Valve electrometers Valve electrometers use a specialized vacuum tube (thermionic valve) with a very high gain (transconductance) and input resistance. The input current is allowed to flow into the high impedance grid, and the voltage so generated is vastly amplified in the anode (plate) circuit. Valves designed for electrometer use have leakage currents as low as a few femtoamperes (10−15 amperes). Such valves must be handled with gloved hands as the salts left on the glass envelope can provide leakage paths for these tiny currents.
valve electrometers valve electrometers use a specialized vacuum tube (thermionic valve) with a very high gain (transconductance) and input resistance the input current is allowed to flow into the high impedance grid and the voltage so generated is vastly amplified in the anode (plate) circuit valves designed for electrometer use have leakage currents as low as a few femtoamperes (10−15 amperes) such valves must be handled with gloved hands as the salts left on the glass envelope can provide leakage paths for these tiny currents