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EssDe

High speed

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HI all, I'm trying to read a prox detector at a fairly high speed. Here is the set-up. A wheel turns at 4000 revolutions per minute, on this wheel a metal piece is read by a prox sensor. This piece of metal is about 1/6 of the complete circonference wich means that the sensor is trigerred only 1/6 of the time per revolution. Knowing that 1 revolution is 15ms in time ( (1/4000)*60), the sensor should be on for about 2,5ms. The scan time of the PLC (CJ1M CPU23) is about 1,8 ms but I can't read the incoming pulses. I see a flashing led at thePLC's input but a high speed timer (TIMH) programmed to read the puses doesn't see them. The timer sees a 0 all the time. I taught that I would be able to read thoses pulses but the PLC is not fast enough. I tried to use an immediate refresh command on the pulse's input but it doesn't make any differencce. What I'm trying to do is to monitor the rotation of this wheel. Two timers time the input when it's either 0 or 1 and give a fault signal, when the pulses are read, neither of the timers reaches it's setpoint and no fault signal is generated. In theory it works, but in practice the timer reading the low portion of the pulse reaches it's point. Am I doing something wrong, what would be the best way to do this function. thanks for your help

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Hi EssDe Within the 'Settings' dialog, you can edit the response time of each rack, and each slot within this rack. Go to the 'Unit Settings' tab. Defaults to 8ms for each slot. Pp

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One of the great features of the built-in I/O on the CJ1M series processors is their ability to handle very high speed functions that are asynchronous with the normal ladder scan. Read this link for details ----> http://forums.mrplc.com/index.php?autocom=downloads&showfile=268 In your application using the PRV and/or PRV2 instructions would be the best approach.

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Our company developes and produces the liquid dispensing equipment. I have similar task, but 5 wheels and two sensors to treat on each wheel. At first, want try CJ1M. Not sure, which modification processor is better.To minimize scanning time I want to separate program, some tasks should be executed when machine is idle, others when the machine runs. Can not find an example. Can somebody recommend me something? Wal

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Assuming that your sensors go ON/OFF at high speed you will need to add a CJ1W-INT01 module to process that number of signals. There are up to 8 high speed capture inputs included on a CJ1M processor but you need 10.

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Hi, thank You for the answer. What about the CJ1W-IDP01, a special card for the short pulses? What difference does it make?

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The IPD-01 will capture the ON state of an input IF the ON state is longer or shorter that the program scan of the PLC. If the input turns ON and OFF multiple times during the program scan its ON state it will only be evaluated once. The INT-01 will interrupt the program scan each time the input changes state [you can select rising-edge OR falling-edge, but NOT both]. Therefore if the input turns ON and OFF multiple times during the program scan each change of state is evaluated.

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wal, You may want to use the cj1w-idp01. The minimum input on time is shorter than the cj1w-int01. 0.01ms versus 0.05ms. Both have minimum off time of 0.5ms. I have experience with the cs1w-ct021 high speed counter. It is easy to setup, read values, and troubleshoot but does not have the inputs you require.

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I would create a 0.5ms timer interrupt (the fastest possible in this PLC), refresh and process these inputs by regular ladder within this interrupt. But probably, the best is to replace the 1/6 metal targets with 50/50 ones. Edited by Sergei Troizky

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Hi Sergei, the bigger ratio of metal targets and quicker permissible speed, the better is the machine. Something like 1/20 ... 1/50 is expected. I am not experienced with interupts. If during 0.5ms another similar event happens, will PLC motice it? Regards, Wal

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??? Explain please how less reliable reading can make the machine better. The timer interrupt mentioned will watch all the events every 0.5ms.

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The goal of the machine - dispensing liquids. The smaller the moving parts, the better, because it reduce the minimum size of shots. The machine becomes more precise. How many inputs, watched every 0.5ms could be at CJ1M?

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My suggestion was to modify (or create) metal targets for the sensors, not to modify the mechanism for sake of the sensors. The IORF instruction allows immediate refresh of any number of consecutive CIO words with execution time about 30mcsec for 2 words in CJ1M-CPU23. Edited by Sergei Troizky

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