SIEB & MEYER SD2, Translation Of The Original Instructions

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8 OSSD Signals
With the aid of OSSD signals malfunction and errors can be detected. For this purpose
dynamic signals are used instead of static output and input signals. The following
errors can be determined:
▶ short circuits
▶ cross circuits
▶ open signals
The PLC pulses its OSSD output signal at regular intervals and reads it back, i.e. the
PLC expects the regular pulses at its input line. Only then, the PLC assumes error-free
operation. If an error is detected, the PLC automatically switches to the safe status and
the error is reported.
The time period, the point in time and the repetition frequency of the pulses should
vary for different signals, so the PLC can detect a crossover of different OSSD signals.
For a HIGH level the signal is pulsed to LOW and for a LOW level the signal is pulsed
to HIGH.
Fig. 13: Example for OSSD pulse
OSSD test signals
The OSSD test signals OSSD1 (X66 / pin 10) and OSSD2 (X67 / pin 10) supply pulsed
signals that are shifted to each other by 2 ms.
Fig. 14: OSSD test signals
The test signals are sent every 200 ms. They have a pulse width of 2 ms.
These signals are to be used for test purposes. The OSSD test outputs are
neither certified nor safety-related.
The pulses in between are generated by the self tests of the drives. They
have a typical pulse width of 1 ms. These test pulses of the drives must be
filtered out by the PLC.
8.1 OSSD Channels and Signal Chains
The drive amplifier SD2 provides 8 OSSD signal channels. There are 2 channels for
SFM and 2 channels for SLOF for each drive A and B.
W
OSSD Signals
Drive System SD2 - Safety Functions SFM / SLOF 47
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