US2059888A - Railway track circuit apparatus - Google Patents

Description

Nov. 3, 1936.

P. N. MARTIN RAILWAY TRACK CIRCUIT APPARATUS Filed Aug. 50, 1935 Fig. 7.

2 Sheets-Sheet 1 X Q I? T Y T (In? 20 fillegmom INVENTOR Paul NMamm BY 412W HIS A TTORNE Y Bridging Nov. 3, 1936. R MA T 2,059,888

RAILWAY TRACK CIRCUIT APPARATUS Filed Aug. 50, 1933 2 Sheets-Sheet 2 f Bridginy BY MW HIS A TTORNE Y Patented Nov. 3, 1936 UNITED STATES PATENT OFFIQE RAILWAY TRACK CIRCUIT APPARATUS Application August 30,

22 Claims.

My invention relates to railway track circuit apparatus, and more specifically to apparatus for improving the shunting characteristics of railway track circuits.

I will describe several forms of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing one form of apparatus embodying my invention. Figs. 2 to 10, inclusive, are diagrammatic views showing modified forms of the apparatus illustrated in Fig. 1, also embodying my invention.

Similar reference characters refer to similar parts in each of the several views.

In the form of track circuit commonly employed for railway signaling, the shunting sensitivity varies over a Wide range, due chiefly to variations in ballast leakage from rail to rail n and the consequent changes in the energization of the track relay. That is, when the ballast is wet and the resulting leakage high, the track relay energy level is low, and a train shunt of relatively high resistance is capable of releasing the track relay. However, under dry ballast conditions, the track relay energization may become abnormally high, so that difficulty may be experienced in obtaining safe shunting under various operating conditions. The use of a current- ?9 limiting impedance at the feed end of the track circuit, although helpful, does not of itself provide sufficiently close regulation of the track relay energy to be entirely satisfactory.

For uniform shunting sensitivity, it is desirable to maintain the normal track relay energy level, prior to the time when the shunt is applied, as nearly uniform as possible, irrespective of ballast leakage, and it is believed that this result can be accomplished most effectively by the use of regulating apparatus located at the relay end of the track circuit. Apart from the effect of ballast leakage on track relay energization, there is an additional factor which noticeably decreases the maximum shunting sensitivity of a track circuit. This factor results from the practical limitation to which track relays are subject, namely, that the energization at pickup must be greater than the energization at release. Therefore, although improved shunting could be obtained by maintaining the energization of the track relay at the release value, some sensitivity must be sacrificed in the usual track circuit because the energization must be at least sufiicientiy high for pickup of the relay. My invention makes it possible to eliminate partly 01;

1933, Serial No. 687,476

wholly the effect of the spread between the pickup and. release values, as well as to offset the disadvantages due to ballast leakage variation, thus providing increased shunting sensitivity as well as decreased shunting time.

Referring to Fig. l, I have shown a section of railway track F-G, one end of which is supplied with rail current from. a suitable source 2, through an adjustable limiting impedance 3. Connected across the rails at the other end. of the section is a track relay A, in the energizing circult of which is included, at times, a resistor R. Relay A controls a pickup circuit for an auxiliary relay B, by means of front contact 6. When relay B is picked up, back contact 5 being open, the short circuit is removed from resistor R, thereby decreasing the energization of relay A.

Let it first be assumed that relay B is used to decrease the sheet of the spread between pickup and release values of relay A. Under normal conditions with section F-G unoccupied, both relays A and B will be picked up. The value of resistor R will be determined by the minimum ballast condition, so that the amount of energy which is permitted to remain in relay A will depend to a large extent on the track circuit regu lation. If the regulation is good, so that the rail voltage at the relay end does not vary widely with ballast conditions, resistor R may be cho sen of such a value as will decrease the energy level in relay A almost to the release point. Maximum shunting sensitivity can be obtained with such an adjustment, assuming other factors to remain constant.

