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How a little device solved a big problem

Safety is paramount in mining because it is a volatile industry where any slip in standards can see an increase in visits to the coroner’s court to explain mishaps and misadventures that should never have happened.

It is an industry governed by strict guidelines – from how a mine is opened, through to the life of its active working, and finally, rehabilitation. It’s a serious business run by serious people.

Winder Controls Australia specialises in machinery for the mining industry. When one of its clients needed a safety solution for its mine winders, only a reliable, adaptable PLC would suffice.

A programmable logic controller (PLC) is a controller that can be programmed to do a job. They come in all shapes, sizes and configurations, and have varying programming abilities depending on the job at hand.

In the case of Winder Controls Australia, it had a project that required a safety PLC that would monitor the mine shaft cage that transported miners up and down a mine shaft, in a safe manner.

“In the old days we used to have a mechanical device that would follow the speed/distance profile of the cage, or skip winder,” said Krishnan Nair, general manager Automation and Drive technology for Winder Controls Australia.

“It made sure that at every point in the shaft the cage was travelling at the correct speed and did not exceed its maximum travel limits. If anything went wrong, you could have a catastrophic situation.”

Because mining technology has evolved, companies have moved away from the mechanical version and are now using electronic PLCs, which is where Pilz’s Programmable Safety System (PSS 4000) came into play. In the not-too-distant past, a cage going up and down a shaft at the wrong speed caused a lot of accidents and even deaths — something that is avoidable today.

“We were evaluating a number of products and came across the Pilz PSS 4000,” said Nair. “Back in the dim dark ages they never had devices like this and they used to have lots of accidents in the shaft because there is a possibility of something failing. For example, if a cage was coming up the shaft, and then for some reason the electronics failed, and it didn’t slow down and went past its normal stopping place, it could go up further and crash into the headframe.”

Nair was at pains to point out that the safety aspect was the key ingredient, therefore reliability and failsafe behaviour were the cruicial aspects of the solution.

“The important thing is that as safety is so paramount, we needed a totally reliable safety PLC that could shadow the cage anywhere in the shaft and make sure the winder kept to it limits,” he said. “The minute it exceeds or breaches any of its limits, it puts out a signal and trips the safety circuits, which in turn applies the brakes and brings the conveyance to a stop. And of course we need to be able to identify why the system has come to a stop, so a simple visualisation of the system is important, along with detailed diagnostics.”

Pilz’s scope of the project was the turnkey supply of the safety PLC cabinet that includes the design, supply, installation and testing of all safety PLC components. The components were selected to be Safety Integrity Level 3 capable and included PSS 4000 hardware, Pilz’s Safe Encoders (PSENenc) and Pilz’s latest visualisation software (PASvisu). With PASvisu the user can track the winder every step of the way as well as quickly and easily identify any faults when and if they occur. While the winder is still at the commissioning stage, Winder Controls has put the system through its paces and is happy with the outcomes.

“We built a prototype, thoroughly tested it and it passed with flying colours,” said Nair. “We did everything in house. We bought the device from Pilz and then programmed it, got it working and commissioned the first one.  We’ve not gone into operation just yet but in the next couple of months we will.

“We have simulated the wind at the top and bottom so you can count by the number of drum revolutions where you are in the shaft. This is what we call Commissioning Without Ropes and that has been very successful.”

As with any type of new application, there were a few minor problems but nothing that held the project up from going forward. This is where the support that was by Pilz was critical.

“I’ve been in contact with them over the journey, said Pilz technical support manager Adam Hallinan. “There were some little teething problems at the start that included working out the exact functions for the application. We had to do a little bit of back and forth between them and Germany to fine tune everything to do exactly what they needed it to do.”

So why a Pilz Safety PLC? There are plenty of others out there, but as Nair points out, “it’s horses for courses. The PSS 4000 had the features necessary to complete the task.
“When it comes to safety, the Pilz PSS 4000 has a number of features that are very useful,” said Nair. “It is in that regard that we picked this Safety PLC. The company has been very helpful. Because this is the first time we are using a Pilz Safety PLC in this application, we had a few teething problems and they came over straight away to help us. Although we wrote the software ourselves, there was a lot of help from them on how to optimise the software. We put it through its paces and initiated all kinds of faults to see how it pulls up the winder. It was all good.”

The next stage is putting the system in place into the mine shaft. As far as the safety aspects go, Nair is happy that the Pilz System will do its job after the rigorous testing and has no issues moving forward with finishing the job.

“When it came to the speed distance protection and safety, the PSS 4000 fit the bill very well.”

Coupled with the PASvisu visualisation software it works well and, most importantly, solved a big problem – the winder is now safe.

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