•
Using positive-opening or direct-drive components, installed and mounted in a positive mode.
4.3.3 Machine Primary Control Elements and External Device
Monitoring
A machine primary control element (MPCE) is an "electrically powered element that directly controls the normal operation of
a machine in such a way that it is the last element (in time) to function when machine operation is to be initiated or arrested"
(per IEC61496-1). Examples include motor contactors, clutch/brakes, valves, and solenoids.
Depending on the level of risk of harm, it may be required to provide redundant MPCEs or other control devices that are
capable of immediately stopping the dangerous machine motion, irrespective of the state of the other. These two machine
control channels need not be identical (they could also be diverse redundant), but the stop time performance of the machine
(Ts, used to calculate the safety distance, see
Minimum Safety (Separation) Distance Formula
on p. 35) must take into
account the slower of the two channels. See
To ensure that an accumulation of failures does not compromise the redundant control scheme (i.e., cause a failure to
danger) a method to verify the normal functioning of MPCEs or other control devices is required. The
SX5-B
model provides
this function only when configured for manual start/restart (reset) with MPCE monitoring contacts wired in series with the
reset (start/restart) switch as shown in
on p. 37). The master
scanner models provide a convenient method for this verification: external device monitoring (EDM).
When the
SX5-B
scanner model is configured for Automatic Start/Restart (Reset) or a master or
SX5-B6
scanner is not
configured for external device monitoring (EDM), to properly monitor the MPCEs, an External Device Monitoring (EDM)
function must be provided from outside the scanner. One example using the
UM-FA-9A/-11A
safety module is shown in
UM-FA-9A/-11A
can be configured for both manual or automatic reset and provide the
required EDM function.
For external device monitoring to function properly, each device must include a normally closed (NC), forced-guided
(mechanically linked) contact that can accurately reflect the status of the device. This ensures that the normally open
contacts, used for controlling hazardous motion, have a positive relationship with the normally closed monitoring contacts
and can detect a failure to danger (e.g. contacts that welded closed or stuck ON).
It is strongly recommended that a normally closed, forced-guided monitoring contact of each FSD and MPCE be connected
to EDM inputs (see
on p. 51). If this is done, proper operation will be verified. Monitoring FSD and MPCE
contacts is one method of maintaining control reliability (OSHA/ANSI) and Category 3 and 4 (ISO13849-1).
If monitoring contacts are not available or do not meet the design requirement of being forced-guided (mechanically linked), it
is recommended to:
•
Replace the devices so that they are capable of being monitored, or
•
Incorporate the EDM function into the circuit as close to the MPCE as possible (e.g., monitor the FSDs), and
•
Employ use of well-tried, tested, and robust components, and generally accepted safety principles, including fault
exclusion, into the design and installation to either eliminate, or reduce to an acceptable (minimal) level of risk, the
possibility of undetected faults or failures that can result in the loss of the safety function.
The principle of fault exclusion allows the designer to design out the possibility of various failures and justify it through the
risk assessment process to meet the required level of safety performance, such as the requirements of Category 2, 3 or 4.
See ISO 13849-1/-2 for further information.
WARNING:
•
Notice Regarding MPCEs
•
Failure to follow these instructions could result in serious injury or death.
•
Each of the machine primary control elements (MPCE1 and MPCE2) must be capable of
immediately stopping the dangerous machine motion, regardless of the state of the other. The two
machine control channels need not be identical, but the machine's stop time performance (TS,
used to calculate separation distance) must be based on the slower of the two channels.
WARNING:
•
External Device Monitoring (EDM)
•
Creating a hazardous situation could result in serious injury or death.
•
If the system is configured for “no monitoring,” it is the user’s responsibility to ensure this does not
create a hazardous situation.
4.3.4 Warning (Auxiliary) Output
The stand-alone scanner can have pins 1, 3, or 4 set as a Warning Output(s). One warning output can be selected when one
or two zone sets are configured. Two warning outputs can be selected when one zone set with one safety zone and two
warning zones is configured. These outputs provide a PNP current-souring output (250 mA maximum) that switches ON
when the defined and active warning field is cleared and switches OFF when the active warning field is interrupted.
SX Safety Laser Scanner
50
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