R.3.22
SEL-421 Relay Reference Manual Date Code 20111215
SELOGIC Control Equation Programming
SELOGIC Control Equation Elements
Timers in protection programming operate in cycles, while timers in
automation programming operate in seconds. As with sequencing timers,
operation depends on the logic processing interval. For protection
programming, the logic processing interval is 1/8 cycle, so the relay
effectively rounds up all operation to the nearest 1/8 cycle. With automation
programming, the execution interval depends on the amount of automation
programming. Determine the average automation execution interval with the
STATUS S command.
The automation timers operate using a real time clock. Each time the relay
evaluates the Input (ASTnnIN) the relay adds the elapsed time since the last
execution to the Elapsed Time (ASTnnET). The accuracy of the timer in
stopping and starting when the input of the timer turns on averages half an
automation execution cycle. If you change automation free-form
programming, you must also check the new automation average execution
cycle to verify that you will obtain satisfactory accuracy for your application.
Example 3.8 describes typical timer programming and describes the resulting
operation.
EXAMPLE 3.8 Automation Sequencing Timer Programming
The equations below are an example of programming for an
automation sequencing timer, AST01. Each timer input is
programmed as a separate statement in automation SEL
OGIC control
equation programming.
# Example programming of sequencing timer to time Input IN101 and IN102
AST01PT := 7.5 # Timer Preset Time of 7.5 seconds
AST01R := RB03 # Reset timer when RB03 turns on
AST01IN := IN101 AND IN102 # Timing time when IN101 and IN102 are on
ASV001 := AST01Q # ASV001 tracks output of timer
AMV256 := AST01ET # AMV256 tracks timing progress
In this example, timer AST01 times the quantity IN101 AND IN102 and
turns on when the total time reaches 7.5 seconds. If the Input,
AST01IN, is on for approximately 1 second every minute, the Output,
AST01Q, will turn on during the eighth minute, when the accumulated
elapsed time exceeds 7.5 seconds.
In free-form programming, the relay evaluates the timer at the timer Input
SEL
OGIC control equation (PSTnnIN or ASTnnIN). If you enter an expression
for the timer Reset (PSTnnR or ASTnnR) or Preset Time (PSTnnPT or
ASTnnPT), the values for Reset and Preset Time that the relay uses are the last
values that the relay calculates before the input SEL
OGIC control equation
calculation. Because the relay uses the last values for Reset and Preset Time
value in this manner, we recommend for most applications that you enter the
Preset Time, Reset, and Input statements together in the order shown in
Example 3.8.
Counters
Use counters to count changes or edges in Boolean values. Each time the
value changes from logical 0 to logical 1 (a rising edge), the counter Current
Value increments. Counters are available in the protection free-form area and
automation free-form area, as shown in Table 3. 17. Counters have three input
parameters, Input, Preset Value, and Reset; and two outputs, Current Value
and Output as listed in Table 3 .18.
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