# How to simulate adjustable 'negative resistance' with active components?

I'm building a decade resistance box using 2W resistors, from 10x1M ohm to 10x0.1 ohm. However, due to some contact resistance, the 0.1 to 1 ohm resistance will likely turn out to be ~1.1 ohm to 2 ohms (the rest of which will be in a tolerable margin of error). Is there a way I can 'offset' the ~1 ohm of wiper and contact resistance with some active components, with an adjustable potentiometer for fine tuning?

I'm thinking -1 ohm +/- 0.5 ohms ought to do, and ideally it would handle up to 2W just like the other resistors. Is such a circuit possible?

• Find lower contact resistances.
– user16324
Commented Nov 29, 2015 at 19:53
• I can't, really. Even passive units costing thousands of dollars have residual resistances of around 1 ohm and report their accuracy after having subtracted their 'zero resistance'. I'm looking for a way to do this internally, if such a thing is possible. Commented Nov 29, 2015 at 20:01
• @Ehryk: My 1953 Siemens resistance decade has a total contact resistance of 80mOhm. Most modern mid price range resistance boxes I know of have contact resistances around 300mOhm. Even my cheap 1% quickly slapped together resistance decade has a resistance of 800mOhm. Maybe you were not looking at the right place? Commented Nov 29, 2015 at 20:16
• Perhaps, but I'm building my own and I'd like to be able to trim out whatever is there so that I get a 'true' 0.1, 0.2, 0.3 ohm with an acceptable percentage of error (the resistors are all 1%). Is this possible? Commented Nov 29, 2015 at 21:58
• I.E. even with 300mOhm, your '0.1 ohm' setting would resultin 0.4 ohms, no? 400% error? Commented Nov 29, 2015 at 21:59