Finding people in ATLAS

23 April 2009

A screen shot of the user interface which shows people moving in the cavern.



Sometimes it’s the simplest ideas that offer the most elegant solutions. Enter the still-evolving ‘Finding People Inside ATLAS Areas’ (FPIAA) system, which tracks people moving in the ATLAS cavern with nothing more hi-tech than the sensors which turn on your garage light when your car approaches.

The project was started by Gianpaolo Benincasa many years ago, when he was the ATLAS GLIMOS, and is a collaborative effort between CERN and the Portuguese institutes LIP and IDMEC in Lisboa.

“The first idea was to use an active transmitter-receiver system which could identify people by name,” explains Sebastien Franz, who has been working on the project within the Detector Control System as part of his PhD. “But that implied that the person had to have something in a pocket, which is contrary to safety system thinking. You should really be able to detect people even if they forget their badge.”

The system they came up with instead – a network of 850 small infra-red sensors, each with a spherical range of around 20 metres – is simple, low cost, works well in the ATLAS environment, and  – crucially – can detect people in any situation. The sensors themselves are essentially identical to those you can buy for your garage, but their magnetic field-sensitive relays were replaced with opto-couplers in order to make them fit for purpose in the ATLAS cavern.

A sensor, white, in the corner of the blue beams

 

Over the last 18 months they have been installed throughout the accessible cavern area. A specially designed software user interface displays each level and sector of the cavern in the form of cells, and flags human movement in each cell in real time.

That was part one. Part two, which is now being debugged, tested and commissioned, is an active tracking mechanism for the Toroid area of the cavern. “The idea is to be able to detect if somebody stops moving, for example because of some malaise or even unconsciousness,” says Sebastien.

As soon as a person crosses into the Toroid area, the system triggers a tracking case. For each effective cell that the person passes through, the system looks for activity either in the same cell or in one of the accessible neighbouring cells. If there is no activity for a given period of time, a first level of alert is triggered, but requires no intervention. After a second period of inactivity, a higher level of alert is triggered and the SLIMOS is notified.

“Then one would have to do something: phone the people who are in the detector, check that they are ok, and eventually call the fire brigade for intervention [if necessary],” says Sebastien. Because the tracking data is stored, the SLIMOS would be able to tell the rescue teams precisely where the missing person stopped moving and disappeared from the picture, which could be imperative in cases of medical emergency.

“For the rescue team to go inside the detector and search somebody out could take hours,” agrees Sebastien. “It’s a huge structure, with many paths and enclosed places.”

The time-periods for first level and higher level alerts are currently being tuned, but right now they stand at three minutes and two minutes respectively. A sneaky nap inside the detector is definitely out of the question.

During the winter shutdown, sensors have been rigged up in areas which weren’t foreseen at the outset – for example on the temporary scaffolding which appears when ATLAS is in an open position and the calorimeter is extracted – and full testing is underway.

“We’re making good progress,” Sebastien reports, “and I hope we can make it fully operational in the Toroid before ATLAS is closed this year.”

 

 

 

Ceri Perkins

ATLAS e-News