Processing Safe Absolute Value With A G-Interface; Safety Requirements For Electrical Connection - Balluff BML Información Básica

Interfaces for BML Magnetic Encoder System
2
Interfaces (continued)
2.7.3 Processing safe absolute value with a
G-interface
The unsafely generated absolute position (BiSS C, SSI,
IO-Link...) for the serial interface can be processed as a
safe absolute value together with the safe incremental
G-interface.
The following requirements must be met:
– Before using the safety function safe absolute value an
initial homing move to a known physical position must
be made at the first startup of the measuring system in
order to detect the true absolute position.
– When using the safety function safe absolute value the
measured absolute position values must be continually
compared with the incremental information provided by
the sensor. At any deviation between relative position
and absolute position the absolute value must be
presumed to be faulty and may not be used in any
safety function. The safe incremental signal can in this
case still be considered as non-faulty. To be able to
consider the absolute signal as not faulty again, the
initial homing move must be repeated.
– When using the safety function safe absolute value the
absolute position may be safely processed at best with
the accuracy of the quadrants of the sine/cosine signal,
i.e. to ¼ of a period of the sine/cosine signal.
After cycling power there are two ways to detect an error
in the non-safe absolute value:
Possibility 1
The user must ensure that the system when turned off
does not experience a position change and must ensure
correct implementation of this requirement through suitable
means of fault prevention (e.g. performing an FMEA). In
addition, the last measured absolute position value must
be persistently stored when the measuring system is
turned off. When the measuring system is turned on again
the current value of the absolute position value must be
measured and compared with the previously stored value.
At any deviation between stored position and the new
value must be presumed to be potentially faulty and may
not be used in any safety function. The safe incremental
signal can in this case still be considered as non-faulty.
To be able to consider the absolute signal as not faulty
again, the initial homing move must be repeated.
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Possibility 2
The user must ensure that the system when turned off
does not experience a position change of greater than ± ¼
of a period (corresponds to ±1 quadrant) and must ensure
correct implementation of this requirement through suitable
means of fault prevention (e.g. performing an FMEA). In
addition, at first startup of the system the user must safely
store the location of the quadrant change of the safe
incremental signal relative to the absolute signal for both
travel directions.
When the measuring system is turned on again the current
value of the absolute position value must be measured and
compared with the safe incremental signal using the initially
determined location of the quadrant change. The value of
the safe absolute signal must lie in the same quadrant as
measured using the safe incremental signal. At any
deviation of the detected quadrant between incremental
position and absolute signal the absolute value must be
presumed to be potentially faulty and may not be used in
any safety function. The safe incremental signal can in this
case still be considered as non-faulty.
To be able to consider the absolute signal as not faulty
again, the initial homing move must be repeated.
2.7.4

Safety requirements for electrical connection

The sensor must be powered by a PELV power supply.
The differential signals A (between +A (+sin) and (−A (−sin))
and B (between +B (+cos) and −B (−cos)) must be loaded
each with 120 Ω ±10 %.
It must be ensured that no external supply can affect the
sin/cos signals. This pertains for example to the use of
Y-cables, correct cable routing, use of appropriate
connectors, etc.