G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
G01R19/0046—Arrangements for measuring currents or voltages or for indicating presence or sign thereof characterised by a specific application or detail not covered by any other subgroup of G01R19/00
G01R19/0076—Arrangements for measuring currents or voltages or for indicating presence or sign thereof characterised by a specific application or detail not covered by any other subgroup of G01R19/00 using thermionic valves
G—PHYSICS
G01—MEASURING; TESTING
G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
G01R17/00—Measuring arrangements involving comparison with a reference value, e.g. bridge
G01R17/10—AC or DC measuring bridges
G01R17/16—AC or DC measuring bridges with discharge tubes or semiconductor devices in one or more arms of the bridge, e.g. voltmeter using a difference amplifier