Fluke CombiScope PM3370B User Manual page 59

4 - 14
VERTICAL COUPLING
The input coupling after AUTOSET is ac. Since the Probe Adjust signal is a pulse
type signal with a 50% duty cycle, its mean value is at the signal's 50% amplitude
level. When the input is ac coupled, the mean value will be displayed at the
ground level of the oscilloscope. As a result of this, the displayed waveform is
centered on the screen.
AC coupling can be used to examine small ac components that are superimposed
on large dc voltages.
- Press the AC DC GND key once for DC input coupling.
Since the Probe Adjust signal is a pulse-type signal with a lower level of 0V, and
a higher level of 600 mV, and since the oscilloscope adjusts the display position
of the ground level to coincide with the screen center, switching from ac coupling
to dc coupling results in an upward shift of the display position of the signal.
The coupling sign in the lower left hand corner of the screen changes from
to = (dc).
The ground level for each of the channels is indicated by a dash after the channel
identifier, i.e., '1-' for the ground level of channel 1.
AUTO SET
1-
AC DC
GND
CH1 200mV
AC Coupled
- Press the AC DC GND key to obtain ground coupling.
A straight line is now displayed. This is the 0V (ground) level of the input. This
level serves as the 0 volt reference for amplitude measurements.
The coupling sign ' ' now indicates ground coupling.
HOW TO USE THE INSTRUMENT
0.5ms
Input Signal
AC DC
GND
1-
CH1 200mV
DC Coupled
AC, DC, GND
600mV
0V
AC DC
GND
1-
CH1 200mV
GND Coupled
(ac)
ST6708