50G ohm Retirement Fund

[TheSteve]

There does seem to some interest - why not list them for sale in the buy/sell section. Sell them in lots of 50 or 100 or something.

[Tom45]

Well, 50 GOhm resistors do exist in 0805 (up to 100 GOhm in that series). Make sure you do not exceed that 1/8 W power rating .

    79 KV is needed to hit 1/8 W power dissipation.  I wonder why they even bother with a maximum power specification for these.

[Red Squirrel]

How do they react to heat, I wonder if they are more meant for less conventional use of resistors such as very sensitive sensory applications?

[Cerebus]

How do they react to heat, I wonder if they are more meant for less conventional use of resistors such as very sensitive sensory applications?

Usually terribly. Typical tempco for this kind of resistor is in the 1000ppm region, worse than won-hung-lo SMD resistors in more 'normal' values at typically 100 - 200ppm. Note the 30% tolerance. These get used in the kind of instruments that you calibrate before every reading and take the reading quickly before the instrument drifts too much. It's no accident that picoammeters come with accuracies on the order of 0.3% when comparable voltmeters have accuracies 100 times better.

[ocw]

I just received four TE Connectivity RH73X2A50GNTN 50G ohm 30% 0805 resistors which were ordered from Mouser.  Attached is a picture of them.  I don't know how many other 50G 30% 0805 resistors are being made, but the pictured large bag does not contain TE's version.  I included an Ohmite MOX-1125-23-4008J 40G resistor for a size comparison.

I measured the four resistors as 37.1G (-25.8%), 38.0G (-24%), 45.8G (-8.4%) and 54.9G (+9.8%). Those measurements were made using my Keithley 610C electrometer.  I'll probably later measure their values using my homemade meter using a ADA4530-1.  The capacitance of the resistors were measured to be about 0.61 pF for each of them.

I'd recommend checking the capacitance of those components in the bag.  I suspect that they will measure significantly above 1 pF and that you have ceramic capacitors which have a leakage around 50G ohm.  You will need to find another source for your retirement fund.

[Zero999]

For what application what would a 50Gohm resistor be used for?

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.

Not very accurate though, as the resistor is 30% tolerance.

[Dave]

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.

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

[Cerebus]

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.

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

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

[floobydust]

wtf these aren't in a reel, who buys SMT in bulk packaging?

[CatalinaWOW]

wtf these aren't in a reel, who buys SMT in bulk packaging?

Ex-buyers.  The existence of this lot is proof that at least one entity didn't use them.  The buyer probably got a killer price on them.  Maybe tthirty percent off of the reel packaged parts.  And couldn't understand why his next paycheck was printed on pink paper.

[Kleinstein]

wtf these aren't in a reel, who buys SMT in bulk packaging?

There are special feeders for bulk part. However this is more for the more common (and not so delicate) ones, like 0 ohms, 47 ohms or 100 nF caps.