
B-64004EN/02 1.OVERVIEW
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1.3.2.1 Latent error detection and cross-check
Detection of latent errors
This detection function can detect latent software and hardware errors
in a system that has a two-channel configuration. So, the
safety-related portions of the two channels need to be tested at least
once within an allowable period of time for latent errors.
An error in one monitoring channel causes a mismatch of results, so
that a cross-check detects the error.
CAUTION
Forced detection of a latent error on the MCC
shutoff path must be performed by the user
through a MCC off Test (after power-on and at
intervals of a specified time (within normally 24
hours)). When the system is operating in the
automatic mode (when the protection door is
closed), this detection processing is not requested
as mandatory. But, before the protection door
opens after the specified time, the detection
processing is required mandatory. If this has not
been performed, lock for the protection door should
not be released.
Cross-check
A latent safety-related error associated with two-channel monitoring
can be detected as a result of cross-checking.
For numeric data, an allowable difference between the two channels is
set in a parameter. (For example, an allowable cross-checked
difference is set for the actual position.)
NOTE
An error detected as the result of forced latent
error detection or cross-checking leads to a safety
stop state. (See Chapter 3.3.3).
1.3.2.2 Safety monitoring cycle and cross-check cycle
The safety function is subject to periodical monitoring in a monitoring
cycle.
The following functions are monitored at every 8ms.
- Safe speed monitoring (servomotor)
- Safe machine position monitoring (servomotor)
- Safe position error monitoring (servomotor)
The cross-check cycle represents a cycle at which all I/O data subject
to cross-checking is compared.
Cross-check cycle: 8 ms