Saturday, September 28, 2013

The Austrian station block: An animated explanation - the internals

Deutsche Version

This second posting about Austrian interlockings of type 5007 has the goal to present some internal mechanical details. Most prominently, it explains the inner workings of the Siemens block instruments, whose fundamental function I explained at the beginning of the previous posting.

The Siemens block instrument was invented by Carl Frischen, a co-worker of Werner Siemens at Berlin, in 1871. Although its initial application was with block working over the line—where the secure communication need was most pressing—, it was soon used to secure the dependencies in the area of a single station with multiple signal boxes, which were under the lead of a single traffic director. This use of block instruments became later known as "Bahnhofsblock," which I translate as "station block."

While I intend to present the internal workings of a command frame and a lever frame in sufficient detail to show the mechanical and electrical dependencies, I have abstracted away many (many many!) parts that are necessary in the real world, but are only distractions for that general understanding. I dropped some parts completely, e.g., all electrical circuits, or the double locking of route bars—maybe I find time to explain these parts later.

To see what is going on inside these frames, I go once more over that sequence of six steps from the previous posting, where the traffic director, the pointsman and the train work together to get the train into the station.


4.1. Traffic bureau: Transmit order


Again, the traffic director tilts the small route lever and blocks the Ba instrument—which at the same time unblocks the Be instrument at the signal box— and then triggers the track indicator:



We now take a closer look at the blocking and unblocking of the two block instruments.
Let me stress a last time that block instruments consist of many more parts than shown in my explanations. However, their basic function is exactly as shown.
A block instruments consists of a
  • toothed rack, whose teeth engage with the two teeth of an
  • anchor, which therefore locks the rack in place.
When, however, the anchor is moved back and forth by two electro-magnets, the rack can wiggle downwards or upwards tooth by tooth. When the block instrument is moved to the blocking position (it is "blocked"), the rack moves only by gravity. However, there is an additional obstacle: On the rack, there is a pin, which is held up by the rack guide of the locking rod. The locking rod is held up by a spring, so altogether the rack is held in its upper position. To free the way for the rack, this rod must be pushed down; the respective operator (in our case, the traffic director) does this indirectly by pushing down the knob (or handle) atop the handle rod which, in addition, also connects the magnets to the inductor.


Therefore, by pressing the knob and turning the inductor crank, the block instrument can be blocked. At the end of this process, the rack has moved down, turning about its axle by about 60 degrees. The stopped anchor again locks the rack in place, which now continues to press down the locking rod even if the handle rod is released. This allows the block instrument to lock whatever it is supposed to lock in the frame below.
Actually, the Siemens block instruments were so predominant in Central and Eastern Europe that all frame designs could be combined with them for locking purposes—down to quite simple devices only used for temporary interlocking installations like the Austrian "Trommelschlüsselwerk" or the German "Schlüsselwerk" (two types of lock-and-key matrices).
In the command frame, the locking rod locks the route bar. Here is an animation of this blocking action:



Blocking the Ba block instrument unblocks the corresponding Be instrument at the signal box. Also there, the locking rod is pulled up by a spring, but because of the blocked-down rack, this locking rod is currently in its lower locking position. When the instrument is unblocked, however, the oscillating anchor allows the rack to move upwards tooth by tooth, pushed at the rack pin by the rack guide, which is lifted by the locking rod's spring. The lock is thus released:
By the way, although springs are used in these devices at crucial places, they are designed in such a way that a broken spring will never compromise security. What might happen is that a rod drops at a place where it should be in its upper position—but this will always lead to secure situations, even if all signalling might come to a grinding halt. Actually, this requirement is not always easy to fulfill—there are, as far as I know, places where this rule requires some additional locking elements.



