GxT Ferret 92 Color Labscope - Manual (Page 18)

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Coupling:
There are two coupling options, AC and DC. The best way to explain
coupling is to look at the AC & DC coupling rules:
1. Pure AC voltage will be displayed the same when either AC or
DC coupling is selected. See Fig. 1 (AC Coupled) & Fig. 2 (DC
Coupled)
2. Pure DC voltage will be displayed with 0 volts on the ground
line and positive voltage above the ground line when DC coupling
is selected. See Fig. 3
3. Pure DC voltage, such as battery voltage, will be displayed on
the ground line and varying DC voltage will be displayed above
and below the ground line equally when AC coupling is selected.
See Fig. 4
This capture is the same signal shown in Fig. 3, but this time AC
coupling was selected. This varying DC voltage is displayed above
and below the ground line equally, so we have no real visual reference
to ground or voltage level. If we were looking at a constant voltage, or
pure DC voltage, it would be displayed on the ground line regardless
of voltage level, so we would have no indication of voltage level. In
either case, DC coupling would usually be the best choice.
4. When AC coupling is selected the constant component of the
signal will be blocked and only the alternating component of the
signal will be displayed. See Fig. 5
This is a capture of AC voltage riding on a DC signal. As you can see,
only the AC voltage, which is the alternating component of the signal
is displayed. The constant component of the signal is the DC voltage
level and is not displayed. If we had used DC coupling here, the AC
ripple would be displayed at the DC voltage level rather than on the
ground line, so we would know what the DC voltage level was.
Ground location:
The Ferret 92 scope offers two options for ground location. With AC
coupling, ground is always in the middle of the channel. We would
also select this ground location to view any signal where voltage drops
below ground. Ground at the bottom of the channel is used when you
want added vertical resolution and works well when viewing multiple
channels on the display.
Ferret 92 Display:
See Fig.6 - The highlighted bars on either side of the display are called
channel labels and show the various settings that have been selected.
If multiple channels were being displayed, they would be stacked
vertically and each would have its own channel labels.
On the left channel label, starting at the top, you will see the Channel
Number, Voltage Scale, Ground Location and Coupling selections. If
ground at the bottom had been selected the ground indicator would
be at the bottom of the label. The settings shown on the left channel
label apply to only that channel and may be set differently for each
channel being displayed.
On the right label you will see the Time Base and Trigger selections,
followed by the Trigger Level setting. The small arrow just below the
Time Base shows the actual Trigger Level on the display. The settings
on the right channel label apply to all channels. All channels will have
the same time base and use the same trigger. You may have different