When a train enters section F-G, relay A will release, opening front contact A to release relay B. As soon as relay B releases, back contact 5 will become closed to shunt out resistor R. Consequently, as soon as the train leaves the section, the energization of relay A will be sufiicient for pickup, and the circuit will be restored to the condition illustrated. From the foregoing, it will be apparent that by a suitable choice of the value of resistor R with reference to the release point of relay A, the shunting sensitivity of the ordinary track circuit can be greatly improved. As is well known, track relays particularly of the direct current type, have an appreciable spread between the pickup and the release energy levels, with the result that the train shunt must be sufficiently effective to by-pass the increment of current above the release point of the relay. Not only does this require a lower resistance train shunt, but the shunting time is also substantially increased because the relay flux requires a longer time to die down from the higher level. A further advantage arising from the use of the resistor R is that the addition of resistance in series with the inductance of relay A results in a much more rapid flux decay, i. e., lower shunting time, than can be obtained at the same value of current but without the series resistance. This result will be understood from a consideration of the time constant of an inductive circuit having resistance in series therewith. Practically, the combination of relays A and B is in many respects the equivalent of a single track relay having pickup and release values which are substantially the same.

Let it next be assumed that relay B and resistor R are used for improving track relay voltage regulation. If the impedance of relay B is made substantially higher than that of relay A, and if the limiting impedance 3 is so adjusted that with low ballast resistance relay A will just pick up, then when the ballast dries out and the track voltages rises, relay B will pick up. The pickup of relay B Will remove the excess energization from relay A, under the dry ballast condition. The resistor R must be of sufliciently high value to insure that relay A will release prior to the release of relay B, otherwise the increased shunting sensitivity will be sacrificed. Because of the relatively high impedance of relay B, this relay will have only a slight effect on the operation of the track circuit under conditions of low ballast resistance. With high ballast resistance, however, when the shunting sensitivity ordinarily becomes very low, the addition of resistor R in series with relay A will greatly increase the shunting sensitivity, as well as decrease the shunting time. Relay A is provided with an additional contact, such as 20, Which may be used to control circuits for signals, or any other traflic governing apparatus.

Referring to Fig. 2, which is identical with Fig. 1 except for the addition of a second auxiliary relay C in parallel with relay B, the operation of the apparatus of this figure, in view of the foregoing description, will be clear without further explanation. Relay C is of higher impedance than relay B, and acts to cut in an additional resistor R by means of back contact 5, when the ballast resistance and the resulting track voltage become sufliciently high for pickup of relay 0. In this manner, track circuits having a large ballast resistance variation can be operated safely. If desired, relay C can be used merely as an adjunct to relay B, to permit adding the series resistance in two small steps, rather than one large step, thus aiding to maintain the shunting sensitivity more uniform throughout the operating range of the relay combination. It will be apparent that if a sufficient number of auxiliary relays is used, the shunting sensitivity of the track circuit can be maintained at a uniformly high value, notwithstanding a variation of track voltage between wide limits.

In Fig. 3, the auxiliary relay B instead of being connected across the two rails of the track as in Fig. l, is connected in series with relay A Relay B is a low impedance current relay having the same functions as relay B in Fig. 1. In explaining the operation of the apparatus, I shall assume that the track circuit current has been adjusted under wet ballast conditions to that value which will enable relay A to pick up. Since the pickup current of relay B is considerably higher than the pickup current of relay A relay -relay D in order that relay A B will be deenergized under the above condition, and the energizing circuit for relay A will include the back point of contact 8 of relay 3 wire 2|, and the winding of relay B. As the ballast dries out, the current through relay B will increase until a point is reached at which relay B will pick up.

As soon as relay B picks up, resistor R will be connected in series with relay A over the front point of contact 8 of relay B thus compensating for the increase in track voltage. At the same time, front contact 9 of relay B will close, connecting resistor R, which replaces the winding of relay A into the circuit of relay B in order that relay B may remain energized even though the current through relay A is substantially decreased. Contact 8 of relay B is of the continuity transfer type in order that the energizing circuit of relay A will not be interrupted during the pickup of relay B When a train enters the track section, relay A will release first, followed by the release of relay B which, in closing the back point of contact 8, prepares the low resistance circuit for pickup of relay A as soon as the train leaves the section.

The operating characteristics of relays A and B should be such that relay A will be the first to pick up when a train leaves the section, and the first to release when a train enters the section. Should relay B pick up ahead of relay A resistor R might prevent the pick-up of relay A or at least retard the pickup unnecessarily. If relay B were permitted to release ahead of A upon shunting of the track, the shunting sensitivity would be decreased because of the higher energization of relay A under this condition. By energizing relay B over the front contact I of relay A a relatively quick release of relay B and one which is necessarily subsequent to the release of relay A is obtained.

