User's Manual of ISaGRAF Embedded Controllers
Contents
1. operation Cocaine User s Manual Of ISaGRAF Embedded Controllers Mar 2007 Ver 5 1 Copyright By ICP DAS 12. How to do periodic operation in ISaGRAF controllers The BLINK function block can apply to generate a Pulse True periodically So it can apply in some periodic operations like as below LD program Pulsel is Boolean Internal Pulsed Periodic operation every 2 sec T 25 ST program IF Pulse1 THEN above LD program will generate a pulse TRUE in pulse1 variable do operation END IF The above program has a disadvantage When the periodic interval time is short for example 200ms or smaller or the controller s PLC scan time is bigger the operation time will not be precise For example to do a periodic operation every 50 milli second Because 50ms is a shorter interval it is much closer to the PLC scan time compared to interval time of 250 ms or 2 seconds the result time will not be precise To improve this following codes can be applied ST program IF INIT THEN INIT False INIT is declared as Boolean Internal T1 THOs And init as TRUE T1_next T1 T 50ms T1 and T1_next are Timer Internal Tstart T1 END _IF IF T1 gt T1_next THEN Timer will be overflow if it is ticking to IF T1 gt T 22h THEN T 23h59m59s999ms So we can reset it to 0 T1 THOs second when it just reach the 22h or 16h T1_next T Os whatever a bigger time you like END_IF T1_next T1_next T 50ms calculate next operation time do
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