Any meter will load the circuit under test to some extent. For example, a multimeter using a moving coil movement with full-scale deflection current of 50 microamps (μA), the highest sensitivity commonly available, must draw at least 50 μA from the circuit under test for the meter to reach the top end of its scale. This may load a high-impedance circuit so much as to affect the circuit, thereby giving a low reading. The full-scale deflection current may also be expressed in terms of "ohms per volt" (Ω/V). The ohms per volt figure is often called the "sensitivity" of the instrument. Thus a meter with a 50 μA movement will have a "sensitivity" of 20,000 Ω/V. "Per volt" refers to the fact that the impedance the meter presents to the circuit under test will be 20,000 Ω multiplied by the full-scale voltage to which the meter is set. For example, if the meter is set to a range of 300 V full scale, the meter's impedance will be 6 MΩ. 20,000 Ω/V is the best (highest) sensitivity available for typical analog multimeters that lack internal amplifiers. For meters that do have internal amplifiers (VTVMs, FETVMs, etc.), the input impedance is fixed by the amplifier circuit.
Any meter will load the circuit under test to some extent For example a multimeter using a moving coil movement with full-scale deflection current of 50 microamps (μA) the highest sensitivity commonly available must draw at least 50 μA from the circuit under test for the meter to reach the top end of its scale This may load a high-impedance circuit so much as to affect the circuit thereby giving a low reading The full-scale deflection current may also be expressed in terms of "ohms per volt" (Ω/V) The ohms per volt figure is often called the "sensitivity" of the instrument Thus a meter with a 50 μA movement will have a "sensitivity" of 20000 Ω/V "Per volt" refers to the fact that the impedance the meter presents to the circuit under test will be 20000 Ω multiplied by the full-scale voltage to which the meter is set For example if the meter is set to a range of 300 V full scale the meter's impedance will be 6 MΩ 20000 Ω/V is the best (highest) sensitivity available for typical analog multimeters that lack internal amplifiers For meters that do have internal amplifiers (VTVMs FETVMs etc) the input impedance is fixed by the amplifier circuit