1 Jan 1970

Pilz PSS Tame Synchrotron’s Silent Hazards Travelling at the Speed of Light

Imagine a machine the size of a football field with noiseless hazards that move literally at the speed of light and you’ve got a safety challenge like no other in Australia. The newest and biggest piece of scientific equipment built here is just that - the Australian Synchrotron shoots electrons around its 216 metre circumference in just 720.5 nano seconds.

The synchrotron’s safeguards are equally as impressive. A system reminiscent of Maxwell Smart’s departure from Control Headquarters incorporates not one, but two, Pilz Programmable Safety Systems (PSS 3000) or "safety PLCs”, 68 emergency stop buttons, keyed interlocks, Fortress gates, video cameras and even an intercom.

The battery of safeguards protects scientists and workers from any possible exposure to what is essentially a giant light source that generates light from infrared to X-ray. In a nutshell, a gun shoots electrons into an inner booster ring and then on to a larger storage ring, accelerating them along the way to 99.99999% of the speed of light. Massive electromagnets are used to deflect the electrons, creating extremely bright light that is then channelled down beam lines to experimental workstations where scientists gather data for research as diverse as forensics and industrial catalysts.

Synchrotrons are highly efficient research machines. An experiment that would normally take one year to do in a lab using conventional techniques can be done using a large synchrotron facility in an estimated few hours or days.
Australian Nobel Prize winner, medical researcher Dr Peter Doherty, underscored the importance of a national synchrotron to his field.

"Synchrotron light technology is currently central to about 80 per cent of drug discovery and development, with the certainty that it will soon move to 100 per cent,” Dr Doherty said. "The net effect is to reduce drug design times from several years to a few weeks."

The uniqueness of the synchrotron in Australia presented the first major hurdle for its safeguarding, according to radiation safety specialist Sergio Costantin.

"Just understanding the hazards was a major issue initially,” he said. "If you’re outside the synchrotron’s rings, there’s absolutely no danger because it all happens inside concrete tunnels with walls up to a metre thick. But you simply can’t be inside when the synchrotron starts.”

Despite this, lead control system engineer Richard Farnsworth explains, the synchrotron’s massive magnets and their cooling circuits require "constant TLC”, making regular human access to the synchrotron’s tunnels essential.

Before turning on the electron gun, a thorough check of all the tunnels must be completed. Put simply, two people start at one end of the tunnel and walk along them, pressing safety or "search” buttons along the way until they complete the search and leave the machine. Each button must be pressed in the right order and within the right time frame and if one is missed, or if the search takes too long, the process must start all over again.

"We can’t have people sneaking in behind the search. It had to be so safe that even Homer Simpson could operate the synchrotron safely,” Farnsworth said.

Rated at Category 4 under AS4024.1 or SIL3 of AS 61508, a redundant safety system is mandatory for the synchrotron but integrator, Sage Automation, faced a fundamental design challenge.

"Since the design of the synchrotron equipment was not complete at the time the contract was awarded, the safety system had to have the flexibility to adapt to new input/output requirements,” said Sage’s Robert Craig. "Remote I/O modules using a Safetybus communications network provide this flexibility.”

Two Pilz PSS 3000 safety PLCs each monitor a discrete area of the plant. PSS 1 monitors the electron gun and the booster ring while PSS 2 monitors the storage ring. A Pilz machine interface (PMI) in the control room interacts with both PSSs via Ethernet cable. Control of the safety system is through a combination of this HMI and a series of Fortress keyed interlocks.

The keyed interlocks, Fortress gate locks, video cameras and an intercom system are used to control access of personnel into and out of the six controlled areas. Sixty eight emergency-stop pushbuttons are located around the installation, both inside and outside the protection tunnels, to provide immediate isolation of energized equipment in an emergency.

It was very important to synchrotron project staff that the safety system and the operations controller were entirely separate with a one way data stream.

"We don’t muck around with safety,” Farnsworth said.

All the safety and operations data is fed into an archive system so that in the unlikely event of an incident, investigators could effectively retrace the steps of synchrotron staff.

Mr Farnsworth says the safety system is ideal for the synchrotron.

"Some other synchrotrons around the world have used similar functionalities but based on the older relay technology, which is more expensive, more difficult to change and makes it more difficult to fault find,” he said. "Those old fashioned systems have proven less reliable, increasing down time and giving no end of trouble.”

"We have a system that is flexible, cost-effective and leading edge rather than bleeding edge.”

The electron gun/booster ring PSS was commissioned during August, while partial commissioning of the storage ring PSS occurred in October 2005. As this story went to print, Sage was waiting for the balance of line equipment to be installed before finalising the safety system’s commissioning.

"It’s been a very straightforward implementation process and a credit to Sage and the Pilz technology,” Farnsworth said.

"The ‘workers’ in this case are accelerator physicists and although they are quite practical people, they’re very happy with the safety system so far because it’s something that works extremely well with minimum training required.” 

More information on the Synchrotron can be found at the Australian Synchrotron website.

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