The animations above show how two corresponding block instrument can exchange a locking requirement between two remote locations. But why use such a complicated mechanism at all? Wouldn't simple direct connection, as e.g. used in English line block instruments, do the same job? I did not find any positive and explicit reasons and reasonings for this decision. However, from the quite interesting book "The Application of Electricity to Railway Working", written in 1877 by William Edward Langdon, and the entry "Blockeinrichtungen" in Röll's railway encyclopedia from 1912, it seems to me that the story could have run about like this:
  • In the 1840s and 1850s, short intervals of current supplied by a battery ("single DC pulses") and weak magnets, like magnetized needles, were a customary design for railway circuits—including long distance applications like block working which would change their state due to short, i.e. non-continuous application of current.
  • During the 1860s, it became clear that such designs had inherent risks: "Atmospheric electricity" could create a sufficient voltage to induce a current capable of activating sensitive magnetic devices; and lightning strokes could create arbitrary voltages and currents—depending on their distance from electric lines they might destroy or merely disturb the instruments. Because of these problems, alternative solutions were actively sought, among them: (a) Continuous currents for danger-carrying states, like "line is free." (b) Strong magnetic fields, by using large magnets (and small soft-iron parts). (c) Alternating currents, which allowed to keep the principle of non-continuous operation for state changes.
  • Additional factors had to be considered: DC could only be provided from batteries, which however had to be changed at intervals—either by replacing the whole battery, or by replacing its depleting components, i.e., the electrodes and vitriolic solution (I have not found any reference what was common practice in those initial years). AC could only be provided by hand-cranked generators, which however did not need any supplies.
  • The number of wires needed for the whole system was an important factor. Therefore, up to the end of the 19h century, an earth link was considered acceptable; electric traction at last put an end to this practice.
  • By around 1875, all the design questions had essentially been settled, and—so it seems to me—electricity research and development for railways went into new areas, e.g. into power applications for traction during the 1880s and points during the 1890s. Thus, the experimental era of block working and communications via electrical currents was over, and the respective solution concepts (battery currents in England, alternating currents in Germany) were never again left, rather the chosen solutions were enhanced and completed for large-scale and standardized application.
If someone could shed more light on the history and reasons of this "division," I'd be happy about a corresponding comment or message!

But now let me continue with the internals of those type-5007 frames!

4.2. Signal box: Set up route and clear signal


After the command from the traffic director has arrived (i.e., the Be instrument has been unblocked), the pointsman sets the points (and reverses the FPL levers where necessary). Then, he locks the points levers of the route mechanically by tilting the route lever, which moves the route bar in the locking bed so that all catch handles of points required for the route (directly or for flank protection) are locked in place. Next, the route bar itself is locked electrically by blocking the Ff instrument (which, at the same time, unblocks the Fa instrument at the traffic bureau). Finally, this enables the pointsman to reverse the signal lever of the corresponding signal:



Let us take a closer look at the reversal of a points lever. The following animation shows that the catch handle releases the lever. After reversing the lever, the catch handle is released, which locks the lever in place. But pulling and letting go of the catch handle each moves the lever leading into the locking bed. Because the points lever is reversed by about 180°, both the movement caused by pulling and the one by letting go of the catch handle add up to a combined movement that raises or lowers a hook in the locking bed used for locking the lever:



One can also see that the catch handle is not connected directly to the levers leading to the locking bed, but rather via a spring. The following animation shows the reason for this design: Locking the points is accomplished by moving the route bar to a position where it prevents the locking hook to be lowered. Therefore, the releasing pin on the lever does not leave the corresponding slot on the frame, and hence the lever cannot be reversed. Still, the catch handle can be fully pulled—but this will only expand the spring without unlocking the lever. If the catch handle were connected directly to the levers leading into the locking bed, a forceful pointsman could possibly warp parts of the delicate mechanics or even overcome the lock and force the lever to the opposite position, both of which must of course be prevented.
Actually, this crucial spring is hidden somewhere inside a lever. A signal engineer and I searched for it at a lever for some time, but we did not find it ... The springs visible at the outside of real levers pull the catch back in normal operation—something I have omitted from my animations.



After the points have been set and the route has been locked mechanically, the Ff instrument is blocked. Here is a short video showing the inductor used for blocking, which generates alternating current of about 70 to 90 volts at around 12Hz. Of course, the traffic director had used a similar inductor in the first step when blocking the Ba instrument:



Here is another video, this time showing the blocking of an Ff instrument. The handle has already been depressed at the start of the video:

For specialists: This is, actually, a DC-AC instrument of a central interlocking—a video of a pure AC instrument is still missing from my collection.



4.3. Train passes by


The train releases the button lock. This is accomplished by a short insulated rail which, when shortcut by the train's axles, energizes a relay which in turn sends a DC current from a battery into a separate electro-magnet (therefore, these special instruments are called DC-AC instruments, in contrast to the AC instruments using alternating current for both blocking and unblocking):



Here is a picture of such an instrument removed from the frame. At the left, there is the rack (without the black-and-white faceplate), at the back are the magnets moving the anchor (the picture has been turned by 90°—actually, the instrument was lying on a table):


The following picture shows the back of the instrument, with the anchor's AC magnets at the top (one is behind the anchor shaft) and the DC release magnets at the bottom:


4.4. Signal box: Return signal to stop


At the released button lock, the handle rod can now move downwards. Therefore, the pointsman can now unblock both the Be instrument and the Ts instrument via the connected handles to their locking positions. At the same time, the Ba instrument at the traffic bureau is unblocked and releases the route bar:



