I‘m making 100 Meg(+) standard resistors(and as 10+ Meg Hamons as well)

[manganin]

Because I'm going to make the resistor as Hamon (a lot of sockets in a box), I'll first try the quick BNC(no twist needed) widely used in LCR test fixtures

How about using cheap insulated BNC connectors and a built in Guard divider feeding the BNC shells? Saves a lot of trouble and connector cost if the goal is higher than 100 Mohm.

[manganin]

What about the good old SO239 UHF socket? It's 500V RF rated, so good insulation and in addition to being screened, I believe the center hole will accept a 4mm banana plug.

And yes, I've just measured, the center hole is 4.0mm in diameter. That is very convenient, I'm considering to use it on the bridge, hi-volt input say.

The SO-239 when used with the mating plug (PL-259) is so unreliable that it is wrong to call it a connector. OK when used with a banana plug.

[zlymex]

Because I'm going to make the resistor as Hamon (a lot of sockets in a box), I'll first try the quick BNC(no twist needed) widely used in LCR test fixtures

How about using cheap insulated BNC connectors and a built in Guard divider feeding the BNC shells? Saves a lot of trouble and connector cost if the goal is higher than 100 Mohm.

That's right, I'm going to use these, I have a few samples, it's easy to make guarding on a metal box.

[lowimpedance]

Just found a box when tidying up a lab that contained some interesting old standards that were not mounted in any enclosure of any sort !. pics below.
1 Box lid
2 inside of box and
3 end on pic of construction, Teflon plug each end with a alum. tube then an outer plastic sleave to protect the hand written value etc.

Dont know if they were made here or not (I suspect they might have been and maybe contain glass envolope resistors)

[zlymex]

Just found a box when tidying up a lab that contained some interesting old standards that were not mounted in any enclosure of any sort !. pics below.
1 Box lid
2 inside of box and
3 end on pic of construction, Teflon plug each end with a alum. tube then an outer plastic sleave to protect the hand written value etc.

Dont know if they were made here or not (I suspect they might have been and maybe contain glass envolope resistors)

Looks very good in quality, and they are individually numbered. They reminds me of old analog null meters that have 1-3-10 range steps.

[Lowpass30Hz]

Are you interested in the Voltage Coefficient? It is an important consideration for precision measurements of a 100 Mohm resistor, if you want to use it over a large voltage range.

Of course if you are only planning on using it with the same applied voltage this isn't an issue. However, if you ever decide to have the resistor externally calibrated you would have to careful of the difference between the lab's test voltage and your own.

Standard resistor design example - The inside of a Welwyn 100 Mohm standard:

[zlymex]

Are you interested in the Voltage Coefficient? It is an important consideration for precision measurements of a 100 Mohm resistor, if you want to use it over a large voltage range.

Of course if you are only planning on using it with the same applied voltage this isn't an issue. However, if you ever decide to have the resistor externally calibrated you would have to careful of the difference between the lab's test voltage and your own.

Standard resistor design example - The inside of a Welwyn 100 Mohm standard:

Thanks very much. Interesting to see inside photo of the  Welwyn 100 Mohm standard. The metal cans must be hermetic 10M(or slightly less) resistors, any idea of what is made of?

I'll consider the voltage coefficient, that's why I decide to use wire-wound type for my 100 Meg as the 1st choice, they have very small voltage coefficient. If I build higher values such as 1G, 10G, 100G, then I must use none-WW. Apart from selection of resistors with small voltage coefficient, I will use 10 resistors of 1/10th the nominal value to reduce the voltage coefficient effect. In one earlier DIY, I use 100 resistors in series.

[Lowpass30Hz]

I have no idea I'm afraid. I can have a proper look next week when I have access to it again.

What did you use for your earlier 100 resistors in series design, foil type?

Thank you for another engaging thread, these DC/LF topics really interest me. Looking forward to the finished item!

[zlymex]

I have no idea I'm afraid. I can have a proper look next week when I have access to it again.

What did you use for your earlier 100 resistors in series design, foil type?

