Description
The 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.
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.