We have been receiving a lot of enquiries regarding the Redundant Communication capability of the MultiSmart Pump Station Manager recently. Each of these customers has different configurations for their redundant communication network.

MultiSmart has support for DNP3 and MODBUS protocols which are widely in use in the Water and Wastewater Industries across the globe. MultiSmart has three serial (RS232) ports and an Ethernet (RJ45) port. Hence we can interface MultiSmart to multiple Serial communication devices as well to an Ethernet switch or router at the same time. Having capability to support multiple DNP and/or MODBUS Master and/or Slaves within the same unit, we can see that MultiSmart can be setup to talk with more than one Master Terminal Unit (MTU) at the same time over different communication channels.

To demonstrate these, we have created four different DNP3 configurations which consist of different combinations of the physical communication channel as listed below.

1)                 TCP/IP as Primary and two Radios as Backup.

2)                 Radio as Primary and another Radio and TCP/IP as Backup.

3)                 TCP/IP as Primary and PSTN as Backup

4)                 Radio as Primary and PSTN as Backup

To achieve channel switching, according to the desired order when communication over a particular channel fails, we have written four simple ISaGRAF PLC programs, one for each configuration. More explanation on ISaGRAF is given towards the end of this blog.

To achieve redundancy over TCP/IP as well as with backup Radios, we have created three DNP slaves within the MultiSmart Pump Station Manager, all having the same slave profiles. The first DNP slave is setup to talk through the Ethernet port, while the second and third DNP slaves were configured to talk through serial ports 2 and 3 respectively. Unsolicited responses are enabled on the TCP/IP channel when the communication begins.

In the event of a communication failure over the TCP/IP channel, the ISaGRAF program changes the IP address of the Master Station to which it is talking with the new IP address of the Backup Master Station. If that also fails, then the unit will try communication over first Radio and will eventually try the second Radio if no response is heard through the first one.

This shows the flexibility which MultiSmart has, so as to meet custom redundant communication networks. The ISaGRAF program can be written to satisfy the communication channel switching, IP address switching, PSTN telephone number switching, DNP Unsolicited response channel switching etc on the fly without a restart of the MultiSmart unit. A part of the ISaGRAF program function block diagram is shown in the figure below.

ISaGRAF Function Block Diagram

The importance of historical data which is vital for adaptive controls and its applicability in preventive maintenance is known to more and more people in the recent past. Redundant communication plays an essential role in bringing all the information from the field equipments without any loss of data.

The MultiSmart Pump Station Manager was able to  satisfy the Redundant Communication requirements of the customers along with meeting their Lift Station management specifications.

Brief Overview of MultiSmart’s PLC extension, ISaGRAF

ISAGRAF is a control software environment which supports all of the internationally recognized IEC61131-3 control languages and offers a combination of highly portable and robust control engine. Support for the latest release, version 5, of the ISaGRAF is available in MultiSmart.

This PLC extension of MultiSmart allows system integrators and end-users to further enhance or adapt the capability of MultiSmart.  The product has enormous amount functionalities built in, but there are always customers or applications that push the envelope.  The product has 1000s of tags, and System Integrator’s or End-Users can now interface to these with the PLC engine.  This means they can extend the capability without having to rewrite existing functions.

The ISaGRAF implementation of IEC61131-3 is added because it is the most proven platform and v5 is chosen as it offers a number of advantages over v3.  One example is the ability in v5 to run different ‘resources’, or applications, at different rates to allow more critical applications to run more frequently.

Praveen Karunambaran Technical Notes