Part Five: "The Control Machine"

The control machine provides the important means for the dispatcher to monitor wayside conditions and to initiate the control codes thru push buttons and levers. The control codes are sent to the field equipment via the code line to control the corresponding signals, switches, and electric locks. As with most, if not all aspects of railroading the control machine is as unique as the prototype railroad. Union Switch and Signal Company (US&S) of Swissvale Pennsylvania manufactured hundreds of its type “C” 500 series machines for many North America railroads.

The prototype control machine was constructed of steel. It was approximately 54 inches high and 16 inches deep. At the option of the customer US&S would furnish the machine with or without a desk. These machines were composed of standard sections that were either 30 inch and /or 60 inches long. These sections were constructed so that if the size of the installation requires, a number of these sections could be placed end to end or in a configuration such as rectangular or hexagonal shape, for more ready manipulation. With any of the above arrangements of sections the appearance was that of one integral unit.

On the front of the machine above the desk top are located the control levers, code starting push buttons and indication lamps for both train occupancy, switch, and signal functions. This section of the machine consists of a number of similar rows that are assigned to a specific field location. Each row is uniformly spaced at 2 inch centers throughout the length of the machine. The 30 inch cabinets have 15 rows, and the 60 inch cabinets have 30 rows that start 1 inch in from the cabinet’s edge.

Each row may consists of a two-position switch control lever with two indication lamps directly associated; a three-position signal control lever with three indication lamps directly associated; a spring return type push button or a two-position toggle switch for the control of a “calling on” signal; a spring return type push button for initiating the control code to the field equipment; and a two-position toggle switch for control of the “maintainer call” lamp and/or horn at each field location with one indication lamp associated.

The track occupancy indication lamps (both intermediate and OS track occupancy track lights) are located in the track diagram extending across the control machine above the control levers. A single stroke bell is provided for audibly announcing of train movements at each interlocking and sounding the approach to the CTC territory.

Figure 16, illustrates a standard US&S type CTC machine and the function of each device: 

Track Model Board:

The track model board shows a simplified representation of the physical track layout. Solid track indicates that the signal system protects that portion of track. Outlined track indicates non-signal protected track. All controlled signals, switches, intermediate signals, and electric locks are shown on the track model board. Above each interlocking is the timetable station name of that location. Traffic, detector, and intermediate track occupancy lamps are also located on the track model board.

OS Track Light:

The OS or interlocking track light indicates train occupancy with interlocking limits (see part 1 for more information on interlocking limits) i.e., between the interlocking home signals. . A single stroke bell is provided for audibly announcing of train movements through this circuit. When this circuit becomes occupied the train dispatcher will show on his train sheet that this train is “on sheet” (OS) by the location that corresponds with that particular circuit.

A two-position push-pull latching button is provided to cut out this audible indication for the OS track ONLY. This bell also sounds on the “approach” of a train to the CTC territory on each side of the machine. This function can be cutout by uses of a second push-pull latching button or a spring return type push button for “Approach Bell Alarm Cutout”.

Intermediate Track Light:

Intermediate track lights indicate train occupancy between interlockings, on the main and/or side track. They will also illuminate if an automatic electric lock is open and/or a slide detector fence is tripped in the block in question.

Traffic Indication Lights:

When illuminated, these lights indicate the direction of traffic through each block between interlockings. When a Home Signal is cleared into the track section in question the traffic indication light will light and will remain so until the last car clears the OS section of the outbound interlocking. Also if the dispatcher manually codes the signal to stop, the traffic light will remain lit until the expiration of “time”, this is part of time locking. Time locking protects against the dispatcher clearing a signal for an approaching train, then putting the signal back to stop and changing the route. When the dispatcher manually puts the signal to stop, the signal system will make him wait a set “time”. While the system is running time the dispatcher cannot change the original route or line any conflicting signals. This is to ensure that the approaching train that may have passed the governing approach signal displaying a Clear (Rule 281) indication has a chance to stop short of the Home Signal that is now displaying Stop (Rule 292). If the approaching train is unable to stop, his route will still be “locked” and free of any conflicting movements avoiding what, without Time Locking may have been a catastrophe (See Part 2 for more information on Time Locking).

Now you may ask why when the signal system is “running time” is the traffic light still lit. Traffic Locking, which is that part of the signal system that ensures that a train does not receive a favorable indication into a block if an opposing route is established, keeps the dispatcher from clearing an opposing signal and prevents him from making a “corn field meet.”