4.5. Traffic bureau: Release route


The traffic director blocks the Fa instrument, which unblocks the Ff instrument at the signal box and releases the route bar in that locking bed. At the traffic bureau, the route lever is returned to its normal position so that other routes can be selected and corresponding commands can be sent to the signal boxes:



4.6. Signal box: Return points to normal position


The electric lock at the signal box has been released when the traffic director unblocked the Ff instrument, and therefore the pointsman can also return the route lever to its normal position. This, at last, releases all the catch handles of the levers that have been locked until now (see animation under 4.2), so that the FPLs and points can be returned to their normal position:



This concludes my animation sequence of the principles of type-5007 command and lever frames. Of course, one could now expand these explanations in quite a few directions:
  • How where the various locks accomplished that prevented unacceptable operations, e.g. clearing the signal as long as no command had been transmitted?
  • How does one deal with failures in the apparatus, and with operational changes like changed order of trains after a command has been given?
  • Which other typical installations are there (e.g., many stations only have a single frame in the middle)?
  • What about more technical details—especially the locking bed with its route bars deserves a more complete explanation, but also levers for points, electrical circuits and the provisions for torn wires might be interesting topics.
  • How does line blocking work, and how does it interoperate with station blocking?
If someone is interested in one of these topics, he or she can leave a comment here—maybe I find time to create additional texts or animations!

Saturday, September 21, 2013

The Austrian station block: An animated explanation

Deutsche Version

This posting is an attempt to explain a piece of railway technology from Central Europe to all who are not fluent in German. Specifically, it deals with the functions of the "station block," which connects the traffic bureau and the signal boxes, on Austria's railways. In contrast to other explanations e.g. in books, I want to use the possibilities of the Internet in these explanations, namely animations and a few short videos.

Explaining railway technology is difficult because the railway is a system where many parts interact closely: Signalling technology for block working with technology at stations, line-side technology with train equipment, and—sometimes more importantly than devices alone—technology with rules and regulations and even concepts like "station" or "line." Therefore, it is almost impossible to explain a piece of railway working separately from its environment. Fortunately, there is a piece of writing that already explains much of this context, namely Jörn Pachl's splendid article "German Block and Interlocking Principles – An Introduction for the Anglo-Saxon Reader." And despite its title, almost all of it is also applicable to Austrian railways.

While quite a lot more could be said about the differences between "Anglo-Saxon" and "German" signalling and operating principles, I will delve head-on into the description of the interlockings of a typical Austrian station. I hope that many direct questions ("how does it work?") are answered by this text. On the other hand, many background question ("but why was it designed like that?") will go unanswered—and whereas I will try to answer some of them in a later posting, I fear that much of that is beyond my knowledge; or might even have to be answered with "because it was customary to do it like this" or the like. See also my short text on "Different ideas on technical risks" for that.

The large difference between German-influenced and English operation and interlocking practices is the result of two inventions:
  • First, the invention of the Siemens block instrument by Carl Frischen in 1871, a device unknown in British and American interlocking technology. This device allowed a technically secure collaboration of persons working at different signal boxes and traffic bureaus. In contrast to English and American practices, this soon lead to (or rather set in stone) a hierarchical organisation of operational responsibilities over the area of each station, even if two, four or more signal boxes were necessary (in contrast to England, where each signal box's signalman is fully responsible for all train moves on the tracks assigned to that signal box).
  • Second, the introduction of route locking by route bars by Büssing in 1875 (after a first use in a command frame by Siemens in 1872), i.e., all points for a route from a signal to the next signal (or the end of the rotue) are locked with a single interlocking movement. This is only viable because shunting movements are not signalled, hence it is necessary to lock points only for train routes.
The central control of each station required the introduction of "command frames" which did not control any points or signals, but were only used to unlock signal levers at distant signal boxes from the central traffic bureau. This resulted in a distinction—retained up to this day—of "stations" (the area under the supervision of a single traffic director, who has a tight technical and organizational control over all "his" signal boxes) and "line territory," where traffic is handled by the co-operation of equal-ranking traffic directors. Somewhat illogical, signal boxes at junctions or simple block posts did not count as stations, even though they required the full technical and (at least in the case of junctions) organizational equipment of a station.
At times, this lead to interesting situations: At the large hump yard at Wels, there was a signal box which counted as a junction for some movements, but as part of a station for others; therefore, some of its signals routes needed orders from one of the station's traffic directors, whereas other routes could be set up under the discretion of the signalman at the signal box.
At this point, I need an English word for the persons working in signal boxes. But ... isn't it simply "signalman"? After thinking about this for some time, and after reading two very enlightening papers by Jörn Pachl that compare German, English, and American operational practices (which are, to my knowledege, unfortunately only available in German), I have decided that it is inadequate to translate one of the two important roles of "Fahrdienstleiter" and "Stellwerkswärter" as "signalman:" Whereas a signalman has roughly the responsibilites of "Fahrdienstleiter", the word "...leiter"=leader implies that there are typically (two to many) people that are lead, i.e., subsidiary to the "Fahrdienstleiter"—which is not a connotation of "signalman." Hence, I use the term "traffic director" for "Fahrdienstleiter" and the word "pointsman" for "Stellwerkswärter" (even though a "Weichenwärter," which is the direct translation of "pointsman," is another role with typically less responsibilities than a "Stellwerkswärter"—but I skip these fine points), and circumvent the term "signalman" altogether. So if someone asks, after reading my texts, "But where is the signalman?," the answer is "the combination of the traffic director's decision-making responsibilities and the pointsmen's manual work is equivalent to the signalmen." In rare cases, however, the term "signalman" seems appropriate—e.g., in the special situation at Wels described above.

