Mitsubishi MELSEC-WS series, User Manual

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Chapter 4
46
Connecting devices
Protect single channel inputs against short circuits and cross circuits!
If a stuck-at-high error occurs on a single channel input with test pulses that was
previously inactive, the logic may see a pulse for this signal. The stuck-at-high first
causes the signal to become
Active (High) and then after the error detection time
back to Inactive (Low) again. Due to the error detection a pulse may be generated.
Therefore single channel signals with test pulses need special attention:
 If the stuck-at-high occurs on a single channel signal input with test pulses that was
previously Active (High), the logic will see a delayed Active (High) to Inactive
(Low) transition.
 If a single channel input is used and an unexpected pulse or a delayed falling edge
at this input may lead to a dangerous situation, the following measures have to be
taken:
– Protected cabling of the related signal (to exclude cross circuits to other signals)
– No cross circuit detection, i.e. no connection to test output (See the Safety
Controller Setting and Monitoring Tool Operating Manual.)
This needs especially to be considered for the following inputs:
– Reset input on the Reset function block
– Restart input on the Restart function block
– Restart input on the Press function blocks (Eccentric Press Contact, Universal
Press Contact, N-break, Press Setup, Press Single Stroke, Press Automatic)
– Override input on a Muting function block
– Reset input on a Valve function block
– Reset to zero input and Reload input on a Counter function block
After the configuration you obtain the following documentation in the Setting and
Monitoring Tool under “Report”:
 Logic report
 Parts list
 Wiring diagrams
ATTENTION