Thank you for another engaging thread, these DC/LF topics really interest me. Looking forward to the finished item!

That one Giga-Ohm is a test resistor consisting of 100 Vishay Dale RN55D-1005F Metal Film Resistors assembled on PTFE sheets.
Value adjustment: by some resistors of slightly less than 10M(9.76M say)
TemCo adjustment: by test and select those with equal but negative TC from more than 1000 pieces.

[Vgkid]

I read a few months ago about a university in South America(Im thinking possibly Mexico) that built a very stable high value resistance standard. It was rather in depth about the issues that were faced, and how they were overcome. The interesting thing is that it was built with off thelf resistors. Unfortunately I did not save it .

[Vgkid]

This one?

That is the one. Though i remembered reading the second one as well.

[zlymex]

This one?

Thanks for the file. That's remind me something similar I found before.

[zlymex]

See page 2...

I've saved this one before. There is another one called 'Evaluation of Guarded High-Resistance Hamon Transfer Standards', too large to upload even if I compressed it to rar file(2.8M).

[zlymex]

I read a few months ago about a university in South America(Im thinking possibly Mexico) that built a very stable high value resistance standard. It was rather in depth about the issues that were faced, and how they were overcome. The interesting thing is that it was built with off thelf resistors. Unfortunately I did not save it .

Thanks for the refreshment. The resistors they use (USG1110) are very good at 0.1%, 10ppm/K, but no shelf life specification. I'm going to build my 100G Hamon based on TF020R-3, similar spec(0.1% and 10ppm/K) but has shelf life specified as 25ppm/year. Because I have more than 25 set of these 100M to choose from, I'm going to rival that.

[lowimpedance]

While looking for the reversing switch I also came accross these Keithley 5155 High value standards that go from 10^8, 10^9......up to 10^13.
Note the connectors used. The standard BNC is the 'low end'. Inside is a glass encapsulated resistor made by Victoreen.

[zlymex]

Here is the spec for Keithley 5155. Interesting to see the guarding, similar to those 100M.

[zlymex]

update: case arrived today. However, I will make a FR4 board according to the case on which to put all the BNC sockets. Also, I need the finished high resistance bridge to test all those 10 Meg resistors. The case for the bridge also arrived.

[zlymex]

Update: design of the FR4 boards finished and sent to a plant for CNC machining. These boards will be used not only for this 100M standard(10M Hamon) but also for all my high standard resistors/Hamons from 10M to 1T.

[zlymex]

In order to test those 10 Meg resistors to be used in these 100 Meg standard, I need a test box for shielding/connection.
I have a very old Keithley 6104 test enclosure but it is un-guarded, and is not compatible with my 100Meg/high resistance bridge.
I modified the original BNC socket to a triax and added a guarding in between the positive and ground. Also added another BNC socket to let the lower end of the resistor flow thru instead of connecting to the ground/shield.

[ZeTeX]

Just wondering, Why would you need such high value resistors? (e.g anything over 10Meg).

[zlymex]

Just wondering, Why would you need such high value resistors? (e.g anything over 10Meg).

Two possible applications are
 - to generate very small current, thus to calibrated/check electrometers such as Keithley 610C, 617, 6517A
 - to calibrate insulate resistance meters/megaohmeters such as HP4329A

[Dr. Frank]

Just wondering, Why would you need such high value resistors? (e.g anything over 10Meg).

A third application is the verification and calibration of DMMs, which have these high OHM ranges.

Frank

[ZeTeX]

Just wondering, Why would you need such high value resistors? (e.g anything over 10Meg).

Two possible applications are
 - to generate very small current, thus to calibrated/check electrometers such as Keithley 610C, 617, 6517A
 - to calibrate insulate resistance meters/megaohmeters such as HP4329A

Fair enough I guess, not that really useful for me. 

[zlymex]

Update: CNC samples of  the FR4 boards finished. The thickness of the board is 3mm.

[zlymex]

Update: FR4 board arrived today, precisely made, fit the case/BNC perfectly. It is crucial that holes on top/bottom part are aligned.