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Advanced Diagnostics
Appendix
C L
Figure 8.2
A
Reference event; first zero crossing point
B
Actual zero crossing point
C
Bit cell jitter, deviation from the ideal timing
D
Ideal zero crossing point
Segment or Field Device Jitter
This parameter monitors the current maximum jitter of all active devices connected to the seg-
ment. The H1 jitter level is a value derived from the device jitter values. Due to noise levels
caused by additional effects, the diagnostic device indicates a first warning at 75 % (2.4 s) of
the maximum allowable jitter level. This is an empiric value that can be modified according to
your requirements. If the jitter level exceeds 3.2 s, a final warning is issued.
Type
Precision
Measuring range
The segment jitter is the maximum value of all device jitter values. A high jitter level causes
communication problems and a lack of operational reliability. The transmitted bit cell jitter can-
not exceed 10 % of 1-bit time. E. g., at 31.25 kbits/s the duration of 1-bit time is 32 s. Thus, the
maximum bit cell jitter cannot exceed 3.2 s. Your system can run at a higher jitter level, but at
the expense of a reduced level of immunity against influences on electromagnetic compatibility.
Jitter can have the following causes:
•
Crosstalk
•
Electromagnetic interferences (EMI)
•
Simultaneous switching outputs
•
Device dependency
•
Bad wiring practice
146
V
A
B
0.5 bit time
Bit cell jitter
1 bit time
C
D
0.5 bit time
Values
0.1 s
0 s ... 8 s
t
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