The Association of American Railroads (AAR) guidelines for vital signal circuits for Traffic Locking states “On track signaled for movements in both directions the vital traffic circuits shall assure that the established traffic remains in effect while the track section between interlockings is occupied. Traffic Locking shall also prevent the manipulation of levers or other devices from changing the direction of traffic on a section of track while that section is occupied or while a signal governing movement into that section is running time or displays an aspect for a movement to proceed into that section.” In a nut shell, the traffic light remains lit on the dispatcher’s panel because Traffic Locking remains in effect until the expiration of time or until all track sections between interlockings are unoccupied.

Maintainer Call (MC) Toggle Switch and Indication Lamp:

The Maintainer Call (MC) feature was simply a light and/or horn that the dispatcher could activate on the side of a relay house located at each interlocking in question. The dispatcher would flip the maintainer call toggle switch to the “on” position he would then press the code start button to activate this feature. The Maintainer Call light would illuminate on the side of the relay house and if so equipped with a horn it would blow for 8 seconds.

The MC indication lamp below the code start button on the control machine simply repeated the field MC light. After the conversation between the employee and the Train Dispatcher was complete, the dispatcher would manually turn the maintainer call light off. This feature was NOT in any way electrically connected with the phone system on most railroads. One important point though, the term “Maintainer Call” is a bit misleading! Most railroads Book of Rules required ANY employee observing the light lit to immediately communicate with the train dispatcher.

Power Switch or Electric Lock Control Lever and Indication Lamps:

The switch control lever is a two-position 60 degree rotary (left to right) switch that allows the dispatcher to initiate the control code to the field equipment to control the corresponding power or electrically locked switch. The “N” and “R” labels on the control lever plate stands for Normal and Reverse. Normal is the main track route and Reverse is the diverging route, either from one main track to another or from the main track to a siding.

Electrically-locked switch lever control plates are also labeled N and R for normal and reverse and are controlled by the Dispatcher. Normal is lined and locked for the main track and reverse being unlocked and the switch lined by hand for the siding. An electric lock provides a means of locking a manually operated switch with the signal system so that the switch cannot be operated unless traffic conditions permit. In conjunction with the N or R prefix switches and electric locks are labeled with ODD numbers, 1, 3, 5, 7, etc..

When the normal and reverse indication lamps are lit, they indicate that the field equipment has responded to the control code sent by the dispatcher and that the power or electrically lock switch has now assumed the new position so indicated.

Signal Control Lever and Indication Lamps:

The signal control lever is a three-position +/-30 degree rotary (left, center, or right) lever that allows the dispatcher to initiate the control code to the field equipment to control the corresponding signals. The label on the control lever plate “L” and “R” stands for Left (west) and Right (east). In conjunction with the L or R prefix signals are numbered EVENLY, 2, 4, 6, 8, etc. (see figure 17 for the six standard CTC and two standard train order signal control lever plates).

The left and right indication lamps indicate that the wayside signal in the field that corresponds with the lever position selected has responded to the control code sent by the dispatcher and is actually now displaying an aspect greater then stop (Rule292).

The signals normal lamp will only light when all signals controlled by the lever in question are displaying stop (Rule 292) and that they are NOT in the process of “running time”. During the process of running time all three indication lamps associated with the signal control lever will be dark. After the expiration of “time” the signals normal lamp will light.

Call On Button or Toggle Switch:

The Call On button is a push button or two-position toggle switch. This feature is used for “back to train” movements. A good example of a back to train move is, a local freight pulls into a siding at a given station and must do some switching downtown. The conductor cuts the head cars away from his train and proceeds out of the siding and down to the local industries. All good local freight conductors would block their train according to their stops along the line. Once his switching is complete downtown, the light engine must now return to the remainder of his train left in the siding. Basic signal logic tells us that the dispatcher will be unable to clear a signal into the occupied block of the siding. By aligning the switch and signal levers appropriately and pushing and holding the “Call On” button or flipping-up the toggle switch while pushing the code start button, a special control code is sent to the field to override the safety feature in the system of protecting the occupied block in the siding. A restricting (Rule 290) signal aspect is then displayed on the governing wayside signal allowing the light engine to proceed into the siding.

A restricting signal requires that the engineer “Proceed prepared to stop short of train, obstruction, switch improperly lined, broken rail or anything that may require the speed to be reduced, but not exceeding fifteen (15) MPH”. In this case, the obstruction is his train which was left in the siding. By requiring the dispatcher to push and hold an additional button or flip an additional toggle switch, there can be no mistake in the dispatchers mind that he is activating this special feature and overriding certain safety features in the system. An important note though for programming logic is that the interlocking limits must be clear and all power switches within the interlocking limits aligned appropriately for the back to train route for this feature to activate.

Code Start Button:

The code start button is a spring return type push button for initiating the control code to the field equipment. The Dispatcher pushes the code start button as the last action needed to initiate this or any code in that column. No command will be sent to the field until this button is pushed. Changing any lever and/or toggle switch position will not cause a change until this action!