Connecting the process station to network

The process stations feature one or two Ethernet interfaces which connect the stations to a technological network. The Merbon process stations can exchange data using the SSCP protocol either over Ethernet, or using serial port, if it is available (i.e. not occupied by I/O modules, room units, or a 3rdparty device). Using serial ports makes sense if an existing RS485 communication infrastructure is available and installation of an Ethernet network is not possible. All process stations connected to the serial line are available over the Ethernet through a PLC configured as a SSCP router: it is possible to read data, change values, upload program, perform commissioning etc. Note that the serial communication offers slower communication response due to the lower data throughput.

R_SSCP_Serial

Example of a SSCP communication over serial. The mark320 is used as a SSCP router.

Data exchange between the process stations

The process stations may exchange data (outside temperature, heating / cooling demands etc.) between each other over the network. No other hardware nor software components are necessary, the only condition is that the process stations must be “visible” for each other in the network..

The number of variables has no physical limitation, however, it is recommended not to use more than about 20 variables per process station to keep the software simple and easy to understand.

Every open connection takes one communication channel. There is a limitation for maximum number of open channels at some PLC: IPLC201, IPLC301 a MXPLCaccepts max. 5 incoming connections, including connections from SCADA, SoftPLC IDE, OPC server and other clients. IPLC500, IPLC510 and SoftPLC Runtime on Windows there is no limitation, although it is recommended not to exceed about 15-20 connections.

For Merbon PLCs there are following limitations: the maximum number of incoming connections is 5. At more powerful platforms, which are mark220, mark320 and markMX, it is 20 connections.

It is not a good idea to configure communication between the process stations inside of the control loops, e.g. a sensor in one station and the controlled valve in another station. The problem is not the data transport delay, which is hundreds of milliseconds. It should be avoided to configure the control loops dependent on the functionality of the network.

Communication betweenSoftPLC and Merbon

If there are both SoftPLC and Merbon PLCs in the network, they can excchange data under certain conditions.

                   server

client

IPLC201,301,MXPLC
(Beck OS)

IPLC5xx, …-L, RT(Linux, Windows)

Merbon

IPLC201,301,MXPLC
(Beck OS)

yes

yes

no

IPLC5xx, …-L, RT (Linux, Windows

yes

yes

yes

Merbon

yes

yes

yes

Communication between SoftPLC and Merbon. 

In other words, the SoftPLC process stations with Beck OS can not connect as clients to Merbon PLCs over the SSCP protocol. All other combinations are possible. The data exchange requires an open communication channel at each PLC, and this has to be considered regarding to the performance limitations above.