Features
- Includes dual RJ45 connectors for daisy chaining of meters without a hub
- Not recommended for new designs, but fully supported for existing designs
- Allows up to 247 meters to be addressed using the Modbus RTU protocol
- Allows up to 31 meters to be addressed using Laurel's Custom ASCII protocol
- Allows data streaming with Custom ASCII protocol
- Selectable full-duplex or half-duplex operation
- Suitable for all 1/8 DIN Laureate DPMs, counters, timers & remote displays
- Selectable baud rates to 19200/sec
- Isolated from meter and power grounds
Certificates of Compliance
The Laureate P/N LMOD interface board with dual RJ45 jacks allows multiple Laureate meters, counters, timers and remote displays to be connected to the same RS485 line.
The LMOD board is not recommended for new designs, but it remains readily available from Laurel for existing designs. For new designs, use the functionally equivalent L485 board with dual RJ11 jacks. That board is better supported by Laurel interface cables and is designed for easy interface to Laurels gateway boards, which are LUSB485, LNET485, LNET1485, LWIFI485, LWFIX485. The gateways boards all provide an RJ11 jack for connection to an RS585 bus with up to 31 Laureate instruments.
The dual jacks of the LMOD board are wired in parallel as for the recommended L485 board. This allows multiple instruments to be daisy-chained using data cables (or patch cords) with RJ45 plugs; however, such data cables are not available from Laurel. Laurel's alternative L485 board with dual RJ11 jacks is supported by our RS485-to-USB converter cable (P/N CBL06) for data I/O and for programming by a PC running Laurel's free Instrument Setup (IS) software. It is also supported by our 6-wire data cables (or patch cords) with RJ11 plugs (P/N CBL03) to daisy-chain meters without use of a hub.
The LMOD or L485 boards can be configured for full-duplex or half-duplex operation using jumpers. Transmission distances up to one mile are possible. To avoid signal reflection with long signal lines, a 120-ohm termination resistor can be selected via jumpers. The meter, counter or timer should be programmed for full duplex operation, even if the RS485 board is jumpered for half duplex.
Two serial protocols are user-selectable for RS485: Modbus RTU and Custom ASCII. For detailed information on our protocols, please see our communication user manuals.
- The Modbus RTU protocol is an international standard and allows Laureates to share the same RS485 data lines with non-Laurel devices. It supports up to 247 digital addresses. Use of more than 31 Laurel RS485 Modbus boards requires repeaters for impedance reasons. Modbus RTU works in a master-slave (or query-response) mode, and its use requires an external Modbus master, which is typically a PC. Meters with a thermocouple input and using the Modbus RTU protocol should be set to full duplex.
- Laurel's Custom ASCII protocol is the simpler of the two protocols and uses ASCII strings. It is recommended if the only devices on the RS485 data line are Laureate meters. It supports up to 31 digital addresses. It can be set to a command mode under control of an external master, or to a continuous streaming mode where data is output at specified intervals at rates up to 60 per second.
Electrical Specifications
| RS485 RJ11 Board Specifications | |
|---|---|
| Laurel Part Number | LMOD |
| Connection | Full duplex (ATX, ARX, BTX, BRX) or |
| half duplex (ATX / ARX, BTX / BRX) | |
| Data rates | 300, 600, 1200, 2400, 4800, 9600 baud |
| No. of devices on data line | Up to 31 without a repeater, 247 Modbus addresses |
| Connectors | Dual RJ11 jacks for daisy chaining without a hub |
| Line length, max | Up to 5000 feet (1500 meters) at 9600 baud depending on cable |
| Isolation | 250V rms working, 2.3 kV rms per 1 min test |
| ESD Protection | 15 kV per IEC 1000-4-2 |
| EMI Immunity | 10 V/m per IEC 1000-4-3 |
| EFT Protection | 2 kV per IEC 1000-4-4s |
| Short Circuit Protection | Continuous |
| Selectable Protocols | Modbus RTU, Custom Laurel ASCII |
Protocol Specifications (protocols reside on Main Board)
| Modbus RTU Protocol | |
|---|---|
| Standards Compliance | Modbus over Serial Line Specification V1.0 (2002) |
| Protocol Type | Master-slave, query-response command mode |
| Data Streaming Mode | Not supported by Modbus specification |
| Data Formats (selectable) | 1. No parity, 8 data bits, 2 stop bits |
| 2. Odd parity, 8 data bits, 1 stop bit | |
| 3. Even parity, 8 data bits, 1 stop bit | |
| Main Board Revision Level | Level 5 or above |
| Custom ASCII Protocol | |
| Standards Compliance | Laurel proprietary protocol |
| Data Format | No parity, 8 data bits, 1 stop bit |
| Protocol Type | Text string based command mode or continuous data streaming mode |
| Data Streaming Mode | User selectable for up to 60 readings/sec |
| Main Board Revision Level | Any |
RS485 Interface Board, Laureate RS485 RJ45 interface board Frequently Asked Technical Questions
RS485 is the preferred serial communications standard for long distance industrial communications. It uses balanced differential signals for send and receive. This provides high noise immunity and allows distances up to 4,000 ft (1200 meters). The older RS232 standard uses single-ended signals, is more sensitive to noise, and is only rated for distances up to 50 ft (15 meters). RS485 is specified for multi-point communicates where multiples devices have their own address on the same communication line, while RS232 is only specified for point-to-point communications.