Referring to Fig. 4, the circuit of this figure shows a method for obtaining compensation for the spread between the pickup and release current values, independently of the compensation for high track voltage under dry ballast conditions. Separate resistors R and B, respectively, are provided for this purpose. The signal control relay D is a repeater of the track relay A and is of the slow pickup and slow release type. By employing relay D for signal control purposes, it becomes possible to use a highly sensitive track relay A since the mechanical work required of relay A is very small.

In explaining the operation of the apparatus of Fig. 4, I shall assume that under the condition of minimum ballast resistance, the track energy has 5 been adjusted to a value which is sufficient to pick up relay A it being understood that the track voltage required to pick up the auxiliary relay B is substantially higher than that required to pick up the track relay A When relay A picks up. front contact I I will close and the repeater relay D will become energized from a suitable current source having the terminals X-Y. As soon as relay D picks up, back contact I 2 will open, thereby opening the branch circuit around resistor R so that resistor R will be included in the energizing circuit of relay A to compensate for the spread between pickup and release current values. A time interval is introduced into the pickup oi will reach its fully energized condition before the energization is de creased through the opening of back contact 42. Should contact l2 be permitted to open before the armature of relay A will have reached its fully closed condition, an undesired release of relay A ill) might occur, with resulting pumping action between the two relays A and D. This difliculty would be particularly prominent under wet ballast conditions, when the track relay energization is low. Another reason for retarding the pickup of relay D is to prevent a momentary clear signal from being displayed, should relay A pick up momentarily due to a temporary loss of shunt. The slow release characteristic of relay D merely introduces an additional time delay before a change of signal indication may occur, thus providing more time within which a low resistance shunt can be established when the shunting 1s intermittently poor.

When the ballast becomes dry and the track voltage rises, relay B will pick up, opening the branch circuit around resistor R to add this resistor also, in series with relay A When a train enters the track section, relay A will release first, followed by relays B and D. Thereupon, both resistors R and R will be short-circuited, in preparation for the pickup of relay A as soon as the train leaves the section.

Referring to Fig. 5, the apparatus of this figure operates in the same manner as the apparatus of Fig. 4. The normal energizing circuit of relay A does not include a front contact of relay A as this contact can be eliminated if relay D is of the nonslow release type. Relay D should preferably have a slow pickup characteristic, for the same reasons advanced in connection with relay D of Fig. 4.

In the modified form of apparatus shown in Fig. 6, the shunting sensitivity of relay A is increased and the shunting time decrease-d not only by adding resistance in series with the relay winding, but also by decreasing the effective turns of the Winding. The operation is as follows: When the ballast is wet, relay A will be energized and relay B deenergized, so that the circuit of relay A will include both windings i3 and M of the relay, and the back point of the continuity transfer contact 15. If the track voltage increases sufficiently to pick up relay 8*.

7 the circuit of relay A will include only portion I3 of the relay win-ding, resistor R and the front point of contact if) of relay B. By properly proportioning the number of turns which are cut out and the value of resistor R with respect to the track voltage at which relay B picks up, the release characteristic of relay A may be raised sufficiently, under the dry ballast condition, to make the shunting sensitivity fully as satisfactory as under the wet ballast condition. The shunting time will, in addition, be much lower with dry ballast because the flux decay will be accelerated due to decreased inductance as well as increased resistance of the circuit. If it is desired to eliminate the bridging feature of contact if, this may be done by placing a permanent connection around the front point of contact l5, without affecting the operation of the circuit in a substantial manner.

Referring to Fig. l, the circuit of this figure represents a modification of the circuit of Fig. 4,

the chief difierence being that the auxiliary re lay B is controlled by the track repeater relay D instead of being controlled by the track relay directly. When the track relay controls the auxiliary relay directly, as soon as the track relay picks up and before it has attained its fully energized condition, the auxiliary relay comes connected across the track, and if the ballast is wet, the added load may be suificient to cause the track relay to release, unless a compensating adjustment of the current-limiting impedance at the feed end of the track circuit is made. Some sacrifice of shunting sensitivity results from such an adjustment. By controlling relay B over the front point of contact iii of relay D relay D being preferably of the slow-pickup type, relay A has ample time within which to reach its fully closed condition, before the current of relay B is added to the track circuit load, so that ordinarily, the adjustment of the track impedance can remain the same as though relay B were not used.

