Baumer BA Scatec2 - Manual (Page 9)

Manual SCATEC-2 17 Baumer Electric AG
Version 2011-05 www.baumer.com Frauenfeld, Switzerland
A helpful rule of thumb is: Output pulse length p in milliseconds must be shorter than 1.2 million
divided by the production rate given in copies per hour
The theoretical maximum production rate where output pulses follow each other without any gap in
between is 3 times higher than the recommended value given by the rule of thumb. Exceeding the
recommended value of the production rate increases the risk of missing edges due to irregular intervals
between copies.
The following table lists the recommended maximum production rate for some values of the output
pulse length.
set
output pulse length
[milliseconds]
recommended maximum
production rate
[copies/hour]
1 1,200,000
2 600,000
5 240,000
10 120,000
15 80,000
20 60,000
If suddenly the Scatec starts to miss copies while the production rate is run up, the reason very often is
too short an output pulse length for the actual production rate in combination with fluctuations of the
interval between copies.
Manual SCATEC-2 18 Baumer Electric AG
Version 2011-05 www.baumer.com Frauenfeld, Switzerland
9.2 False pulse suppression
It is generally recommended that the SCATEC-2 should be operated with the false pulse suppression
feature active. In this way, multiple pulses caused by thicker copies (newspapers, folded cardboard
boxes etc.) or by a small crease at the edge can be suppressed.
The false pulse suppression feature ensures that no further pulses can be issued when an output pulse
is active and during the dead time. Activating the false pulse suppression feature causes the sensor to
automatically initiate a dead time when each pulse is issued, whose duration is 18% of the average
overlap spacing. If an output pulse is followed by another in less than about 1/6 of the current average
overlap spacing time, this pulse is suppressed, as it lies within the dead time of the preceding pulse.
The average overlap spacing time is constantly recalculated automatically by the SCATEC-2. This
ensures that the dead time is adjusted if the conveying speed changes. In certain cases, one edge may
be suppressed if the conveying speed is very quickly accelerated, whereas one false impulse may not
be suppressed during very fast braking. However, gaps in the overlapping stream caused when
individual copies are removed or when the overlapping stream is briefly diverted have no effect. The
false pulse suppression feature has no effect on the maximum counting rate as the dead time is
shortened as the counting frequency rises and can even become shorter than the output pulse length.
This occurs when the average copy spacing time becomes less than 6 times of the output pulse length.
Ideally, the sensor would not issue further pulses after a valid output pulse for a specific length, as the
typical distance between two edges is often known regardless of the speed. Anything between these
would be false pulses. However, to allow the sensor to suppress pulses for a specific length and not for
a defined time, it must be synchronized to the conveying speed. This is possible with the Scatec-10 and
Scatec-15.
Always switch on false pulse suppression unless the overlap spacing is highly unregular.
Individual copies may be ignored during abrupt acceleration or if the overlap spacing suddenly
becomes smaller.