Sel 751A, Instruction Manual

Page: 182 / 640

4.90
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Logic Settings (SET L Command)
Figure 4.49 shows an example of the effects of the input precedence, with
SC01PV set to 7. The vertical dashed line indicates the relationship between
SC01CU first being seen as a rising edge and the resultant outputs. This
indicates that there is no intentional lag between the control input asserting
and the count value changing. Most of the pulses in the diagram are on every
second processing interval. The “one processing interval” valley is an example
where the CD and CU pulses are only separated by one processing interval.
Figure 4.49 Example of the Effects of the Input Precedence
The shaded areas illustrate the precedence of the inputs:
➤
When SC01R is asserted, the SC01LD input is ignored.
➤
When SC01R or SC01LD is asserted, rising edges on the
SC01CU or SC01CD inputs are ignored.
➤
When input SC01CU has a rising edge, a rising edge on
SC01CD is ignored (unless SC01 is already at the maximum
value SC01PV (= 7), in which case SC01CU is ignored, and the
SC01CD is processed). An example of this exception appears
in the above diagram, just before the “one processing interval”
notation.
A maintained logical 1 state on the SC01CU or SC01CD inputs is ignored
(after the rising edge is processed). A rising edge received on the SC01CU or
SC01CD inputs is ignored when the SC01R or SC01LD inputs are asserted.
A maintained logical 1 on the SC01CU or SC01CD inputs does not get treated
as a rising edge when the SC01R or SC01LD input deasserts.
The same operating principles apply for all of the counters: SC01–SC mm ,
where mm = the number of enabled counters. When a counter is disabled by
setting, the present count value is forced to 0 (SC nn := 0), causing Relay Word
bit SC nn QD to assert (SC nn QD := logical 1), and Relay Word bit SC nn QU to
deassert (SC nn QU := logical 0).
SC01QU
SC01QD
Relay
Word
Bits
SC01R
SC01LD
SC01CU
SC01CD
SEL
OGIC
Settings
SC01PV = 7
Setting
SC01
Analog
= Sample
One Processing Interval
Two Processing Intervals
6
5
4
3
2
1
0