A true Georg Simon moment.

 

Where does one get a 100GΩ resistor?

Obsolete ionization chambers are an inexpensive yet high quality source for such components (e.g. CDV-715 and its ilk) -- the high value resistors (typically up to 220GΩ) are encased in glass envelopes to facilitate maintenance of cleanliness...

Best regards
HP

 

... Poor writing skills on your part does not imply poor reading skills on our part. ...

I´d still blame this to poor reading skills, posts #4 and #17 were the clues.
Also the poor moderating skills on the side of the trigger happy moderator should be mentioned, as it is he who created this trainwreck.

 

Friends - such components do exist!

For example (please note R15 [pg #13]) -- And this readily available, inexpensive instrument is one of many in it's 'class'
https://www.orau.org/ptp/Library/cdv/victor715-1a.pdf

FWIW I'll try to up an image of such a resistor today (time permitting)

Best regards
HP

 

Rethorical it was; here is the logical follow up: how to measure it? A true Georg Simon moment.

I ran into this problem recently while sorting through a large batch of LDRs looking for units that had exceptionally high dark resistance. My bench DMM only goes up to 50 MΩ, and many of the LDRs had dark resistance well above 1 GΩ, with some approaching 100 GΩ.

Easiest solution I came up with was to form a voltage divider with the unknown resistance (the LDR) on top and a 1 MΩ resistor on the bottom, then calculate the unknown resistance from the applied voltage and the voltage measured across the 1 MΩ resistor.

I'm sure you can buy instruments that will directly measure and display such large resistances, but I shudder to think what they must cost. The voltage divider method is cheap, easy and accurate, though a bit slow. But being retired, I've got lots of time on my hands...

 

I ran into this problem recently while sorting through a large batch of LDRs looking for units that had exceptionally high dark resistance. My bench DMM only goes up to 50 MΩ, and many of the LDRs had dark resistance well above 1 GΩ, with some approaching 100 GΩ.

Easiest solution I came up with was to form a voltage divider with the unknown resistance (the LDR) on top and a 1 MΩ resistor on the bottom, then calculate the unknown resistance from the applied voltage and the voltage measured across the 1 MΩ resistor.

I'm sure you can buy instruments that will directly measure and display such large resistances, but I shudder to think what they must cost. The voltage divider method is cheap, easy and accurate, though a bit slow. But being retired, I've got lots of time on my hands...

Aha, a divider. I should have thought of that...! Wondering how the actual value of the small one would affect the measurement of the big one. I will try something later. On paper, I mean.

 

Aha, a divider. I should have thought of that...!

Don't feel bad. After doing analog circuit design for a living for over 40 years, I can't BELIEVE how much head-scratching I had to do before that simple idea came to me.

Wondering how the actual value of the small one would affect the measurement of the big one.

It just comes down to using the voltage divider formula, taking into account the DMM's input resistance being in parallel with the 1 MΩ resistor. Given that my DMM's input resistance is 100 MΩ, the 1 MΩ resistor had a 1% tolerance, and I wasn't really interested in getting a terribly precise measurement anyway, I did a simplified calculation:

Runknown ≈ 1 MΩ ⋅ Vin / Vmeter.

Accurate enough for my purposes...

 

Rethorical it was; here is the logical follow up: how to measure it? A true Georg Simon moment.

I'm sure you can buy instruments that will directly measure and display such large resistances, but I shudder to think what they must cost.

Surprisingly, the price of acceptably accurate (± 2%) instruments is quite reasonable!

For instance, I can personally vouch for the offerings of Alphalab for accurate resistance measurement up to 2TΩ (2000GΩ) -- especially useful where application of EHT is contraindicated...

Best regards
HP

 

Surprisingly, the price of acceptably accurate (± 2%) instruments is quite reasonable!

For instance, I can personally vouch for the offerings of Alphalab for accurate resistance measurement up to 2TΩ (2000GΩ) -- especially useful where application of EHT is contraindicated...

Best regards
HP

Wow, 2TΩ!! All secured to a two mundane (are they?) crocs?? And then the sandapaper... Not a game I could expect to play in this life, it seems.

BTW, could you mention one or two components (are there some?) measuring some GΩ? Standing on my ignorance, if not, what other meaningful things could you measure with it? My dry hands when I have too many hours not sleeping?

 

Runknown ≈ 1 MΩ ⋅ Vin / Vmeter.

Accurate enough for my purposes...

How much Vin was?

 

I ran into this problem recently while sorting through a large batch of LDRs looking for units that had exceptionally high dark resistance. My bench DMM only goes up to 50 MΩ, and many of the LDRs had dark resistance well above 1 GΩ, with some approaching 100 GΩ.

Many megger units will read to 2 G (1999 meg) easily enough and I have seen a few 'Giggers' (1999 G) for HV utility cable and related testing before as well.

 

We use these types of testers to quality high voltage insulators after cleaning and baking. Standard values for most are in the high GΩ range with several thousand volts applied.
http://ecmweb.com/ops-amp-maintenance/basics-insulation-resistance-testing

http://www.lesker.com/newweb/feedthroughs/power_feedthroughs.cfm?pgid=20kv_cf