Electrometers from Keithley Instruments can be compared to digital multimeters (DMM´s) but with extreme high input resistances for measuring high impedances. With Electrometers, voltage, current, resistance and charge can be measured without burdening the source. The typical input resistance of an Electrometer (eg model 6517B) is about 200TΩ (=2x10E14 Ohm). The input noise is below 1fA (1x10E-15A).
With these attributes, Electrometers are perfect tools for measuring extreme small currents in modern semiconductor physics or material research. Of course Electrometers are also suitable for the precise measurement of extreme high resistances above 1GΩ. Measurements on isolation materials, transformer oils or dielectrics can be done up 10E17 ohms.