Power meter concentrators: energy logging and MQTT without a server

Once the meters are installed, something has to read them at regular intervals, store the values and pass them on to the people and systems that need them. A PC with data collection software can do this, but it is one more machine to maintain. A power meter concentrator does the same job in a DIN-rail or panel-mounted unit. This article explains what the ICP DAS PMC and PMD concentrators do, how local logging protects data during network outages, which protocols they offer for SCADA, MQTT brokers and IT systems, where IoTstar fits in, and how to choose a model.

What a power meter concentrator does

A concentrator is the Modbus master for a group of power meters. It polls ICP DAS PM series meters over RS-485 or Ethernet and makes their data available on its own interfaces. The PMC-5231, PMC-2241M and PMD-2201, for example, read up to 24 ICP DAS power meters plus 8 Modbus I/O modules. Each of the two RS-485 ports takes up to 16 Modbus RTU devices, the LAN port up to 16 Modbus TCP devices, and at most four of the meters can be PM-4324 multi-circuit meters. The PMC-2841M supports up to 48 modules in total.

Configuration is done on web pages in a browser, with no programming and no separate software tool. Real-time and historical power data and statistics reports are also shown in the browser. The PMD series adds a touch panel for viewing data and setting parameters on site.

Local logging and send-back after a network outage

The concentrators log power data to a microSD card. The PMC-5231, PMC-2241M, PMC-2841M and PMD-2201 come with a 32 GB card, and the PMC-2841M accepts cards up to 2 TB. The PMC-5151 comes with a 4 GB card. Data log files are sent automatically to a back-end system, and ICP DAS names its PMC Data Server software or SCADA software as typical receivers.

For reporting, the important question is what happens when the link fails. On the PMC-5151, PMC-5231, PMC-2241M and the PMD series, data log files are sent back and recovered automatically when the disconnected network is restored. Because polling and logging take place locally, an outage of the upstream connection does not stop the log on the card, and the central database is filled in afterwards instead of keeping a gap. The PMC-2841M also logs data and sends back data files.

Two points to check when planning: set up SNTP time synchronisation, which the concentrators support, because correct time stamps are what make recovered data usable; and make sure the receiving system accepts late data without creating duplicates.

Getting data out: Modbus TCP, MQTT, SNMP and FTP

One concentrator can serve several systems at the same time. The table lists the interfaces of the PMC-5231, PMC-2241M and PMD-2201. The PMC-5151 offers Modbus TCP/RTU, FTP and SNMP but not MQTT.

The IIoT models also connect to Microsoft Azure and IBM Bluemix, and the PMC-2841M adds Amazon Web Services. Where IT security requirements are strict, the PMC-2841M supports HTTPS, VPN, SNMP v3, SFTP, FTPS and blacklist or whitelist filtering, and its MQTT client supports SSL/TLS.

IoTstar for many sites

With concentrators at several sites, IoTstar is the ICP DAS cloud management software for PMC, PMD and WISE controllers. It collects real-time and historical power data from the controllers into a database (MS SQL, MySQL or Oracle), where SCADA systems or analysis tools such as Microsoft Power BI can read it. It also handles remote maintenance and firmware updates of the controllers through a web interface.

IoTstar runs on Windows or Windows Server for a private installation, or on a virtual machine on Microsoft Azure, IBM Bluemix or Amazon AWS. IoTstar 2025 includes dashboards, reports and a bot service for LINE and Telegram in one package, and is licensed for 50, 200 or 500 controllers.

Choosing a power meter concentrator

The PMD-4201-EN has the same functions as the PMD-2201-EN with a 10.4" touch panel. For wireless metering, the PMC-2241M-iWSN works with iWSN wireless modules such as the iWSN-9603 power meter, up to 93 modules in total.

Before choosing, clarify:

• The number of meters and I/O modules, and how they split between RS-485 lines and Ethernet
• Which systems need the data: SCADA, an MQTT broker, SNMP monitoring or IoTstar
• Whether wired Ethernet is available or a 4G connection is needed
• Whether a local display is needed, and which IT security rules apply

Send technical sales the number of meters, the systems that need the data and the network available on site, and we will suggest a configuration.