Questioning Kiln Controllers

[HencoV]

Kiln control systems have come a long way since capillary tubes, but, how effective and flexible are modern kiln control systems really? Did you ever get the feeling that the control system is over kill? It dazzles with so much brilliance from a software developer with so many fail safes build in that it misses some of the basics required by the control system. I have come across systems where “fail safe” slows down the fundamentals of drying so much that it borders on ridiculousness.  What is even more ridiculous is that this is perceived to be the best, because it is “high tech” and “state of the art”.  Trying to fine tune the drying process on such control systems leads to the system going into shut down. Unfortunately, raising questions to the kiln supplier ends up in a dead end.

This leads to the next question (and I know I’m treading on thin ice!) How many kiln operators are there with the know how to see that a control system is feeding them BS? And the next question: (even thinner ice!) How many true drying specialist with the years of hands on drying experience and know how, are bold enough (know enough about the actual controlling technology and logic) to question the controller, and not just accepting blindly what it is displaying?

Are we as drying managers/kiln operators not left at the mercy of clever software developers? The old school hands on drying gurus are becoming fewer and fewer world-wide.

Have you ever looked at the kiln interface, and thought “why the hell is this or that happening or not happening  at this time?”

What have you come across on your kiln controller that did not make sense? Where you able to bypass this? Could the kiln supplier help you to solve this?

[Craig Jensen]

Good questions:
We as operators should all be asking ourselves these questions, and if we can't answer them . . . . we have homework to do.

Thanks for the challenge HencoV.

When we find the answers to our "why in the heck did it do that?" question, we should make a point of recording that instance, and then reviewing it with our other operators so that we don't all have to learn everything by experience.

There is always an answer. . . . but sometimes we get superstitious.

[HencoV]

Let me give you an example

I was asked to help improve a kiln's performance. After studying the manual and monitoring the kiln for about a week, I took it out of “fail safe mode”, changed some user select able parameters which would improve control and tried to implement some schedule improvements.

These were some of the things that went wrong.

See graph 1. The time the vent takes before it starts opening when above EMC Setpoint: EMC act was higher than EMC set point (±16:51 at vertical line), meaning vent must start opening. The vent only started opening at ± 17:16. – This is a dead time of 25 minutes!

On graph2, just before 18:30 and fan direction change, EMC was way over set point, however, vent was only open 45%. It looks like the sample rate to decide to open the vent further is very long, hence very slow increase in proportionate vent position. Also after direction change, it took Temp actual about 70 minutes to get back to set point.

At the next direction change ±21:30, the controller lost it. The EMC went high, and it opened the vents to 100%...so far so good. This is where it all stopped making sense.  Instead of opening main steam to increase DB temp, which would also have helped to bring EMC down, it started closing the main steam, resulting in EMC to rise even further.  Fortunately the controller has a manual override function, with which I forced the main steam open, and vent closed until actual and set points matched. I then put it back to auto and it carried on as if nothing happened. At the next direction change, no one was there to help it recover. The system went into “over EMC error” mode and shut down the kiln

[HencoV]

And graph 2...