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17.3.4 For Any XY Pair (2oo2 Enforced)
In this block, channels X and Y must be UMM channels 1,2 (or 3,4) and have the same channel type.
This is called a channel pair. All paired channels in the selected asset group (“With: The Rack”, or
“With: Motor A”) are included in this logic.
Channel A
Table 17-6) "For Any XY Pair (2oo2 Enforced)" truth table
This block performs as follows:
1. Logical AND function between the two channels in the pair. Both channels must vote TRUE for
the block to vote TRUE. This is called “2 out
of 2 Enforced” voting. For example: (1X and
1Y) where both 1X and 1Y must vote True.
2. Logical OR function between other pairs in
the selected asset group. For example: (1X
and 1Y) or (2X and 2Y) or (3X and 3Y) or…
3. Bypassed channels are removed from the
logic. For example, If Channel 1X is
bypassed the relay logic ((1X and 1Y) or (2X and 2Y)) will become ((1Y) or (2X and 2Y)). Note:
2oo2 falls to 1oo1 when a channel is in Bypass.
4. A Faulted channel votes ‘False’. For example, If Channel 1X is in fault (Not OK) the relay logic
((1X and 1Y) or (2X and 2Y)) will become ((False and 1Y) or (2X and 2Y)).
This block minimizes false trips because both channels must vote. However, this strategy may
increase missed trips because a failed probe votes False. This block is not commonly used. A few
scenarios are shown in Table 17-7.
Relay Active True True True False False
Table 17-7) For Any XY Pair (2oo2 Enforced)’ scenarios
Figure17-8) For Any XY Pair (2oo2 Enforced)
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