U.S. patent number 3,870,952 [Application Number 05/379,662] was granted by the patent office on 1975-03-11 for ballast resistance and track continuity indicating circuit.
This patent grant is currently assigned to General Signal Corporation. Invention is credited to Henry C. Sibley.
United States Patent |
3,870,952 |
Sibley |
March 11, 1975 |
Ballast resistance and track continuity indicating circuit
Abstract
A track quality meter for determing ballast resistance of a
track section, regardless of whether or not the track section is
insulated. An oscillator produces a signal at an appropriate
frequency which is applied to the track section. Detector means,
connected across the track section, is responsive to the voltage
across the track section. From this voltage the characteristic
impedance of the track section can be determined in a number of
ways. In a preferred embodiment, the signal applied across the
track section is also applied across a variable resistor. By
adjusting the variable resistor so that the voltage across it
equals the voltage across the track section, the resistor value is
a measure of the characteristic impedance of the track section at
the frequency produced by the oscillator. The characteristic
impedance of the track section has a number of parameters, but only
the ballast resistance in the track section is variable. As a
result, the ballast resistance for the track section can be read
off a calibration table.
Inventors: |
Sibley; Henry C. (Adams Basin,
NY) |
Assignee: |
General Signal Corporation
(Rochester, NY)
|
Family
ID: |
23498159 |
Appl.
No.: |
05/379,662 |
Filed: |
July 16, 1973 |
Current U.S.
Class: |
324/693; 324/713;
246/28F; 324/510; 324/705 |
Current CPC
Class: |
B61L
1/187 (20130101); G01R 27/02 (20130101) |
Current International
Class: |
G01R
27/02 (20060101); G01r 027/02 () |
Field of
Search: |
;324/65R,51
;246/34CT,34R,128,126,182A,28F |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Krawczewicz; Stanley T.
Attorney, Agent or Firm: Pollock, Philpitt & Vande
Sande
Claims
What is claimed is:
1. A measuring device for measurement of ballast resistance in a
section of track comprising,
an oscillator producing a high frequency signal,
coupling means connected to said oscillator,
a variable resistor connecting said coupling means to said track,
and
detector means connected to said track and to said variable
resistor including further means to indicate, as the variable
resistor is varied in value, when the voltage across said resistor
is equal to the voltage across said track.
2. The device of claim 1 wherein said further means comprises a
meter selectively connectable across either said track or said
variable resistor.
3. The device of claim 1 wherein said further means comprises
comparison means producing a signal whose magnitude is indicative
of whether or not said voltage across said track is greater or less
than said voltage across said resistor,
and indicating means connected to said comparison means for
indicating whether the voltage across said track is greater or less
than the voltage across said resistor.
4. The device of claim 3 wherein said indicating means includes a
pair of indicating lamps, each of said lamps being connected to the
collector of a pair of complementary transistors,
the emitters of said complementary transistors being connected
together and connected to a bias potential,
the bases of said complementary transistors being connected to said
comparison means.
5. A method of determining ballast resistance of a section of track
comprising the steps of,
injecting a high frequency signal in both rails of said track,
determining the impedance presented to said signal by said
track,
determining whether the currents flowing in each of the rails of
said track are uniform,
and determining, if said currents are uniform, from the
characteristic impedance the ballast resistance presented by said
track.
Description
FIELD OF THE INVENTION
The invention relates to measuring devices and more particularly a
device for determining the ballast resistance in a section of track
regardless of whether or not the track section in question is
insulated or uninsulated.
BACKGROUND OF THE INVENTION
A keystone of railroad signaling and control is the well-known
track circuit which is used for detecting the presence or absence
of a train in a particular section of track. In the well-known
track circuit, a voltage is impressed across the track rails at one
end of a section of track, sometimes referred to as the feed end of
the section. The resulting voltage produced at the other end of the
track section (sometimes referred to as the receiving end) is
monitored. The decrease in this voltage, at the receiving end of
the track circuit, when a train is present in the track section, is
used to signal the presence of the train in the section. The
voltage normally produced at the receiving end of a track section
is dependent, of course, upon the resistance presented to the
current flowing in the track circuit. This resistance undergoes an
abrupt decrease when the steel wheels and axle enter the section
and shunt the circuit.
