Dc Current Measurement Errors; True Rms Ac Measurements - HP E1312A User Manual

DC Current Measurement Errors

True RMS AC Measurements

32 HP E1312A/E1412A Multimeter Application Information
When you connect the multimeter in series with a test circuit to measure
current, a measurement error is introduced. The error is caused by the
multimeter's series burden voltage. A voltage is developed across the wiring
resistance and current shunt resistance of the multimeter as shown below.
True responding multimeters, like the HP E1312A and HP E1412A,
RMS
measure the "heating" potential of an applied signal. Unlike an "average
responding" measurement, a true
determine the power dissipated in a resistance, even by non-sinusoidal
signals. The power is proportional to the square of the measured true
voltage, independent of waveshape. An average responding ac multimeter is
calibrated to read the same as a true
other waveform shapes, an average responding meter will exhibit substantial
errors as shown below.
The multimeter's ac voltage and ac current functions measure the ac-coupled
true value. This is in contrast to the ac+dc true
RMS
Only the "heating value" of the ac components of the input waveform are
measured (dc is rejected). For non-offset sinewaves, triangle waves, and
square waves, the ac and ac+dc values are equal since these waveforms do
not contain a dc offset. Non-symmetrical waveforms, such as pulse trains,
contain dc voltages which are rejected by ac-coupled true
measurements.
An ac-coupled true
RMS
are measuring small ac signals in the presence of large dc offsets such as
when measuring ac ripple present on dc power supplies. There are situations,
however, where you might want to know the ac+dc true
measurement can be used to
RMS
meter for sinewave inputs only. For
RMS
measurement is desirable in situations where you
RMS
value shown above.
RMS
RMS
value. You can
RMS
Chapter 2