Extracting Energy Data from MODBUS Devices Using CIP

Technical Abstract

As increased importance is placed on measuring and managing energy, companies are making energy management a key component of their control systems. In response, the ODVA Energy Special Interest Group (SIG) has been working over the past two years on defining a standard way to represent energy within the Common Industrial Protocol (CIP) model. As a result of this work, several new CIP objects have been defined to offer energy information in a common form.

While these new energy objects will standardize how energy is represented in CIP devices, the current marketplace is filled with MODBUS based energy devices from many vendors. Unlike CIP, which is object-based, MODBUS is based on a flat memory structure. No standard method of representing energy is present, either within or across manufacturers. This requires consumers to learn the MODBUS layout of each of these devices or to use proprietary software from the device manufacturer to extract relevant energy data from their energy devices.

This paper will explore the definition of a device that would extract MODBUS energy data from various energy devices and place it into common CIP energy objects. Ideally, this would be best accomplished for legacy MODBUS products without any modification to the device, but it will be shown why this is not always possible. Use of Electronic Data Sheet (EDS) or Extensible Markup Language (XML) files to define the MODBUS device is also considered. Also considered are modifications that could be made to MODBUS energy devices that would enable direct interrogation to determine its data formats and mappings.

In addition to defining where the data is located within a MODBUS energy device, there is the challenge that data may not be in the same format. Data conversion between the various formats will also be discussed.

Energy devices based on the MODBUS protocol will continue to be developed and sold, regardless of the improvements made in the CIP protocol. Hopefully, the ideas and recommendations presented in this paper will allow the creation of a data extraction device that can be used by those customers that want to manage and optimize their energy usage using CIP.

Paper and presentation from the 2012 ODVA Industry Conference & 15th Annual Meeting

Rick Blair, Schneider Electric