Making the switch to microwave protection

Microwave switches are being used to ensure iron ore booms on Pilbara mines are safe from collisions.

Hawk Measurement Systems has deve­loped a fail-safe method of protecting booms from collid­ing with iron ore stockpiles in the Pilbara.

The company’s Gladiator microwave switches are de­signed to warn the boom’s control system whenever it approaches a stockpile.

The units are replacing traditional devices such as lanyard rope switches.

Lanyard switches, normally attached below and to each side of the boom, comprise a wire rope attached to a mech­anical limit switch.

When the rope comes into contact with the stockpile and drags through the ore, it will theoretically pull at the limit switch and cause the boom to stop.

However, these switches need to have their tension adjusted at the right level in order to quickly detect any potential collisions, accord­ing to Hawk application sup­port engineer Brian Tiede­mann.

“Despite their size, these booms are not rigid structures and can often flex under loads,” he told Australian Mining.

“Over the length of a 30 to 40 m boom there might some fairly substantial flexing and movements, which means the switches cannot be cali­brated as exactly as they should be without risking false trips.

“The booms can also have a bucket-wheel dredge at one end, which can often bite into the stockpiles and cause the whole boom to bounce around.

“The brackets that support the lanyard ropes can also be bent when the boom hits the stockpile.”

According to Tiedemann, the Gladiator microwave switch­es are mechanically simpler than the alternatives.

“The units create a line of protection between sender and receiver switches using a beam of microwave energy,” he said.

“The switches are placed in similar locations to where the lanyard switches would be, below and to each side of the boom.

“Anything that breaks the microwave beam will cause the switches to send a signal to the control system and stop the machine.”

Aside from predicting colli­sions, Tiedemann said the switches will not allow the boom to start up unless the beam is transmitted properly between the sender and receiver.

“The fail-safe system is very robust, because the whole system must work for the control system to know there are no hazards present,” he said.

“If there is a fault in the sender or receiver, the system will not get the OK signal.

“Microwave beams are also ideal for this application, because light beams and lasers are ineffective in really dusty environments.”

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