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gentlevoice 28th January 2011 08:07 PM

1Gohm or higher resistor ...
 
Hi diy's,

I'm looking for a way to make a 1Gohm or preferably higher value resistor (low wattage). Any of you have experience with this?

Might I take an older carbonblock resistor and scrap away the surplus or is there a more feasible way to do this? Please note that it is not an option to buy materials for this so need be surplus, second hand, things for waste, or the like ...

Suggestions are appreciated,

Greetings,

Jesper

P.S.: It need not be more precise than 10-15% and temperature stability is less important.

Arnulf 28th January 2011 08:09 PM

Why not simply buy one ?

If you merely need extremely high resistance (for input reference etc.) you can use a neon bulb, as long as you don't exceed its striking voltage.

HollowState 28th January 2011 08:46 PM

1 Attachment(s)
You can make a very high gigohm resistor with a suitable ceramic form and India ink. I once made one from a choke that I unwound like to one below. A single straight line or multiple lines will do it. The more ink you use, the lower the resistance. But I'm talking very high resistance, and you'll probably need a good megohmmeter to measure it.

cliffforrest 28th January 2011 09:21 PM

You need to specify required accuracy, power rating and expected voltage before anyone can give a serious response.

10 x 100M 5% 1/2W resistors in series is trivial to do, will give you a 1KV rating easily. But it needs space and the bandwidth will be c**p.

If it is in a feedback loop, a much lower value "T" network will often serve.

What do you need?

gentlevoice 28th January 2011 09:35 PM

Quote:

Originally Posted by cliffforrest (Post 2449672)
You need to specify required accuracy, power rating and expected voltage before anyone can give a serious response.

10 x 100M 5% 1/2W resistors in series is trivial to do, will give you a 1KV rating easily. But it needs space and the bandwidth will be c**p.

If it is in a feedback loop, a much lower value "T" network will often serve.

What do you need?

Hi - thanks for your tips.

Bandwidth is very low (<10 Hz), power rating is 1/10 watt, precision is 10-15%, voltage is max 50 volts.

@hollowstate: Hmmm... yes, you're addressing the issue of how to measure it? I have access to a tonegenerator, a multimeter with frequency counter and an oscilloscope.

Greetings,

Jesper

P.S.: Will also try with a thin line drawn with a pencil.

kavermei 28th January 2011 10:08 PM

Like hollowstate suggested, a lot of materials can be painted, sprayed or drawn upon an insulating carrier. Inks, antistatic sprays, wallpaper glue (methyl cellulose), etc. etc.
You need to experiment with dosage and concentration to get the right value.

Another possibility (also for higher wattages) is a saline solution in a glass tube with metal end caps.

Easiest would be to just buy one for 10c.

Kenneth

a_rabid_monkey 28th January 2011 10:10 PM

Wouldn't a tube of water work?

trobbins 29th January 2011 12:44 AM

Your catch 22 is how to measure - if you want 10-15% - and you want to make it yourself.

I suggest you won't be able measure what you make if you only have 50V rating capability, as that would indicate you have an extremely exotic grade multimeter DC current measurement capability. The concept of testing at AC would I suggest be fraught with even more difficulty.

Do you have an existing circuit with a 1G resistor in it (for whatever your application is) - which you could then swap your new part for, and presumably do a comparison of equipment performance (whatever that may be).

As suggested, you could buy resistors, then you don't have to measure. You may be able to get standard footprint 0.5W 10M or 22M, and just solder away!

Ciao, Tim

Doz 29th January 2011 12:45 AM

Surely any home brew thing on an insulator is going to drift hideously with humidity .... aren't this sort of thing immersed in oil?

Ty_Bower 29th January 2011 02:52 AM

I still want to know why he needs such a thing...


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