For many years, one method utilized to define the extent of a track
circuit was to insulate each rail at both ends of the circuit.
Thus, the voltage impressed at one end of the track circuit will
produce a current flowing only toward the receiving end of the
track circuit by reason of the insulated joints immediately
adjacent the point at which the voltage is impressed. More
recently, however, railroads have begun to use what is known as
welded rail for the vast majority of their trackway. In this
application, the sections of rail, as they are laid, are welded
together so that the rail forms a continuous conductor. In this
type of application, the track circuit is defined by the points at
which voltage is impressed and the point at which it is received.
In order to segregate these voltages, the frequencies of the
voltages in adjacent track circuits are different and the receiving
apparatus is tuned to the frequency of interest.
Unfortunately, however, there is at least one other parameter which
enters into determining the voltage at the receiving end of a track
circuit other than the presence or absence of the wheels and axles
of a train shorting out the track circuit. This other factor is the
effect of current leaking from one rail to the other through the
ballast on which the rails are laid. The particular complicating
factor of this ballast resistance is the fact that it is variable
with weather conditions and other factors. When the track is
relatively dry, the ballast resistance is relatively high, and
conversely in humid or rainy weather, when the ballast is wet, the
ballast resistance is relatively low. As a consequence, the
parameters in the track circuit must be adjusted so that there is
sufficient voltage at the receiving end when the ballast resistance
is low and no train is present to indicate the absence of a train.
By the same token it is necessary that when the ballast resistance
is high and a train is present in the track section, that the
voltage be reduced sufficiently at the receiving end of the track
circuit so that the presence of the train will be recognized.
Thus, it is apparent that for the track circuit to operate
properly, the parameters of the circuit must be adjusted in
accordance with the ballast resistance in that circuit. Thus, it is
necessary for measurements to be made of the ballast resistance in
each section of track so as to properly adjust the parameters of
the track circuit.
The prior art exclusively used DC measuring techniques for making
ballast resistance measurements. In the case of welded rail
applications, this measurement is obviously highly inaccurate as
there are no readily available means for determining the length of
track over which the measurement has been made. This particular
disadvantage is not applicable to insulated rail track section
measurements. However the art has found that in making DC
measurements of ballast resistance, the indicated value varies
appreciably with current level. This leaves the operator in doubt
as to the ballast resistance value that should be used in adjusting
the parameters of the track circuit. Also, using a DC measurement
technique does not allow for indication of non-uniform ballast
characteristics. Thus, if there is a portion of the section in
which the ballast is non-uniform in resistance, this effect will be
averaged in with the ballast resistance of other portions of the
track section which will result in an inaccurate measurement. If
the parameters of the track circuit are adjusted in accordance with
that reading, the track section will exhibit poor shunting
sensitivity adjacent the feed end of the track circuit.
To overcome these difficulties and to obtain an accurate reading of
ballast resistance, I employ a high-frequency oscillator to
generate the voltage applied to the track section in question. For
high frequency throughout this application, I mean high audio
frequency extending up from about 10 khz to the order of 50 khz. At
frequencies in this range the track section can be analyzed as a
transmission line. As is well known, the impedance of an infinite
transmission line is known as the characteristic impedance of that
line. Departing upon the frequency of measurement, the length of
the track section which is necessary to appear as infinite can vary
from some 400 to 2,000 feet. Using a high frequency voltage for
measurement effectively isolates a section of track for the
measurement. The length of the track section isolated depends upon
the frequency utilized.
A number of different detectors can be used in order to make the
characteristic impedance measurement. In the preferred embodiment,
the track section is fed through a variable precision resistor. The
resistor is adjusted in value so that the voltage across the track
rails equals the voltage across the resistor. This can be indicated
either by a meter arrangement or a differential amplifier. In any
case, the value of resistance is then equal to the magnitude of the
characteristic impedance. An alternative detecting arrangement
would be to provide a constant current source power supply. Thus
merely measuring the voltage across the track rails would give an
indication of the track characteristic impedance. In a further
elaboration of this arrangement, an analog multiplier could be so
connected that by manipulating the voltage and current applied to
the track rails, a signal will be obtained proportional to the
characteristic impedance. Regardless of the detecting arrangement
used, the result is a value for the characteristic impedance of the
track section.