The arrangement shown in Fig. 8 is similar to Fig. 1, except that a time delay relay T of any suitable type, is added to insure that once the track relay A has released, it wil remain deenergized until such time, at least, as is required for relay T to complete its pickup movement. In this manner undesired changes of signal indication arising from momentary loss of shunt are prevented. When relay A releases, relay T becomes energized over back contact i1, and closes its front contact l8, to close the energizing path for relay A around the open front contact IS.

The apparatus of Fig. 9 is similar to that of Fig. 3, differing chiefly in that the relay B of Fig. 9 is controlled over a back contact of the track relay A rather than a front contact of this relay. Relay B is designed to have a higherpickup value than relay A In operation, the track circuit is so adjusted that relay A will just pick up under the most unfavorable ballast condition. When the ballast resistance increases sufliciently, relay B will pick up over a circuit which includes the winding of relay A and the back point of contact 22. The opening of the back point of contact 22 will cause resistor R to be inserted in series with relay A and the closing of the front point of this contact will connect resistor R in parallel with relay A thus reducing the energization to increase the shunting sensitivity.

Relay A is designed to release ahead of relay B so that when the track is shunted, relay A will release, and in closing back contact ll will short-circuit relay B causing it to release also. With relay B released, the pickup circuit for relay A is restored, so that the track relay will pick up as soon as the train leaves the section.

Referring to Fig. 10, the apparatus of this figure is similar to that of Fig. 9, differing chiefly in that the relay A has a tapped coil, for reasons brought out more fully in the description of Fig. 6. The pickup circuit for relay A includes both of the relay windings l3 and I4, back point of contact l5, and the winding of relay B The track circuit is so adjusted that relay A will just pick up under the most unfavorable ballast condition. Relay B having a substantially pickup value, will remain released under this condition. When the ballast dries out, relay B will pick up, opening the circuit for winding M at the back point of contact l5, and inserting resistor R in series with winding it by virtue of the closin of the front point of contact l5.

In order to prevent relay A from releasing during the pickup interval of relay B contact 15 is made of the continuity transfer type. If it is desired to eliminate the bridging feature of contact [5, this may be done by placing a permanent connection around the front point of contact [5 so that the holding circuit for relay A will always be closed, irrespective of whether the pickup circuit is or is not closed at the back point of contact IS. The operation under this condition will be the same as described above.

When a train enters the section, relay A will release ahead of relay B closing back contact 23 which short circuits relay B As soon as relay B releases, relay A will have its pickup circuit restored through the closing of the back point of contact 15, in readiness for the pickup operation as soon as the train leaves the section.

Although direct current track circuits and direct current relays have been illustrated for simplicity, it will be apparent that the fundamental principles of connecting one or more impedances after pickup of the track relay, or altering the number of turns, or both, as a means for increasing the shunting sensitivity and decreasing the shunting time, can be applied as well to track circuits of the alternating current type, or those employing any other suitable form of electrical energy.

Although I have herein shown and described only a few forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, What I claim is:

1. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay, a pickup circuit for said track relay connected across the rails of said section and including a back contact of said auxiliary relay, a circuit for said auxiliary relay connected across the rails of said section and including a front contact of said track relay, and an impedance connected across said back contact for decreasing the energization of said track relay to improve the shunting sensitivity of said track section.

2. The method of increasing the shunting sensitivity of a railway track circuit, which comprises connecting a track relay and an auxiliary r-..ay in such manner that both receive energy over the rails of the track circuit, said auxiliary relay having a pick-up value of track voltage higher than that required for pickup of said track relay, and using said auxiliary relay when picked up to decrease the energization of the track relay by means of a normally ineffective impedance which becomes effective when and only when said auxiliary relay is picked up there-- by rendering said track circuit more sensitive to shunting.

