Page 97 - 捷運技術 第35期

捷運技術半年刊 第 35 期 95 年 8 月 89

Each segment has a name associated with it that includes its Region Number and Segment
Number（within that Region）. The segment layout provides for the determination of location which
is handled through what is called the “Moving Block Coordinate System”（MBCS）, which defines
the location of by a Region Number, Segment Number, and Offset into that segment. For example,
suppose that a train was 25% through segment R1S4 which is, say, 100 m long, then the location of
the train in MBCS is R1, S4, O25; for Region 1, Segment 4, and Offset 25.

3.2 Norming Points

A Norming Point is a “Passive Device” or “Passive Tag” containing “location data”. These tags
are situated along the track and contain their own location data in the form of the MBCS.

When a train passes over a tag, the tag is “energized” by the RF energy from the train’s tag
reader antenna. The tag in turn transmits its location to the train. The tag location is used by the
train for two important elements within its train control system:
1. Verification of the train’s location

2. Normalizing the train’s positioning error（discussed below in detail）
As the train travels along its route it incurs a Norming Point. The train reads the location
information embedded within the Norming Point Tag and verifies the tag location with its
calculated location.

The second purpose for which Norming Points are used is the “re-normalization” of the train’s
accrued position error. As the train moves along its route, it continuously calculates its location
using its onboard positioning system. This system is made up of tachometers that have an associated
error. This error is accrued as the train continues its movement along its route. The Train Control
System places a maximum on this position error accrual and the Norming Points are used to “reset”
this positioning error to a minimum. The following figure illustrates the error accrual and
normalisation.

Figure 5：Position Error Accrual Mitigation

In the event of a faulty or missing norming point, the train just continues past that point
without having “normalized” its error until the next norming point where the error is finally
normalized. This usually does not have any influence on the operation or on the headway.

3.3 Conflict Points