FS (UK/World) 7 decades (10K to 10G) resistor set.

[krish2487]

I ll try and check Alex..
Thank you once again for the inputs. 

[Alex Nikitin]

As a possibility- a heavy condensation internally, if the box came from cold into a warm and humid environment, the box is not sealed. Still unlikely in my opinion. Open it and have a look, if needed, dry it at an elevated temperature, the box would happily survive 100C.

Cheers

Alex

[krish2487]

Okay.. I opened the box and it looks normal. no signs of condensation or any such thing. and the resistors were very well soldered. :-)
No signs of any broken contact.

I did measure the resistance directly at the resistors using a handheld fluke 287 and keysight 1242a - for the 10M and 100M resistors and I ended up reading 9.978M and 97.8M.
I did not expect the handhelds to do any better. but it indicates that the resistors are infact okay.
( I made two measurements - one directly at the resistor legs and one one the adjacent resistor legs after the BNC to verify that there was nothing broken at the BNC connector itself.)

It looks like there is something amiss in my measurement setup.. I will have to check the instruments and the measurement setup once again...
Its not like there is anything to go wrong with the box - especially after checking

[HighVoltage]

ohhhhkay...
It  shows the same reading as when it was connected.. 3.5-3.6M ohm...

Then you most definitely have a problem in your BNC to banana plug adapter.

[krish2487]

You hit the nail on the head!! 

I measured the resistance across the banana plugs and I was reading a little over 6M.
Measured between the BNC centre pin and the outer body - same.

I checked  the resistance for another BNC connector I had lying around and it was open... 
I just got the adapter today!! and I did not even bother to take the receipt.. being supremely confident that nothing can go wrong in such an adapter.
Murphy I tell ya!!

[Kjelt]

I was going to say that as well but 4M is pretty low. I had adapters at around 100M so not suitable for large resistance measurements. As Alex pointed out in his post, the kind of plastick , nylon, pom etc used is critical for very hig ohms measurements. As well as contaminants such as oil from your fingers and humidity.

[krish2487]

The higher ohms 1G and above are pretty much not possible as the multimeters at my disposal cap out at 100M.
but it is nice to know the gotchas even in the Mohm range. :-)

I ll invest in some quality connectors.. and maybe build shorter cables as well.

[Hydron]

I've had issues with leaky adapters too but in the giga-teraohm range - in the megohms is pretty terrible!

[Alex Nikitin]

It is a horribly badly made or contaminated adapter. I have several similar adapters here and they all measure about 10 Tohm, not perfect but good enough for most measurements up to 10-100M.

Cheers

Alex

P.S. two more units are sold to forum members.

[unseenninja]

I received a very similar and very useless BNC to banana adapter from Amazon...

[HighVoltage]

I received a very similar and very useless BNC to banana adapter from Amazon...

One has to wonder, what kind of material they are using.
I would take it apart and look for the area that is causing this breakdown.

[Alex Nikitin]

I just wonder what plastic is used in this rubbish, even PVC wouldn’t have such a low resistance! I had a reasonably good luck with BNC to BNC cables from Amazon when I needed them in a hurry, however it looks like the adapters could be a minefield. The ones I use were bought from RS and Farnell.

To make life a bit easier from now on I’ll offer a free BNC shorting plug with each unit (as a couple of buyers did ask for it and already received such a plug). It is also worth noting that for higher resistances (1M and more) a 2W Ohm measurement with a coaxial cable and a BNC to a dual banana plug adapter is a better way of connecting.

Cheers

Alex

[SeanB]

One has to wonder, what kind of material they are using.
I would take it apart and look for the area that is causing this breakdown.

I would say the black colour is the issue, as it generally is carbon black blended into the plastic, so it has a very high resistance, but is still conductive in thin areas, even if it will withstand 500VDC testing without passing appreciable current. Better ones use different materials, possibly black iron oxide powders, which provide higher resistance, though the best is plain natural PVC, or even better nylon or PTFE, which is a lot more expensive. More expensive adaptors only have the black as outer cover, inner is made with virgin uncoloured HDPE, and there is a gap between the metal parts and the connectors.

