Ubiquitous Controllers

Refrigerators and sump pumps. Hot water heaters. Interesting, all these are integrating systems which are inherently easy to control. On/off works well.

Walter

From personal experience I can tell you that 'public facilities' in France are usually significantly different from UK where the common practise is to have a head tank with ball-c*ck level float. (what are the other 2 systems?) In France they sem to prefer wide-bore pressurized mains with mechanically timed push-button. They also have have a version local pressure vessel and the street corner self-cleaning variety.

More examples:

Temperature control in Fridge/ Freezers. Thermostatic mixer taps for showers. Engine idle speed governors Pressure relief valve on pressure cookers Electric toaster time/temperature Electric kettle which auto switches off Lights which come on when it is dark Doors that open when you approach Traffic lights which respond in correct sequence to pedestrian push button.

Michael

"Michael Tombs" wrote in news:cbe7hq$7ap$ snipped-for-privacy@news.ox.ac.uk:

I think universally, those buttons do nothing ;)

In fact, I like to imagine that every time somebody in the world pushes one, Jimmy Hoffa gets a shock.

Scott

I've come to the same opinion myself.

Walter

I think they are there to get you to wait for the walk light. If you push the button you are more likely to wait than if there is no button and you feel like crossing before you get the walk sign. I don't know; just my guess.

I do know of one large building full of engineers who would always try to adjust the HVAC. The building crew finally installed area thermostats with a temperature control knob, but with a locked, clear plastic cage around it. Within a day people had bent paper clips to reach in and turn the knob. What they didn't know was that the knob was not connected to anything; the temperature measurements were sent back to a central control system that then positioned the dampers. But reaching in with the paper clips and turning the knobs made everybody feel like they had made a change.

Of course, the trick to that type of system is to take a deep breath, hold it, and then slowly blow on any of the boxes with both temperature and humidity measurement.

John

Kids round here have worked out the sequence, if you do not push the button for about 3 minutes on a local crossing on a main road the lights respond almost immediately - so an individual car can be targetted!

When training people new to automatic control I frequently use toilet tank level control, particularly when discussing proportional only control, proportional band, and level control.

I use air temperature control of the classroom when discussing action (heating requires direct action, cooling reverse), disturbances (what happens when the sun come out, cold rain hits the window, etc. and setpoints (knob on the wall).

In discussing process dynamics I often use the example of the open loop control of a boiling pot of green beans on a stove top, with the danger of the pot boiling over. I can often make the comparison of an electric and gas stove (second large lag due to electric heating element mass)--OK, this usually works best with women, particularly those who are old enough to have cooked on both gas and electric.

I have only used the toilet tank example in the US and some other countries with similar residential toilets (tank on back where you can easily open it and see the float and rod). I have been places where you lose the students by talking about flush toilets :-)

"The city deactivated most of the pedestrian buttons long ago with the emergence of computer-controlled traffic signals, even as an unwitting public continued to push on, according to city Department of Transportation officials. More than 2,500 of the 3,250 walk buttons that still exist function essentially as mechanical placebos, city figures show. Any benefit from them is only imagined."

-- Steve

snipped-for-privacy@duke.edu wrote in news:cbpe8d$8qo$ snipped-for-privacy@gargoyle.oit.duke.edu:

Damn. I hate having my conspiracy theories confirmed. It gives me the willies.

What about the Jimmy Hoffa part??

Scott