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Registered Member #32
Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549
Firkragg wrote ...
It depends heavily on rubber type and 'hardness' of vulcanisation. Some small rubber bands I have here measure few hundred kiloohms per centimeter, while some enforced black rubber 'tape' I couldn't measure at all, <2000 megaohms.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
How are you measuring these resistances?
I have a (relatively cheap) RC meter wich measures up to 2 gigaohms. It's slow but does measure high-resistance (>100 megaohm) carbon resistors pretty accurately.
And, it didn't work much at all on that piece of rubber. I found tha tit conducts only after I put some high voltage across it.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Liquid resistors using aqueous copper copper sulphate or sodium thiosulphate solution are sometimes used in big very fast Marxes.
Designs typically involve a perspex tube with end plugs and disc electrodes. It's important to allow for a small amount of expansion of the electrolyte or the resistor will leak. Some designs use a small number of hollow polythene spherules which can be compressed when the electrolyte expands.
Resistance can be adjusted by altering the strength of the electrolyte, but resistances of more than a few hundred ohms become unwieldy.
On the plus side, liquid resistors have very low self-inductance, and can handle a great deal of power.
I have also seen them used as dump resistors - dummy loads - for discharging Marxes into, since they can readily be scaled up to handle high dissipation.
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source for good HV resistors?
