Bradley Smoker PLC-5 user manual Effects of Different Input States on Logic Scan Time

C-2Maximizing System Performance

Effects of False Logic versus True Logic on Logic Scan Time

The rung below—which changes states from one program scan to the next— will change your scan time by about 400 ∝s.

I:000

00

LN

NATURAL LOG

SourceN7:0

5

DestF8:20 1.609438

If I:000/00 is	Then the Rung is
On	True, and the controller calculates the natural log.
	A natural log instruction takes 409 ∝s to execute.
Off	False, and the controller scans the rung but does not execute it.
	It takes only 1.4 ∝s to only scan the rung.

Other instructions may have a greater or lesser effect.

Effects of Different Input States on Logic Scan Time

You can write your logic so that it executes different rungs at different times, based on input conditions. The amount of logic executed in logic scans causes differences in program scan times. For example, the simple differences in rung execution in the following example cause the program scan to vary.

I:000		rung 1
	02	rung 2
B3:0
		rung 3
00

20	rung 4
LBL

20

JMP

MVM

MVM

O:013

JMP 02

If I:000/02 is Rungs 2 and 3 are

OnSkipped

OffExecuted

Publication 1785-UM012D-EN-P - July 2005