Blog Case story:  Monitoring noise to prevent mill damage

With the goal of increasing productivity and reducing operational downtime on mills, the Australian consultancy Manta Controls has developed an acoustic analyser that imports the entire frequency spectrum from sound level meter Type 2250 into a control system – without a computer as a gateway.

This has never been done before, and it is quite an interesting case. In this article, we’ll explore, how they went about this. 

The Manta Controls Advanced Control System, called the SAG Cube, automatically monitors and controls a SAG Mill, keeping track of critical process variables impacting mill throughput. The cost of downtime
The Manta Controls Advanced Control System, called the SAG Cube, automatically monitors and controls a SAG Mill, keeping track of critical process variables impacting mill throughput. For most sites, one hour of operation provides a revenue between AUD$ 20,000 per hour up to or greater than AUD$ 100,000 per hour. Therefore, any downtime is very costly. 

Eliminating the computer as a gateway

John Karageorgos, Managing Director of Manta Controls, explains the challenge they were looking to solve: “In essence, we are trying to listen to a grinding mill and measure when the mill can be damaged from the steel balls hitting the steel liners of the mill. If we have a reliable measure of ‘damage’ then we can control the mill and not operate in the damaging mode.”

This challenge paved the way for a new generation of SAG mill acoustic analysers, the Manta Mic, which takes advantage of Brüel & Kjær’s products for analysing acoustic emissions. However, it wasn’t a straightforward development process.

Manta Controls had previously been using a Type 2238 sound level meter. When Type 2238 became obsolete, Manta Controls looked at Type 2250 for their replacement solution. “The only catch was that we lost our capability of having a 4–20 mA signal, because Type 2250 had an Ethernet connection,” explains John Karageorgos. 

One key objective of the new solution was to eliminate the need for a computer from the architecture; Manta Controls invested approximately AUD$ 200,000 in R&D to find a robust solution to communicate with Type 2250 directly from a control system, without a computer connected to the sound level meter.

Manta Controls develops unique advanced control systems to help optimize semi-autogenous grinding (SAG) mills.About Manta Controls
With its headquarters in Southern Australia, Manta Controls develops unique advanced control systems to help optimize semi-autogenous grinding (SAG) mills. SAG mills are primarily used at gold, copper and platinum mines where steel balls are used for the grinding.  

Next up: live data for monitoring operating conditions

“When we started this project, no one knew if it was achievable, so in the beginning it was pure research work. We were prepared to try and then walk away if it didn’t work. That’s the risk with developing anything new,” explains John Karageorgos.

After almost 12 months of development, things were not going so well, and the research team had not managed to communicate directly with the sound level meter from a control system without having a computer as a gateway.  

From sound level meter to acoustic cameraJohn Karageorgos explains: “We were nearly ready to pull the pin on the project, but we gave it one last chance. We tried a new idea, and we finally got the control system to communicate with Type 2250, directly. I will never forget that day! Once we did that, we knew we had a product!” 

“So now we are able to listen to any SAG or AG mill and measure the entire frequency spectrum live from a Type 2250, or a Type 2270, and pass the entire frequency spectrum directly into a control system with no computer. This makes the entire solution simple and elegant and very robust,” explains John Karageorgos.

This discovery has started a new R&D project where Manta Controls are trying to use the live data to monitor operating conditions, such as the optimum volumetric percentage filling and the condition of the lifters. This could also be deployed on other mining equipment as well, not just on SAG or AG mills.

John Karageorgos, Managing Director of Manta Controls

“We have been working directly with Brüel & Kjær for two years but working with Brüel & Kjær equipment for the past 20 years. Brüel & Kjær provides the ‘Rolls Royce’ of equipment with regard to anything acoustic, and we rely on it to be reliable and robust.”
John Karageorgos, Managing Director of Manta Controls

Protecting and optimizing mills

The main benefits of this type of reliable SAG mill monitoring are accurate and repeatable decibel signals at the various frequencies – information that is used to protect the mills. 

The next phase of the project is to provide measurements that can help customers operate a SAG or AG mill optimally. John Karageorgos explains: “Optimization is our bread and butter, so once we have the measurements we are looking for, incorporating them into our SAG Cube solution is easy. The hard part is developing these new operating parameters that tell us whether a mill is operating optimally or not.”

“Now we can offer a simple and elegant yet robust solution with the added benefit of the quality that Brüel & Kjær equipment provides. This has also opened the door to some new ideas. We have plans to further develop the solution to offer additional capabilities. For example, we are looking at capturing even more data with two microphones to monitor two locations, and then we’ll try an array of microphones,” concludes John Karageorgos.

From sound level meter to acoustic camera