need a rotary switch with a insulation resistance > 1 T ohm for the 200 G ohm feedback resistor of LMC 6001? could you please recommend which rotary switch can be used.

Hello Peng,

Ceramic based rotary switches can reach that level, particularly the "high voltage" (wider spacing) ones. One thing to look for is the insulator between the rotor and the shaft is also ceramic, not plastic or phenolic. Look for C&K or Centralab. A good one will NOT be cheap.

But they must be cleaned thoroughly and kept dry (sealed enclosure with desiccant), since ceramic will absorb moisture over time.

The "big-boys" like Keithley use sealed reed switches and magnets.

Regards,