A few more notes on command frames: Historically, there have been instances of connecting command frames with lever frames by mechanical (instead of electrical) means. One example that survived into the 1980s and which is now a heritage signal box is located at Kerzers in Switzerland. Moreover, there were stations where the traffic bureau was located near one throat of the station, which sometimes (but not always!) lead to the integration of this throat's lever frame with the command frame for the signal box at the other throat. In such a case, the "Fahrdienstleiter" would have both roles and could properly be called a "signalman." Examples of such setups were Oberdrauburg in Carinthia or Bad Ischl Frachtenbahnhof (goods yard)—at the latter one, the type-5007 frames are still in use up to now!
In Germany, the combination of command frame and one side's lever frame was the rule (rather than the exception, as in Austria), and hence the traffic director is almost always located in one of the signal boxes, whose abbreviation is then, customarily, followed by an "f"—e.g. Wf for "Walheim Fahrdienstleiter(stellwerk)". This would, in turn, require an additional employee at the station building proper for selling tickets and handling goods contracts—a role that in Austria was, at least in smaller stations, traditionally filled by the centrally placed Fahrdienstleiter.
In our modern times, where operational and commercial responsibilities have been completely separated at each station, this lead to locked traffic offices everywhere—however, older people in Austria still knock on the Fahrdienstleiter's door to ask him everything from timetables (ok) to train delays (mostly ok) to ticket prices (not ok) to policies for returning unused tickets (not at all ok), only to get told that he no longer can answer that. In Germany, where the operational and commercial responsibilities had been separated in many more stations, this change was not felt so sharply as in Austria (the exception being many German stations with a single lever frame in the middle). So much for that.

But now let me finally start with the explanation of station block working!

This and a following posting show the interaction of the command frame and the lever frames from the viewpoint of its users, viz. the traffic director and the pointsmen. The exact mechanical details of the interlocking and the necessary electric circuits are not part of my explanation. However, I will nevertheless present animations of an "inside view" of the frames involved—this should help to understand the dependencies between the various parts much better. Yet, I'll present a very simplified version of these inner parts, because their actual construction would again require many more explanations.

As a teaser, here is a drawing of all the mechanics that will come to live in the animations (I did not change the German texts in the animations—I think the operation can nevertheless be understood from the diagrams and my texts):


This is my first attempt at such larger animations. Even though I have worked on them for almost two months, I am not yet satisfied with them. E.g., the "camera work" is quite static—that could be better! I am therefore happy about any comment, hints or ideas about improvements

My explanations are based on the traditional frame setup at an Austrian station:
  • The traffic bureau is located in the central station building. The traffic director uses a "command frame" in the traffic bureau to dispatch "commands" (routes to be set up) to the signal boxes.
  • At each station throat, there is a separate signal box ("throat box"; "Endstellwerk") controlling the points (and FPLs) as well as the home and starting signals in its "half" of the station tracks. In each signal box, a lever frame controls the points, FPL, and signal levers. Electric locks on top of the lever frame provide the necessary interlocking between the command frame and the levers at the signal box.
Of course, many smaller stations had a simpler layout with only a single lever frame in the traffic bureau, which then would have the function of a signal box ("central box" = "Mittelstellwerk"). I will not explain how such a box works, and also ignore the (rare) direct interaction of signal boxes as well as the interaction between multiple traffic bureaus at very large stations. Finally, I will also totally ignore block working for the moment, i.e., I assume that the station is on a line with "telephone block," where all train movements on the lines are only secured by (prescribed) messages exchanged via telephone.

