In his article this issue, control loop expert Michael Brown tackles the subject of PID controllers, and how these are most definitely not all created equal. For many automation engineers, proper tuning of the PID values is more of a ‘black art’ than a science because of the complex mathematical theory at work behind the scenes. In essence, even those with a good classroom understanding of PID theory struggle to achieve stable control in the field, due to the myriad of external factors that may, or may not, be important to consider within the context of a specific application.
What sets Michael’s understanding apart is the combination of excellent theoretical knowledge with more than 30 years of practical experience troubleshooting a variety of ‘moody’ control loops in production facilities around the world. When it comes to controllers, the point he stresses is that, apart from the underlying PID equations, there are no universal standards that manufacturers are required to follow, which means they are all free to design their controllers any way they choose.
Compound this lack of standardisation with a dearth of specialised education and training courses, and the potential consequences for plant efficiency can become dire. In extreme cases, operators simply decide to control certain processes in manual because of wayward loop recovery, or sometimes even instability, under changing process conditions.
To address this, Michael plans to provide an in-depth explanation of controller operation – and the range of possible features that may be available within them – in a series of Loop Signature articles to be published in future issues of SA Instrumentation and Control. Interested readers will find the introductory article here http://www.instrumentation.co.za/14386r.
Smart production line configuration
In another thought leadership article this issue, Iritron’s Gerhard Greeff and Machiel Engelbrecht discuss production line optimisation in response to increased consumer demand for ‘personalised’ purchasing options. The quest for ‘batch size one’ production has put manufacturers under increasing pressure to deliver on time, while retaining the flexibility to handle unexpected changes.
In essence, manufacturers need to operate with shorter lead times while satisfying the growing customer demand for individualised products. To achieve this, they need the ability to schedule production dynamically with as little downtime as possible. Since orders often come in erratically, optimum scheduling relies on access to a real-time overview of machine status and raw material availability.
Discrete manufacturing operations typically achieve this through real-time monitoring of activity on their production floors, combined with the latest production-scheduling software packages. Using the intelligent software, planners can now schedule orders quickly and efficiently, while retaining the ability to make manual tweaks to the plan based on experience or unforeseen problems.
Since the systems described can be customised to integrate with an organisation’s existing MES and ERP systems, the trick is to tailor the solution to suit current production requirements while allowing easy upgrade for future expansion. See the article here http://www.instrumentation.co.za/14380r if you need to resolve a scheduling-related production problem in your company.
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