Knowing the characteristic impedance of the track section and the
frequency of measurement, one can, from a calibration curve, read
off the value of the ballast resistance.
The factors that dictate the characteristic impedance of a section
of track are all fixed except for the ballast resistance, that is,
the cross-sectional area and shape of the rails, spacing between
rails, material of the rails, etc. Furthermore, the variation of
log Z.sub.o (where Z.sub.o is the characteristic impedance) with
log R.sub.B (where R.sub.B is the ballast resistance) is
essentially linear as shown in FIG. 4. Therefore, construction of a
calibration curve or table to relate characteristic impedance to
ballast resistance at a particular frequency with specified rail
materials, shape and spacing can be performed by insulating a
section and making two DC measurements of ballast resistance under
different conditions. At the time of each DC measurement, another
measurement is made with the apparatus disclosed herein. Since the
logarithmic relationship is linear, from these two points a
calibration curve or table can be constructed.
I also provide an accessory to determine whether or not the
characteristic impedance value determined by the meter is or is not
meaningful. Discontinuities or lack of uniformity in the track
section can result in a characteristic impedance value which is
inaccurate. A current probe is provided which is capable of
measuring the current in the track rails. Assuming a measurement is
made at a location where it is reasonable to assume the current
flow equally in opposite directions from the point of voltage
application, the current in two directions in both track rails
should be approximately equal if there is a lack of
discontinuities. Nonuniform current would indicate the presence of
a discontinuity. Discontinuities can occur by reason of faulty
insulation adjacent track switches, faulty insulation in insulated
rail, nonuniform ballast resistance, or metallic masses whose
location is not symmetric with respect to the two rails in the
track section. These masses could be adjacent tracks or bridges or
the like. Nonuniform current values where there is no obvious
explanation for the nonuniformity are a signal to the operator that
before he can accept the impedance measurement as being valid, he
must locate the cause of the non-uniformity and determine if it is
affecting the characteristic impedance measurement.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings of this application, when taken in conjunction with
the descriptive portion of this specification, provide a
description of applicant's invention. In the drawings,
FIG. 1 is a block diagram schematic of the track quality meter,
FIG. 2 is a circuit diagram of the preferred embodiment detector
arrangement,
FIG. 3 is a circuit diagram for the accessory current probe,
FIG. 4 is a graphical representation of the variation of
characteristic impedance with ballast resistance at a constant
frequency,
FIG. 5 is a schematic diagram of another embodiment of a detector
arrangement, and
FIGS. 6a-6d show the variations of track length measured with
frequency and ballast resistance.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a block schematic diagram of the track quality
meter of the instant invention. The power supply comprises DC
voltage sources 1 and 2 which are connected to the rest of the
circuit through on-off switch 3. An oscillator 4 is connected
across the power supply and provides a high frequency signal to
amplifier 6. The range of usable frequencies lies between 10 khz to
50 khz. At 10 khz the length of track which is measured becomes too
long to obtain the advantages of the invention and above 50 khz the
effective track length measured becomes too short for practical
use. Preferably a frequency in the range 30-40 khz is employed. In
this range the effective length of the measurement is a few
thousand feet with high ballast resistance and three to four
hundred feet with low ballast resistance. The effective length over
which the measurement is made is that length of track which appears
infinite, under the measurement conditions. This length is
qualitatively shown in FIGS. 6a-6d. The output of amplifier 6 is
fed to tuned coupler 7. The coupler is tuned to the frequency of
oscillator 4 and ensures that it presents a low impedance to the
track rails only at the frequency of oscillator 4. Thus, the track
quality meter can be connected to a track section and it will not
affect the operation of the associated track circuit, assuming the
track circuit operates on a frequency different than that produced
by oscillator 4. The output of tuned coupler 7 is fed to the track
section through terminals 9 and 10. Terminal 9 is connected to the
output of the tuned coupler 7 through a precision decade resistor
8. The decade resistor is an operator-controlled resistor whose
controls indicate the resistance actually in the circuit. Power is
supplied to detector 11 through its terminals 12 and 13 from the
power source. The detector 11 is connected to the circuit ground
through terminal 14. The voltage across the precision decade
resistor 8 is provided to the detector 11 through its terminal 16.
