Rockwell Automation 1771-PD PID MODULE (+DU) - Manual (Page 117)

Programming
Chapter 3
3Ć74
the number of transfers in the sequence multiplied by the sum of all
possible block transfer times.
T
LE
= (# transfers in the sequence) x(T
Q
) (equation 5)
Example Problem 1
A PID module in a remote system controls two expanded loops. It is the
only block transfer module in the remote system.
Processor = PLC -2/30
I/O = 2 remote chassis (two rack numbers)
Program = 1K words
Words transferred = 18
a. Calculate the time for a single read or write block transfer.
b. Calculate the time required for a load/enter sequence.
Solution, part a)
1. Calculate the system values
PS = Program Scan = (5msec/lK)(1K) = 5msec
PI0 = Processor I/O Scan = (0.5msec/rack number)x(2 rack numbers)
= 1msec
RI0 = Remote I/O Scan = (7msec/chassis)x(2 chassis) = 14msec
W + Number of words transferred = 18 for a read or write
2. Calculate the time for a single read or write operation.
TW = PS + PI0 + 2 RI0 + .5W + 9
= 5 + 1 +2(14) + .5(18) + 9
= 52 msec
NOTE: This is less than 100 msec. Use the alternate formula for the
transfer time.
TW’ = 100 + RI0 + .5W + 9
= 100 + 14 _ 5.(18) +9
= 132msec
Solution, part b)