S
Self-Checking (Circuitry)
A circuit with the capability to electronically verify that
all of its own critical circuit components, along with
their redundant backups, are operating properly.
Banner safety light curtain systems and safety
modules are self-checking.
Safety Distance
The minimum distance required to allow the
machine’s hazardous motion to stop completely,
before a hand (or other object) can reach the nearest
hazard point. Measured from the midpoint of the
defined area to the nearest hazard point. Factors that
influence minimum separation distance include the
machine stop time, the light curtain system response
time, and the light curtain minimum object detection
size.
Specified Test Piece
An opaque object of sufficient size used to block a
light beam to test the operation of a safety light
curtain system. When inserted into the defined area
and placed in front of a beam, the test piece causes
the outputs to de-energize.
Supplemental Guarding
Additional safeguarding device(s) or hard guarding,
used to prevent a person from reaching over, under,
through or around the primary safeguard or otherwise
accessing the guarded hazard.
T
Test Piece
An opaque object of sufficient size used to block a
light beam to test the operation of a safety light
curtain system.
Auto Start/Restart (Trip) Condition
The safety outputs of a safety light curtain system
turn off when an object completely blocks a beam. In
an Auto Start/Restart condition, the safety outputs re-
energize when the object is removed from the defined
area.
Auto Start/Restart (Trip) Initiate
The resetting of a safeguard causing the initiation of
machine motion or operation. Auto Start/Restart
Initiate is not allowed as a means to initiate a machine
cycle per NFPA 79 and ISO 60204-1, and is
commonly confused with PSDI.
U
UL (Underwriters Laboratory)
A third-party organization that tests products for
compliance with appropriate standards, electrical
codes, and safety codes. Compliance is indicated by
the UL listing mark on the product.
S4B Safety Light Curtain
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