According to the EIA there is a maximum of 32 Unit Loads on one cable segment. This means that when RS485 is used in a 4-wire application and the transmit and receive circuits are thus separated that you can add up to 64 devices on a segment. Unlike what happens in many energy distribution systems, the manner in which the devices are connected in parallel is important. Henceforth, we shall consider Slave devices to be measuring instruments with serial communication, even if the cabling is similar for all Modbus devices. PCs are normally not equipped with an RJ11 socket for serial RS232 communications. RS485 is the preferred serial communications standard for long distance industrial communications. The probes communicate using the standard Modbus RTU protocol. 00-3) or standard 12V power supplies. The cabling of the industrial communication systems (Modbus RS485) is different in some ways from the cabling used for power cabling and the electrician may experience some difficulties if he is not an expert in Modbus communication networks. To get the solar PV power from the roof down to the basement shed, we purchased 20 meters of 6mm armoured cable; this was routed down the back of the house and into the shed through the stone wall.

We decided to move our solar PV inverter installation from its previous location in the loft to the shed below the house. On the Raspberry Pi, we also installed a 1-Wire Pi Plus board, and this is used with a temperature sensor fitted in the shed to monitor the air temperature, which is also posted to the MQTT server and Home Assistant. With the Solis inverter connected to the Raspberry Pi, we were initially unable to communicate with the inverter, and the Python scripts returned connection errors. The data COM port on the base of the Solis inverter uses a small round 4-pin plug with a screw thread to hold it in place when connected. Using the Solis Data Logging Stick, which uses WiFi to communicate, we were able to set up the inverter to send data to the remote soliscloud service, but we could not find any way to get capture data apart from scraping the basic status page built into the WiFi adapter which only gave watts being produced and daily output. The board with dual RJ11 jacks is the more popular since is can use commercial straight-through, non-reversing, 6-wire data cables with RJ11 connectors. Should I use RJ11 or RJ45 connectors?

A challenge is that Laureate meters use RJ11 jacks, while Laureate LT series transmitters use screw-clamp connectors for three discrete wires. Laureate RS485 boards are available in versions with dual RJ11 jacks (ordering option 2, board P/N L485) and with dual RJ485 jacks (ordering option 4, board P/N LMOD). Laureate meters are modular with a middle slot reserved for a communication board, as illustrated in our Laureates Overview web page. The maximum number of repeaters that should be serially connected is 3. A higher number introduces excessive delays in the communication system. Both protocols (or communication languages) are built into the instrument’s firmware and are user selectable. The presence of a new board and the type of board are automatically sensed by the meter’s firmware or by Instrument Setup (IS) software. What are setup steps for RS485? Setup is the same when multiple meters are interconnected via cables CBL03, except that all meters now need to be set to a different digital address via their front panel.

Then use front panel programming to set the baud rate, protocol, digital address, half or full duplex, and other available parameters. If the PC is connected to the multiple Laureate instruments on an RS485 bus via an Ethernet-to-RS-485 gateway board or a USB-to-RS485 gateway board, use Laurel’s free XLOG2 datalogging software. This is how we wanted to use the data with Home Assistant reading the MQTT data from the broker. How fast can I collect data via RS485? Can I mix Laureate LT transmitters and meters on the same RS485 line? The solution is provided by the Laureate DIN rail mounted breakout board, which provides two RJ11 jacks with six screw clamp terminals all wired in parallel. Laureate meter and LT series transmitters support the Modbus RTU protocol and Laurel’s simpler ASCII character based Custom ASCII protocol. RS485 uses two wires and sometimes a ground connection, so we used a twin-screen cable to go between the inverter to the EM112 Series Energy Meter and then onto the Raspberry Pi with a DB9 connector connected to the RS485 Pi board.

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