5/6/2010 11:06 AM | |
Joined: 10/7/2005 Last visit: 10/13/2024 Posts: 3024 Rating: (1054)
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Hello irb6 well, you already correctly identified that you must have a 1 Signal in the PLC for at least 200ms to ensure that you can count it. Assuming you do a rising edge detection youmust also have it followed by a0 Signal in the PLC for at least 200ms. So here are my ideas of what could be wrong and should be checked and all is based on "Signal at card does not mean signal in PLC at the same time". - Input card delay (~5 ms for standard Di) - ET200M internal delay (~1ms) - Profibus update time (potentially the big ticket item here, moresoassuming you do NOT use isochrone mode and have additional acyclic traffic or other Class 2 Masters like HMI's or PDM etc. on it) - Other higher priority interrupt OB's which will make OB35 have to wait That's allI can think of for now and hope it helps |
Cheers |
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5/7/2010 4:37 AM | |
Joined: 10/7/2005 Last visit: 10/13/2024 Posts: 3024 Rating: (1054)
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Hello again irb6
Input card delay values can be found inthe S7-300 Module data ET200M internal delay value can be found in the ET200M Operating Instructions Idoubt that this will be your main problem though and still wonder if you are sure that you have a long enough 1 and long enough 0value. I am a bit confused too, you say that: "with f=0,5Hz, I connected counter to this input and tryed to count pulses and after 1 minute counter should count 60x2=120" I believe you mean f=2Hz rather than f=0.5Hz (the first will give 120 counts per minute, the latter will give you 30 counts per minute). Lets assume you have2 Hz (or 120 counts per minute),the best (ideal) you can hope for is 250ms ON and 250ms OFF input assuming a pulse/pause ratio of 1 of your "motion sensor" DI. You are now trying tocount this in a200ms OB35 related call which - in my humble opinion -is just fast enough and you mayalready miss values if the previously listed delays compound to conspire against you. Question: Can you change your OB35 Runtime group to lets say 100ms and test it? I hope this helps |
Cheers |
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5/10/2010 12:31 AM | |
Joined: 7/2/2008 Last visit: 9/30/2024 Posts: 928 Rating: (308)
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Helloirb6,
I'm quite sure that fritz can go quite far with you until you solve your problem butI would like to tell some few things. I would like to go back to the main problem.
On which pulley do youfix the flag/motion sensor?Master(Driving) pulley or slave (Driven)pulley?or do you have flagsfor both pulleys? 1- I will assume that you put your flag on the slave pulley. Now the frequency doesn't matter because either you continuously see the signal or continuously don't see it for certain small period of time then the belt is broken (if motor is already running). 2- If your flag is attached to the driving pulley then it's very hard to sense the change in flag's frequency and the thing that you can easily sense would be a broken shaft. 3- In some applications flags are attached to both driving and driven pulleys to measure slipping and also to indicate low speed or a broken shaft. In this case the frequency of each flag is important. However, sometimes it's veryhard to measure (calculate) both frequencies in some PCS7 systems due to both big CPU cycle time and big bus cycle time
In such case I recommend to use an externalevaluation unit that can measure slip and gives outputs at acertain slipping valueand also at low or high speeds. Probably there are many manufacturers for such evaluation units but I just have experience with this IFM evaluation unit. Best regards. H-H |
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