Model 175A
Section IV
Paragraphs 4-34 to 4-41
diode CR106. The switch diode returns the input of
integrator V106 to its pre-sweep level, discharging
the sweep capacitor.
4-35. During a sweep time, hold-off cathode follower
V105B charges a hold-off capacitor. After the sweep
ends, this capacitor lets the input to gate generator
V103/V104A down slowly enough to prevent that cir-
cuit from being triggered again until the remaining
sweep circuits have recovered completely. The
I SWEEP TIME switch changes the size of the hold-off
capacitor with sweep time.
4-36. Clamp V104B ensures that each sweep starts
INPUT from the same voltage level, about -50 volts.
m
OUTPUT 4-37. The SWEEP MODE control R172 (figure 5-22)
determines the no-signal bias at the input to gate gen-
A. CIRCUIT erator V103/V104A by setting the bias on the A sec-
tion of bias control cathode follower V109. With the
control set to PRESET or in the TRIGGER portion of
its adjustable range, the gate generator bias cannot
drop below its lower hysteresis limit unless the trig-
ger generator provides a trigger. With the control
set in the FREE RUN portion of its adjustable range,
the gate bias is allowed to drop below its lower hys-
teresis limit. Thus as the hold-off capacitor dis-
charges, it lets the gate generator bias all the way
down to the lower hysteresis limit, and another sweep
starts automatically.
4- 38. SINGLE - SWE EP OPERATION.
4-39. The SWEEP OCCURRENCE switch (on the panel
of the horizontal plug-in unit) selects normal or
V single-sweep operation. Normal operation is dis-
cussed above. For single-sweep operation, the
B. COMPOSITE CURVE LO - M - 643
SWEEP OCCURRENCE switch converts V109 into a
Schmitt circuit. As the sweep signal from hold-off
cathode follower V105B rises to end the gate from
Figure 4-5. Trigger Generator Simplified Circuit
the gate generator, the sweep signal also switches
and Composite Characteristic
the Schmitt circuit of V109 so that V109B conducts
and V109A is cut off. The B section of V109 then
holds the input to gate generator V103/V104A high
enough so that triggers from the trigger generator
change in voltage at the input to integratorV106 dur-
cannot actuate the gate generator, and the sweep
ing the sweep time is only about one volt. Voltage A pos-
generating circuits are effectively disabled.
across the sweep resistor, then, changes by about
itive signal applied to V109A switches the Schmitt
1%, and the current through the resistor changes by
circuit of V109 so that V109A conducts and V109B is
the same amount. The current through the sweep
cut off. The A section of V109 then sets the input to
resistor is the charging current for the sweep capaci-
the gate generator according to the setting of the
tor; therefore, the voltage across the sweep capacitor
SWEEP MODE control, and the sweep generating cir-
changes quite linearly with time, and the sweep sig-
cuits are effectively armed. The switching signal
nal is a nearly linear voltage ramp. The SWEEP
for V109A can be an external signal applied to the
TIME switch changes the value of sweep resistor or
ARMING INPUT connector or an internal signal ob-
capacitor to change the sweep time. The sweep out-
tained by switching SWEEP MODE control out of its
put is applied to the horizontal amplifier through the
PRESET position.
horizontal plug-in.
4-40. SCHMITT TRIGGER CIRCUIT.
4-34. An attenuated sweep signal is applied to the 4-41. The Schmitt trigger circuit is a form of bi-
input of gate generator V103/V104A through hold-off stable multivibrator used where fast-rising signals
cathode follower V105B and section B of bias control are required. Figure 4-6 shows a simplified Schmitt
cathode follower V109. This signal drives the input trigger circuit and input and output waveforms. If
of the gate generator up to the upper hysteresis limit initially the input voltage is such that V1 is cut off,
and causes the gate generator to switch back to its V2 conducts. As the input voltage becomes more pos-
pre-sweep state. The gate generator then ends the itive, it will eventually reach a predetermined level
the gates, blanking the crt and forward biasing switch (a) at which the circuit changes state; V1 conducts
01526-2
4-4 |
ACEC
