Scan time of a Siemens S5 PLC

[Tomsci]

Hi,
Can anyone kindly suggest how i can know the scan cycle time (scan time) of a S5 PLC (CPU 135U) using STEP 5?

Thanks,
Tomsci

 

[seppoalanen]

135U is as sub-brand including numbers of different CPU's as 921, 928B etc. There are different ex.times for every CPU's in manuals or you can measure couple of program scan average by timer value.

 

[DL06]

You can always set up a timer and a counter to do this. Set up a counter with a preset of 100 cycles and increment it once each scan. Record the timer's current value to two different registers, once when C=0 and once when C=100. Subtract the difference, divide by 100, and that will be your scan time (in whatever units your timer is counting in - hundredths, thousandths, etc). The scan time may be slightly larger due to these extra few calculations, but in a medium to large sized program the percentage error will be negligable. You can always subtract out the 'textbook' execution times for the cycles that you added to correct for this.

I have not worked with this processor, so there may be a built in function to show min/max/avg scan time. Someone else will definitely chime in if this is the case.

 

[seppoalanen]

I am very much afraid that there are not build-in tools for max/min/ave scan-time.

Estimating scan-time command by command:
Fe. CPU 928-3UA12 EX. TIMES IN MICRO SECONDS

LOAD IW ?? 13
OPEN DB ?? 19
LOAD DW ?? 14
AND I N.N 0.9
AND D N.N 29 ! note diff. between Input and databit handling

but this can be very hard method.