May 2014System 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.
Mike,
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.
Modernising Vertical Filter Press Machines with Future-Focused Control Systems
System Integration & Control Systems Design Project and Industry
Pressure Filter Specialists approached us to modernise vertical filter press machines for the Minerals and Metals industry. The goal was to improve reliability, reduce downtime, ...
Read more...Loop Signature 31: Non-linearity in control loops (Part 2) Michael Brown Control Engineering
Fieldbus & Industrial Networking
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...Project & industry
System Integration & Control Systems Design Project and Industry
This project involved delivering a complete electrical, instrumentation, and automation solution for a new OEM drum-twister machine, replacing an ageing unit in a major cabling production ...
Read more...It’s a risky business not to challenge standard language
System Integration & Control Systems Design
On the surface, contracts all look alike. Once you’ve seen one, you’ve seen them all, or so it seems. Maybe so, but hidden within the standard language can be language that shifts the other party’s risk to you.
Read more...Loop Signature 30: Nonlinearity in control loops (Part 1) Michael Brown Control Engineering
Editor's Choice Fieldbus & Industrial Networking
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...Control system upgrade: Smelting SAM Systems Automation & Management
System Integration & Control Systems Design
Systems Automation & Management recently completed a major control system upgrade in the smelting industry. The project was delivered on budget and achieved a positive ROI for the client.
Read more...Gottwald drives upgrade: Ports and harbours Abacus Automation
System Integration & Control Systems Design
In the ports and harbours sector, Abacus Automation completed a significant modernisation of a Gottwald crane, improving both operational reliability and serviceability.
While every effort has been made to ensure the accuracy of the information contained herein, the publisher and its agents cannot be held responsible for any errors contained, or any loss incurred as a result. Articles published do not necessarily reflect the views of the publishers. The editor reserves the right to alter or cut copy. Articles submitted are deemed to have been cleared for publication. Advertisements and company contact details are published as provided by the advertiser. Technews Publishing (Pty) Ltd cannot be held responsible for the accuracy or veracity of supplied material.
printer friendly version