Field block
The field block is an electromechanical component of railway safety technology . It is primarily used as a route block (in mechanical , partly in electromechanical interlockings and occasionally in relay interlockings ) and often as a station block (in mechanical interlockings).
History and meaning
The block field was invented in 1871 by the German engineer Carl Ludwig Frischen , which decisively shaped the development of the German and German-influenced railway system. The principle that locks occur at one point that can only be lifted by another point or with the help of the train has shaped German security technology to this day. The principle of the route block, which is based on this logic, cannot be applied to tracks on which trains begin and end. This resulted in the usual clear demarcation between the railway station and the open route, both technically and operationally, as is common in German principles. Elsewhere, especially in the English-speaking world, the block field remained unknown and development took a significantly different direction.
functionality
A block field can assume two states, the unblocked state (basic position) and the blocked state (active position). The field is blocked directly by the operator of the relevant interlocking . It is unblocked by the flow of electricity from the outside, either by a corresponding block field, a rail contact or a key switch. The unblocking process is triggered by another operator (guard in another signal box at the same or a neighboring station) or by a train ride.
The connection to the rest of the interlocking is established via electrical contacts or via the position of the mechanical locking bar (in the case of the route setting field also by the extended push bar). The locking bar and the extended push rod act, for example, on the locking hooks of the block locks in the block base or on block shafts in the valve body. If this possibility is missing, for example because of the use of light signals with button control or generally in electrical interlockings, the block locks are electrically simulated ( lockless block ).
The status of the block field is displayed on a colored disk. In most countries, u. a. In Germany , Switzerland, Poland and the Netherlands, the colors red and white are or were used, in Austria and the other successor states of the Austro-Hungarian monarchy the colors black and green are also used. Which color indicates the blocked state and which indicates the unblocked state depends on the use of the field. Mostly the color red is used for the basic position of the train station block and white for that of the route block. Red means that the main signals are directly or indirectly locked in the stop position.
AC block field
The AC block field is the most widely used and older form of field block. The block field is blocked by pressing and holding the block key at the top of the field while the block inductor is operated via a crank that protrudes from the side of the block box . The block inductor generates alternating voltage , the block current flowing through it flows through the magnet system of its own and, in some cases, the corresponding block field (s). By means of the alternating current, your own block field is brought into the blocked position in an electromechanical way and the corresponding block field is unblocked at the same time. Instead of a crank inductor, the block alternating voltage can also be generated by a motor, relay or electronic inductor, which replaces cranking.
The field is also unblocked by alternating current, which in this case is fed in by an external line and comes from another block field. This is usually located in another signal box that can be many kilometers away.
In the field block systems that are widespread today, two alternating current fields ("corresponding fields") always work together. The blocking of one field ensures the unblocking of the other and vice versa. However, this is not absolutely necessary, with alternating current fields far more complex systems can be built. Blocking a block field can unblock no or several other fields at once. Many older station and line block systems have made use of these possibilities, examples of which are the Saxon station block, the line block form A, the Austrian field line block or the line block form B, which was widespread in the Netherlands. In the meantime, such block designs are rarely found. In the case of approvals from mechanical to electromechanical or track diagram signal boxes, there are usually no corresponding fields.
The great advantage of the alternating current fields was that - operated with a crank inductor - they do not require an external voltage source. This made it possible in the early days of mechanical interlockings to build interlockings without being connected to the power grid. In addition, the AC block is inherently immune to interference and external voltage. Neither ingress of DC voltage nor AC voltage can erroneously unblock a block field. DC voltage only moves the armature by half a tooth, it is too sluggish for AC mains voltage. In the early days, the earth could therefore be used as a return line to save veins. With the introduction of electric train transport, however, the block circuits had to be switched to floating.
DC block field
In the case of the DC block field, blocking is also carried out by pressing the button on the block field. In this case, however, the blocking process is purely mechanical; it is not necessary to operate the inductor's crank.
The field is unblocked by a direct current impulse, which is given either manually via a key switch or with a pulling effect via a rail contact . The unblocking always takes place - as is the case with the alternating current fields - from outside the own signal box, since the block field is supposed to maintain a state that the signalman is not allowed to resolve himself.
The power for deblocking is taken from the signal box battery. In the early days, these had to be exchanged regularly. Since the introduction of easy-to-use copper oxide and selenium rectifiers and the expansion of the power grid in the 1920s, the signal box batteries have been continuously buffered, i.e. H. charged from a local power grid.
Additional facilities
The field block is expanded by additional facilities. Mainly these are the electric key locks, which have a significant impact on the security of the field block. From an electrical engineering point of view, they can be divided into permanent current and jump button locks, and from an operational point of view into route button and station button locks. A special and therefore also rare form of the key lock is the AC key lock, which is comparable in structure to the AC block field.
The task of the key locks is to make the operation of a block field dependent on a condition or to prevent the operation of a block field as long as a certain condition is not fulfilled.
A typical application for the electrical route key lock is the arrangement above the end field of the route block. Here the key lock prevents backblocking until the train to be blocked back triggers the key lock via track switch. Thus, the blocking back is dependent on the cooperation of the train to be blocked back. The typical case for the use of a station key lock is the issuing of a permit at a guard interlocking. It makes the issuing of a permit dependent on the cooperation of the dispatcher, as only he knows the appropriate time by communicating with the neighboring dispatchers. A station key lock can also be used if the approval of a platform supervisor must be obtained for a train to enter. The platform supervisor actuates a so-called lock trigger, which is usually a key switch if the requirements (route check) for an entrance are met. In this case, the station key lock would be arranged above the corresponding route definition field or else above the command or approval output field.
Auxiliary resolution
Block fields that lock turnouts in a blocked position are provided with a sealed auxiliary release. This applies to approval, command and route definition fields. This prevents operations on the interlocking concerned from coming to a standstill in the event of a fault.
Special designs
In addition to the fields mentioned above, there are other designs that are used less frequently.
Combined alternating current and direct current block fields are often found in Austria. Here, the blocking takes place with the AC function using the crank inductor, while the unblocking is triggered by a DC pulse. Key locks, but also the route definition fields of central interlockings are practically exclusively structured in this way. There are also simple buttons without their own block field, with which the alternating current of the inductor can be used directly to unblock an alternating current field.
AC block fields can also be used to create a dependency on keys. The block field can only be blocked here if the necessary key has been enclosed in the block lock of a block field. The blocked block field then prevents the key from being removed and thus fulfills the task of a key lock .
literature
- H. Möllering: The safety devices for train traffic on German railways. Published by S. Hirzel, Leipzig 1927.
- Author collective: Railway safety technology. 2nd edition, Transpress Verlag for Transport, Berlin 1974, DNB 750062967 .
- Heinrich Warninghoff: The mechanical signal box. 3. Edition. Josef Keller Verlag, Starnberg 1972, ISBN 3-7808-0083-7 .
Individual evidence
- ↑ Jörn Pachl : Special features of foreign railway operating procedures: Basic terms - interlocking functions - signaling systems . 1st edition. Springer Fachmedien Wiesbaden, Wiesbaden 2016, ISBN 978-3-658-13481-5 , p. 8-9 .