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Voting in Dual Input (1oo2) Safety Architectures

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    Last Modified: May 15, 2018

    The module FPGA employs a pessimistic voting strategy in a dual input (1oo2) architecture. When the module reads different currents on the two configured channels, the module FPGA will return the safest region of the two.

    Figure 1. Dual Input (1oo2) Voting
    1. The C Series Functional Safety module reads the current on the two input channels.
    2. The module FPGA assigns a current region to each channel based on the configured thresholds.
    3. If the channels are in the same current region, the voting selects that region. If not, the voting selects the most safe of the two current regions.
    4. The User Program uses the single current region selected and returned by the voting strategy.
    Figure 2. Dual Input (1oo2) Signal Diagram

    The following table shows the voting results for each combination of current regions in a dual input configuration.

    Table 1. Dual Input (1oo2) Voting
    AIn Current Region AIn+1 Current Region Region Returned to the User Program
    High high High high High high
    High high High High high
    High high Normal High high
    High high Low High high
    High high Low low Low low
    High High high High high
    High High High
    High Normal High
    High Low Low
    High Low low Low low
    Normal High high High high
    Normal High High
    Normal Normal Normal
    Normal Low Low
    Normal Low low Low low
    Low High high High high
    Low High Low
    Low Normal Low
    Low Low Low
    Low Low low Low low
    Low low High high Low low
    Low low High Low low
    Low low Normal Low low
    Low low Low Low low
    Low low Low low Low low

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