Laurel Electronics
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Panel Meters - Counters - Timers - Transmitters, 4-20 mA & Modbus - Ethernet - USB - RS485 - RS232
Ethernet-to-RS485 Converter Board Frequently Asked Technical Questions
The Ethernet-to-RS485 gateway board allows a single Ethernet line to collect data from up to 32 Laureate instruments, which include the host meter and up to 31 remote meters and transmitters on a half-duplex RS485 bus. It provides all capabilities of the basic Laureate Ethernet board plus connection to the remote devices. It has three communication connectors: an industry-standard Ethernet RJ45 jack to the Ethernet and an RJ11 jack to the RS485 bus.
Laurel offers two RS485 boards of its meters: an RS485 board with dual RJ11 connectors (ordering code 2, P/N LUSB), and an RS485 board with dual RJ45 connectors (ordering code 4, P/N LMOD). Use the board with dual RJ11 connectors. These are wired in parallel and allow daisy chaining of meters with commercial 6-wire RJ11 data cables (Laurel P/N CBL03), with no need for a hub. Do not use the board with dual RJ45 connectors, as it does not have an associated data cable.
Use a standard Ethernet cable with RJ45 connectors on the Ethernet side. Use a CBL03 non-reversing serial data cable with RJ11 connectors on the RS485 side.
The challenge is that meters use RJ11 connectors and plug-in CBL03 data cables for half-duplex RS485, while Laureate LT series transmitters use three screw terminals for discrete wiring. To establish wiring compatibility, use Laurel’s RS485 Breakout Board. This board provide a parallel connection two dual RJ11 connectors like a meter and to two a 6-position screw clamp connecter for discrete wires. A signal breakout board should suffice for an RS485 bus with multiple Laureate meters and LT transmitters by splitting the RS485 line into a data cable line and a line with 3 discrete wires.
Use Modbus TCP to communicate with the Ethernet-to-RS485 gateway board, and that board will then communicate via Modbus RTU with the meters and LT transmitters on the RS485 bus. Do not use the Custom ASCII protocol, which only works with RS232, RS485 or USB, not Ethernet.
Use Laurel’s free Instrument Setup (IS) software running on a host PC to discover the Ethernet Node and the Devices (or instruments) associated with that Node. The Devices will be the host meter of the Node and the Devices on the RS485 bus. The host meter and remote Devices that are meters can be programmed by the host PC via IS software, or they can be programmed from their front panel. Remote Devices that are transmitters can only be programmed via IS software.
Built-in DHCP server capability allows Laurel Nodes to constitute themselves into a network and be connected directly to a host computer when no router or dedicated DHCP server is present. When a Node fails to find a DHCP server that responds to its request for a private IP address, it assigns one. When several Nodes fail to receive a Private IP address, they mutually agree to make one of the Nodes a temporary DHCP server that assigns a Private IP address to each device on the network.
Normally a dynamic IP address is assigned using DHCP. A static IP address can be assigned to a Laureate Node by our free Node Manager software, but not by our free Instrument Setup (IS) software.
Use Laurel’s XLog2 datalogging software to log readings to disk from all meters and transmitters attached to a PC via an Ethernet-to-RS485 gateway board. That software can also display data on the PC screen in the form of simulated meters, which can replicate the readings of real meters or be virtual meters that show arithmetic combinations of readings from multiple meters. See our XLOG2 Datalogging Manual. For many applications, XLOG2 software may avoid the need to write custom software. It can be downloaded from our website and is at no charge.
Laureate meters and transmitters can output data at about 2 readings per second when used with the Modbus protocol, whether Modbus TCP or RTU. Data streaming can be at up to 60 readings per second with the Customer ASCII protocol, but is not allowed by the Modbus standard, which only specifies query-response (or master-slave) operation.
The RS485 specification allows for cable lengths up to 4000 ft or approximately 1200 meters.
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