John appeals to radio manufacturers to pay attention to this predicament. “For me it would be the jackpot if these guys could help us to start a repair centre in South Africa”, he says, flourishing the dead radio sadly. “Ten to one, it’s probably a board or something, and it will probably cost maybe R1000 [US$120]. If I was that company, I would say, ‘How can I help you to support the radios?’

“If I was that company, I would have come and said, ‘OK, here’s the test equipment, here’s the training in how to repair it, here’s everything you need for repairing’.”

Users’ experience

With users generally, the digital system has been a big hit because the radios are easy to use, like cellphones; there’s the option for some users of making telephone-style full duplex calls (though the team prefers to see this facility used sparingly, because it consumes twice as much radio capacity); and the system gives clear speech quality even in high-noise environments.

“Noise is one of our biggest problems, and that’s one thing where I have to sing the praises of TETRA”, John comments. “In our experience, the oxygen plant is one of the noisiest plants. You can hear the noise, but just barely. The voice can be heard.”

Christo finds that discipline on the air is better with the TETRA radios. “We had a lot of horseplay with the old system”, he recalls. “But that cannot be done now because, if you key, your radio code gets recorded. Previously, some guys would hog the channel and scratch the speaker, and it would irritate all the people in the control room and in their group. But you never knew who it was, because there were eight or ten guys on the shift.

“With the new system, it’s possible to go back to the recording and check every single keystroke, and exactly who said what.”

Some minor teething troubles were encountered with the system in the beginning – such as when users switched themselves to the wrong talk group or forgot to check that their battery charger was plugged in. The longest interruption so far to network service lasted just 30 minutes when, one morning, a log-file which had been growing slowly on a PC in the operations centre finally filled up all the space on the hard drive and halted the system.

“We learnt a lesson”, Christo admits. “Now the guys rigorously check certain file sizes every morning, and delete log files that are no longer needed, keeping the discs 60 per cent empty. This is part of the normal system management processes.”

New applications

So far, voice communication is the dominant application for the TETRA network, although opportunities for using wireless data are beginning to emerge. One example mentioned by Christo relates to the time-consuming procedure of carrying out safety inspections of scaffolding, a frequent task during plant shutdowns. He says: “The person must go out do his thing and table his inspection on paper, return to the office, give the findings to the planner. The planner completes the required form, updates the plan, then informs the colleagues that the scaffolding is ready, and then the teams can move in.

“But now, things have changed with the implementation of the TETRA system. A person can go to the scaffolding, do the inspection on TETRA, press a button, which automatically updates the system in the office and the team can come out to work. This exercise means you have saved five hours just for an inspection on scaffolding.”

With tens of thousands of such tasks to be completed during a six-week shutdown, a few hours saved each time would make an enormous difference, he argues. And the essential information would be delivered promptly and accurately.

Another data scheme under consideration is an RF tag project, similar to asset tracking. For example, a technician would be able to go to a valve, the tag would then identify the valve over the radio to the central SAP plant management software, and the SAP system would respond with instructions for the technician.

And there is also a plan to enhance the public address (PA) systems, the loudspeaker systems installed at every building in the complex to broadcast announcements such as safety alerts. With the TETRA system, John explains, it will be possible to extend the PA network wirelessly to the many construction sites where work is in progress at one location or another around the plant. Sometimes there can be as many as 1000 of them. “So we are going to now start building up little boxes with a radio inside”, he says. “TETRA is giving us the possibility to provide solutions.”

Network control

All this TETRA experience gained at the Secunda complex has now been distilled into a new installation some 140 kilometres away. This is the Sasol Infrachem petrochemicals factory at Sasolburg, another giant industrial site within the Sasol group. The big TETRA rollout began there in January this year.
(中國集群通信網(wǎng) | 責任編輯：陳曉亮)