Banner SC22-3E Safety Controller with Ethernet - Manual (Page 96)

Category 3 Interlocked Guard Circuit
A dual-channel hookup switching +24V dc is typically a Category 3
application, because a single failure does not result in a loss of
safety. Loss of the switching action in one channel is detected by
the actuation of opening and closing the guard, allowing the moni-
toring function of the safety inputs to detect the discrepancy be-
tween the channels. However, a short circuit between input chan-
nels or Safety Outputs may not be detected. It should be noted
that an accumulation of faults may cause loss of the safety func-
tion. The principle of fault exclusion must be incorporated into the
design and installation to either eliminate, or reduce to an accepta-
ble (minimal) level of risk, the possibility of undetected faults or
catastrophic/common mode failures that could result in the loss of
safety function. +24V dc
Open Open Open
Figure 61. Category 3 Interlocked Guard Circuit
Category 4 Interlocked Guard Circuit
The self-monitoring safety inputs can be interfaced to achieve a
Category 4 level of safety. The principle of fault exclusion must be
incorporated into the design and installation to either eliminate, or
reduce to an acceptable (minimal) level of risk, the possibility of
catastrophic/common mode failures that could result in loss of the
safety function. Open
Figure 62. Category 4 Interlocked Guard Circuit
Interlock Switch Hookup Options
All figures are shown with the gate (guard) in the closed (Run) state.
The safety contact is considered to be the normally closed contact that is of a positive-opening design (unless otherwise noted), normally
marked with the symbol.
Single-Channel (1 terminal, 2 terminals or PNP device): These
circuits can typically meet ISO 13849-1 Category 2 requirements,
depending on the safety rating of the device(s). At a minimum, a
safety-rated device must be used to achieve a Category 2. The 1-
terminal and the PNP device circuits can not detect a short circuit
to another source of power. Two-terminal hookup uses pulse moni-
toring and can detect a short circuit to another source of power.
Fault Exclusion must be used to achieve a higher level of safety
circuit integrity. 24V
SC22-3/-3E Safety Controller Instruction Manual
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