Banner EZ-SCREEN Low-Profile Safety Light Curtain Systems - Manual (Page 67)

P/N 13348
65
Banner Engineering Corp. • Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
Overview
P/N 140044 rev. E 65
Banner Engineering Corp. • Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
EZ-SCREEN LP
Instruction Manual Cascadeable EZ-SCREEN
Monitoring Series-Connected Positive-Opening Safety Switches
When monitoring two individually mounted safety switches (as
shown in Figure 7-9), a faulty switch will be detected if it fails
to switch as the guard opens. In this case, the EZ-SCREEN LP
will de-energize its OSSD output and disable its reset function
until the input requirements are met (i.e., the faulty switch is
replaced). However, when a series of interlocking safety switches
is monitored by the EZ-SCREEN LP, the failure of one switch in
the System may be masked or not detected at all (refer to Figure
7-10).
Series-connected, positive-opening interlock switch circuits
do not meet ISO 13849-1 Category 4 and may not meet
Control Reliability requirements because of the potential of
an inappropriate reset or a potential loss of the safety stop
signal. A multiple connection of this type should not be used
in applications where loss of the safety stop signal or an
inappropriate reset could lead to serious injury or death. The
following two scenarios assume two positive-opening safety
switches on each guard:
1. Masking of a failure. If a guard is opened but a switch fails to
open, the redundant safety switch will open and cause the
EZ-SCREEN LP to de-energize its outputs. If the faulty guard
is then closed, both cascade input channels also close, but
because one channel did not open, the EZ-SCREEN LP will
not reset.
However, if the faulty switch is not replaced and a second
“good” guard is cycled (opening and then closing both of the
cascade input channels), the EZ-SCREEN LP considers the
failure to be corrected. With the input requirements apparently
satisfied, the EZ-SCREEN LP allows a reset. This system is
no longer redundant and, if the second switch fails, may result
in an unsafe condition (i.e., the accumulation of faults results
in the loss of the safety function).
2. Non-detection of a failure. If a good guard is opened, the
EZ-SCREEN LP de-energizes its outputs (a normal response).
But if a faulty guard is then opened and closed before the
good guard is re-closed, the failure on the faulty guard is not
detected. This system also is no longer redundant and may
result in a loss of safety if the second safety switch fails to
switch when needed.
The circuits in either scenario do not inherently comply with
the safety standard requirements of detecting single faults and
preventing the next cycle. In multiple-guard systems using series-
connected positive-opening safety switches, it is important to
periodically check the functional integrity of each interlocked
guard individually. Operators, maintenance personnel, and
others associated with the operation of the machine must
be trained to recognize such failures and be instructed to
correct them immediately.
Open and close each guard separately while verifying that the
EZ-SCREEN LP outputs operate correctly throughout the check
procedure. Follow each gate closure with a manual reset, if
needed. If a contact set fails, the EZ-SCREEN LP will not enable
its reset function. If the EZ-SCREEN LP does not reset, a switch
may have failed; that switch must be immediately replaced.
This check must be performed and all faults must be cleared, at
a minimum, during periodic checkouts. If the application can
not exclude these types of failures and such a failure could
result in serious injury or death, then the safety switches
must not be connected in series.
Figure 7-10. Monitoring positive-opening safety switches on multiple gates
WARNING . . .
Not a Category 4 Application
When monitoring multiple guards with a series connection of multiple safety interlock switches,
a single failure may be masked or not detected at all.
When such a configuration is used, procedures must be performed regularly to verify proper
operation of each switch. See “Monitoring Series-Connected Positive-Opening Safety Switches”
(Section 7.9.1) for more information. Failure to do so could result in serious injury or death.
Wh
Open
Bk
Bn
Bu
Open Open
RDLP6G-4..D
RDLP6G-4..D Cordset Pinout*
Brown ― Ch 1a
White ― Ch 2a
Blue ― Ch 2b
Black ― Ch 1b
* Other cordset options may also be used; see
Figure 7-8 for more information.