Philips PM3219/01 Notice D'emploi page 24

1.5.4.
7.5.5.
1.5.6.
27
SINGLE sweep triggering is useful for observing effects that occur only once. In this event, it is often desirable
that only one sawtooth is generated, even though several trigger pulses may be produced after the pheno-
menon of interest. When the SINGLE pushbutton is depressed, the first trigger pulse that appears triggers the
MTB. The RESET pushbutton allows the SINGLE action to be set for the next event.
When either DC or AC is selected, AUTO is inoperative. Sweeps are then only produced when a trigger signal is
present and the LEVEL control is set correctly.
The hold-off circuit, as its name implies, 'holds off' trigger pulses from the MTB input until the flyback trace
has completely returned and the time-base circuits are completely reset.
The TIME/DItV switch positions control the speed of the time-base sweep in a 1-2-5 sequence together with
the uncalibrated continuous control.
Setting the TIME/DIV switch in the X DEFLECTION position inhibits the main time-base output of the
FINAL X AMPLIFIER and permits horizontal deflection from another source.
Delayed Time-base Triggering
The pushbuttons associated with the DELAYED TIME-BASE TRIGGER SELECTION circuit enable trigger
signals to be derived from the A and B vertical channel amplifiers, externally and from the MTB. Composite
triggering on A and B is also available from the delay-line driver stage of the Y amplifier channels. AC and DC
coupling is provided by the TRIGGER AMPLIFIER.
A LEVEL/SLOPE control for the DTB provides the same functions as that for the MTB circuit.
Selection of the MTB pushbutton enables the delayed time-base to start directly after the delay time
determined by the setting of the DELAY TIME control on the COMPARATOR circuit.
Delayed Time-base
The DELAYED TIME-BASE is operative unless its TIME/DIV switch is in the OFF position, and starts imme-
diately after the selected delay time, or on receipt of the first trigger pulse after the delay time.
In the COMPARATOR, the sawtooth signal derived from the MTB is compared with an accurately adjustable
d.c. voltage, controlled by the ten-turn DELAY TIME potentiometer.
The comparator output produces the required delay pulse for the sweep-gating logic of the DTB generator to
initiate the sawtooth voltage.
The delayed sweep is reset by the hold-off circuit of the DTB (end of sweep detection) or by the MTB.
After the start of the next main time-base sweep, the delayed sweep is started again by the output signal from
the comparator.
When the MTB pushbutton of the horizontal deflection mode controls is selected, the part of the trace that
coincides with the delayed sweep is intensified.
When the ALT TB mode is selected (pushbuttons DTB and MTB selected together) an electronic switch in the
HORIZONTAL CONTROL LOGIC enables the MTB and DTB to be alternately traced on the screen, by
switching the vertical channel bistable muitivibrator.
The two displays can be separated by varying the voltage applied to the FINAL Y AMPLIFIER from the driver
circuits of the electronic switch, using the front-panel TRACE SEPARATION control.
Storage Circuits
The STORAGE CONTROL circuits provide the voltage levels and waveforms that are necessary for the storage
operation.
Retention of the stored signal on the memory mesh of the c.r.t., which carries the storage layer, is controlled
by a variable duty-cycle square-wave generator. The duty-cycle depends on the PERSISTENCE control setting,
and storage takes place in the WRITE position (released) of the READ/WRITE pushbutton.
The ERASE pushbutton is only operative in the WRITE mode.
The AUTO STORE facility enables single-shot signals to be stored for very long periods (in excess of 24 hours).
The READ mode enables the captured signal to be stored for display. The signal display intensity can be varied
by the BRIGHTNESS VIEW TIME potentiometer.