IEEE Power & Energy Magazine - March/April 2015 - 84

initiated automatically by the dispatching equipment (see Figure 4).
Unique to the Grand Central Terminal end of the automatic shuttle was the
use of two ultrasonic vehicle detectors.
These operated by means of a pulsed
20-khz signal beamed at the train via
a transmitter transducer and received
by a receiver transducer when reflected
by the presence of the train or from the
empty track space. The detectors were
used to ensure proper station stopping or
"berthing." Vacuum tubes were used in
that system.
Train detection and the transmission of coded speed commands to
the automatic train was performed by
six single-rail coded alternating current (ac) track circuits. GRS furnished
three of the track circuits on the Grand
Central end to the midpoint of the line,
and US&S furnished the remaining
three track circuits to Times Square.
The track relays operated from 60-hz
power, and the speed commands were

injected directly into the rail through a
transformer. The carrier frequency for
speed commands was 91-2/3 hz supplied by a normal and reserve inverter
with automatic transfer in the unlikely
event of an inverter failure. The normal
and reserve inverters were located in a
wayside case on the Times Square end
of the shuttle and powered by storage
batteries, which, with the carrier equipment, were supplied by US&S. The
Interborough Rapid Transit (IRT) Division of the subway uses both 25-hz and
60-hz signal equipment. Thus the carrier frequency had to be such that there
could be no electromagnetic interference issues. After thorough testing, it
was decided to use 91-2/3 hz for the
coded cab signal carrier frequency.
GRS track circuits on the Grand
Central end of the shuttle were of
the balancing reactor type and used a
matching transformer on the relay end
as well. US&S track circuits on the
Times Square end of the shuttle were

figure 3. The track view at Times Square showing proximity detectors, electropneumatic train stops, and a door command loop (photo courtesy of Richard
White).
84

ieee power & energy magazine

of a matching transformer type. From
the early days on the New York system,
single-rail ac track circuits furnished
by GRS were often of the balancing
reactor type, which provided excellent
immunity of direct current (dc) propulsion return current finding its way to
the track relay coils. US&S used the
matching transformer single rail ac
track circuit for immunity of propulsion return current finding its way to
the track relay coils (see Figure 5).

Operation
The transmission of commands to the
receiver coils on the train was coded
by switching on and off the 91-2/3 hz
carrier frequency to produce code rates.
Code rates of 270 pulses/min were
30-mi/h (48.3-km/h) maximum speed,
180 pulses/min for 5.5-mi/h (8.9-km/h)
maximum speed used for slowing the
automatic train into a station platform,
and 75 pulses/min used for door opening. The absence of a coded carrier frequency would bring the train to a stop.
This was used for the final station stop
at both station platforms.
The generation of the code rates
and carrier frequencies transmitted via
the track to the train was dependent on
a number of relay logic subsystems.
Additional subsystems consisted of
the two ultrasonic vehicle detectors
used at the Grand Central Terminal platform as well as electropneumatically operated, track mounted,
train stop mechanisms controlled by
proximity detectors. Safety and cycle
checking was made in the circuits to
ensure the vital criteria of the entire
automatic operation.
The coded 91-2/3-hz carrier frequency relays were defined by direction of travel: north (Grand Central to
Times Square) or south (Times Square
to Grand Central) to provide for double-direction running. With directional
steering, the coded carrier frequency
was injected into the ac track circuit to
always be ahead of the train's receiver
coils. The shuttle train operation was
completely automatic at the terminals.
Those automatic terminal functions
included door opening and closing,
march/april 2015



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2015

IEEE Power & Energy Magazine - March/April 2015 - Cover1
IEEE Power & Energy Magazine - March/April 2015 - Cover2
IEEE Power & Energy Magazine - March/April 2015 - 1
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IEEE Power & Energy Magazine - March/April 2015 - Cover3
IEEE Power & Energy Magazine - March/April 2015 - Cover4
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