Railway switches and signals – Block-signal systems – Automatic
Reexamination Certificate
2002-02-06
2002-12-17
Le, Mark T. (Department: 3617)
Railway switches and signals
Block-signal systems
Automatic
C246S03400A, C324S207200
Reexamination Certificate
active
06494409
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention deals with railway control and, more particularly, to code following apparatus, such as code following track relays, for receiving pulsating rail current from a railway code transmitter.
2. Background Information
A conventional railroad track circuit typically includes a battery, a resistor, a track, and a relay. The feed or battery end and the relay end of the track circuit are electrically connected to the two rails of the track. Under conditions when a vehicle, such as a train, is not within the track circuit, the battery energizes the coil of the relay through the series combination of the-resistor, the first rail, the coil and the second rail. In turn, the normally open contact of the energized relay closes. The track circuit employs the shunting properties of the train's wheels and axle (i.e., a train shunt) to sufficiently reduce the current in the relay coil and, thus, open the normally open contact, in order to indicate the presence of the train in the track circuit.
As shown in
FIG. 1
, a conventional code following railway track relay (TR)
2
is used in a railway track circuit
3
in which a low voltage battery source
4
, at one end
6
of the circuit, is interrupted at a low frequency (e.g., generally less than about 3 Hz) by a conventional railway code transmitter
8
. At the other end
10
of the track circuit
3
, the code following track relay
2
responds to the pulsating current on the rails
12
,
14
, thereby opening and closing its contacts
16
. The series combination of a resistor
18
, the low voltage battery source
4
and the railway code transmitter
8
are electrically connected to the rails
12
,
14
at the one circuit end
6
. The series combination of a resistor
20
and the coil
22
of the track relay
2
are electrically connected to the rails
12
,
14
at the other circuit end
10
.
Typically, the coil resistance of code following relays, such as TR
2
, is typically in the order of about 0.5 &OHgr;, with operating current being in the order of 0.5 A. Again, because code following relays are electro-mechanical devices and operate constantly, they are subject to wear. Particularly, the contacts, such as
16
, pit and erode from constant electrical switching. For safety reasons, it is important for the relay operating current to remain relatively stable. If it were possible for the operating current to reduce significantly, then a broken rail could go undetected and, thus, jeopardize train safety. Periodic re-calibration to ensure consistency of the operating current is the process by which safety is assured.
As employed in railway signaling, the dynamic action of the code following relay indicates that the particular track circuit is not occupied. If the relay is not responding to the dynamic action of the rail current, then the particular track section is occupied. Hence, restrictive signals are displayed in order that a train has sufficient distance to stop.
In such railroad code following relays, the term “BACK” corresponds to relay contacts that are closed when the relay is de-energized. Similarly, the term “FRONT” corresponds to relay contacts that are closed when the relay is energized.
In general, electro-mechanical relays wear out after long periods of constant cycling. In particular, code following railway track relays suffer the same problem.
There is a need, therefore, for a circuit that improves the reliability of code following railway track relays after long periods of constant cycling.
U.S. Pat. No. 3,661,089 discloses a code reader for an automated vehicle, which moves along a path having a plurality of magnetic code elements located at sensing stages along the path. The code reader includes a plurality of Hall-effect devices. For each of the Hall-effect devices, a pulse driving circuit couples an actuating pulse of current through the device terminals responsive to a common pulse generator. A difference amplifier is coupled across the output electrodes of each of the Hall-effect devices. The difference amplifier produces a positive or negative potential output signal based upon the magnetic orientation of the magnetic code elements. Bipolar outputs provide a logic level “1” for respective positive and negative potential output signals, again based upon the magnetic orientation of the magnetic code elements. A downstream control system preferably includes error-detecting circuitry to detect the occurrence of two simultaneous logic level “1” output signals from the same sensing state.
U.S. Pat. No. 4,415,134 discloses a Hall effect track circuit-receiving element. Wires are connected to two track rails and are series-connected with a Hall effect cell through a switch. The Hall effect cell includes a coil forming a part of an electromagnetic device, which is located within the cell. A receiver receives its input from the Hall effect cell along output lines.
U.S. Pat. Nos. 4,498,650; and 4,451,018 disclose a toroid including a first conductor forming a winding, which is coupled to track rails via a switch. The MMF of one of two polarities is induced in the toroid depending on whether one of two check winding conductors is energized. An air gap in the core of the toroid has a Hall sensor located therein to respond to the MMF induced in the core as a result of current flowing in any of the conductors. In turn, the Hall sensor provides an output voltage.
U.S. Pat. No. 4,320,880 discloses an electronic track current switching relay system, which emulates the operation of a polar relay for applying coded pulses to railway tracks. A timer circuit includes a high-limit threshold circuit and a low-limit threshold circuit, which trigger a flip-flop or latch.
U.S. Pat. No. 4,935,698 discloses a dual-Hall integrated circuit (IC) including two essentially identical Hall elements, which are connected in series. In the IC, the outputs of the two Hall elements are differentially connected to the input of a differential amplifier, in order that the output voltage is a function of the difference between the magnetic fields at the Hall elements. The output of the amplifier is connected to the input of a Schmidt trigger circuit having an output connected to the IC output terminal. The IC and a magnet form a proximity sensor.
U.S. Pat. No. 4,737,710 discloses a Hall-effect position sensor apparatus, which senses the position of a moving body and provides an output signal indicative of the position of the moving body. The apparatus includes a predetermined number of Hall-effect sensors, which are positioned in a straight line and in operating proximity to a moving body made of a ferromagnetic material.
U.S. Pat. Nos. 5,694,038; and 6,232,768 disclose a Hall element having an output connected to the input of a Hall voltage amplifier. The Hall element may be mounted at a pole of a magnet, in order that when a ferrous article approaches, the Hall voltage and, thus, the amplified Hall voltage increase (or decrease depending on the polarity of the magnet pole).
SUMMARY OF THE INVENTION
The present invention employs a Hall effect digital current sensor, which has a Hall sensor in the gap of a toroid, in order to turn on and off in response to pulsating rail current. This provides electrical isolation of rail current to downstream solid state switching devices that function like the mechanical contacts of an electro-mechanical relay.
As one aspect of the invention, a code following apparatus for receiving pulsating rail current from a railway code transmitter comprises: first and second inputs structured to receive the pulsating rail current; two Hall effect digital current sensors, each of the Hall effect digital current sensors having a coil and an output, which responds to current flowing through the coil, the coils of the Hall effect digital current sensors being electrically connected in series between the first and second inputs and being structured to receive the pulsating rail current, the outputs of the Hall effect digital current sensors being structured to turn on
Eckert Seamans Cherin & Mellott , LLC
Houser Kirk D.
Le Mark T.
Union Switch & Signal Inc.
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