Sy
halfeanplituce cutoli frequency of +S cps.
a filter volume with a dleeler
provides a low-frecuenmcy cutoff (half power) of 0.0079 cps on the sensing
head.
Sensing is ome Sy a teisted Sourdca etude carrying an araatere ia the
fiel2 of a reluctance Sriczsge bawing four active arms.
Changes ia the araature
modulate a O75-cps carrier whica is tramsziticd through a four-coacuctor cable
to che receiver up to 3 2aile away.
At che receiver,
the sodulared signal is
inpressed across a sensitivity-rasyge attemuator with eight full-scale settings
froa 4 co 12,000 zicrobars.
After range attemoation, the signal is amplified
to about 50 volts by a conventional four-stage, resistance-coupled aaplifier.
A phase-sensitive dematulator cemodulates the signal and sends it to an adjustable band-pass filter, which attenuates aost of the poise while agintaining most of the signa! at mearly full amplitude.
The filtered signal is next
amplified by two DC aaplifiers in parallel, one of which has four times the
gain of the other.
These azplifiers drive the pens of two Brush recorders.
A side pen on the recorders marks I-, 10-, and 1W-second intervals on signal
froma a Cise-maork generator.
Since the range setting of the attenuator aad
the cising on the record are known, the record can be interpreted for amplitude and period.
This time-aark generator has been added to the system since the reports
teferred to above 19727 were writtaa and is therefore described in some detail.
The time-nark generator drives the marker pens on both Brush recorders at a
l-second rate and identifies by length every teoth and hundredth l-second
Pulse.
The equipment sazing up the time-aark generator consists of a Type
2001-2D frequency-standard time box manufactured by American Tine Products,
Inc.,
four Type 7OOA Berkeley decade scalers, phase-inverting amplifiers,
monostable cultivibrators, and a power supply.
The output of the ¢O001-2D time box is taken from the grid circuit of the
cathode follower ourpuc tube in tae form of nezative-going, GO-vole pulses at
100 cps.
This output drives a Type 7OOA decade scaler, the 10-cas output of
which drives a second ececade scaler.
The l-cps output from the second JOOA
drives both a third 7OOA and a phase-inverting anplifier stage whica triggers
a oonostable saultivibrator.
The output of this culcivibrator is a positive-
going volrage, 0.1 second wide, that energizes a relay coil for 0.1 second.
Tue seisy cuntaccs connect a O-volt DC power supply co the side-asrking pens
on beth Brush recorder? «nich are, in turn, ceflected for 0.1 second to record