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TM 11-6660-204-25
the input to the detector circuit (para 213d).
resistor R209; and the third is through slide-wire
Discharge current through load resistors R203
potentiometer R501B.
and R207 will be proportional to the voltage built
b. Path B is replaced with potentiometer B (fig.
up across the
capacitor combination.
2-10), which represents the slide-wire circuit.
The zero adjust circuit is eliminated. The resist-
e. The voltage across the
capacitor combi-
ance from the wiper arm of potentiometer R202,
nation is directly proportional to the charge (in
through either leg to circuit ground, depends on
coulombs ) stored there which, in turn, is directly
the position of the arm (fig. 210). The sum of
proportional to the rate it receives pulses, because
the currents in path A and path B is practically
each pulse delivers a uniform charge. The dis-
constant, so the current in path B is proportional
charge current at any instant is almost equal to
to the resistance in path A, and is adjusted by
the voltage across the capacity divided by 385
potentiometer R202. The voltage across the slide-
(the resistance of R203) ; this value would not be
wire can be changed by adjusting potentiometer
exact because of the slight effect of the calibrating
R202, the position of the balance point can be
voltage and current involved in resistor R207.
changed with a corresponding change of the re-
These facts all indicate an output voltage that is a
corder pen position. This method is used to align
linear function of the audio frequency of the ini-
t h e reference (calibration) signals with the
tial input signal to the converter, and can be cali-
correct frequency indication on the chart. The
brated on a suitable indicator.
voltage from the slide-wire circuit is fed to the
center tap of the primary of transformer T302
f. The output voltage (that potential which ex-
ists mainly across resistor R207, because resistor
(fig. 2-9) through trolley-wire resistor R501A,
where it is compared with the dc voltage devel-
R203 is comparatively very small) will range
oped by the input signal.
from near 0 to approximately 30 millivolts, which
is again filtered before being applied to the vibrat-
c. The recorder test circuit consists of two re-
ing reed of inverter G301 (para 213).
sistors, R210 and R212, in series with REC.
TEST ADJ. potentiometer R211 and is in parallel
with the slide-wire, The wiper arm of potentiome-
2-12. Measuring Circuit
ter R211, as determined by the resistance values,
will control 91 to 97 percent of the voltage being
applied to the slide-wire, through the contacts of
The measuring circuit provides a dc voltage of
REC TEST Switch S204 to the vibrator, Poten-
approximately 30 millivolts across slide-wire po-
tiometer R211 is adjusted so the recorder pen will
tentiometer R501B. This is used as a comparison
print at 95 chart divisions.
voltage for the dc signal voltage developed across
load resistor R203. Slide-wire potentiometer
d. The zero adjust circuit (path C, fig. 29) is
R 5 0 1 B and trolley-wire resistor R501A are
similar to the reference voltage circuit explained
mounted on a common shaft in the frequency-time
in b above. A voltage, determined by the position
recorder chassis. The common shaft is mechani-
of the wiper arm of REC. ZERO potentiometer
cally coupled to balancing motor B501, recorder
R208, is obtained across resistor R207. The volt-
pen, and the indicator pointer. The remaining
age across resistor R207 is applied through load
parts of the measuring circuit are mounted on the
resistor R203 to detector circuit G301 and is used
control panel. Zero adjust and recorder test cir-
to balance out the slight voltage from the slide-
cuits are also included in the measuring circuit,
wire circuit when the recorder pen is at zero and
the slide-wire wiper arm contact is about one-half
a. Current from the regulated +300 volts is fed
of one percent of full scale position from the
t o the arm of REF. ADJUST potentiometer,
ground end of the slide-wire resistance.
R202, through R201. The current flowing through
potentiometer R201 is divided into two main cir-
2-13. Detector and Balancing Circuit
cuits (paths A and B, fig. 2-9). (A slight current
(figs. 2-9,2-11, and FO-2)
which flows through path C is considered later. )
Path A is through resistor R206 to ground. Path
The detector circuit detects any difference (or
B is through resistor R205 and then divides into
error) between the millivolts of potential created
three parallel resistive paths to ground. One
by the incoming signal and fed to the vibrating
branch is through a series circuit which consists
reed of G301, and the potential delivered by the
of resistors R210, R212, and REC. TEST ADJ.
wiper arm of the slide-wire potentiometer to the
potentiometer R211; another branch is through
center tap of the primary of transformer T302.

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