As shown in the last issue of CROSSROADS, some of my features are based upon questions I receive from readers of this publication. This month's topic will be a description of the cab signal system used aboard Conrail locomotives; its basis is a question handed to me by an engineer who experienced a condition called a Limiting Fault during a tour of duty a few months ago on a Conrail SD60MI locomotive outfitted with the E-Brake and integrated display screens.
To best answer this inquiry requires a detailed look at the items installed on Conrail locomotives. It is my hope that this will be of use to anyone who is subject to operate on Conrail run- thru power along with provide a satisfactory answer to the engineer who asked it.
The Equipment and How It Functions
The Conrail cab signal system is a four indication Coded Cab Signal-Automatic Train Stop format which displays wayside signals. It works in conjunction with the block signal system , and operates on a carrier frequency of 100 Hertz (The UP's version, called the Coded Cab Signal - Safety Control system [CCS-SC] works on a carrier frequency of 60 Hertz).
Also used in conjunction with the cab signal system on many of their locomotives is a control system called the LSL (Locomotive Speed Limiter); this feature is operational only when the locomotive is setup in CAB mode (Note: System mode arrangements will be described later in this presentation).
The LSL monitors the cab signal indication, and whenever the indication changes to a more restrictive aspect, LSL will then automatically invoke a braking profile curve to slow the train speed to the indicated cab signal status. The cab signal and LSL systems, depending upon the model of locomotive, may either be the separate stand alone boxes used on the pneumatic air brake units, or electronic version which contains their operating status in the display screens.
System Setup on UP Property
There are two mode states that the LSL/Cab Signal system can be setup in; they are CS only mode, and CS & LSL mode. In the CS only mode, the LSL system is not active; only the cab signal system is active.
Whenever Conrail locomotives are in operation on UP property (along with when they are in use on Conrail property and all railroads except Amtrak), they are to be setup in the CS only mode.
It is easy to identify which mode the LSL is setup in by looking at the displays; depending upon the type of locomotive being operated, you will find these conditions in effect for CS only mode:
1. The older stand alone box format: The display is used as
as a speedometer only; the speed display will be lit, and all other LED's will be turned off.
2. On the newer integrated locomotives with the color LCD displays: The mode block on the display will say CS ONLY.
When in the CS only mode, should the operator incur a "hit" on the cab signal system, all you have to do is to acknowledge the cab signal aspect alarm within six seconds by pressing the foot pedal in front of you for one second.
Failure to do this will result in a full service penalty brake application.
The CS & LSL Mode
The CS & LSL mode is used on Amtrak's Northeast Corridor. The way it may be identified as being so conditioned are as follows:
1. The older stand alone box format:
(A). The display will have different LED's lit.
(B). The speedometer will be active.
(C). The Non Cab or Cab LED around the mode switch will be lit.
(D) The Low Speed LED will be lit below 3 MPH.
2. The newer integrated locomotives: The cab signal mode block will say NON CAB or CAB mode.
If for some reason the locomotive enters the UP property in the CS & LSL mode, then the LSL must be kept in the NON CAB mode in order to avoid any speed restriction by the LSL.
In the event that a "hit" of five seconds or longer should occur, the LSL will then switch to CAB mode. Should this take place when the locomotive is traveling faster than 20 MPH, the LSL will enforce a braking profile curve when the cab signal aspect falls to Restricting (Restricting will be the only aspect you will receive when the unit is on UP trackage).
The engineer will be required to reduce the locomotive's speed to 20 MPH to satisfy the braking curve and avoid a full service penalty brake application.
Once the LSL switches to CAB mode, it will stay there. Therefore, if the locomotive is in CAB mode, and the cab signal aspect is Restricting , the locomotive will be limited to 20 MPH.
Any attempt to move the locomotive faster than 20 MPH will result in a full service penalty brake application at 23 MPH (Note: At 21 and 22 MPH, the LSL sounds a warning alarm that you are getting too fast. The LSL will also sound an alarm every 30 seconds when in CAB mode, Restricted aspect, and below 20 MPH to remind the engineer that the LSL is CAB mode).
Corrective Actions
If you find that the locomotive is in CAB mode, it will require that you take it out of CAB mode and place in NON CAB mode. Remember -- in the NON CAB mode, the LSL will be disabled and allow the locomotive to travel faster than 20 MPH on a Restricted signal.
In order to perform this on a stand alone LSL, the locomotive must be moving less than 20 MPH; if the speed is greater than 20 MPH, LSL will prevent you from switching to NON CAB.
If the locomotive is moving while switching modes, just press the mode button once; this will switch the LSL to NON CAB. If the locomotive is below 3 MPH, the mode button must be pressed three times to bypass LSL test and CS test to get to NON CAB mode.
On the integrated display units, the engineer will have to select the cab signal function key and then select the NON CAB function key. The NON CAB key will only be displayed when the condition is allowed.
THE LIMITING FAULT CONDITION
A Limiting Fault could be caused by the system "seeing" a flaky speed signal; although not that likely, a cab signal "hit" could in some way cause a Limiting Fault to be registered.
In the event you get this message, you will incur a penalty brake application at 23 MPH, regardless of which mode the cab signal system is setup for at the time or whatever the cab signal indication is when this happened. Unless the cause for the fault can be corrected, you will be nailed to keeping your speed to under 20 MPH.
Perhaps the easiest way to correct this, if the circumstances lend themselves to it, is to make the locomotive a trailing unit in the consist; in the trail mode, it will function normally. But if this is not an available option, then other methods for attempting to clear a Limiting Fault must be performed.
CS ONLY Mode Limiting Fault Correction
If the Limiting Fault was logged while the unit was in CS ONLY mode (the setup while on the UP), a method you can attempt is to turn off the cab signal circuit breaker for a minimum of 10 seconds; this amount of time is necessary for draining the power levels stored in the capacitor bank of the system, creating a power outage. After cycling the circuit breaker, the system will power up without going into the LSL self test mode.
If the Limiting Fault was logged while the unit was in CS &LSL mode, perform the same action of cycling the cab signal circuit breaker.
Upon powering up the system, it will then go into a mode called LSL self test. As part of the test conditions, it will require these items:
1. The automatic brake released.
2. The independent brake fully applied.
3. The reverser in the forward position.
When doing this procedure with an integrated displays unit, you will receive message prompt instructions on how to do this test. At the end of the test, the locomotive will "dump" the air brakes, and you should get a message of Self Test Pass. Recovery of the air is done during the self test before the system exits to NON CAB mode.
On the units outfitted with the pneumatic air brake systems, these same techniques for correction of a Limiting Fault will apply; if the air brake handles are not properly setup for the test, or when the time comes for you to recover the air brakes, you will receive a message prompt of "Do Air".
As this month's feature draws to a close, let me emphasize the following point: The resetting of a Limiting Fault condition by cycling the circuit breaker is not a permanent fix to this situation.
If the LSL system sees the condition which created the Limiting Fault again, it will create the fault again.
Marcel is a locomotive engineer working the Fort Worth to McAlester Freight Pool.