2
0
1
5
-0
9
38
Operation and communication
7.2
Operating with event markers
In numerous position coding system applications, defined processes must be started at
specific positions so that the controller can evaluate the position data measured by the reading
head. However, this means that the exact positions for triggering events of this kind must be
defined as early as the system planning stage and can no longer be modified during the
construction phase or commissioning. If modifications are made, the position data stored in the
control software must be adapted accordingly, which involves a great deal of time and effort.
Activating a process through the detection of so-called event markers is a much more flexible
method. Only a specific event and the process linked with the event have to be programmed
into the system controller. The position in which the corresponding event marker is placed
along the code strip can be decided immediately before final commissioning of the system.
Even if subsequent changes are made to the layout of a system, the relevant event marker is
simply moved to the new position without requiring program modifications.
Event markers are short code strips one meter in length. The event marker bears the encoded
event number and position information in incremental form. Event markers are available with
event numbers from 001 to 999. To transfer the exact position data, the reading head calculates
the last absolute position of the code strip before it entered the event range and adds the
incremental offset from the codes of the event markers.
When the reading head enters the range of an event marker, it sets an event flag in the output
data. You also have the option of triggering a defined action when an event occurs by
parameterizing one of the outputs accordingly (see parameterization software description).
Actions of this type can be initiated when a certain event, all events or events from an event list
occur.
The 1 meter long event marker can be shortened. However, the minimum length should be 30
mm (3 codes). If the travel speed of the reading head increases, a longer event marker is
required. If the reading head travels at maximum speed, a full length event marker of 1 meter
must be positioned over the code strip.
The minimum length of an event marker can be calculated according to the following formula
depending on the travel speed and the trigger period:
L
Event marker
= 30 mm + V
max
[m/s] * T
trigger
[s] x 2
With auto trigger, the trigger period is 0.025 s.
15
No Position
Value Y
Y value if no
code tape is
visible
Array of
unsigned8
Bytes 0 - 3
rw
0x00: Last
Valid Position
0x01:
Specified
Position
Specific Value
Y
Specific Y
value
Bytes 4 - 7
rw
0 mm
-
±
10,000,000
mm
16
No Position
Value Speed
Speed value if
no code tape
is visible
Array of
unsigned8
Bytes 0 - 3
rw
0x00: Last
Valid Speed
0x01:
Specified
Speed
Specific Value
Speed
Specific
speed value
Bytes 4 - 7
rw
0 mm/s
-
65535 mm/s
Table 7.17
Bold
= default values
Subindex
Designation
Function
Data type
Attribute
Primary data
