LINK Systems Max Presence Sensing Device - Manual (Page 8)

Link Lite Black Max Section 3 - Installation
3-3
T
s
= the stop time (in seconds) of the
machine measured from the control
output stop signal to the actuator(s)
(valves, etc.) that govern machine
motion till the machine actually
stops.
T
c
= the response time (in seconds) of the
machine control to a stop signal from
the presence sensing device (Black
Max).
NOTE! If the Link Lite Black Max output
contacts are connected to the emergency
stop circuit of relay controls, most control
designs will cause the Black Max contacts
to directly remove power from the actua-
tors that cause motion without waiting for
other control elements to de-energize. This
means that T
c
=0 in the case of these
controls. If the machine is a part revolu-
tion mechanical power press and is
equipped with Link Electric and Safety
Control Co.'s SS501 controls or OmniLink
5000 controls, use T
c
=0.005 seconds (5
milliseconds).
T
r
= the response time of the presence
sensing device (Response time for
Black Max units is less than 20 ms -
see unit label for specific time).
T
bm
= the additional amount of time over
the actual average stopping time
allowed by a brake monitor (stop-
ping performance monitor) to permit
some normal wear of friction brakes
and other components before the
safety distance, Ds, is violated and
the brake monitor prevents
successive strokes.
NOTE! Stopping performance monitors
(brake monitors) are required on part
revolution presses when light curtains are
used for safeguarding mechanical power
presses. See ANSI B11.1 1988 sections
6.3.2(15) and 4.11 and OSHA's CFR
1910.217 sections (c)(5) and (b)(14).
Where time based monitors with the ability
to set predetermined stop time limits are
provided on machines, T
bm
is determined by
the relation:
T
bm
= Brake Monitor Time Setting-T
s
Where T
s
is the actual machine stop time
already described.
NOTE! On machines where stopping time
performance monitors are not required, a
marginal amount of stopping time to allow
for some normal wear or degradation of
machine stopping mechanisms without
violating safety distance must be substi-
tuted for T
bm
. Link recommends that a
value from 10% to 20% of the actual
machine stopping time T
s
, i.e. from .1T
s
to
.2T
s
, be used in place of T
bm
. Periodic
measurement of actual stopping time must
be performed to prevent stopping time
increase beyond the allowed margin.
D
pf
= the added safety distance required to
compensate for the possibility that
fingers or hand could penetrate
beyond the plane of the light curtain
sensing field plane before the profile
of the finger/hand/arm is large
enough to be detected by the sensing
field.
All presence sensing devices have a limited
object sensitivity, i.e., it takes a certain size
object to be detected at all points in the
sensing field. Penetration depth depends
on the minimum object sensitivity, M.O.S.,
of the light curtain. M.O.S. is defined as
the smallest object profile that will be
detected at all points in the active sensing
field of the light curtain. The penetration
depth factor, in inches, is described by the