Section IV Model 185B
Paragraphs 4-85 to 4-87
TRIGGERS
TO 220K
SAMPLING
PLUG-IN
- R255A
RAMP RESET TRIGGER PULSE f fm
iy-
RAMP-SATE
EXTENDER
MULTIVIBRATMI
RAMP
RESET
PULSE r
t 250VF I-
1 STAIRCASE I
I4
RESET I-
PULSE BLOCK. OX. I
AMPLlf IER I
1-
I
TUNNEL
DIODE
FIT RAMP RESET
DELAY
REFERENCE
SENERATOR
I0-L-m
Figure 4-7. Time-Base Block Diagram
marks the time of coincidence. The resulting current a. The time scale in sec/cm is the value selected
through Q205 and CR209 exceeds IP (figure 4-3), by the TIME SCALE switch when no attenuation is
CR209 changes state (paragraph 4-29), and the volt-
age across CR209 rises.
4-65. As mentioned above (paragraph 4-61), this
pulse from CR209 (the comparator pulse) lasts until
ramp reset blocking oscillator Q203 resets the ramp.
Meanwhile the horizontal-scan generator has stepped RAMP
VOLTAGE
the Q206 base voltage to a slightly more positive value,
the actual step amplitude depending on the setting of
SCAN DENSITY. When the next trigger arrives the
ramp again takes its initial voltage step to -0.2 volt
and then rises linearly (this time alittlefarther) until I I I
G-S-554
the base voltage or 4205 again reaches coincidence tl 5' t3
with that of Q206. The comparator fires again, and TIME -
the process continues until a horizontal sweep is
completed. Figure 4-8. Ramp Voltage vs Time
inserted (by TIME SCALE MAGNIFIER and/or its
4-66. TIME SCALE/MAGNIFIER RELATIONSHIP.
VERNIER) between the scan voltage at the input to
the horizontal amplifier and the scan voltage applied
4-67. The following discusses why time scale is de- to the base of Q206 in the comparator.
pendent only on the slope of the ramp (determined by
the setting of TIME SCALE) and attenuation of the b. Any particular level of voltage applied to the
horizontal-scan voltage (determined by the setting scan-voltage side (base of Q206) of the comparator
of TIME SCALE MAGNIFIER). There are two im- represents a particular point in time (paragraph
portant p9ints to remember when thinking about the 4-58), as measured from the startof the ramp. There-
TIME SCALE/TIME SCALE MAGNIFIER relationship: fore any change in the voltage applied to the Q206
4-8 01255-1 |