In the following, I will explain a train movement at a signal box about four times, starting with a short overview and ending with detailed animations. I will skip most details related to rules and regulations, mainly because this would make the explanations even longer, and second because.


1. Short description of a train movement


When a train runs through a station (with or without stopping there), the following happens:

  • About three to five minutes before the train is due, the traffic director selects both a route for entry into and one for exit out of the station on his "command frame" and then transmits the corresponding orders via block instruments to the signal boxes. By pushing a button, he also informs them about the (line and running) tracks to be used for the movement.
  • Each of the pointsmen now sets his points and FPLs and locks them mechanically and electrically, which allows him to clear the corresponding signals. The mechanical interlocking between points and FPLs levers one the one hand and signal levers on the other hand enforces the legally required dependencies between points and signals.
  • When the train traverses the route, it releases the "button lock" at the lever frame.
  • Each pointsman checks the train's tail lamp and then returns the signal(s) to their stop position. Then he "blocks back the order" to the command frame via a block instrument.
  • The traffic director blocks, for each ordered route, another block instrument, which releases the electric route lock at the signal box.
  • Both the traffic director and the pointsmen can now reverse their route levers. At the signal boxes, the points levers are now no longer locked, and hence the points can be used for shunting or other train moves.


2. Functional groups


The following images show the parts of the frames that are necessary for setting up routes.

The command frame in the traffic bureau contains devices for three purposes:
  • Small route levers select the running tracks to be used (step 1 above).
  • Block instruments transmit the orders (step 1) and release the routes at the signal box later (step 5).
  • A track indicator button triggers the track indicator at the signal box (step 1).

The following picture shows a traffic director transmitting an order (step 1) to signal box no.1 at Ziersdorf. The abbreviations on the block instruments are as follows:
  • Ba = Befehlsabgabe; literally "command dispatch"
  • Fa = Fahrstraßenauflösung; literally "route release"
Actually, these terms and their abbreviations were only introduced in the 1930s and, more consequently, when Austria was occupied during WW II. The terms used before that time are mentioned and explained below.


At the signal box, four purposes are served:
  • The block instruments receive and return orders (steps 1 and 4) and lock routes electrically (step 2).
  • The track indicator shows which running track is to be used (step 1).
  • Route levers lock routes—i.e., all levers needed by a route—mechanically (step 2).
  • Finally, the lever frame holds the points and signal levers (step 2).

The next two pictures show these devices at the signal box no.1 of Ziersdorf. The abbreviations on the block instruments are:
  • Be = Befehlsempfang; literally "command receive"
  • Ff = Fahrstraßenfestlegung; literally "route lock";
  • Ts = Tastensperre; literally "button lock";
I'll explain their working below.



Ziersdorf was a real, albeit small station with three running tracks. However, for my explanations I will reduce the complexity even more to the bare minimum: I will look at one signal box, one direction of travel and one running track—in effect, one single route. Thus, I "cut" the following parts from Ziersdorf's frames (the two abbreviations mean: "Fdl"="Fahrdienstleitung"="traffic bureau" and "Stw"="Stellwerk"="signal box"):


I will place this single route in a station that
  • has only one set of points on each side of the station,
  • does not need FPLs (presumably, the maximum speed on the line is only 40kph),
  • has only single-arm semaphores (which is allowed on such a slow line)
  • and still has "throat boxes," i.e., a signal box at each end of the running tracks.
(I do not know whether any real station had all these properties. But there were at least signal boxes at the end of stations that moved only a single set of points—e.g. at Hintergasse on the Arlbergbahn or at Strechau in Styria).

But before I present the working of 5007 frames in animated detail, let me describe with one more piece of text, namely a "sequence table."

3. Sequence table of a train movement


The following table describes the standard procedure for a train movement past a signal box equipped with a type-5007 frame, together with the necessary actions on the command frame in the traffic bureau. The table shows, in each column, the state of a part of the system—in this case, block instruments and levers. Each state change is marked by a bold black line that is accompanied by the state descriptions. For block instruments, these short descriptions are shown in the respective colour shown in the block instrument's window. On the left, there is a "narrative" of who does what during the train movement. A click on the table opens a more readable PDF file:


Of course, there are many more operation sequences in the case of technical or operational problems. For example, it must be possible to revoke an order if the station in the rear needs to change the order of trains on short notice; or it must be possible to run trains as securely as possible even if a signal is out of order. This type of problems has a significant impact on the design details of the various parts involved—however, I'll ignore all this in the following description and proceed as if everything worked completely regularly.

