System Integration & Control Systems Design

Reader feedback sent to Michael Brown

May 2014 System Integration & Control Systems Design

SA Instrumentation and Control contributing editor, Michael Brown, recently received some feedback on a loop optimisation article we published in the August 2013 edition. Since it is such a topical experience from a C&I engineer, we decided to publish it.


I was reading your article in the August 2013 edition of SA Instrumentation and Control about strangely behaving valves and it reminded me of an experience I had when I was tuning a loop in a DMS plant. It was a simple loop controlling density with water flow, but I did not have a flowmeter to check the flow rates.

An I/P valve manufacturer had been issued with an order to provide a valve of a certain flow range that they did not have in stock, but they could modify the range of another valve by exchanging the seat. What they failed to do, however, was to recalibrate the valve for 4-20 mA: valve fully closed to fully open.

The valve only started opening above 8 mA and, since the loop was quite slow, this caused some problems as you will appreciate. Subsequently the project leader accused me of not knowing what I was doing, since the loop was not controlling the density satisfactorily. I stuck to my guns and said that the valve was not opening when it should.

I checked the density control later when I could open an outlet to see if there was water flowing, and sure enough there was no flow. Now it was my turn to make accusations about who had not done their job. Needless to say there were no apologies.


Richard Mackay.


Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Loop Signatures 1: Introduction to the Loop Problem Signatures series
May 2020, Michael Brown Control Engineering , Editor's Choice
Over the years I have had many requests to write a book giving more detailed explanations of some of the problems I have encountered in my work on practical loop optimisation. I am by nature and inclination ...

SCiBOTRON’s quality culture the key to success
May 2020 , System Integration & Control Systems Design
The company was founded on lean principles and quickly grew into a QSE (Qualifying Small Enterprise). Ricardo Paddy, managing director and founding member, attributes one of the reasons for the company’s ...

Visualisation using vision-specific controls
June 2021, Beckhoff Automation , System Integration & Control Systems Design
TwinCAT Vision combined with TwinCAT HMI.

Modularity boosts performance
June 2021, SEW-Eurodrive , System Integration & Control Systems Design
Integrated technologies automate, upgrade and streamline existing production processes, while still allowing for future technology to be incorporated.

Changing negative attitudes towards alarms
June 2021, Omniflex Remote Monitoring Specialists , System Integration & Control Systems Design
Why technology is only as good as the people using it.

Loop Signatures 7: Final control elements – Part 3 hysteresis and deadband
June 2021, Michael Brown Control Engineering , Editor's Choice
Some of the biggest problems associated with the final control element are hysteresis and backlash.

Smart traffic management for Syntell
April 2021 , System Integration & Control Systems Design
Syntell is a leading South African technology company. One of its key projects is the running and management of one third of Johannesburg’s traffic lights. Syntell’s system is a full traffic management ...

Case History 177 - Valves, valves, valves!
May 2021, Michael Brown Control Engineering , Editor's Choice
75-85% of all industrial control loop problems are caused by valve issues.

PCS Global implements 5-phase control system upgrade at Kiara Health
May 2021, PCS Global , System Integration & Control Systems Design
Kiara Health is the first African company equipped with a fully-scaled server deployment in the AWS Cloud, as well as the first South African company to implement the AVEVA Flex Model.

Loop Signatures 6: Final control elements – Part 2: characteristics.
April 2021, Michael Brown Control Engineering , Editor's Choice
Feedback theory generally assumes that the process has a linear transfer function, which means that equal changes on the input will result in equal changes on the output.