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Thread: Cycle Time, Busload, SYNC

  1. #1
    Join Date
    Nov 2016
    Posts
    6

    Default Cycle Time, Busload, SYNC

    Hi!

    I have issues with the correct setup of our CAN Bus together with our ifm PLC (CR2532).

    On our construction machine, we have alot of PWM valves to control. These valves are controlled via CAN Bus, by means of CAN PWM Output modules (CR2011).

    We have a total of 11 CR2011 Modules, 1 RF Remote Control with CAN Receiver(CAN) 4 Input Boxes, tilt Sensors, Length Sensors.. A total of 20 CANopen Nodes. Right we have the following settings:

    Com Cycle Period: 200000
    Synch Window Length: 200000

    PLC Cycle Time: Average arround 30ms, with a max. of about 45ms

    Bus Load: 40% up to 100% (when online)
    20% when not online


    So, the problem now is the following:

    As the input values to control the valves are comming from the remote control, the need first to transfered from the Receiver to the PLC and then undergo processing (scaling and so on) and the be transfered to the PWM Modules. This takes at least two synch periods + 1 PLC Cycle. Together with the delay from the remote control (150ms-200ms), this results in a noticable delay in the performance of the hydraulic functons (about 0.8s), which is unacceptable in this application.


    As soon as I try to lower the Com Cycle Period and Synch Window Length, the systems becomes unstable and I have problems login in and loading new code to the PLC and also sometimes some CR2011 Modules do not respond. So 200ms is a safe value which Im now working with.

    What would you recommend to resolve this problem?

    - Change PDO to event driven (Asynchronous Transfer)? I already tried to setup that in Codesys, but with no sucess.

    - Disable some TX PDOs from the PWM Modules?

    - What are typical cycle times for these PLCs? As I only now Beckhoff PLCs which are much faster, I didnt expect a cycle time this high.

    - Why cant I set the Com Cycle Period not lower, without causing unrelated issues like connection problems with CANfox? I mean, where is the problem, when the PLCs outputs data faster, than the bus can transfer? Only the newest data shall be transferred.

    - Shall I go to 500 kbps CAN Baudrate? This would lower the transmit time on the bus, thus declining the bus load.


    Any advise is greatly appreciated.

  2. #2
    Join Date
    May 2009
    Location
    Minneapolis, MN
    Posts
    299

    Default

    You have to remember that the CR2532 is part of our Basic Series. You are actually to the point of asking the PLC to do a bit to much. I suggest you start looking at something like a CR0133.

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