4. Animations


The following six animations, finally, show the actions during a train movement as experienced by the traffic director and a pointsman. In these animations, green covers hide the inner details—in the next posting, I will then reveal what's going on "behind the scenes." Each animation has flashing orange arrows that point to the place where someone has to do something. My main modelling work went into the central and signal box frames, whereas I neglected the details of the points and the signal—for example, the points should have blade locks (when I have lots of time, I might add such details). The numbers besides the paragraph headings refer to the steps of the table in the previous section. The animations should be detailed enough to view them in full-screen mode—this might reveal one or two details that are hard to detect otherwise.

4.1. Traffic bureau: Transmit order (2,3)


In this first step, the traffic director selects a route and blocks the Ba block instrument. This unlocks the signal lever (therefore the block instrument was called "signal lock" in earlier times) and counts as an order to set up the route at the signal box. In the command frame, this route selection prevents the selection of other, conflicting routes.

A tap on the track indicator button, together with a turn of the inductor crank, drops a small sign in the signal box that shows the track to be used. However, this operation is not connected to the interlocking proper, and it can be (and is) omitted if the train will use the track indicated in the schedule.



The following short video shows this sequence in the traffic bureau of Sigmundsherberg, ...



... and here we see how the Be block instrument at the signal box is unblocked:



(Unfortunately, these videos are without sound, so you miss the characteristic rattling of the block instruments; but there will be a video with sound in the next posting).

4.2. Signal box: Set up route and clear signal (4,5,6,7)


The pointsman sets the points and, where needed, their FPLs for the required route. As the points have to be in their normal position when not used otherwise, this often means that only a few FPL levers have to be reversed. In my example, however, the train should go into track 2, and therefore points W1 have to be reversed. One can see that the rod leading into the locking bed is moved by the catch handle, but not by the lever itself: When the catch handle is pulled, the rod moves the first half of its travel; it remains stationary during the reversal of the lever, and moves the second half when the catch handle is released.

After all levers have the required position, the route is mechanically locked by tilting the small route lever. The route bar in the locking bed now prevents any movement of the rod leading to the lever and therefore locks the catch handle, which in turn locks the lever in place.

By now blocking the Ff block instrument, the pointsman locks the route bar electrically. From this point on, he cannot (except by emergency measures) unlock any lever without a release action of the traffic director. But on the other hand, the blocked Ff instrument now releases the signal lever, so that, finally, the pointsman can clear the signal.



Here are two short videos that show the blocking and unblocking sequences: At the signal box, the Ff block instrument is blocked ...



..., in the traffic bureau we see the sequence from above, extended by the unblocking of the Fa block instrument (the signal man must have stood near the instrument so that he could block his Ff instrument right after the order was transmitted):



4.3. Train passes by (8)


Instead of returning the order (by blocking the Be instrument) after the train has passed, an eager pointsman might do this too early. A careless traffic director might then release the route, and the pointsman could then reverse points right in front of or under the train. Of course, this must be avoided, and therefore, the train itself takes part in the release sequence: By shortcutting a short insulated piece of rail, a relay is energised which in turn unblocks the "button lock" block instrument. Only when this has happened, can the pointsman block the Be instrument.

However, the animation shows two problems with this design:
  • The button lock is released by the first axle of the train! It seems that the Be instrument could be unblocked at a very early point of time, while a long train is still rattling over the points. This problem is solved by putting a contact of the relay mentioned above in the Be circuit, so that blocking of the Be instrument is prevented while that relay is energised. This remains so as long as train axles move over the insulated rail.
  • When a train enters the station, its wheels pass the insulated rail before negotiating the points! Therefore there is, at least with a slow train, still the possibility that the pointsman blocks back the Be instrument after the train's last axle has left the insulated rail, but still rumbles over the points. If blocking the Be instrument released the route directly, the pointsman could then immediately reverse points under the train! This possibility was the original reason that the traffic director is involved in the route release process at all: One hopes that two people together might not make that mistake in the limited time when the rear end of the train traverses the points—especially when one of them is responsible for all train movements in the station area. Still, from the 1930s onwards, for entry into a station, separate insulated rails were put inside each running track, so that a train entering the station would unblock the button lock only after it had passed all points with all axles. The participation of the traffic director in the release sequence was nevertheless kept also after this enhancement. By the way, the insulated rails in each track lead to the introduction of two different markers for fouling points in Austria: The "small marker," two red-and-white knobs, marked the actual "geometric" fouling point where the tracks after a turnout had the minimum clearing distance; the "large marker," the common black-and-white bar, marked the end of the insulated rail, i.e., the point to which a train's rear end must advance so that the button lock is unblocked.

