Thin clients may be the answer

InTech, Jun 2004 by Edwards, John

The key component of the thin client is its network connection. This allows the client -with the little bit of intelligence it has built-in-to go onto your plantwide network to find a PC configured as a thin server.

Thin clients are dumb-but using them may be one of the smartest decisions you can make in deploying your plant human-machine interface (HMI) system.

Let me explain. A thin client is a very simple computer, typically with no hard drive (clients with hard drives are known as "fat clients") and a so-so processor. You can connect standard peripherals to a thin client, including a mouse, keyboard, and monitor. Thin clients do not have an operating system. So what good are they?

The key component of the thin client is its network connection. This allows the client-with the little bit of intelligence it has builtin-to go onto your plantwide network to find a PC configured as a thin server. Once it finds the thin server, the thin client establishes a session where it sends all of the input it receives (mouse and keyboard) across the network. The thin server processes the input and generates an updated image display that it then sends back to the client to display on its monitor. The client does not do any"thinking" of its own.

A Windows 2000 server can handle multiple thin-client connections, each running different applications or multiple instances of the same application. When configured in this way, the server is known as a "terminal server."

Thin clients have been around for quite a few years and have not really taken off as much and as fast as industry experts predicted, but if the latest reports from industry analysts are any indications, they finally may start to pique users' interest.

Enterprise thin clients-network-based computer devices with no local storage-will ship 3.4 million units worldwide in 2007, up from just 1.5 million in 2003, a compound annual growth rate of 22.8%, according to research from Framingham, Mass.-based computer industry research firm IDC.

As with any technology there are issues both pro and con.

Pros of thin client/server computing:

* Centralized management:You can monitor, upgrade, and control all of your thin-client applications from a single point-even from a remote site.

* Scalability: Adding new clients or applications to the network can be as easy as connecting a thin-client PC to your network or installing client software on an existing Windows-based PC.

* Cost savings: By installing client software on an out-of-date PC (now a "fat client"), you allow that PC to access any functionality your Windows 2000 server has available to it.

* Maintenance: If a thin client fails, simply replace it with a new thin client. It will connect to the server in minutes and continue interacting with the same application where the other client left off. Also, you can do away with running from stand-alone computer to stand-alone computer updating your virus definitions.

* Security: By enforcing security on your servers in a thin-client environment, you can automatically enforce security on all of the connected clients.

* Accessibility: The freely available Terminal Services Advanced Client (TSAC) is a Web-based tool that can connect to the terminal server across any accessible network connection, including across the Internet.

Cons to thin client/server computing:

* Deployment: There are some nuances and complexities to implementing the thin client/server model that you must consider before deployment. Network layout, server hardware, and licensing can be especially critical. Not all applications can transition without some modification.

* Single-point of failure: Consolidating all of your valuable plant-control applications onto one server could be disastrous if that server failed. That is why most software packages and operating systems include "instant fail over" that allows switching to an alternate piece of hardware within seconds of the first piece failing.

* Multiuser performance issues: Each user (i.e., client) connecting to the main server will contend with other users for CPU time, disk access, network bandwidth, and memory. In a control network, this may result in unacceptable delay.

If you have multiple control applications running on various stand-alone PCs, aging PCs that have difficulty running the latest software, and an expanding network that is difficult to manage, then thin clients may be a less expensive way to go.

Behind the byline

John Edwards is an automation engineer for Automation Horizons, Inc., a Des Plaines, Ill., control system integration firm. His e-mail is jedwards@autohorizons.com.