Monday, February 23, 2009

Feedback Controls

A big chunk of my work life has been in the automotive finance industry, but I can't really say that I am a car guy. A car is a necessary evil, not the raison d'etre of existence.

So it was that in early January, after delivering our friend Annalee to the airport, I noticed an instrument panel light that I had never seen before. A quick check showed no flames or smoke or other serious issues, so I continued driving, and got the car home before I hauled out the manual.

This particular problem, it said, was related to the exhaust system, prompting dark thoughts about the expense of replacing a catalytic converter. According to the manual, this problem was serious and needed fixing. Or Bad Things Would Happen.

The mechanic at our favourite garage was more enlightening. It wasn't the catalytic converter -- instead, it was an oxygen sensor. Of which there were three -- two in the engine itself, one in the exhaust. Our failure was the one in the exhaust.

At which point a light came on over my head. The oxygen sensor in the exhaust is the last part of a feedback loop providing information to the car's onboard computer. The computer adjusts the fuel mix until it achieves a preset level of oxygen in the exhaust, indicating that a predesgned fuel to air ratio had been achieved. The system is designed to monitor the output so that the input can be tweaked. Leaving this uncorrected would have meant that the car would have been doing strange things to the fuel mixture -- potentially damaging the engine, but certainly not optimizing for fuel consumption efficiency.

So, a feedback loop. A useful idea -- one could imagine monitoring the activity of, say, a financial institution and its effect on the economy. Then tweaking the government bailout money going in until the required output goals were achieved. Or one could imagine feeding bailout money into the auto industry based on what kind of vehicles it was producing -- set the feedback loop to optimize for fuel efficiency and low carbon emissions.

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