4.4. Signal box: Return signal to stop (9,10)


When the train passes the signal box, the pointsman checks the tail lamp. Only after that, he may return the signal to the stop position. This now allows him to "return the order" by blocking the Be instrument. The points levers, however, are still locked by route bar that is in turned locked by the Ff instrument. Together with blocking the Be instrument, by mechanical linkage, also the button lock (Ts instrument) is blocked into its locking position. Thus, the next train movement will require a new transmitted order (unlocked Be instrument) from the traffic director.


4.5. Traffic bureau: Release route (11,12)


The route release proper is done by the traffic director: He blocks the Fa instrument, which unlocks the Ff instrument at the signal box and hence releases the route bar at the signal box.


4.6. Signal box: Move points to normal (13)


The unblocked Ff block instrument makes it now possible for the pointsman to return the small route lever to its vertical position. This, finally, releases the mechanical lock on all the locked levers (or rather their catch handles) so that FPLs can be returned to their normal, unlocked position; and points and shunt signal can be set as needed for shunting or other train movements.



So much for the first three explanations—a short one, a table, and a sequence of animations—of the co-operation of a traffic director and a pointsman (or, rather, a command frame and a frame at a signal box) under Austrian station block working.

In the next posting, I want to present animations of the inner workings. They will be of quite simplified versions of all the instruments, but still should allow to understand part of what happens behind these green covers!

Wednesday, September 18, 2013

Signal boxes at two Austrian stations in 1983: Ziersdorf and Limberg-Maissau

This posting shows the mechanical interlockings of two stations on Austria's Franz-Josefsbahn in 1983. Shortly afterwards, these interlockings were replaced with electromechanical ones of the ÖBB type 212 (or EM5007, as it is now known), which in turn were to be replaced with relay interlockings of the type VGS80. However, because of problems at the suppliers, the latter replacement was not fully completed, so there are still EM5007s at various stations on this line right now in 2013.

I have selected these stations because I plan to publish a few postings with explanations about the Austrian standard interlocking type "5007:" The stations presented here have 5007-type frames that best resemble the animations I will present in these upcoming postings.

But now let me introduce the stations of Ziersdorf and, after that, Limberg-Maissau in Lower Austria.

At Ziersdorf, one can see that the electrification of the line is under full development. However, in front of the building two old hand carts stir up memories of older, more quiet times:

Ziersdorf station, 10.12.1983

The signal boxes contained good old 5007-type frames, although block working had already been converted to the relay "ZG block" system on the whole line.

The following picture shows a somewhat stressed train director, who is talking to the next station and at the same time unblocking the signal block instrument for a train from Gmünd (the red lamp in the right "ZG" arrow at the top shows that the train is already on the line):

Block instruments, traffic bureau Ziersdorf, 10.12.1983

Above the block instruments in the traffic bureau, one can see the schematic track plan. It is plainly visible that the line once had two tracks, but had been single-tracked in the past: The home signal Z is still shown near a somewhat sloppily erased left-hand track, both home signals are shown at the left of the line (which would only be done on double-track lines with left-hand running; so actually, both home signals were on the right of the single track in 1983), and starting signals are missing from track 1 on the left side and track 2 on the right (although they were of course installed in 1983 so that all tracks could be used in both directions). By the way, all other tracks plans I've seen that had to be modified after changes to the stations's layout were corrected much more diligently than this one—it is a small wonder that this sloppy patchwork was allowed here.

Block shelf and track diagram, traffic bureau Ziersdorf, 10.12.1983

Signal box no.2 was a small single-storey building:

Signal box 2, Ziersdorf, 10.12.1983

Inside, there was a quite small and quite original 5007-type lever frame, the only newer parts being the arrows of ZG block above and a comparably new buzzer for the barriers of a level crossing (the buzzer would sound if a signal block instrument was unblocked, but the barriers were still raised). The small lever on the frame is the "king lever" which locks all points during the nightly closing of the line:

Lever frame and block instruments, SB 2 Ziersdorf, 10.12.1983

Next to a milestone (or rather, "hectometre stone": Yes, this is the official name), I took a picture of the supporting pulleys for the double wires leading to the points, facing point locks, and signals. In earlier times, old boiler tubes from steam engines were used as supports of these pulleys:

Rollenträger beim SB 2, Ziersdorf, 10.12.1983

I also visited the other signal box:

Block instruments, SB 1 Ziersdorf, 10.12.1983

Here is the whole frame, perfectly cleaned so that the mirror images of the track indicator and other parts can be seen:

Lever frame and block instruments, SB 1 Ziersdorf, 10.12.1983

This picture shows signal box no.1. The form of the building is similar to the other box, but this one is still the traditional wooden building:

