INTERFERENCE INFERRED

Or - The Art Of Noise Reduction

This may come as something of a shock, but before I was a teacher, I was an engineer. No, not the train driving kind. Although I did my apprenticeship on diesel-electric locomotives and I know how to drive a train.

I'm qualified as an Electrician and both an Electrical Engineer and an Electronic Engineer. Specifically one with six year's field experience installing sensitive monitoring equipment.

Excuse me while I remove my teacher's gown and close my Vana exercise book. I need to put on my hard-hat and insert my pen-filled plastic pocket protector. In my pocket.

Why on earth would I tell you this?

Well, it's because I want to write about something I've rarely mentioned here at the AGB. Road safety – ha ha – cameras.

Yesterday in The Age, the Over-funded Liability, Andre Haermeyer was quoted on the presumed causes of the erroneous camera readings....

"The evidence seems to suggest that there is not any sort of systemic problem where cameras routinely record false speeds," Mr Haermeyer said.

"It seems to be that it is itinerant, that it is very intermittent and that we don't know when and where it is going to happen. That seems to be consistent with some sort of electromagnetic interference."

"Electromagnetic interference" is commonly referred to as "noise".

In short, noise primarily occurs for two reasons. One, equipment generates a rogue signal that induces distortions in the signal voltages of adjacent equipment. And two, changing current in one circuit (standard AC, harmonics, spikes, etc) induces an unwanted voltage in the circuitry of a separate system.

Generally speaking, both those sources of noise are transient in nature. In fact they are sometimes referred to as "transients". They are precisely, in Andre's words, "itinerant", "intermittent" and "we don't know when and where it is going to happen".

A simple example is the static you might hear coming from a car radio as the speed of an engine increases. To stop it you install circuitry to intercept and quash the engine's undesired electromagnetic emissions. Another is the flicker lines across your TV as your neighbour fires up his band saw, blender or unseen vibrating device. You can usually stop the latter's interference if you jump the fence and whack your neighbour with said vibrating device.

None of these problems may be "systemic" per se, but they can certainly be a significant influence on a poorly installed "system".

I've never yet worked on a monitoring system where noise was not a consideration. And I've worked on only a few where it wasn't a problem that didn't require detailed attention.

In it's most simple form that attention usually consists of "shielding" the conductors and conductive parts of the installed system by diverting away from them any of the deleterious signals/voltages mentioned above. However, the worse the problem, the more elaborate the solution so other devices may be needed.

Most significantly from a transactional perspective, on none of the projects I've worked was the installed system accepted by the client until such time as it was shown the system operated correctly every time.

In other words, the commissioning time was extended and we got the system running right before we handed it over.

Where our road safety – Guff! Aww! – camera system is concerned there is one obvious cause of noise. I've already alluded to it, the cars themselves. But extreme road temperatures (both very hot AND very cold) around the sensors, moisture and anything unforseen can cause trouble.

There's another article in yesterday's Age detailing the system....

The most likely cause of false speeds were false "inputs" - right from the start. Trucks can set off false readings through "seismic vibrations" that can mistakenly set off the piezo sensors. Badly worn car suspension can cause wheels to bounce and momentarily lose contact with the road surface, confusing the readings. Loose cabling connections can produce noise and false camera signals.

Faulty amplifiers and noise filters can allow stray signals to pass.

Therefore, if "noise" is occurring in our road safety – ho ho – camera system, and it appears from Andre's admission it is, then it's badly shielded/protected and therefore isn't ready to be handed over for service.

More particularly, it's possible ANY photo/reading taken since it was installed – but not successfully commissioned – is wrong.

So far it's been shown three cameras were way out. However, not all transients are large. Who's to say twenty, thirty, forty or one hundred and seventy-six readings of, say, between five and ten over aren't also erroneous.

And if that's the case then there's no way that the system can accurately adjudicate speeds and therefore the benefit of the doubt must be given to the driver every time.

As it stands, the system cannot be relied upon and until it is it must be stopped, as well as all fines and points already issued rescinded.

The companies I did work for all operate under the Quality Assurance banner. That is, they guarantee the product they deliver conforms to a designated set of parameters. If their product falls short of those parameters it's not accepted.

Is it too much to ask that the government, which after all is driving the idea of Quality Assurance, operates within the same framework it promotes.

Finally, here's a tidy little chart to show how us Chumptorians are getting milked down here in Poohtown.

Yeee! Owww!

Comments

[Wayner]

Surely you're not implying that our illustrious State Govt are concerned with revenue more than our safety, happiness and wellbeing? Perish the thought.

The thing that gets me is the way people have just copped these fines on the chin, myself included. As if paying 50% tax wasn't enough.

Funny how often the term "police state" was used when Jeff was in, but Labour gets a pass. Speed cameras and the police files issue are far more fitting of the phrase than anything Jeff ever did.

[Tony.T]

Not implying anything of the sort Wayner. Wait a tick. Yes I am. Well I am in the sense that I'm saying it outright.

I think more than anything it's the idea that Labor won government based on a massive whinge campaign spearheaded by their "special interest" mates, mainly the unions, the labor lawyers, the ABC and The Age, that really bite me. And yet now we hear fuck all. The hypocricy is stunning. Everything that the Libs did, Labor now embrace. the only diff is that they've thrown a lot more money at their mates in the public sector unions. I often wonder how Bernie Finn feels. He lost the seat of Tullamarine based on Labor's anti-toll campaign and now look what's happened.