Specifications

Encoder Signals IP 240
13.1.2 Timing Requirements
The following diagrams show the timing requirements for signals A, B and Z at the IP 240's inputs.
These requirements must be observed in order to enable proper evaluation of the signals.
Z signal
During reference point approach and zero mark monitoring, the Z signal is evaluated while A=1
and B=1. The state A=1 and B=1 may occur only once for the duration of the Z signal (Z=1). In
addition, one of the following conditions must be satisfied to ensure that the correct edge of the
Z signal is used in every instance:
• When using a symmetrical encoder, the Z signal must go to ”1” no more than 250 ns (t
5
) after
the last positive signal edge of pulse train A or B ( Fig. 13-2c).
• When using an asymmetrical encoder, the Z signal must go to ”1” at least 2.5 µs (t
5
) before the
pending positive signal edge of pulse train A* or B* ( Fig. 13-3b).
When your encoder can maintain this timing only in one direction of rotation, the reference point
must be approached with this direction of rotation. Zero mark monitoring is then carried out in
this direction only.
When the encoder cannot maintain this timing, you must disable zero mark monitoring during
configuring (configuring parameter IMP=0).
Timing requirements for encoders with symmetrical signals
t
1
t
1
A Signal
A Signal
B Signal
B Signal
t
2
t
1
a) Skew between tracks A and B (minimum edge spacing):
t
1
t
2
Fig. 13-2. Timing Diagrams for Symmetrical Incremental Encoders
t
1
: min. 500 ns t
2
: min. 1 µst
3
: max. 20 ns
Signals:
A, B, Z
Signals:
A, B, Z
t
2
b) Skew between the signals of a track:
t
3
t
3
t
3
t
3
t
3
t
2
13-2 EWA 4NEB 811 6120-02a