Measuring Ac Voltage; Induced Interference; Common Mode Rejection; Lead Considerations - Fluke 8508A User Manual

Measuring AC Voltage

Induced Interference

If inference signals are present or lead pickup takes place during AC measurements, any
induced interfering signals will combine with the signal being measured and result in
measurement errors. In some circumstances, it may be possible to filter out the unwanted
external signals, but it is generally more effective to reduce the interference before it is
induced. This is most easily accomplished by operating in a quiet environment, e.g.,
using a screened cage and, if possible, using twisted or shielded measurement leads as
discussed below.

Common Mode Rejection

The principles of external guarding, outlined in the description of DC voltage
measurement, apply generally to AC voltage measurement. For AC a further advantage
can be gained by using the external guard as a shield for the input leads.

Lead Considerations

In all cases, AC voltage measurement accuracy is improved by shortening the leads to the
minimum practical length to reduce lead capacitance, lead inductance and loop area.
Shielded twisted pair leads are recommended for low frequency measurements and
coaxial leads are recommended for low and high frequency measurements. Users should
take care to avoid measurement errors from the interaction of lead capacitance and
inductance with any source output impedance. Additional information and guidance is
available in the Fluke publication Calibration: Philosophy in Practice
(ISBN 0-9638650-0-5).

Resistance

Press Ω to go to the OHM menu.
This function provides both 2-wire and 4-wire measurements, in decade


ranges from 2 Ω to 2 GΩ.
To cancel autoranging and enter a manually selected range, press any range


selection or the Auto softkey. The Multimeter enters the selected range or
reverts to the auto-selected range.
OHM Menu
Making Measurements
Using the Measurement Functions
adj073f.eps
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