Application examples • 195

Test of MODBUS protocol and fieldbus nodes

8 Application examples

8.1 Test of MODBUS protocol and fieldbus nodes

You require a MODBUS master to test the function of your fieldbus node. For this purpose, various manufacturers offer a range of PC applications that you can, in part, download from the Internet as free of charge demo versions.

One of the programs which is particularly suitable to test your ETHERNET TCP/IP fieldbus node, is for instance ModScan from Win-Tech.

More information

A free of charge demo version from ModScan32 and further utilities from Win-Tech can be found in the Internet under: http://www.win-tech.com/html/demos.htm.

ModScan32 is a Windows application that works as a MODBUS master. This program allows you to access the data points of your connected ETHERNET TCP/IP fieldbus node and to proceed with the desired changes.

More information

For a description example relating to the software operation, please refer to:

http://www.win-tech.com/html/modscan32.htm

8.2 Visualization and control using SCADA software

This chapter is intended to give insight into how the WAGO ETHERNET fieldbus coupler/controller can be used for process visualization and control using standard user software.

There is a wide range of process visualization programs, called SCADA

Software, from various manufacturers.

More information

For a selection of SCADA products, look under i.e.:

http://www.abpubs.demon.co.uk/scadasites.htm.

SCADA is the abbreviation for Supervisory Control and Data Acquisition.

It is a user-orientated tool used as a production information system in the areas of automation technology, process control and production monitoring.

The use of SCADA systems includes the areas of visualization and monitoring, data access, trend recording, event and alarm processing, process analysis and targeted intervention in a process (control).

The WAGO ETHERNET fieldbus node provides the required process input and output values.

WAGO-I/O-SYSTEM 750 ETHERNET TCP/IP

196 • Application examples

Visualization and control using SCADA software

Attention!

When choosing suitable SCADA software, ensure that it provides a MODBUS device driver and supports the MODBUS/TCP functions in the coupler.

Visualization programs with MODBUS device drivers are available from i.e. Wonderware, National Instruments, Think&Do or KEPware Inc., some of which are available on the Internet as demo versions.

The operation of these programs is very specific.

However, a few essential steps are described to illustrate the way an application can be developed using a WAGO ETHERNET fieldbus node and SCADA software in principle.

•The initial prerequisite is that the MODBUS ETHERNET driver has been loaded and MODBUS ETHERNET has been selected.

•Subsequently, the user is requested to enter the IP address for addressing the fieldbus node.

At this point, some programs allow the user to give the node an alias name, i.e. to call the node "Measuring data". The node can then be addressed with this name.

•Then, a graphic object can be created, such as a switch (digital) or a potentiometer (analog).

This object is displayed on the work area and is linked to the desired data point on the node.

•This link is created by entering the node address (IP address or alias name) of the desired MODBUS function codes (register/bit read/write) and the MODBUS address of the selected channel.

Entry is, of course, program specific.

Depending on the user software the MODBUS addressing of a bus module can be represented with 3 or, as in the following example, with 5 digits.

WAGO-I/O-SYSTEM 750 ETHERNET TCP/IP

Application examples • 197

Visualization and control using SCADA software

Example of the MODBUS function code

In the case of SCADA Software Lookout from National Instruments the MODBUS function codes are used with a 6 bit coding, whereby the first bit represents the function code:

The following five digits specify the channel number of the consecutively numbered digital or analog input and/or output channels.

Application example:

Thus, the digital input channel 2 of the above node "Measuring data" can be read out with the input: "Measuring data. 0 0000 2".

More information

Please refer to the respective SCADA product manual for a detailed description of the particular software operation.

WAGO-I/O-SYSTEM 750 ETHERNET TCP/IP