Feedforward control tuning is not nearly as critical as feedback tuning, and fairly simple models are usually fine for the purpose in hand.
read more

Feedforward control is a powerful technique that can dramatically improve control variance in cases where load changes cause big deviations from setpoint and the actual process dynamics are too slow to allow the feedback controller to operate fast enough to catch these disturbances.
read more

The previous series of loop signature articles dealt with the basics of control loop optimisation, and concentrated on troubleshooting and ‘SWAG’ tuning of simple processes. In this new series, consideration will be given to dealing practically with more difficult issues like interactive processes, and with processes with much more complex dynamics.
read more

This article is a continuation of Loop Signature 30 published in the last issue in this series, exploring reasons for non-linearities which may be encountered in feedback control loops
read more

For this final article I have chosen to relate a problem that existed in a desuperheater temperature control on a boiler in a petrochemical refinery.
read more

If nonlinearity occurs it means that if one is to carry on controlling with the same response to changes in load or setpoint, then the tuning of the controller will also need to be adjusted to meet the new conditions.
read more

In my last article I wrote about how cascade control systems can effectively overcome valve problems. This article gives another example of how a temperature control was able to perform well, in spite of really severe valve problems.
read more

A large petrochemical refinery asked me to perform an audit on several critical base layer control loops. This article deals with a problem found on a valve controlling the flow of fuel to a heat exchanger.
read more

I was giving a course at a remote mine in the middle of the Namibian desert. We were discussing tuning responses, and as I always do on my courses, I mentioned that in my opinion ¼ amplitude damped tuning is not desirable, and is in fact not good.
read more

It is very important that reboiler temperature controls operate well in petrochemical refineries, or the product quality can really suffer. I was asked to check such a control in a refinery where they were having problems with one of these controls.
read more

The operators in a petrochemical refinery were having great trouble in trying to stabilise the condensate level in a vessel, and this was adversely affecting other loops downstream. Several unsuccessful attempts had been made to retune the controller.
read more

The purpose of this particular article is to try and give those unfortunate enough to have to use SWAG (scientific wild ass guess) tuning a bit of an idea of how to go about it, and even more importantly some understanding of a couple of basic principles.
read more