Philips PM3320 Operating Manual page 137

A-Q1E
Trigger section
This oscilloscope can be triggered via signals which are internally derived irom channel A or
channel B and via two externally applied input signals.
The EXTERNAL trigger signal must be applied to the EXT TRIG. input and is then fed to the
TRIGGER SOURCE SELECTOR together with the LINE
signal, which is a mains-voltage related trigger signal from the POWER SUPPLY.
In the TRIGGER SOURCE SELECTOR the different trigger sources are selected by the
pushbutton (TRIGGER) SOURCE.
When pushbutton SOURCE is pressed, the following trigger sources can be selected via the
softkeys:
-A : trigger derived from channel A
-B : trigger derived from channel B
- EXT : trigger derived from EXT TRIG input
~ EXT:10 : trigger derived from EXT TRIG input divided by 10
- LINE : trigger derived from the mains voltage
The selected trigger signal is fed to the TRIGGER AMPLIFIER where the trigger coupling, trigger
level and trigger slope is determined by respectively the frontpanel controls: COUPLING, LEVEL
AND NEGATIVE SLOPE.
The pushbutton COUPLING makes via the softkeys the selection of the following junctions
possible:
- AC-DC AC : DC components are blocked.
DC : fulf trigger bandwidth
- AUTO : The level range is determined by the signal amplitude (peak-peak
triggering)
~- VF : Television Frame signal synchronisation
~ LF reject : LF trigger signals are rejected (up to 50 kHz)
- HF reject : HF trigger signals are rejected (higher than SO kHz)
- SLOPE + - : trigger slope selection: positive or negative (can also be selected with
button NEGATIVE SLOPE)
- DUAL : triggering on both positive and negative slope of trigger signal
The LEVEL control determines the level of the trigger signai on which an output signal is
generated to the ACQUISITION AND CONTROL LOGIC, to start the signal conversion.
The AUTO PEAK-PEAK DETECTOR and the TRIGGER LOGIC are controlled for AUTO LEVEL
mode (peak-peak triggering) via the MICROPROCESSOR MANAGEMENT INTERFACE.
For AUTO OFFSET mode the mean value of the trigger signal is fed via the MICROPROCESSOR
MANAGEMENT INTERFACE to the microprocessor to calculate the AUTO-OFFSET level.
Trigger moments can be delayed by events which can be applied to the EVENTS/EXT CLOCK
input socket.
The LEVEL on which these external EVENT signals pass the EVENTS AND EXTERNAL CLOCK
circuit is determined by the LEVEL contro! via the EVENT LEVEL signal coming from the
MANAGEMENT INTERFACE.
These EVENTS are fed to an EVENT COUNTER in the ACQUISITION AND CONTROL LOGIC.
The oscilloscope can operate on an external clock signal, which is applied to the EVENTS/EXT
CLOCK input socket. The LEVEL on which the external clock signai passes is determined in the
same way as the event level. The externai clock signal is fed to the ACQUISITION AND CONTROL
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