HIMA HIQuad X - Noise Blanking Sequence; Figure 30: Transient Interference

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Page 60 of 110 HI 803 211 E Rev. 1.01.00
4.12.3 Noise Blanking Sequence
The following examples illustrate the sequence of noise blanking:
 A transient interference is blanked out.
 An interference present for longer than the maximum noise blanking time triggers the safe
response.
Example 1: Transient interference is successfully blanked out
Cycle, duration = watchdog time
Reading in cycle 1
Reading in cycle 2
Reading in cycle 3
Reading in cycle 4
Processing (in all cycles)
Output process in cycle 1 and 2
Output process in cycle 3
Output process in cycle 4
Duration of safety time
Figure 30: Transient Interference
In example 1, valid input values are read within one cycle. For this cycle, the system
processes the valid input values, even though an interference occurred directly upon completion
of the read-in process. If the interference is still present in the following cycle during the read-in
process , the module detects the interference and the system decides if noise blanking can
be performed at this point in time based on the following rule:
Safety time - elapsed time - (2 x watchdog time) > 0
Elapsed time = Time interval between the moment, in which the last valid values were read in,
and the moment, in which the interference was detected.
In this example, noise blanking is possible since the interference is present for less than a cycle
( = elapsed time) and two additional cycles (2 x watchdog time) are available for triggering a
safe response. For this cycle, the system processes the last valid input values of and no
fault response is triggered. The transient interference was successfully blanked out.
If the interference is no longer present in , new valid values are read in and processed. If
noise blanking is not active, the system immediately triggers the defined fault response during
the read-in process .