Philips PM3350A - Page 49

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4 APPLICATIONS
- Trigger Slope selection
by pressing the f\ key.
For triggering on a positive-going slope select,/", for triggering on a
negative-going slope select"V.
II trigger coupling TVF or TFL is selected, LCD indicates -I- and - instead ofj^
and\.
+ = positive video,
- = negative video.
If horizontal mode X DEFL is selected, LCD indicates + and • instead of f and\
-I- = signal not inverted,
- = signal inverted.
- Hold-off time
by using the HOLD OFF rotary knob.
The HOLD OFF rotary knob is used to prevent "false" triggering and "double
writing" when examining multiple pulse signals. After the horizontal sweep is
completed triggering is inhibited for period of time set by the HOLD OFF knob.
Adjustment of the HOLD OFF enables triggering to be synchronized on the same
pulse in the pulse train and so gives a stable display.
For example, consider a double pulse repetitive input signal. The selected trigger
signal sees the same condition on the second pulse as the first pulse, and so the
time base sweep starts too soon. The double-writing effect is seen as an
extended base-line on the upper trace.
Adjusting the hold-off time will inhibit the trigger unit until it sees the first pulse
again.
4.1 USE AS AN ANALOG OSCILLOSCOPE