S5-115F Manual Technical Description
Discrepancy times
The operating system tests the logical signal levels of the digital inputs in both subunits. If the
level of a DI bit differs between the two subunits, this is referred to as a discrepancy.
Discrepancy can be caused by
• Fleeting errors (e.g. edge change)
• Permanent errors (e.g. hardware errors)
The duration of the discrepancy is monitored by the 115F operating system. The discrepancy time
begins when the discrepancy is first detected, and ends only when the operating system detects
that both DI bits match or when the discrepancy time has elapsed.
You can choose between two different discrepancy times when configuring the I/Os with the
COM 115F programming software:
• Short discrepancy time
This is configured for inputs with a typical discrepancy time of less than 50 ms. When a
discrepancy occurs, the 115F operating system scans the relevant input continuously until the
discrepancy has disappeared or until the discrepancy time has elapsed. After the maximum
discrepancy time has run, the 115F operating system initiates an error response.
You configure the short discrepancy time
- Uniformly between 10 and 2550 msec. for all noninterrupt DIs.
- Uniformly between 1 and 255 msec. for all interrupt DIs.
Figure 2-5. Definition of the Short Discrepancy Time
PLC cycle n
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Digital input
in subunit A
Digital input
in subunit B
Operating system detects discrepancy
Discrepancy persists
Discrepancy no longer exists
PII
Discrepancy time
EWA 4NEB 811 6148-02
2-7
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