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). Both boards support the Modbus protocol and Laurel’s Custom ASCII protocol, as well as half-duplex or full-duplex RS485 communications. 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. Note that these cables are different from4-wire telephone cables or crossover cables.
Use Laurel’s cable CBL06, as described in https://www.laurels.com/Cables. This cable provides a USB type A connector for the PC end and an RJ11 connector for the meter end. It works in 3-wire half duplex mode, where red & black = GND, green = ATX/ARX, white = BTX/BRX. It incorporates an FTDI RS485-to-USB converter chip which is compatible with all versions of Windows.
Use Laurel’s 6-wire data cables CBL03-1 (1 ft) and CBL03-7 (7 ft) to interconnect meters if these lengths fit your application. These cables allow the dual RJ11 jacks of the RS485 option board of Laureate meters (digital interface ordering option 2) to be daisy chained and to be addressed digitally with no need for a hub. RJ11 jacks support half-duplex or full-duplex communications.
The two jacks are wired in parallel by circuit traces on the circuit board. The two jacks are for RS485 cable in and RS485 cable out. By using two jacks, up to 31 L485 boards can be connected in parallel for daisy chaining using readily available CBL03 data cables with no need for a hub.
Both will work with RJ11 connectors and CBL03 cables. A meter will a thermocouple input and set for Modbus RTU needs to set to full duplex even if the wiring and the receiving unit are for half duplex. In all other cases, half duplex and full duplex will work equally well. Half duplex has the advantage of only using three wires: ARX/ATX, BRX/BTX and GND. With Modbus RTU, sending and receiving are never simultaneous, so half duplex is as fast as full duplex.
A challenge is that Laureate meters use RJ11 jacks, while Laureate LT series transmitters use screw-clamp connectors for three discrete wires. 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. With this boards, a CBL03 lines with RJ11 connectors can branch out to support an RS485 line consisting of three discrete wires. Not more than one breakout board is required per RS485 line.
Laureate meters are modular with a middle slot reserved for a communication board, as illustrated in our Laureates Overview web page. Boards can be ordered installed with a new meter, and they can also be purchased separately later and be simply plugged in. 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. If you change boards, also change the model number on the meter label.
Laureate meter and LT series transmitters support the Modbus RTU protocol and Laurel’s simpler ASCII character based Custom ASCII protocol. Both protocols (or communication languages) are built into the instrument’s firmware and are user selectable.
A single analog input meter or transmitter can stream readings to a PC at up to 60 readings per second and the Custom ASCII protocol set to continuous (or streaming) model. If multiple analog input meters or transmitters are digitally addressed in command mode on an RS485 line using the Modbus RTU protocol or the Custom ASCII protocol, the rate becomes about 2 readings per second. Read rates vary with counters, since they are normally controlled by the user entry Gate Time.
When a single RS485 meter or counter is connected to a PC via a cable CBL06, set the PC to 9600 baud. Set the PC to N81 for the Custom ASCII protocol, or to N82 or E81 for the Modbus RTU protocol. To set up communications for your meter or counter, see the Serial Communications section of its user manual. First set jumpers for your type of communications. Then use front panel programming to set the baud rate, protocol, digital address, half or full duplex, and other available parameters. 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.
See page 7 of the Laurel digital panel meter manual, page 7 of the Laurel counter manual, page 8 of the Laurel scale meter manual, or page 8 of the Custom ASCII protocol manual.
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. That software is described in our web page at https://www.laurels.com/Sitemap/Logging-Meter-Counter-Readings and user manual at https://www.laurels.com/downloadfiles/datalogging-manual.pdf.
