Simtars calls for entire system design

SOME of the biggest advances in the use of new technologies in mining equipment have been made through the use of programmable electronics (PE). But PE technologies have brought a new level of complexity and new hazards, such as
Simtars calls for entire system design Simtars calls for entire system design Simtars calls for entire system design Simtars calls for entire system design Simtars calls for entire system design

Continous miner. Courtesy World Coal Institute.

Staff Reporter

Queensland testing and certification body, Simtars (Safety in Mines Testing and Research Station) is calling on equipment manufacturers and end-users alike to pay closer attention to a new standard introduced in 2001 which outlines a general approach for the whole safety related system of equipment.

Known as Australian Standard 61508 Functional Safety of electrical/electronic/programmable electronic safety-related systems, the new standard will require a change in thinking related to equipment that relies on PE technology.

The problem, according to principal research engineer, Andre De Kock, is that designers have approached PE technology in isolation from the entire system's functionality. He said equipment still tends to be designed first and only when it is commissioned are safety factors added on. No continuous miners in the field at present, were to his knowledge, fully compliant with AS 61508, he said.

For example, a software program for a transmitter and receiver may be designed in isolation but its effect on the entirety of the machine is frequently not considered. Rather than viewing a machine as a set of discreet 'blocks' or individual components, De Kock supports the lifecycle approach that considers all phases of the system, from concept through to the decommissioning of the equipment.

This latter point is important in the instance a mine takes a transmitter and receiver designed for a continuous miner and puts it onto an LHD for example. Even with modifications this system will not comply with AS 61508.

"The machine must now be evaluated as an entire system, including the software, hardware, human interface and the environment," he said.

Thus, when a failure occurs the control system must behave in a defined manner to lower the probability of injuring people.

"With unplanned movements you can't look at just individual components the complete system has to be considered.

"The solenoid, the actuator and processor that drives the solenoid, the sensor and interface that initiate the movement of the solenoid. It also includes the software used in the processor.

"Therefore a claim that the software of a PLC is AS 61508 compliant may be incorrect as it is only a part of the entire system that is considered."

He said Simtars was looking at ways of verifying the safety integrity levels of systems.

Eventually all equipment will have to comply with AS 61508.