Control.com - Nerds in Control

Hi to everyone,

I am working with the engineering of a remote unit using Modbus as fieldbus from the remote unit to the DCS.

In other fieldbus systems (i.e. Foundation Fieldbus) i read about acyclic time for diagnostic and emergency signals. to have a correct communication the cyclic communication time must be in the range of 30-50% of total time (as i remember, maybe I'm in wrong :)). I would know if there is a guideline of this kind for Modbus too. i searched on the internet bu I haven't found anything.

Thanks to everyone will respond to me.

Modbus is strictly a communications protocol. The DCS, PLC, or other controller determines how and when to communicate. Foundation Fieldbus is intended to replace some of the functions of a DCS and distribute the functionality to the field devices.

With most communications protocols (including Modbus) the features you are referring to are part of the controller. In the end, it's all just software providing policy and function. It's just a matter of where you want the policy to be located - in the central controller, or in the field devices.

Some of the functionalities are located on the field, in particular the diagnostic functions. I want to be sure that cyclic and acyclic data (diagnosis, alarms, etc) communications can communicate with the DCS without problems.