Bummer!

Seems to be. The test resistors are big long blue things from Digikey, IRC maybe. I have a set of resistors from 1K to 5G ohms, each mounted on a Pomona dual banana plug.

I'm using two DVMs, one to measure the upper (Z1) voltage and one across the lower (Z2). I can short either pair of terminals and zero out the respective DVM. If I plug in 1G and 5G resistors and apply a few volts, I get a voltage ratio of 5.002. A good diode makes a nice log curve down to 20 fA, which is comforting.

Being a little paranoid, I've done a number of cross-checks and everything looks good so far.

I do have some surface-mount 100G and 1T resistors; maybe I'll ratio them just for fun.

My ebay Keithley electrometer just arrived and seems to work. The lowest range (on the analog meter) is 1e-14 amps full scale. It measures the 1G and 5G resistors within a couple per cent. Looks like this:

John

spec'd to

volts

than

to the

becomes

transistors

Gees i think i did that in high school about 40 years ago.

Sounds good, i presume you are taking steps to keep them clean?

At 5 Gohms, it doesn't seem to matter. I just tried a 100G 0805 surface-mount resistor; it read 95 G on the Keithley, 89 on my rig. I tried cleaning the connectors and such with IPA and the resistance went negative! Bad move. Looks like you have to be careful in the 100G sort of range. Everything's baking now and may recover.

John

OK, > 1e14 ohms today after baking. IPA seems OK on teflon, but it's hell on polyethylene type connectors and adapters. The Pomona dual banana plugs are excellent.

John

ground

2. >>>>>>>>>

What a

That's what i was talking about. It actually pays to be careful at 1G Ohm and above.

ground

2. >>>>>>>>>>

What a

Digikey,

Di-ethyllphthalate IIRC. Thermoset, very low G.

IPA will craze acrylic instantly, as well.

Cheers

Phil Hobbs

(Currently working on linearizing optocouplers. A volt or so of 20 MHz helps the toe linearity amazingly.)