GW Instek GOS-652G - Manual (Page 30)

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4.10 Waveform Magnification with Delayed Sweep(623G/653G/658G only)
With sweep magnification of the preceding paragraph, although the magnification method is simple, the magnification ratio is limited to
10. With the delayed sweep method of this paragraph, the sweep can be expanded for a wider range from several times to several thousand
times according to the ratio between A sweep time and B sweep time.
As the measured signal frequency increases, the A sweep range for the non-expanded signal becomes higher whereas the available
expansion ratio becomes smaller. Furthermore, as the magnification ratio becomes larger, the trace intensity becomes lower and the delay
jitter increases. To cope with these situations, a continuously variable delay circuit and a triggering delay circuit are incorporated into the
oscilloscope.
(1) Continuous variable delay
Set the HORIZ. DISPLAY MODE switch to A and display the signal waveform with the A sweep in the regular operation mode. Next,
set the B TIME/DIV switch to a position several steps faster than that of the A TIME/DIV switch. After ensuring the B TRIG’D button of the
HORIZ. DISPLAY MODE switch is disengaged, engage the HORIZ. DISPLAY MODE switch to the A INTEN position. A portion of the
displayed waveform will be accentuated as shown in Figure 4-14, indicating the state ready for delayed sweep. The portion of the
accentuated brightness indicates the section corresponding to the B sweep time (DELAYED SWEEP). This portion is expanded on the B
sweep.
The period from the start of the A sweep to that of the B sweep (the period to the start of trade accentuation) is called “SWEEP DELAY
TIME”. This period is continuously variable by means of the DELAY TIME POSITION knob. Next, change the HORIZ.DISPLAY MODE
switch to the B position. The B sweep time will be expanded for the full span of the CRT screen as shown in Figure 4-15. The B sweep time
is set by the B TIME/DIV switch, the magnification ratio becomes：
A TIME/DIV indication
Magnification =
B TIME/DIV indication
(2) Triggering delay：
When the display waveform is magnified by 100 or higher in the above-mentioned continuous delay method, delay jitter is produced.
To suppress the jitter, the triggering delay method may be used. With the triggering delay, delay jitter is reduced by triggering the B sweep
again, after a sweep delay time as effected by the continuous delay method has elapsed.
For this operation, the A trigger circuit continues to operate even after the B TRIG’D button is engaged and the B sweep is triggered by
the triggering pulse. Therefore, even when the delay time is continuously varied by turning the TIME DELAY POSITION knob, the starting
point of the sweep moves discretely, not continuously. In the A INTEN mode, this operation is characterized by the discrete shifts of the
brightness-accentuated section of sweep across the CRT screen; while in the B mode this section remains stationary.