This article deals with several options of communication provided by datalogger unit SM-MU, also known as „energy gateway“.
Energy gateway offers four communication options. With the exception of XML, they all work as M2M, which means that one device communicates with another device (Machine-2-Machine).
In the first type of communication the device (server) generates XML file from collected data when requested from a client. This file is then processed (parsed) by client. If the client is a web browser, the file is rendered (visualised) on a user's PC.
Second communication type uses SOAP protocol, which is a standard for web services. It makes implementation on large servers much easier. Using this protocol the data gets into the cloud. The cloud provides customer with clearly arranged data on his/her PC or mobile phone with Android OS. Our cloud solution offers not only one way communication (from device/client to server), it can communicate the opposite way too. Advantage of this is a remote configuration of the device or updates of its firmware.
Third type of communication is suitable for NMS - Network Management System with SNMP protocol. It means that data is requested in 5-60 second interval and primary function is detection of outages or possible bottlenecks. Server is called agent, a client can also be a so-called MIB browser. The Management Information Base (MIB) is a file, that describes which variables device provides. The device can implement even more MIBs that can hierarchically merge. At the same time there is an active type of communication so-called trap, when agent itself sends an alarm notification. There are servers online that collect the traps and react with e.g. SMS, email or other action.
The last option is communication using the Modbus protocol, commonly used in automation. This protocol is very easy to implement and is used for prompt communication, i.e. in milliseconds. It is therefore also suitable for direct communication with a PLC e.g. In a smart house.
Modbus is an open protocol for mutual communication of numerous devices (PLCs, touch screen displays) that allow data transfer over various networks and buses. Communication works on the most common principle we deal with every day - passing data messages between client and server.
There is one „master“ device sending requests to „slave“ devices. The „slave“ devices respond. PLC is a typical „master“. „Slave“ devices usually control or monitor (e.g. Sensors, actuators or meters). Modbus protocol also enables communication with devices, which have a very different type of communication. In this case we use the term gateway.
Our SM2-MU unit communicates with operated devices via its serial buses (RS485, RS232) and the ethernet (LAN). It can collect data or set up parameters. Data is then available on ethernet via Modbus /TCP protocol. By default, Modbus uses a generic addressing method. In our case, we have covered the diversity of the devices by dividing each device brand or even every single device type into objects, which are accessed as blocks. Most of the blocks correspond to the Sunspec Alliance standard definition, of which our company is a member, only for some technologies (such as Studer-Innotec) we used custom blocks. Block numbers pre-define the block format, which is the same for different devices.
This method also offers the possibility for enumeration, when we can search the address space and find out which blocks are supported in a particular device. Each device can provide only certain attributes of an object, other attributes aren't neccessarily present. Enumeration enables finding out which objects are in a particular device and whether a particular attribute is present.
SM2-MU unit with a Modbus SunSpec implementation represents a universal gateway to energy applications e.g. PV plant. It makes using multiple various devices much easier because we needn't worry about time-consuming configuration and implementation of numerous communication protocols.
More on SunSpec benefits will be described in some of our next articles.
The project Energy Gateway for Renewables is provided with financial support from the European Union.