Controlling the temperature

In industry, space is expensive. The space occupied by control panels is seen as non-productive, leading to pressure to minimise panel sizes. This is a problem for traditional temperature controllers, which have large front panel displays. Even a modest number of controllers needs a large panel.

The obvious solution is to make smaller controllers, and many manufacturers have adopted this approach. Omron, for example, offers a 1/32 DIN controller which, despite its small size, displays the set point and the process value simultaneously.

Small controllers still need to be mounted on the enclosure door or wall, so that the display is visible. In installations with many temperature control loops, they still dictate overall panel size.

An approach which reduces the space needed for displays is now gaining popularity. This is to use 'blind' controllers without integral displays. A group of these controllers is linked to one setting and display unit, which the plant operator can use to address any of the controllers in the group. If the plant has an HMI panel, this can be used in place of the dedicated setting and display unit.

This approach allows controllers to be mounted inside the control panel, arranged to make best use of the available space rather than to ensure optimum visibility. As they have no displays, blind controllers can be made very small: units are available which provide two control loops in a DIN-rail mounting module which is just 22.5mm wide.

If several temperature controllers are using a common setting and display unit, there must be facilities for the controllers to communicate with the display. If the controllers have communication facilities, however, why not go further and mount them on the plant, close to the process that they are controlling?

This not only allows the control panel to be smaller, but also means that the wiring between the temperature controller and the plant can be short and, therefore, inexpensive. The only connection needed between the control panel and the temperature controller is a simple network cable.

To allow users to take advantage of these benefits, temperature controllers are now being offered with networking facilities which support established networking standards, such as Profibus or DeviceNet.

It's worth noting that, in the best devices, these networking options not only allow process values and set points to be exchanged between the control system and the temperature controller, they also allow the controller to be configured remotely. This allows the control system to reconfigure the controller automatically, for example to cope with different types of product that the plant may be producing.

But even the best and most versatile temperature controller is of little value unless it is set up correctly. Recent developments in Windows-based configuration programs are now making it possible for even inexperienced users to get the best from their temperature control equipment.

Omron's SYS-Config package, for example, incorporates a configuration wizard which guides the user through a simple, step-by-step set-up process. It also provides facilities for fine tuning, allowing stability, overshoot and speed of response to be tailored by the user, and optimising plant operation and efficiency.

The software also allows PCs which are networked to the temperature controllers to log and analyse data from the individual controllers. This data is invaluable for maintenance planning, and for spotting long-term drift in process conditions before it compromises production.

Mike Irvin is a temperature control product specialist at Omron Electronics.