The voltage appearing across the track section is provided to the
detector 11 through its terminal 15. The two outputs of detector 11
appear at terminals 17 and 18 and are respectively connected to
indicator lights H and L.
In operation, when it is desired to make a characteristic impedance
check upon a particular track section, it is only necessary to
connect terminals 9 and 10 to the track section by conventional
clamps (not shown). Closing on-off switch 3 energizes the track
quality meter and supplies a high frequency signal to the track
rails. Depending upon the setting of precision decade resistor 8,
one or the other of the indicator lamps H and L will be lit.
Manipulation of the precision decade resistor 8 will allow it to be
adjusted so that the voltage provided detector 11 at terminal 15 is
equal to the voltage provided detector 11 at terminal 16. When this
condition is achieved, the characteristic impedance can be read off
the controls of decade resistor 8. Assuming that the track quality
meter had been connected to a section of welded rail, the length of
track whose characteristic impedance has been measured is
determined by the frequency of oscillator 4. The higher the
frequency of the oscillator, the shorter the length of track whose
characteristic impedance has been measured. In practice
measurements are made at periodic intervals along the track
section. The intervals are between 400 and 1,000 feet depending on
the frequency of the oscillator. When making measurements on welded
rail the characteristic impedance read from the controls of
resistor 8 will be one-half of the characteristic impedance of the
track. The voltage provided to the track produces current flowing
in both directions from the connection from the connection point.
As a result the impedance presented by the track is actually a
parallel combination of two impedances, each equal to the
characteristic impedance of the track.
When making measurements far from insulated joints the same
considerations apply. However, when making measurements close to an
insulated joint the setting of decade resistor 8 will equal the
characteristic impedance of the track. In order to determine the
actual ballast resistance that has been measured, it is necessary
to refer to a calibration curve such as the one shown in FIG. 4.
The calibration curve shown in FIG. 4 must be one for the frequency
at which the oscillator 4 is tuned. Entering the graphical
representation at the value of characteristic impedance Z.sub.o
equal to that measured, one can read from a horizontal scale the
value of ballast resistance corresponding thereto.
FIG. 2 shows a detailed schematic of the detector 11 wherein like
reference numerals identify identical apparatus. Thus, terminal 16,
shown in FIG. 2, is the same as terminal 16, shown in FIG. 1, etc.
The voltage input signal from the precision decade resistor 8 is
provided to input terminal 16 and it is amplified by operational
amplifier 22. The voltage provided detector 11 from the track rails
is introduced to terminal 15 and it is amplified by operational
amplifier 23. These voltages are then compared one with the other
in a diode network comprising diodes 24 through 27. The difference
between these voltages provides an input signal to operational
amplifier 28 whose output is fed to the bases of transistors 29 and
30. The emitter of transistor 29 is connected to the emitter of
transistor 30 which are both connected to a positive source of
potential. The collector of transistor 29 is connected to terminal
17 and the collector of transistor 30 is connected to terminal 18.
Depending upon the relative magnitude of the potentials applied to
terminals 16 and 15, the voltage provided to the bases of
transistors 29 and 30 will be either above or below the bias
potential applied to the emitters of these transistors. Assuming
that the potential applied to the bases of transistors 29 and 30 is
above the bias potential, then transistor 29 will conduct which
will cause the H indicator lamp connected to terminal 17 to be lit.
On the other hand, if the voltage provided to the bases of
transistors 29 and 30 is less than the bias potential, then
transistor 30 will conduct energizing the L indicator lamp
connected to terminal 18. This informs the operator of the
direction in which the value of precision decade resistor 8 should
be changed so as to equalize the voltages across the decade
resistor and across the track rails.
