Solid-state electrometers are often multipurpose devices that can measure voltage, charge, resistance and current. They measure voltage by means of "voltage balancing", in which the input voltage is compared with an internal reference voltage source using an electronic circuit with a very high input impedance (of the order of 1014 Ω). A similar circuit modified to act as a current-to-voltage converter enables the instrument to measure currents as small as a few femtoamperes. Combined with an internal voltage source, the current measuring mode can be adapted to measure very high resistances, of the order of 1017 Ω. Finally, by calculation from the known capacitance of the electrometer's input terminal, the instrument can measure very small electric charges, down to a small fraction of a picocoulomb.
Solid-state electrometers are often multipurpose devices that can measure voltage charge resistance and current They measure voltage by means of "voltage balancing" in which the input voltage is compared with an internal reference voltage source using an electronic circuit with a very high input impedance (of the order of 1014 Ω) A similar circuit modified to act as a current-to-voltage converter enables the instrument to measure currents as small as a few femtoamperes Combined with an internal voltage source the current measuring mode can be adapted to measure very high resistances of the order of 1017 Ω Finally by calculation from the known capacitance of the electrometer's input terminal the instrument can measure very small electric charges down to a small fraction of a picocoulomb