Multimode electrometer for atmospheric ion measurements

A computer-controlled electrometer capable of either high impedance voltage measurements or femtoampere current measurements has been developed. It is intended for use with a Gerdien ion counter in atmospheric temperatures. Temperature variations can cause significant thermal errors arising from offset voltage and bias current changes that compromise the measurements. Use of high impedance switching permits the offset voltage and input bias currents of the electrometer to be measured, and allows regular software compensations to be applied in both modes. (C) 2000 American Institute of Physics. [S0034-6748(00)01101-7].