An alternate embodiment of a detector arrangement is shown in FIG.
5 again where like reference numerals indicate identical apparatus.
FIG. 5 shows the tuned coupler 7 and omits the power supply,
oscillator and amplifier. The output of the tuned coupler is fed
through the decade precision resistor 8 to the track rails. A volt
meter 19 is connected between the poles of single pole double throw
switches 20 and 21. In the position shown, the volt meter 19 would
indicate the voltage across the track rails. When pushbutton switch
21 is depressed, the volt meter 19 will read the voltage across the
precision decade resistor 8. By manipulating pushbutton switch 21
and the controls of the precision variable decade resistor 8, the
operator can adjust the resistor 8 so that the voltage read by volt
meter 19 does not change when pushbutton switch 21 is depressed.
This is the equivalent condition indicating that the controls of
decade resistor 8 read the characteristic impedance of the track
section.
As a further alternative to the detector means arrangement
illustrated in FIGS. 2 and 5, the oscillator 4 and amplifier 6
(shown in FIG. 1) are arranged to act as a constant current source
at the frequency of oscillator 4, by means well known in the art.
In order to obtain a measure of the characteristic impedance of the
track to which the tuned coupler 7 is connected, it is then only
necessary to measure the voltage across the track rails. Since the
current supplied the track rails is constant, the volt meter could
be calibrated in terms of characteristic impedance. In further
elaboration of this embodiment, the voltage across the track rails
could be fed to a multiplying circuit, such as an integrated
circuit solid state multiplier. A second input to this multiplier
would comprise a signal proportional to the inverse of the current
supplied by the constant current source. The resulting output
voltage from the multiplier would then be directly proportional to
the characteristic impedance of the track rails.
The foregoing portion of the specification demonstrates the manner
in which the track quality meter can determine the characteristic
impedance of a section of track. However, as has been explained
above, before the operator can rely upon this value of
characteristic impedance in determining the actual ballast
resistance of the section of track, it is necessary for the
operator to be informed as to whether or not the reading he has
obtained is an accurate one, that is, whether or not any
discontinuities or nonuniformities have entered into this value. As
an aid to making this determination, the current probe, illustrated
in FIG. 3, can be utilized. The operating principle of the current
probe illustrated in FIG. 3 is as follows. When the track quality
meter is connected across a section of track which is uniform and
exhibits no discontinuities, the current in both rails of the track
will be equal. Furthermore, the current proceeding away from the
connection point in one direction in one rail will equal the
current proceeding in the opposite direction from the same
connection point of that rail. A discontinuity or nonuniformity in
the track section will cause the currents to be nonuniform. The
coil of the current probe shown in FIG. 3 is placed adjacent each
rail, on each side of the connection point of the track quality
meter. The ammeter 31 will provide a value for the current flowing
in the rail adjacent the coil. If the current values are
substantially equal, the operator is assured that there are not
discontinuities or nonuniformities. On the other hand, if the
values of current are unequal, the operator is informed that he
must examine the track section, either visually or otherwise to
determine the cause for the nonuniform current readings.
The current probe comprises a coil 32 connected across a capacitor
33. The combination of these elements is tuned to the frequency of
oscillator 4. A calibration potentiometer 34 is in parallel with
the coil 32 and capacitor 33 to provide a scale adjustment for the
meter 31. The signal from potentiometer 34 is provided to an
operational amplifier 35 which is powered by a DC source of
potential 36a. Power is applied to the current probe through on-off
switch 37. The signal from the operational amplifier 34 is fed
through a capacitor diode network comprising capacitors 36 and
diodes 37 and 38. A protective resistor 39 provides a current path
from the diode 38 through the meter 31. A capacitor 40 is connected
in parallel with the resistor 39 and meter 31 to shunt any higher
frequency signals.
When making measurements adjacent insulated joints, of course, the
current probe should measure equal currents in the two track rails
flowing away from the joints and little or no current flowing
towards the joints. If there is an appreciable amount of current
flowing towards the insulated joints, then a defective insulated
joint or joints has been located.
* * * * *