SB 1, Ziersdorf, 10.12.1983

Here are the semaphore starter signals R1 (one-arm signal for the main track on the left), R2 (two-arm signal for limited speed from track 2—however, the sign "6" allows a speed of 60kph through the points), and R4 (two-arm signal for track 2, for signalling a maximum speed of 40kph through the turnouts):

Ausfahrsignale R1, R2 und R4 Richtung Gmünd, Ziersdorf, 10.12.1983

In the next picture, one can see that the two Austrian two-armed semaphores R2 and R4 had been fitted with German electric signal arm clutches so that, according to German rules, they would drop to "stop" after the train had entered the block section ahead. The signalman is here on his way to grease the points:

Starter signals R, Ziersdorf, 10.12.1983

And here, a train blazes through the station:

2143.61 with goods train 60813, Ziersdorf, 10.12.1983


After Ziersdorf, I visited Limberg-Maissau which had similar signal boxes. The signal arms there had been replaced with reflecting ones, and therefore all lamps were gone. In the background, one can see the new colour light signals, with their screens still facing away from the tracks:

Starting signals H2, H1 and H3, Limberg-Maissau, 10.12.1983

The signal box 1 still had the fully equipped lever frame of a single-track line with "ZG block": Signal levers on the left, points and FPL levers on the right. All the levers are in their normal position here—the three upwards pointing levers are the "right halves" of a double-lever for the three-aspect home signal and for the FPL of points no.1 and no.2 (with three positions each: "locked left", "unlocked," and "locked right"), respectively:

Block instruments, lever frame, and track indicator, SB 1, Limberg-Maissau, 10.12.1983

Block instruments and lever frame, SB 1, Limberg-Maissau, 10.12.1983

In contrast to Germany, Austrian stations were rarely equipped with distant signals for starting signals—Limberg-Maissau, however, had them for both directions. These distant signals were not operated from the box for the corresponding starting signals, but for the opposite box. An electric clutch at the signal would ensure that the distant signal could only be cleared when one of the corresponding starting signals was also clear. However, the signal box clearing the distant signal would have to know whether a starting signal was clear, because the clutch would not clear the distant signal if its lever was reversed too early. Therefore, the box was provided with a corresponding repeater. As this sort of equipment is of German design, these distant signals and the corresponding levers and circuits were added after 1938:

Block instruments and signal repeater, SB 1, Limberg-Maissau, 10.12.1983

Here is the lever for the distant signal r of the starting signals, wedged between home signal lever A and starting signal levers H2, H1 and H3 for the opposite direction.

Signal levers, SB 1, Limberg-Maissau, 10.12.1983

In contrast to the functional signal boxes in Ziersdorf, Limberg-Maissau's box no.1 resembles a nice little cottage with a pointed roof:

SB 1, Limberg-Maissau, 10.12.1983

Here are the very standard (and badly photographed) block instruments in the traffic bureau:

Block instruments, traffic bureau, Limberg-Maissau, 10.12.1983

Outside, a newly built bridge hid the semaphores towards Gmünd. Therefore, repeaters had to be erected. Here, the middle one (for main track 1) shows clear, and the corresponding starting signal R1 can just be seen next to the right pillar of the bridge:

Starting signal repeaters 1R3, 1R1, and 1R2, Limberg-Maissau, 10.12.1983

Here is R1 once more—a German semaphore with extra-slim mast. To the right if it, R2 is an Austrian semaphore, with overlapping arms and a tubular mast:

Starting signals R1 and R2, Limberg-Maissau, 10.12.1983

Signal box 2 had a typical building for this line, which had been re-erected with bricks at some earlier time:

SB 2, Limberg-Maissau, 10.12.1983

Inside, one can again see the repeater for the distant h for the starting signals H3, R1, and R2 of the other box. Signal lever R1 is reversed, and next to the home signal lever Z, one can see the lever for distant signal h:

Block instruments and lever frame, SB 2, Limberg-Maissau, 10.12.1983

Track indicator and lever frame, SB 2, Limberg-Maissau, 10.12.1983

And here, we see the home signal Z and the distant signal h for the starting signals:

Home signal Z and distant signal h, Limberg-Maissau, 10.12.1983

The distant signal z for the home signal was located directly on the famous hill-side bridge (which became necessary when the whole slope was found to move downwards under the tracks soon after the line had been built; the pillars of this apparently low bridge reach deeply into the ground to a stable rock). One can see here the girder for the former second track, which is now used solely as support for the distant signal:

Distant signal z, Limberg-Maissau, 10.12.1983