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  • Serial Communication Boards are Plug & Play Field Installable
  • Connects host meter to a computer via USB 2.0 and to a bus with up to 31 DPM-3 instruments
  • Includes USB Type-B receptacle to PC plus RJ11 jack to RS485 bus
  • Selectable baud rates to 9600
  • Powered by USB line
  • Isolated from meter and power grounds

USB-to-RS485 device server board


The DPM-OPT-U485 can connect a computer with a USB port to a DPM-3 host meter and to up to 31 DPM-3 remote meters on an RS485 bus. It features a USB Type-B connector for connection to a PC via a standard USB cable, plus an RJ11 jack for interface to an RS485 bus with up to 31 DPM-3 meters equipped with Transducer Techniques RS485 interface board That board provides dual RJ11 connectors wired in parallel for RS485 daisy-chaining using commercial 6-wire RJ11 data cables, with no need for a hub.

Network of DPM-3 meters connected to a PC via USB-to-RS485 device server

Two serial protocols are user-selectable: Modbus RTU and Custom ASCII. The text string based ASCII protocol is the simplest and is recommended if DPM-3 is the only devices on the network. For more information, please see our Modbus Protocol Serial Communications Manual and our Serial Communication Manual. The ASCII protocol supports 31 device addresses, one of which needs to be the converter board. The two Modbus protocols support 247 device addresses; however, only 31 addresses can be electrically driven on an RS485 line without a repeater.

Multiple DPM-3’s on an RS485 bus can also be digitally addressed using our interface-ethernet-server. Ethernet-to-RS485 converter board Ethernet-to-RS485 converter board, which can be connected directly to a PC via an Ethernet cable or via the Local Area Network (LAN) to with the PC is also connected.


Connecting the DPM-OPT-U485 board to a PC will cause the PC to download the required driver. The board is connected to PC via a UART, so you need to specify RS485 communications. Specify the baud rate, normally 9600, and enter the COM port number assigned by the computer. The individual meters, including the host meter, are selected in software by their own digital address, which can be entered from the meter front panel or by using free Windows-based Instrument Setup Software.

USB & RJ11 connectors in back of DPM-3 panel meter DPM-3 USB cable, P/N CBL05
USB & RJ11 connectors AUS-B2.0A/B 10ft cable


RS485-to-RS485 Converter Board DPM-OPT-U485

Baud Rates 300, 600, 1200, 2400, 4800, 9600
Devices per PC USB Port 1 for host meter plus up to 31 on RS485 bus
USB Connector USB Type-B receptable
USB Compliance Universal Serial Bus Spec Revision 2.0
USB Line Length, Max 5 m
Devices per RS485 Line Up to 31
RS485 Connector RJ11 jack
RS485 Compliance EIA/TIA-485
Power to Converter Board Via USB line
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 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 Our 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

Software Requiring a Communications Board

  • Instrument Setup Software runs on a PC and provides a Windows Graphical User Interface (GUI) as an alternative to programming the meter from the front panel. This software can be downloaded from this website at no charge. Its use requires a serial communications board in the meter, but following setup that board can be removed if desired. Compatible with Modbus or a ASCII protocol.
  • Data Logging Software turns a PC into a data logging system. The RS232 board allows data logging with a single meter. Use of RS485 boards allows data logging with up to 31 DPM-3 instruments. Data can be logged from selected meters into an ASCII file, which can then be imported into MS Excel. Data can also be displayed on the computer screen in the form of up to 64 actual or virtual panel meters in 4 groups (or screens) of up to 16 meters each. Compatible with a ASCII protocol only.
DPM-OPT-U485 N/A 178.00