[Zucca]

Thanks I will check mines... the devil always hides in details.

[coromonadalix]

man  quality as gone down the drain    .... 

had problems with bnc to sma cables lately,  same resistance effects .... mostly intermittant

[Zucca]

IDEA: krish2487 I would post big pictures of the affected adapter and open a new thread in the "General technical Chat" section or "Test Equipment".

I can imagine many people are using them without knowing they are bad.

[Kjelt]

It is almost as low as ESD safe plasticks 

[krish2487]

@Zucca
Thats a good idea actually.. I ll do that over the weekend..
Bear in mind, the pics are from an iphone.. so they may all not be all that great.. but I will try my best.

[unseenninja]

One has to wonder, what kind of material they are using.
I would take it apart and look for the area that is causing this breakdown.

I would say the black colour is the issue, as it generally is carbon black blended into the plastic, so it has a very high resistance, but is still conductive in thin areas, even if it will withstand 500VDC testing without passing appreciable current. Better ones use different materials, possibly black iron oxide powders, which provide higher resistance, though the best is plain natural PVC, or even better nylon or PTFE, which is a lot more expensive. More expensive adaptors only have the black as outer cover, inner is made with virgin uncoloured HDPE, and there is a gap between the metal parts and the connectors.

It's not the plastic. I ordered two adapters. One has 2M between the terminals, the other has > 1G.
Most likely, the connection between the BNC plug and the 4mm sockets is made in a less than optimal way and when the assembly is put inside the moulding machine to add the plastic, it causes a partial short to develop.

[Alex Nikitin]

One has 2M between the terminals, the other has > 1G.

By the way, one of the benefits of having a calibrated high Ohm resistor array is that you could at least try to estimate much larger resistances than your meter can measure, by connecting the unknown in parallel to 1G resistor and observing the difference. This way you should be able to see the effect of values up to 100G, possibly more. For starters you could try it with the 10G resistor in the array and see how accurate it can be.

Cheers

Alex

[Alex Nikitin]

I've started a separate thread in the Metrology section to show some TC measurements and to discuss application matters as it would be more appropriate than here.

Cheers

Alex

[EC8010]

Those poor adapters put the willies up me as I use BNC-4mm adapters a lot. I've just been through my ten adapters and they were all >1G.

[HighVoltage]

Many years ago I had contact problems with BNC to Banana plug adapters.

Then I switched to Stäubli / Multi Contact / MC brand and never had any problems again.
Especially for any kind of metrology grade measurements, these adapters are perfect.

[zepto]

I bought a set of 2 bnc->banana adapters 2.5 years ago from amazon, maybe the same ones. One had 1Mohm resistance and the other had 10Mohm, so it was possible to identify them as trash using the cheapest multimeter. They were plastic waste the second they were produced. There were no bad reviews so amazon must delete them. I just mean to say this isn't some one off bad batch thing, they have been selling useless trash for years uninhibited. I threw them away and bought some Philips adapters that were probably 30+ years old and still tested good with an electrometer.

Since then I have not bought a single piece of amazon/ebay JDAOIDJS chinesium test cabling/adapter. I won't buy banana patch cables or even insulated wire from these morons. I passionately avoid giving them business. The one advantage of these trash vendors filling ebay with garbage is that people will sometimes sell surplus cables for a decent price. I bought a used set of 30x minigrabber to minigrabber cables for $30. They were all ez-hook/pomona. I just cut one in half whenever I need to build another banana-> minigrabber cable. They are high quality and they will probably outlast me.

I am sorry to further derail your listing. I'll take one if you are making more.

[Alex Nikitin]

I am sorry to further derail your listing. I'll take one if you are making more.

Yes, I’m making more of these boxes, PM me for details if you would like to order one.

Cheers

Alex