Selecting AC, DC or GND
- The CRO has two of these selection switches (one
for each input channel ). They are used to select the
characteristics of the input signal that we want to view
on the CRO display.
The selector switch has three positions, A.C. D.C. and
GND, all of which are detailed below:
1.The A.C. Position:
- When the A.C-GND-D.C selector is in the A.C.
position the CRO input signal is said to be A.C. coupled.
- A.C coupling means that only A.C. signals are
allowed to pass from the input terminal through to the
measuring devices within the CRO. This is achieved by
passing the input signal through a large capacitor which
"blocks" any D.C. component of the incoming
|Pro's And Cons of the A.C.
- Can be used to view A.C. ripple in a D.C.
signal as it allows us to focus only on the
ripple itself at any magnification without the
signal being moved off the display by a large
D.C. offset. (e.g 7V
D.C. with 20mV ripple)
- This method distorts A.C. signals that
have a low frequency. This is due to the charging
and discharging of the large capacitor that is
used to effect A.C. coupling. An example of this
can be found by clicking here.
2. The GND
- When the GND position is selected the input
terminal is completely isolated from the display. The
trace on the display becomes a horizontal line that
corresponds to an input that is grounded.
- This is only useful when the zero position of the
trace requires adjusting using the Trace Vertical
Position Control. More information
concerning the adjustment of the vertical position of the
trace can be found by following the previous link and
checking the link to the display.
3. The D.C. Position:
- The D.C. position is the "fool proof"
setting to have the input signal set to. This is because
when this setting is used the input signal is able to
pass directly to the display unchanged.
- The only problem with this arrangement is that
there may be occasions where the D.C. component of a
signal would be a hinderance to the accurate measurement
of the A.C. component of the same signal. An example can
be found by following this link.
to CRO Features
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Revised: 15 September 2004