Temperature Controller Survey, Part 2
There was a time when a temperature controller had three pairs of terminals: power input, temperature sensor and output. Three knobs were on the front: proportional band, integral time and derivative time. Wiring was easy and tuning procedures were not hard to master.
In year 2005, a typical 1/4 DIN controller comes densely packed with features. You can adapt it yourself to virtually any control task without sending it back to the factory. So how to put it to work? If this job is dumped on you, I hope you played a part in selecting the product and that you have some knowledge of its features and how they fit in with your process. If you didn't get on the decision team, there is a serious defect in the organization.
At the earliest stage possible, you should try to evaluate the degree of complexity involved in configuring, setting up and applying your instrumentation. This issue varies greatly among suppliers and it is a long and hard hands-on study to compare offers. Talk to users of different brands and models. In previous columns, I have preached about the costs and dangers of complexity and the human interface. Put it high on your list of points to compare.
When you need help configuring and applying your controller, remember that it is a cooperative effort between you and the manufacturer or supplier.
I know that user manuals can contain some 250 confusing pages and a lot of buzzwords. Give it your best shot and show some self-reliance first. Your encounter then with the supplier's helpline will be much more productive, and you are not seen as just one more of those time-wasters that have forced help desks to be heavily defended.
Two More ResourcesLook on Your Manufacturer's Web Site. You find specifications, data sheets, valuable application information and printable user manuals. Manuals go astray, and you rarely see a high tech product that you can use without doing some heavy reading. The best manufacturers realize how a process can suffer an expensive shutdown for want of operating information. They post all manuals including those for obsolete products. Evaluate them on brevity, clarity and ease of extraction of information.
Use That Valuable Human Link to the Experience Base: the Technical Sales Rep. He has an interest in selling his product and has both product and application knowledge. Make him your friend. Invite him to you plant. He is often articulate, good with his hands and can cut through the clutter right to your specific application. “Oh don't bother with that, or that -- this is all you need.”
Some time, but not yet, there will be a way to buy your controller ready configured. The other 101 built-in features that you don't need can stay asleep. And there will be a built-in file that can print a specific brief manual to match the configuration that you bought.
Meanwhile, probe the different entry points of user help from suppliers. See who employs battle-hardened technicians who have had their hands on controllers and processes. They will know what you are talking about and won't need a long introductory seminar from you about your process.
Spares And Repair BackupWith a view to heading off shutdowns, survey your installed base of controls and add in any contemplated new project requirements.
- Look on the shelf and make sure all spares are there, identified and serviceable -- not suspect items parked there waiting for repair.
- Check that all your user and maintenance manuals and drawings are on hand to deal with faults.
- Put each supplier's name and phone number stickers on the enclosure doors and equipment. Find out who offers 24-hour spares stocks and maintenance assistance.
Should You Update?Should you keep your aging controllers or replace the lot? If they are reliable, new control technology would not benefit your process, and you have spares enough, keep them. Look at your supplier’s policy on spares for what they call legacy products. If your controllers and parts are still available, be ready for long deliveries and high prices.
As an alternative, look on eBay. Of three most popular manufacturers, 18, 13 and 8 offerings are currently listed. You will rarely pay more than 20 percent of list price.
All of this consumer research is a lot of work, but it enables you to evaluate and find your best -- not cheapest -- choice of supplier and puts in place a solid response to both regular maintenance and shutdown threats. PH