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DeviceNet - How to calculate update rate from devices on segment?

Does anyone know what the rate data that can be referenced in a control module is pulled in from a DeviceNet segment in to DeltaV?

I know the DeltaV DeviceNet card (M-series) is a master on the DeviceNet segment and that it uses Polling to send/receive data from the devices.    Is this a fixed time to scan all devices or is it automatically determined (a.k.a. as fast as it can) based on number and type of devices, amount of input and output bytes configured for each device, baud rate, and trunk and drop cable length?

With Foundation Fieldbus I can see the network schedule in DeltaV Explorer.   I cannot seem to find an equivalent for DeviceNet.

chris williams
  • Rune Reppenhagen
    The Baud rate is set when configuring the DeviceNet card; the options are 125, 250, or 500 kbit/sec

    See Product Data Sheet at www2.emersonprocess.com/.../PDS_M-series_DeviceNet_IO.pdf

    Regards,
    Rune
  • Andre Dicaire
    The update rate of the segment will depend on the device data communicated and the configured baudrate. This will follow ODVA specifications with respect to delays between packets and response times.

    The DeviceNet card receives the data and maps it into the defined Signals, so one might not pass all the data received.

    The IO card itself is polled by DeltaV over the LocalBus, which has a minimum of 20ms, and polls all cards as fast as possible. Some cards have more data, such as AI 16 channel, or Bus cards, vs a simple 8 channel DI. Typically, the IO bus poll is 35 to 50ms, but ultimately is determined by the number and type of cards.

    So the segment scan time plus the IO bus scan time will be the longest time for the data to be present in the controller's IO map. The control modules pull from this map at the configured execution speed of the module.

    Andre Dicaire

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