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50G ohm Retirement Fund
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Zero999:

--- Quote from: Cerebus on March 15, 2017, 07:29:24 pm ---
--- Quote from: Bryan on March 15, 2017, 05:34:09 am ---For what application what would a 50Gohm resistor be used for?

--- End quote ---

Feedback resistor in a transconductance amplifier for measuring nano/picoamps. One of these would give you 0-5V out for an input current of 0-100 pA.

--- End quote ---
Not very accurate though, as the resistor is 30% tolerance.
Dave:

--- Quote from: Cerebus on March 15, 2017, 07:29:24 pm ---Feedback resistor in a transconductance amplifier for measuring nano/picoamps. One of these would give you 0-5V out for an input current of 0-100 pA.

--- End quote ---
You're thinking of transimpedance amplifiers. Transconductance amps are voltage in, current out - the exact opposite.

Cerebus:

--- Quote from: Dave on March 17, 2017, 08:41:58 am ---
--- Quote from: Cerebus on March 15, 2017, 07:29:24 pm ---Feedback resistor in a transconductance amplifier for measuring nano/picoamps. One of these would give you 0-5V out for an input current of 0-100 pA.

--- End quote ---
You're thinking of transimpedance amplifiers. Transconductance amps are voltage in, current out - the exact opposite.

--- End quote ---

What I actually meant to say was transresistance amplifier but for some reason I seem to regularly get a brainfart with 'trans-x amplifiers' and use the wrong term at least 50% of the time. The only time I reliably get it right is when I mean transconductance I do actually write transconductance.
amspire:
One of the things you could do with these is to make a High Resistance transfer standard similar on configuration to these:

http://www.ietlabs.com/esi-sr1010-resistance-transfer-standard.html

Select sets of 5 resistors for parallel use so you end up with 10 or 12 10G resistors that match to better then 1%.

Many DVM's can measure up to 1G. This transfer standard can  give you 9G and 100G of known values to 0.01%. All it needs is short term stability. The actual resistance values are not very important.

Also if you select resistors to give you 10 100G resistors within 1%, you can transfer 10G to 1000G. Not sure who needs it, but you can do it.

I am planning something like this with 100M resistors and with cheap reed relays to do the shorting and un-shorting so I can calibrate 100M and 1G ohms ranges of multimeters from the 1M range.  Just have to make cards with small magnets glued on to short the relays I want for a particular type of transfer.

The only catch is if these resistors end up having a big voltage coefficient, then they are not much use for this.

MartinKantola:
It's been a long time, but I'm interested in those...

Martin
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