Amprobe 38XR-A User Manual page 23

True-rms Measurements
For ac measurements most DMMs average the ac
input signal and display the result as an estimated rms
value. This average-responding method is accurate
for sinusoidal waveforms, but can be very inaccurate
for distorted waveforms. To ensure the most accurate
measurements, always use a true-rms DMM when
measuring ac voltage or ac current on circuits for the
following kinds of applications:
• Power Supplies - diodes
• Controllers
• Power Limiting - SCR or Triac
• Starting - motors
• Florescent Lighting - ballasts
• Speed Control - motors
• Pulsed Signals
• Any non-sinusoidal ac waveform
The 38XR-A displays the dc, ac, or ac+dc components of
a voltage or current measurment. The dc component
is the shift level or baseline. The ac component is the
area under the waveshape. The ac+dc component is the
combined effect of the ac and dc components.
MIN MAX AVG Measurements
Note: The MIN MAX AVG feature does not work the dBm
nor the dutycycle function.
The MIN MAX AVG feature reads and updates the display
to show the maximum, minimum, or average value
measured after you press the MIN MAX AVG button.
Pressing the MIN MAX AVG button for less than 1
second will put the meter into a mode of displaying the
maximum, minimum, average, or actual readings. Each
time the button is pressed, the meter will cycle to the
next display mode as shown in the table below. Press the
MIN MAX AVG button for more than 2 seconds to disable
this feature.
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