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  • Serial Communication Board is Plug & Play Field Installable
  • USB Type-B connector for plug-and-play connection to a PC USB port
  • Allows multiple meters to be connected to a PC via a hub
  • Data rates selectable up to 9600 baud
  • Powered by instrument
  • Isolated from meter and power grounds

DPM-3 Option U


Meter connected to a PC via USBThe DPM-OPT-U USB serial communication board allows a DPM-3 1/8 DIN digital panel meter to be interfaced to a PC with an available USB port. Connection to a PC allows programming via free Windows-based Instrument Setup Software or to output readings to a PC for display and datalogging. Connecting the USB board to a PC will cause the PC to download the required driver.

A single USB meter is normally connected to a host computer via an off-the-shelf USB cable with A and B connectors. The line can be up to 5.0 m (16.4 ft) long according to the USB standard. The PC driver software will assign a COM port address to the connected device, which is then treated like an RS232 device.

DPM-3 Meters connected to a PC via USB hubs

Multiple USB meters can also be connected to the host computer by using powered hubs, which can branch the original USB line from the computer into multiple lines. Theoretical limits are up to four hubs in series for five tiers of lines, a maximum line length of 5 m per tier (up to 25 m total), and up to 127 devices including the hubs. The PC driver software will assign a unique COM port address (out of an available 256 addresses) to each connected device, which then needs to be addressed as a single device via its unique COM port.

Multiple meters can also be digitally addressed using alternative interface boards: Ethernet board, Ethernet-to-RS485 converter board, Ethernet-to-RS485 converter board, USB-to-RS485 converter board, RS485 board with dual RJ11 connectors, RS485 board with dual RJ45 connectors. A USB board is recommended if the objective is to interface a single meter to a PC with an available USB port.

Two serial protocols are user selectable for custom software: 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 DPM-3 to share the same RS485 data line with non-DPM-3 devices. It supports up to 247 digital addresses. Modbus RTU works in a master-slave (or query-response) mode, and its use requires an external Modbus master, which is typically a PC.
  • Custom ASCII protocol is the simpler of the two protocols and uses ASCII strings. It supports up to 31 digital addresses and is recommended if the only devices to be addressed are DPM-3 meters. 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.


USB Type A and Type B connectorsThe DPM-OPT-U USB 2.0 board provides a USB Type-B connector for plug-and-play connection to the USB port of a PC. It is ideal for use with a PC to program a DPM-3 meter using Instrument Setup Software. The required USB cable is readily available from our online store as cable USB-2.0A/B.

Meter board with USB Type-B connector USB-2.0A/B
USB Type-B connector AUS-B2.0A/B 10ft cable

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 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 ASCII protocol only.


RS485 RJ11 Board Specifications

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 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
DPM-OPT-U N/A 115.00