RSlogix-Problem with CTU

I'm new using RSLogix and the MicroLogix 1500. I'm facing problems when I use the CTU. The implementation that I use is the following

The problem starts when I add the counter. The frequency slows down, no matter which is the input of the sequencer. As a matter of fact, if I use too fast inputs, the transitions are even slower.
I contacted the local reseller and says it's implementation's problem.

The S:4 time base in the ML1500 is 100 microseconds. S:4/3 will therefore increment at 800 microseconds. Your PLC scan time is likely longer than that. The SQC instruction is a transitional instruction. That is it must be processed on a false rung and then processed again on a true rung. I suspect that because your time base is so fast that you are missing transitions. Likewise the CTU instruction is a transitonal instruction. Again, it must first process a false rung, and then a true rung to upcount. Try using a longer time base.

Thank you for your answer. Doesn't that mean that it needs 25(length of SQC)x2(true-false)=50 times the time base to complete the scan? That's why it's so slow? Is this acceptable?

Hi,

On a quick check on a Micro 1000 instruction set manual, I found a SQC instruction takes 60.52 micro seconds. That means, as Alaric mentioned your instruction will execute in every 800 micro seconds.

I do not know why you need to execute your sequencer so fast - if really need to, other method of programmming may be better to achieve the results.


Regards
_______

it seems that using the RSemulate, everything functions much-much slower. this is something that the local representative didn't seem to know!

polpol said:

it seems that using the RSemulate, everything functions much-much slower. this is something that the local representative didn't seem to know!

Click to expand...

An Emulator is NOT the same as actual Hardware. Don't make the mistake of believing it is.

An Emulator is a handy tool, to play with, and try things out, but it is NOT the actuall controller. Final checks, timings, and safety validations should be made only on the target hardware.