[sdiy] Giga-Ohm Resistors--Where?

[Scott Gravenhorst]

Many years ago, I worked on electronic gas analyzers.  There was one type that
measured combustible gasses that used this range of resistor.  I wish I could
tell you who made them, but I remember that they were encased in glass and that
you aren't supposed to touch them with your fingers.  Any dirt/oil/moisture from
your skin would cause the value of the resistor to decrease.  These won't be
common electronic components that Digikey and the like would carry.  I would
suggest going to the web sites of the large resistor manufacturers and see if
they have them, then contact them to see if there are distributors.  Be prepared
for price shock.  If you're clever with words, and only need a few, you might be
able to get free samples.  The company that I worked for that made the gas
analyzers is Mine Safety Appliances, but who you could call would be a mystery
to me at this time.  Laboratory instrumentation manufacturers might also be able
to help, such as Hewlett Packard.

I'm curious, what sort of circuits would use such resistors?  

I don't think I've seen any synth circuits that would use such things.  The
circuits MSA used were high gain opamp instrumentation amplifiers for amplifying
very tiny currents.  The resistors were used in the feedback loop.

Glen <mclilith at charter.net> wrote:
>I've been looking at some schematics recently that mention 1G and 3G
>resistors. Does anyone know of a place to purchase such large value resistors? 
>
>10M is the largest resistor that I've been able to find so far. I really
>wouldn't like the idea of chaining 300 10M resistors in series, just to get
>a single 3G resistor.
>
>thanks,
>Glen Berry
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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