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:
- The PCs had frequent hardware failures. The Disk Drives were especially prone to failure.
- Windows 3.1 was not stable in this application. A PC may run for a couple days or weeks, but eventually it would crash. This included frequent NetDDE crashes because of the excessive NetDDE traffic.
- When one of the PCs crashed it was necessary to turn off all PCs and restart them in a specific order.
- When making WonderWare changes, the PCs had to be brought down and the changes had to be copied to all PCs.
- A full backup of each PC had to be maintained.
Because of system age and reliability problems, this company decided that it was time to upgrade the control and monitoring system. The main goal of the replacement system was to eliminate the problems of the old system, and they picked Automation Control Products (ACP) Thin Client computers to replace the Industrial PCs.
A PC running Windows NT Terminal Server was located in a climate controlled computer room, with ACP’s Thin Clients replacing the existing Industrial PCs in the control room and on the manufacturing floor. The server was responsible for communicating to both PLCs via Ethernet. This new system resolved the problems of the old system as follows:
- ACP’s Thin Clients have no disk drives (or other moving parts) so the reliability is significantly increased.
- System uptime has improved. In the first three months of operation, there have been no Thin Client related failures and, more importantly, no loss of production as a result of the new system.
- No Thin Clients have failed. If a Client was to fail, however, it can simply be replaced without impacting the rest of the system.
- WonderWare changes only have to be made on the Server PC – the new screens are displayed when the Clients visit them, and no computer has to be restarted.
- Only one backup of the Server PC needs to be performed. This single backup takes care of the entire system.
This company is now looking forward to the continued benefits of Thin Client technology, and the ease of future system expansions.