500 days

It you assume no net loss or gain from the water surface then it shrinks very slightly between 0C and about 4C. See for example:

Certainly very true if the ice is floating in pure fresh water but clearly untrue when it is floating in denser 3.5% brine seawater.

It's just after sunrise here... humidity is 14% and will drop to near zero by this afternoon.

...Jim Thompson

How does it work (i.e. to get the 10^15+ ohms impedance)?

Best regards, Piotr

If everyone in Florida dumped their coffee grounds in their yards, instead of in the trash, the land would rise faster than the ocean.

Not if they drink American coffee.

Anthony Watts seems to be objecting to the word "collapse", for something t hat is going to take a number of decades.

The word is used both for something that falls down suddenly, and for somet hing that folds up into a more compact compass, where speed is irrelevant.

The situation of the west antarctic ice sheet is that it had previously bee n held up - and somewhat crumpled - in it's flow out to sea by occasional c ontact with the local sea floor, and it has now floated off the bottom, and is now in a position to flow faster and uncrumpled.

Ice sheets don't crumple much, and don't flow all that fast, even when not dragging themselves across sticking up bits of the sea-bottom, so while the previous structure has "collapsed", you'd be hard placed to see the differ ence.

But I'd still steer clear of shore-front property as a long term investment .

Here's the manual.

It says to replace the high-ohm resistors every two or three years. My unit must be 30 years old, and it seems pretty accurate.

I built a homebrew fA range parts tester, using a cmos opamp. My worst problem was the (expletive deleted) Radio Shack binding posts, which leaked like hell. I had to machine a slot in the chassis and hack in a piece of polycarb, after it was all assembled. Nuisance.

I think someone here has mentioned an even better opamp.

Probably nylon, or some cheap 'n' cheerful Chinese ersatz of nylon. That's the same stuff that makes packaged reed relays leaky.

Once life gets a bit less crazy round here, I'm planning to to a brain transplant on my Keithley 602 with a CMOS op amp and some Russky glass resistors. 10 pA FS minimum, zillions of batteries--what a piece of crap. Nice switch and meter, though, hence the transplant.

It took Keithley at least a decade to recover the 100 fA FS range their electrometer tube units had.

Cheers

Phil Hobbs

Depends on whose bowels Jim put the block of ice into, I suppose.

You can get surface-mount resistors up to 1T ohm these days. That 100G in my pic is an 0805, I seem to recall.

The trick will be to come up with a circuit that can do fA measurements without needing half an hour to settle. My Keithley has a "fast" (feedback) mode, but it doesn't work.

One thing I've done, when no real instrument was available, is let some current charge a polystyrene cap for a while, and then measure it. A mosfet follower can be used to measure its own gate leakage, with just a cap from gate to ground.

An ordinary DVM with 10M voltage-range input impedance and 1 mV resolution is an ammeter with 100 pA resolution, good enough for a lot of measurements.

Remember my 2N7000 games?

That trick with the bootstrapped guard might do pretty well. If it's down to 0.015 pF-ish like the 50M TIA, the TC with 100G would be about

Cheers

Phil Hobbs

Thanks - I bought the tube version, since they are just as good, but much lower in price. (I heard.)

If I walk on a carpet, and there is a short lead on the plug, it wiggles the meter from a few feet away. Very sensitive.

I was looking for a circuit to pick up ambient background radiation - usually from building materials and Radon daughters.

There are several designs I like: 1. Charging a probe in a chamber at only 40 V bias. A 2n4117 or equiv. collects the charge, and an ADC periodically reads the voltage. (the chamber forms a big capacitor.) The other design is to use the cmos imaging array as a detector (paint it black.)

About leakage, Bob Pease put this boards in a dishwasher, he said.