Thin Client I/O

There are two methods for getting data into a Thin Client system – through the Server, or through the Clients.

Getting data through the Server

For small installations, where input/output devices are not very far from the Server, and there are not many devices to read, this can be a very good solution. It is certainly the most traditional, with I/O devices being connected to serial ports or special hardware installed in the Server. As all Thin Client software runs on the Server anyway, there is no problem with each client identifying its input or output devices with physical addresses on the Server. This is also very efficient, as data doesn’t have to travel through the Client, to the Server, and back to the Client. However, it is very limited – a Server can only handle so much I/O, and if devices are far removed there will be difficulties in moving data (especially serial data) over the distance.


Upgrading a Glass Coating Plant

Several years ago, a glass manufacturer was building a new glass coating facility. They wanted to use all the latest technology, especially for the control and monitoring system. It was decided that one of the new MS-Windows based HMI packages, Wonderware, would be used.

The operator interface screens (HMI or Human Machine Interface) were used to monitor every aspect of the coating operation. A particular challenge in this application is that the customer wanted almost all of the points needed for process monitoring displayed at the same time. This resulted in a main display consisting of tiled InTouch screens showing about 1500 points. These screens are displayed almost all of the time

The control system consisted of 3 industrial computers in the main control room and 2 on the manufacturing floor. Each computer ran Microsoft’s Windows 3.1 and WonderWare’s Intouch HMI package. Two large PLCs were responsible for controlling the manufacturing process – one PLC for each of the manufacturing floor PCs – with Ethernet communications between the PC and the PLC. All required data was then distributed to the other PCs via NetDDE. The system performed very well, but over the time many limitations were discovered. The following is a list of the major issues: