Balluff BIS M-408-082-401-07-S4, Руководство по настройке, Страница: 89 / 128

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4.6 Signal Quality
4.6.1 Description
The signal quality is specified in percent steps as a value
between 0 and 100%. If the signal quality cannot be
provided, a substitute value of 0xFF (255) is output. The
threshold value for the monitoring function can be set and
is used to define two states of the signal quality. The signal
quality is considered to be good at or above the threshold
value; the signal quality is considered to be bad below the
threshold value. A state change from good to bad signal
quality triggers the Low Signal Quality Level IO-Link event.
The output of the current signal quality can provide
support both when setting up as well as during predictive
maintenance. When setting up, the location, the orientation
and the environmental conditions can be adapted to
achieve a satisfactory signal quality level. If the signal
quality is regularly logged, a deterioration of the
performance can be countered in a preventative manner
by adapting the location, orientation and environmental
conditions to prevent failure.
In addition, the monitoring of the signal quality offers an
immediate response in the event of a critical failure. This
reaction is triggered if the signal quality drops below the
adjustable threshold value and gives the all clear if a
satisfactory signal quality level is once again achieved. The
signal state is also indicated by an orange LED that
illuminates if the signal quality is below the threshold value.
The function can be deactivated by setting the threshold
value to zero.
4
Primary Device Functions (continued)
4.6.2 Mathematics/Algorithm
If the read/write head has to repeat accesses to a data
carrier, these are the first signs of poor signal quality.
Possible causes of repetition are:
– Disturbance of the RF field by other nearby data
carriers or read/write heads
– Positioning of the data carrier at the boundary of the
read/write field
– Change to the read/write field due to field-affecting
changes such as soiling or attachments (new
boundaries due to deterioration of the read/write field)
The maximum number of repetitions is limited because a
data carrier can also be permanently removed from the
field during an access attempt. The signal quality is
therefore determined from the ratio of the repetitions
actually required to the maximum possible number of
repetitions. If no repetitions are required, the signal quality
for this access attempt is 100%. If all repetitions are
required, the signal quality is 0%. At 70%, out of 10
maximum possible accesses, 2 accesses will have failed
and the third will have been successful. The signal quality
of an access is offset against that of previous accesses.
This reflects the general state of the system.
Even in an optimally configured system,
repetitions can occur. For example, access
attempts are started the first time the data carrier
is detected in fast dynamic mode. If the data
carrier is then not yet safely in the field, the
access attempt may be repeated. A signal
quality of 100% is therefore not absolutely
essential.
Signal quality can be used to evaluate a system during
startup and to detect changes to the RFID system at an
early stage during operation.
BIS M-4 _ _ -082-401-07-…
Industrial RFID-System BIS M