Date Code 20010518 SELOGIC Control Equations 7-5
SEL-2020 Instruction Manual
Limitations
Table 7.1 lists unacceptable combinations of SEL
OGIC Control Equation operators:
Table 7.1: Unacceptable SEL
OGIC Control Equation Operator Combinations
*+ ** !* !+
+* ++ !!
Equation Disabling
Programming an equation to NA disables that function, i.e., OUT4 = NA..
OUTPUTS
You use SELOGIC Control Equations to control contact outputs, intermediate logic, and auto-
message triggers.
Contact Outputs
Four contact outputs on the optional I/O board are controlled by SEL
OGIC Control Equations.
The contact output equations are processed every 3.9 milliseconds. An output contact will be
asserted (closed for a type A contact) when its corresponding SEL
OGIC Control Equation is true;
it will be de-asserted when its corresponding SEL
OGIC Control Equation is false. Contact output
SEL
OGIC Control Equations are established in the global settings.
Global Intermediate Logic
Five intermediate logic elements (V, W, X, Y, Z) may be used to hold intermediate results.
Three elements (X, Y, Z) also have associated pickup/dropout timers which the SEL-2020 may
use for various timing functions. These elements are processed every 15.6 milliseconds.
The timers operate as standard pickup/dropout timers. For a timer output (XT, YT, or ZT) to
assert, the corresponding input must be true for the pickup time. Similarly, for a timer output to
de-assert once it has asserted, the corresponding input must be false for the dropout time. Pickup
and dropout times can be set to zero to disable them.
Intermediate logic SEL
OGIC Control Equations and timer values are established in the global
settings.
Local Intermediate Logic
There are 96 intermediate logic elements associated with each port. These elements operate
together to form 32 S-R latches where 32 elements are set elements, 32 are clear elements, and
32 are the latch outputs. The set and clear elements are driven by SEL
OGIC Control Equations
(SET L), by master port Fast Operate commands, and by Modbus and DNP operations. (See
Appendix G: Modbus Protocol, Appendix H: SEL-2020 Configuration and Fast Operate
Commands, and Appendix I: Distribution Network Protocol (DNP) V3.00.) Figure 7.2
illustrates the relationship of these elements.
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