Banner SC22-3E Safety Controller with Ethernet - Manual (Page 117)

WARNING: . . . Muting Limitations
Muting is allowed only during the non-hazardous portion of the machine cycle.
A muting application must be designed so that no single component failure can prevent the stop command or allow
subsequent machine cycles until the failure is corrected (per OSHA 1910.217(c)(3)(iii)(d), and ANSI B11.19).
WARNING: . . . Mute Inputs Must Be Redundant
It is not acceptable to use a single switch, device, or relay with two N.O. contacts for the mute inputs. This single
device, with multiple outputs, may fail so that the System is muted at an inappropriate time. This may result in a hazardous
situation.
10.11.2 Muting Function Requirements
The beginning and end of a mute cycle must be triggered by outputs from either pair of muting devices, depending on the application.
The mute device pairs both must have normally open contacts, or have PNP outputs, both of which fulfill the Muting Device Require-
ments, described below. These contacts must close (conduct) when the switch is actuated to initiate the mute, and must open (non-
conducting) when the switch is not actuated and in a power-OFF condition.
The Controller monitors the mute devices to verify that their outputs turn ON within 3 seconds of each other. If the inputs do not meet this
simultaneity requirement, a mute condition can not occur.
Several types and combinations of mute devices can be used, including, but not limited to: limit switches, photoelectric sensors, positive-
driven safety switches, inductive proximity sensors, and “whisker” switches.
Mute Device Requirements
The muting devices (typically sensors or switches) must, at a minimum, comply with the following requirements:
1. There must be a minimum of two independent hard-wired muting devices.
2. The muting devices must either both have normally open contacts, PNP outputs (both of which must fulfill the input requirements
listed in the Specifications), or complementary switching action. At least one of these contacts must close when the switch is actu-
ated, and must open (or not conduct) when the switch is not actuated or in a power OFF condition.
3. The activation of the inputs to the muting function must be from separate sources. These sources must be mounted separately in
order to prevent an unsafe muting condition resulting from misadjustment, misalignment, or a single common mode failure. (For
example, physical damage to the mounting surface could cause both muting devices to be knocked out of alignment, resulting in
false muting input signals.) Only one of these sources may pass through, or be affected by, a programmable logic controller or
similar device.
4. The muting devices must be installed so that they can not be easily defeated or bypassed.
5. The muting devices must be mounted so that their physical position and alignment can not be easily changed.
6. It must not be possible for environmental conditions to initiate a mute condition (e.g., extreme airborne contamination).
7. The muting devices must not be set to use any delay or other timing functions (unless such functions are accomplished so that no
single component failure prevents the removal of the hazard, subsequent machine cycles are prevented until the failure is correc-
ted, and no hazard is created by extending the muted period).
Examples of Muting Sensors and Switches
WARNING: . . . Avoid Hazardous Installations
Two or four independent position switches (at M1–M2 or M3–M4) must be properly adjusted or positioned so that
they close only after the hazard no longer exists, and open again when the cycle is complete or the hazard is again
present. If improperly adjusted or positioned, injury or death could result.
SC22-3/-3E Safety Controller Instruction Manual
P/N 133487 rev. C www.bannerengineering.com - tel: 763-544-3164 117