The method of increasing the shunting sensitivity of a railway track circuit and decreasing the shunting time, which comprises connecting a track relay and an auxiliary relay in such manner that both receive energy over the rails of the track circuit, said auxiliary relay having a pick-up value of track voltage higher than that required for pickup of said track relay, and using said auxiliary relay when picked up to add a resistor in series with said track relay to decrease the energization thereof and to accelerate the flux decay in the core thereof, said resistor being normally ineffective and becoming effective when and only when said auxiliary relay is picked up.

4. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay, a pickup circuit for said track relay connected across the rails of said section and including a back contact of said auxiliary relay, a branch path around said track contact including a resistor, and a circuit for said auxiliary relay connected across the rails of said section and including a front contact of said track relay.

5. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay, a pickup circuit for said track relay connected across the rails of said section and including the winding and a back contact of said auxiliary relay, a. holding circuit for said track relay connected across the rails of said section and including a front contact of said auxiliary relay, and a circuit for said auxiliary relay including a second front contact thereof and a front contact of said track relay.

6. In combination with a section of railway track and source of current connected across the rails of said section, a track relay and an auxiliary relay, a pickup circuit for said track relay connected across the rails of said section and including the winding and a back contact of said auxiliary relay, a holding circuit for said track relay connected across the rails of said section and including a front contact of said auxiliary relay and an impedance for decreasing the energization of said track relay; and a circuit for said auxiliary relay including a second front contact thereof, a front contact of said track relay, and a second impedance of substantially the same magniture as the impedance of said track relay.

'7. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay, an auxiliary relay, and a slow pickup track repeater relay; a pickup circuit for said track relay connected across the rails of said section and including a. back contact of said repeater relay as well as a back contact of said auxiliary relay, a first branch path around said back contact of the repeaterrelay including a front contact of the track relay and an impedance, a second branch path around said back contact of the auxiliary relay including a second impedance, a holding circuit for said track relay connected across the rails of said section and including said first branch path, a circuit for said repeater relay including a second front contact of said track relay, and a circuit for said auxiliary relay including a third front contact of said track relay.

8. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay, an auxiliary relay, and a slow pickup track repeater relay; a pickup circuit for said track relay connected across the rails of said section and including a back contact of said repeater relay as well as a back contact of said auxiliary relay, a. first branch path around said back contact of the repeater relay including a front contact of the track relay and an impedance, a second branch path around said back contact of the auxiliary relay includingasecondimpedance. a holding circuit for said track relay connected across the rails of said section and including said first branch path, a locally energized circuit for said repeater relay including a second front contact of said track relay, and a circuit for said auxiliary relay connected across the rails of said section and including a third front contact of said track relay.

9. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay, an auxiliary relay, and a slow pickup track repeater relay; a pickup circuit for said track relay connected across the rails of said section and including a back contact of said repeater relay as well as a back contact of said auxiliary relay, a first branch path around said back contact of the repeater relay including an impedance, a second branch path around said back contact of the auxiliary relay including a second impedance, a holding circuit for said track relay connected across the rails of said section and including said first branch path, a circuit for said repeater relay including a front contact of said track relay, and a circuit for said auxiliary relay including a second front contact of said track relay.

10. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay, an auxiliary relay, and a slow pickup track repeater relay; a pickup circuit for said track relay connected across the rails of said section and including a back contact of said repeater relay as well as a back contact of said auxiliary relay, a first branch path around said back contact of the repeater relay including a resistor, a second branch path around said back contact of the auxiliary relay including a second resistor, a holding circuit for said track relay connected across the rails of said section and including said first branch path, a locally energized circuit for said repeater relay including a front contact of said track relay, and a circuit for said auxiliary relay connected across the rails of said section and including a second front contact of said track relay.

11. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay, an auxiliary relay, and a track repeater relay; a pickup circuit for said track relay connected across the rails of said section and including a back contact of said repeater relay, a holding circuit for said track relay connected across the rails of said section and including a front contact of. the track relay as well as a back contact of the auxiliary relay, a branch path around said back contact of the auxiliary relay including an impedance, a circuit for said repeater relay including a second front contact of said track relay, and a circuit for said auxiliary relay including a front contact of said repeater relay.

12. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay, an auxiliary relay, and a track repeater relay; a pickup circuit for said track relay connected across the rails of said section and including a back contact of said repeater relay; a holding circuit for said track relay connected across the rails of said section and including a front contact of the track relay, an impedance, and a back contact of, said auxiliary relay; a branch path around said back contact of the auxiliary relay including a second impedance, a circuit for said repeater relay including a second front contact of, said track relay, and a circuit for said auxiliary relay including a front contact of said repeater relay.

13. In combination with a section of railway track and a. source of current connected across the rails of said section; a track relay, an auxiliary relay, and a track repeater relay; a pickup circuit for said track relay connected across the rails of. said section and including a back contact of said repeater relay; a holding circuit for said track relay connected across the rails of said section and including a front contact of the track relay, a resistor, and a back contact of said auxiliary relay; a branch path around said back contact of the auxiliary relay including a second resistor, a locally energized circuit for said repeater relay including a second front contact of said track relay, and a circuit for said auxiliary relay connected across the rails of. said section and including a front contact of said repeater relay.

14. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay, a pickup circuit for said track relay connected across the rails of said section, an auxiliary relay which requires a higher track voltage for pickup than said track relay, a pickup circuit for said auxiliary relay including the rails of said section and effective only when said track relay is picked up, and normally ineffective means governed by a contact of said auxiliary relay and effective when the auxiliary relay is picked up for decreasing the energization of said track relay to increase the shunting sensitivity of said track section.

15. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay and an auxiliary relay both energized from said source over the rails of said section, the energization of said auxiliary relay occurring only if said track relay is picked up, said auxiliary relay having a pickup track voltage characteristic higher than the pickup track voltage characteristic of said track relay; and normally ineffective means governed by said auxiliary relay and effective when and only when the auxiliary relay is picked up for raising the release characteristic of, said track relay to increase the shunting sensitivity of said track section.

16. In combination with a section of railway track and a source of current connected across the rails of said section; a track relay and an auxiliary relay both energized from said source over the rails of said section, the energization of said auxiliary relay occurring only if said track relay is picked up, said auxiliary relay having a pickup track Voltage characteristic higher than the pickup track voltage characteristic of said track relay; and normally ineffective means governed by said auxiliary relay and effective when and only when the auxiliary relay is picked up for decreasing the time constant of said track relay to accelerate the flux decay therein, thereby decreasing the time required to shunt said track relay.

17. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay, a pickup circuit for said track relay connected across the rails of said section and including the winding and a back contact of said auxiliary relay, means controlled by said track relay for releasing said auxiliary relay when the track relay is released, and means controlled by said auxiliary relay effective when the auxiliary relay is energized for decreasing the energization of the track relay to improvev the shunting sensitivity of said track section.

18. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay having a given pickup value which is higher than the pickup value of said track relay, a pickup circuit for said track relay connected across the rails of said section and including the Winding and a back contact of said auxiliary relay, said pickup circuit serving also to pick up said auxiliary relay when the track voltage is at or above said given value, means controlled by said auxiliary relay effective when the auxiliary relay is picked up for decreasing the energiaation and increasing the rate of flux decay in the core of said track relay, and means controlled by said track relay effective when said track relay is released for releasing said auxiliary relay.

19. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay both receiving: current from said source over the rails of said track, and normally ineficctive means controlled by a contact of said auxiliary relay and effective upon the pick-up of the auxiliary relay for decreasing the energization of said track relay to improve the track shunting sensitivity.

20. In combination with a section of railway track and a source of current connected across the rails of said section, a traclr relay and an auxiliary relay both receiving current from said source over the rails of said track, a normally ineffective resistor, and means controlled by a. contact of said auxiliary relay and effective upon the pick-up of the auxiliary relay for adding said resistor in series with said track relay to decrease the energization thereof and to accelerate the flux decay in the core thereof.

21. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay both receiving current from said source over the rails of said track, and normally ineffective means effective only upon the pickup of said auxiliary relay for increasing the track voltage value at which said track relay will release.

22. In combination with a section of railway track and a source of current connected across the rails of said section, a track relay and an auxiliary relay both receiving current from said source over the rails of said track, a normally ineffective impedance, and means eflective only upon the pickup of said auxiliary relay for conmeeting said impedance in series with said track relay to thereby decrease the track relay energication and improve the track shunting scnsitivity.

PAUL N. MARTIN.

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