In the recent past a few customer enquiries came regarding the capability of MultiSmart to act as a DNP gateway RTU in addition to its standard pump station / lift station management functionality. MultiSmart can certainly act as a RTU gateway along with its normal functionality; however, it has certain memory constraints which limit the number of DNP slave profiles it can support within the gateway.

To come up with an alternate solution we decided to trial the Linux based MultiTrode applications for the communication on an Embedded PC. A small form factor MOXA V481-XPE is selected for the testing and implementation. The MOXA V481 is a compact, DIN – rail mountable, industrial embedded PC with relatively good hardware resources. The additional advantage with this MOXA PC is that it has got 8 built in serial ports (all can be configured for RS-232/422/485) and 2 GBit Ethernet ports which ease the physical communication interfacing. Having a large number of physical communication ports the V481 is an ideal choice for implementing the MutiTrode RTU applications. It also has a large capacity hard disk built in so that MultiTrode historian (MySQL Database) can also be installed to save the historical data at the gateway as well.

Installation of CentOS was performed using a USB disk rather than the conventional ways since the V481 does not have a CD/DVD drive. Unetbootin-windows or Unetbootin-linux software is used to copy the Linux ISO image to the USB and to make the USB disk bootable with the installation launcher. Once the installation is complete I had to compile the serial port drivers and update Linux boot scripts to load these drivers every time when the system reboots. Now the base platform for the gateway system is ready. Setup and configuration of the MultiTrode DNP applications seems to be very easy on the embedded computer.

In the MOXA system, having 8 Serial ports and 2 Ethernet ports, we tested running 10 DNP masters one for each physical communication ports, at the same time successfully. The V481 system is shown in the figure below.

MOXA V481 Embedded PC

In addition to the data concentrator functionality, this setup has another major feature. ISaGRAF, an IEC61131-3 based PLC platform is part of the MultiTrode applications installed and hence you can implement custom PLC based applications and control logics within the gateway system.

You can also run a MODBUS gateway RTU which is already a part of the MultiTrode application pack installed. The MOXA embedded computer with the MultiTrode application can act as a DNP gateway RTU, MODBUS gateway RTU and perform PLC control logics simultaneously. Only constraint is that different communication protocols cannot utilize the same physical communication port.

Praveen Karunambaran Technical Notes