9-33
ET 200U Distributed I/O Station
EWA 4NEB 812 6087–02b
Synchronization of Actual Value Detection (Reference Point Ap-
proach)
The synchronization of actual value detection is necessary after power–up
and after a counter overflow.
Synchronization performs the following functions:
Sets the count (actual value) to 0 and
Sets the SYNC bit (bit 0 in the diagnostics bit) after power–up
or
Resets the overflow bit (bit 3 in the diagnostics byte) after an overflow
The following factors are prerequisites for synchronization:
1. The reference signal
The sensor for the reference signal is connected to terminals 7 and 8 of
the terminal block.
Synchronization is enabled with a leading edge (transition from 0 to 1) at
terminal 8. If the signal was already on 1 when the module was switched
on, then the reference signal must be turned off to restart the synchroniza-
tion.
If the reference signal lies in the normal traversing range, the actual value
will be constantly resynchronized by the reference signal. To prevent the
unwanted resynchronizing, you have to mask out the reference signal af-
ter the first reference point approach.
2. Traversing path after a positive edge of the reference signal
After the reference signal has been reached, the module has to recognize a
positive traversing path (up–counting) while the reference signal is still
active (1). This means you have to input the reference signal with increas-
ing actual value to synchronize the module.
3. Reference pulse (V
a0
; 0 mark of the sensor)
The reference pulse is generated by the position encoder at least once per
revolution.
The first reference pulse that the module recognizes after a leading edge
of the reference signal synchronizes the module. This is also valid if, after
the first positive traversing path, the direction is changed and a reference
pulse is encountered (see Figure 9-19). If, during post synchronization,
the reference point is again passed, then you have to mask out the refer-
ence signal after the synchronization reference point approach to avoid
resynchronizing the module.
Function Modules